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MATERIALS

FOR THE

STUDY OF VARIATION

TREATED WITH ESPECIAL REGARD TO

DISCONTINUITY

IN THE

ORIGIN OF SPECIES.

BY

WILLIAM BATESON, M.A.

FELLOW OF ST JOHN'S COLLEGE, CAMBRIDGE

Pontoon :
MACMILLAN AND CO.

AND NEW YOKE.
1894

[All Eights reserved.]

Cambridge :

PRINTED BY C. J. CLAY, M.A., AND SONS,
AT THE UNIVERSITY PRESS.

PREFACE.

This book is offered as a contribution to the study of the
problem of Species. The reasons that have led to its production
are as follows.

Some years ago it was my fortune to be engaged in an investi-
gation of the anatomy and development of Balanoglossus. At the
close of that investigation it became necessary to analyze the
meaning of the facts obtained, and especially to shew their bear-
ing upon those questions of relationship and descent which modern
morphology has attempted to answer. To this task I set myself
as I best might, using the common methods of morphological
argument and interpretation, and working all the facts into a
scheme which should be as consistent as I could make it.

But the value of this and of all such schemes, by which each
form is duly ushered to its place, rests wholly on the hypothesis
that the methods of argument are sound. Over it all hung the
suspicion that they were not sound. This suspicion seemed at that
time so strong that in preface to what I had to say I felt obliged
to refer to it, and to state explicitly that the analysis was under-
taken in pursuance of the current methods of morphological
criticism, and without prejudging the question of possible or even
probable error in those methods.

Any one who has had to do such work must have felt the same
thing. In these discussions we are continually stopped by such
phrases as, " if such and such a variation then took place and was
favourable/' or, " we may easily suppose circumstances in which
such and such a variation if it occurred might be beneficial," and
the like. The whole argument is based on such assumptions as
these — assumptions which, were they found in the arguments of
Paley or of Butler, we could not too scornfully ridicule. " If," say
we with much circumlocution, " the course of Nature followed the

p

S J^-

VI PREFACE.

lines we have suggested, then, in short, it did." That is the sum
of our argument.

Were we all agreed in our assumptions and as to the canons of
interpretation, there might be some excuse, but we are not agreed.
Out of the same facts of anatomy and development men of equal
ability and repute have brought the most opposite conclusions.
To take for instance the question of the ancestry of Chordata, the
problem on which I was myself engaged, even if we neglect
fanciful suggestions, there remain two wholly incompatible views
as to the lines of Vertebrate descent, each well supported and
upheld by many. From the same facts opposite conclusions are
drawn. Facts of the same kind will take us no further. The
issue turns not on the facts but on the assumptions. Surely we
can do better than this. Need we waste more effort in these vain
and sophistical disputes ?

If facts of the old kind will not help, let us seek facts of a new
kind. That the time has come for some new dej)arture most
naturalists are now I believe beginning to recognize. For the
reasons set forth in the Introduction I suggest that for this new
start the Study of Variation offers the best chance. If we had
before us the facts of Variation there would be a body of evidence
to which in these matters of doubt we could appeal. We should
no longer say " if Variation take place in such a way," or " if such
a variation were possible ; " we should on the contrary be able to
say " since Variation does, or at least may take place in such a way,"
''' since such and such a Variation is possible," and we should
be expected to quote a case or cases of such occurrence as an
observed fact.

To collect and codify the facts of Variation is, I submit, the
first duty of the naturalist. This work should be undertaken if
only to rid our science of that excessive burden of contradictory
assumptions by which it is now oppressed. Whatever be our
views of Descent, Variation is the common basis of them all. As
the first step towards the systematic study of Variation we need a
compact catalogue of the known facts, a list which shall contain as
far as possible all cases of Variation observed. To carry out such a
project in any completeness may be impossible ; but were the plan
to find favour, there is I think no reason why in time a consider-
able approach to completeness should not be made.

PREFACE. Vll

Difficulty has hitherto arisen from the fact that Variation is
not studied for its own sake. Each observer has some other object
in view, and we are fortunate if he is good enough to mention in
passing the variations he has happened to see in following his own
ends. From the nature of the case these observations must at
first be sporadic, and, as each standing alone seems to have little
value, in the end they are unheeded and lost. If there were any
central collection of facts to which such observations might from
time to time be added, and thus brought into relation with cognate
observations, their value would at once appear and be preserved.
To make a nucleus for such a collection is the object of the present
work.

The subject treated in this first instalment has been chosen for
the reasons given in the text. Reference to facts that could not
be included in this section of the evidence has as far as possible
been avoided, but occasionally such reference was necessary,
especially in the Introduction.

It was my original purpose to have published the facts with-
out comment. This course would have been the most logical and
the safest, but with hesitation it was decided to add something of
the nature of analysis. I do this chiefly for two reasons. First,
in starting a method one is almost compelled to shew the way in
which it is to be applied. If it is hoped that others may interest
themselves in the facts, it is necessary to shew how and why their
interest is asked. In the old time the facts of Nature were
beautiful in themselves and needed not the rouge of speculation
to quicken their charm, but that was long ago, before Modern
Science was born.

Besides this, to avoid the taint of theory in morphology ' is
impossible, however much it may be wished. The whole science
is riddled with theory. Not a specimen can be described without
the use of a terminology coloured by theory, implying the accept-
ance of some one or other theory of homologies. If only to avoid
misconception matters of theory must be spoken of.

It seemed at first also that the meaning of the facts was so
clear that all would read it alike ; but from opportunities that
have occurred for the discussion of these matters I have found
that it is not so, and reluctantly I have therefore made such com-
ments as may serve to bring out the chief significance of the

Vlll PREFACE.

phenomena, pointing out what they shew and what they do not
shew, having regard always to deficiencies in the evidence.

That this is a dangerous course I am aware. But in any
discussion of a problem in the light of insufficient knowledge the
real danger is not that a particular conclusion may be wrong, for
that is a transient fault, but rather that the facts themselves may
be so distorted as to be valueless to others when the conclusions
that they were used to shew have been discarded. This danger I
have sought indifferently to avoid by printing the facts as far as
possible apart from all comment, knowing well how temporary the
worth of these comments is likely to be. I have thus tried to
avoid general statements and have kept the descriptions to
particular cases, unless the number of similar cases is great and
an inclusive description is enough.

Each separate paragraph relating a fact has been as far as
possible isolated and made to stand alone ; so that if any one may
hereafter care to go on with the work he will be able to cut out
the discarded comments and rearrange the facts in any order
preferred, inserting new facts as they come to hand. Most of
these facts are numbered for reference. The numbers are distrib-
uted on no strict system, but are put in where likely to be useful.

For almost every fact stated or mentioned one reference at lea>t
is given. When this is not the case the fact is either notorious,
or else the result of my own observation. In collecting evidence I
have freely used the collections of former writers, especially those
of Geoffroy St Hilaire, Ahlfeld, and Wenzel Gruber, but unless
the contrary is stated, each passage referred to has been seen in
its original place. By this system I hope I have avoided evidence
corrupted by repetition. Several well known conceptions, notably
that of the presence of order in abnormality, first formulated by
Isidore Geoffroy St Hilaire, have been developed and exhibited
in their relation to recent views.

The professed morphologist will note that many of the state-
ments are made on authority unfamiliar to him. I have spared no
pains to verify the facts wherever possible, and no case has been
admitted without remark if there was reason to doubt its authen-
ticity. So long as skilled zoologists continue to neglect all forms
that are abnormal the student of Variation must turn to other
sources.

This neglect of the Study of Variation may be attributed in

PREFACE. IX

great measure to the unfortunate circumstance that Natural History
lias come to be used as a vehicle for elementary education, a
purpose to which it is unsuited. From the conditions of the case
when very large classes are brought together it becomes necessary
that the instruction should be organized, scheduled, and reduced to
diagram and system. Facts are valued in proportion as they lend
themselves to such orderly treatment ; on the rest small store is
set. By this method the pupil learns to think our schemes of
Nature sufficient, turning for inspiration to books, and supposing
that by following his primer he may master it all. In a specimen
he sees what he has been told to see and no more, rarely learning
the habit of spontaneous observation, the one lesson that the
study of Natural History is best fitted to teach.

Such a system reacts on the teacher. In time he comes to
forget that the caricature of Nature shewn to his pupils is like
no real thing. The perspective and atmosphere that belong to
live nature confuse him no more. Two cases may be given in
illustration. Few animals are dissected more often than the
Crayfish and the Cockroach. Each of these frequently presents
a striking departure from the normal (see Nos. 83 and 625) in
external characters, but these variations have been long unheeded
by pupil and by teacher; for though Desmarest and Brisout
published the facts so long ago as 1848, their observations failed
to get that visa of the text-books without which no fact can
travel far.

It is especially strange that while few take much heed of the
modes of Variation or of the visible facts of Descent, every one is
interested in the causes of Variation and the nature of " Heredity,'"
a subject of extreme and peculiar difficulty. In the absence of
special knowledge these things are discussed with enthusiasm.
even by the public at large.

But if we are to make way with this problem special know-
ledge is the first need. We must know what special evidence each
group of animals and plants can give, and this specialists alone
can tell us. It is therefore impossible for one person to make any
adequate gathering of the facts. If it is to be done it must be
done by many. At one time I thought that a number of persons
might perhaps be induced thus to combine ; but though I hope
hereafter some such organized collection may be made, it is
perhaps necessary that the first trial should be single-handed.

X PREFACE.

As I have thus been obliged to speak of many things of which
I have no proper knowledge each section must inevitably seem
meagre to those w7ho have made its subject their special study,
and I fear that many mistakes must have been made. To any one
who may be willing to help to set these errors right, I offer thanks
in advance, " humbly acknowledging a work of such concern-
ment unto truth did wTell deserve the conjunction of many heads."

In the course of the work I have had help from so many that
I cannot here give separate thanks to each. For valuable criticisms,
given especially in connexion with the introductory pages, I am
indebted to Mr F. Darwin, Dr C. S. Sherrington, Dr D. MacAlister,
Mr W. Heape, Mr G. F. Stout, Dr A. A. Kanthack and particularly
to Mr J. J. Lister. I have to thank the authorities of the
British Museum, of the Museum of the Royal College of Surgeons,
of the Musee d'Histoire Naturelle in Paris, and of the Museums
of Leyden, Oxford, Rouen, NewTcastle-upon-Tyne, of the Ecole
Veterinaire at Alfort, and of the Dental Hospital for the great
kindness that they have shewn me in granting facilities for the
study of their collections. In particular I must thank Mr Oldfield
Thomas of the British Museum for much help and advice in con-
nexion with the subject of Teeth. I am also greatly obliged to
Messrs Godman and Salvin for opportunities of examining and
drawing specimens in their collections. To many others who have
been good enough to lend specimens or to advise in particular
cases my obligations are acknowledged in the text, but I must
especially express my gratitude to Dr Kraatz of Berlin, to Dr L.
von Heyden of Frankfurt, and to M. H. Gadeau de Kerville of
Rouen for the large numbers of valuable insects wuth which they
entrusted me.

My best thanks are due to Dr A. M. Norman for many useful
suggestions, for the loan of specimens and for the kindly interest
he has taken in my work.

My friend Mr H. H. Brindley has very kindly given me much
assistance in determining and verifying several points that have
arisen, and I am particularly indebted to him for permission to
give an account of his very interesting and as yet unpublished
observations on the variation and regeneration of the tarsus in
Cockroaches.

Through the help of Dr David Sharp I have been enabled to
introduce much valuable evidence relating to Insects, a subject of

PREFACE. XI

which without his assistance I could scarcely have spoken. It is
impossible for me adequately to express my obligation to Dr Sharp
for his constant kindness, for the many suggestions he has given
me, and for the generosity with which he has put his time and
skill at my service.

It is with especial pleasure that I take this opportunity of
offering my thanks to Professor Alfred Newton for the encourage-
ment and sympathy he has given me now for many years.

As many of the subjects treated involve matters of interpret-
ation it should be explicitly declared that though help has been
given by so many, no responsibility for opinions attaches to anyone
but myself unless the contrary is stated.

The blocks for Figs. 18, 19, 25, 13:3, 161 and 185 (from Proc
Zool. Soc.) were very kindly given by the Zoological Society of
London; that for Fig. 28 (from Trans. Path. Soc.) by the Pathological
Society; and for Fig. 140 which is from the Descent of Man I am
obliged to the kindness of Mr F. Darwin. Figs. 5 B, 5 c, and 77 were
supplied by the proprietors of Newman's British Butterflies, and
Figs. 5 A, 82 and 84 by the proprietors of the Entomologist. The
sources of other figures are acknowledged under each. Those not
thus acknowledged have been made from specimens or from my
own drawings or models by Mr M. P. Parker, with the exception
of a few specially drawn for me by Mr Edwin Wilson.

The work was, as I have said, begun in the earnest hope that
some may be led thereby to follow the serious study of Variation,
and so make sure a base for the attack on the problems of
Evolution. Those who reject the particular inferences, positive
and negative, here drawn from that study, must not in haste
reject the method, for that is right beyond all question.

That the first result of the study is to bring confusion and
vagueness into places where we had believed order established
may to some be disappointing, but it is best we deceive ourselves
no longer. That the problems of Natural History are not easy but
very hard is a platitude in everybody's mouth. Yet in those days
there are many who do not fear to speak of these things with
certainty, with an ease and an assurance that in far simpler
problems of chemistry or of physics would not be endured. For
men of this stamp to solve difficulties may be easy, but to feel

Xll PREFACE.

difficulties is hard. Though the problem is all unsolved and the
old questions stand unanswered, there are those who have taken
on themselves the responsibility of giving to the ignorant, as a
gospel, in the name of Science, the rough guesses of yesterday
that tomorrow should forget. Truly they have put a sword in the
hand of a child.

If the Study of Variation can serve no other end it may make
us remember that we are still at the beginning, that the com-
plexity of the problem of Specific Difference is hardly less now
than it was when Darwin first shewed that Natural History is a
problem and no vain riddle.

On the first page I have set in all reverence the most solemn
enuntiation of that problem that our language knows. The priest
and the poet have tried to solve it, each in his turn, and have
failed. If the naturalist is to succeed he must go very slowly,
making good each step. He must be content to work with the
simplest cases, getting from them such truths as he can, learning
to value partial truth though he cheat no one into mistaking
it for absolute or universal truth; remembering the greatness
of his calling, and taking heed that after him will come Time,
that "author of authors," whose inseparable property it is ever
more and more to discover the truth, who will not be deprived
of his due.

St John's College, Cambridge.
29 December, 1893.

CONTENTS.

INTRODUCTION.

SECT.

1. The Study of Variation

2. Alternative Methods .....

3. Continuity or Discontinuity of Variation

4. Symmetry and Meristic Eepetition

5. Meristic Variation and Substantive Variation

6. Meristic Repetition and Homology

7. Meristic Repetition and Division .

8. Discontinuity in Substantive Variation : Size

9. Discontinuity in Substantive Variation : Colour and Colour-Patterns

10. Discontinuity in Substantive Variation : Miscellaneous Examples

11. Discontinuity in Meristic Variation: Examples ....

12. Parallel between Discontinuity of Sex and Discontinuity in Variation

13. Suggestions as to the nature of Discontinuity in Variation .

11. Some current conceptions of Biology in view of the Facts of Variation

1. Heredity. 2. Reversion. 3. Causes of Variation. 4. The
Variability of "useless" Structures. 5. Adaptation. G. Natural
Selection.

PAGE

1

6
13
17
22
28
33
36
42
r,i
GO
66
68
75

PART I.

MERISTIC VARIATION

Linear Series .....
Radial Series .....
Bilateral Series .....
Secondary Symmetry and Duplicity .

CHAPTER I. Arrangement of Evidence
CHAPTER II. Segments of Arthhopoda

87—422
jj;5_447

448—473

171— 56G

83

91

XIV

CHAPTER
CHAPTER
CHAPTER
CHAPTER

III.

IV.

V.

VI.

CHAPTER VII

CONTENTS.

Vertebra and Ribs

Spinal Nerves

Variation in Arthropoda

Cpletopoda, Hirudinea and Cestoda

Branchial openings of Chordata and struc-
tures IN CONNEXION WITH THEM .

1. Ascidians. 2. Cyclostomi. 3. Cervical Fistula? and Super-
numerary Auricles in Mammals

CHAPTER VIII. Mammjs

CHAPTER IX. Teeth

Preliminary. Primates. Canidae. Felidas. Viverridas. Muste
lidae. Pinnipedia. Marsupialia. Selacbii. Radulse of Buccinum

CHAPTER X. Teeth— Recapitulation

CHAPTER XI. Miscellaneous Examples ....

Scales. Kidneys; Renal Arteries; Ureters. Tentacles and Eyes
of Mollusca. Eyes of Insects. Wings of Insects. Horns of
Sheep, Goats and Deer. Perforations of shell of Haliotis.

CHAPTER XII. Colour-Markings

Ocellar Markings. Simultaneity of Colour-Variation in Parts
repeated in Linear Series (Larvae of Lepidoptera : Chitonidae)

CHAPTER XIII. Minor Symmetries: Digits .

Cat. Pp. 313—324.

Man and Apes. Pp. 324—360.

Increase in number of digits, p. 324.

Cases of Polydactylism associated ivith change of Symmetry. A.

Digits in one Successive Series, p. 326. B. Digits in two

homologous groups forming "Double-hands," p. 331. Complex

cases, p. 338.
Polydactylism not associated ivith change of Symmetry, p. 344. (1)

A. Single extra digit external to minimus, p. 345. (1) B.

Single extra digit in other positions, p. 349. (2) Duplication of

single digits, p. 349. (3) Combinations of the foregoing, p. 352.

(4) Irregular examples, p. 353.
Reduction in number of phalanges, p. 355. Syndactylism, p. 356.

Absence of digits and representation of two digits by one, p. 358.

Horse, pp. 360 — 373. Extra digits on separate metacarpal or meta-
tarsal, p. 361. More than one digit borne by metacarpal III.,
p. 369. Intermediate cases, p. 371.

Artiodactyla, pp. 373—390. Polydactylism in Pecora, p. 373. Poly-
dactylism in Pig, p. 381. Syndactylism in Artiodactyla, p. 383.

Birds, pp. 390—395.

Possibly Continuous numerical Variation in digits : miscellaneous
examples, pp. 395 — 398 (Chalcides. Cistudo. Rissa. Erinaceus.
Elephas.) Inheritance of Digital Variation. Association of
Digital Variation with other forms of Abnormality.

PAGE

102
129
146
156

171

181
195

265

274

288

311

CONTEXTS.

XV

CHAPTER XIV. Digits: Recapitulation

CHAPTER XV. Minor Symmetries: Segments in Appendages

CHAPTER XVI. Radial Series

Coelenterata. Pedicellariae of Echinoderms. Cell-Division.

CHAPTER XVII. Radial Series: Echinodermata

CHAPTER XVIII. Bilateral Series

CHAPTER XIX.

Further Illustrations of the Relationship
between Right and Left Sides

CHAPTER XX. Supernumerary Appendages in Secondary

Symmetry

Introductory. — The Evidence as to Insects.

CHAPTER XXI.

The Evidence

CHAPTER XXII.
CHAPTER XXIII.

CHAPTER XXIV.
CHAPTER XXV.

Appendages in Secondary Symmetry .
as to Crustacea.

Duplicity of Appendages in Arthropoda .

Secondary Symmetry in Vertebrates. Re-
marks on the Significance of Repetition
in Secondary Symmetry : Units of Repe-
tition

Double Monsters

Concluding Reflexions

PAGE

400
410
423

432
448

4G3
474

525

539

553
559
567

INDEX OF SUBJECTS, p. 576.

INDEX OF PERSONS, p. 593.

CORRIGENDA.

p. 23, line 5. For " and that in " read " and in."

p. 27, line 29. For " appear" read " appears."

p. 37, line 18. For " their " read " the."

p. 54. Note 2. For "xxviii" read "xx."

p. 55. Parra is now known not to have affinities with the Eallidae.

p. 141. In description of Fig. 15 insert "After Solgee."

p. 151, line 2 and p. 153, Note. For "W. B." read "G. B."

p. 198. For " Pinnipediae" read "Pinnipedia." For "Dent." read "Deuf."

p. 212. In description of Fig. 40 delete " pl of the left side is in symmetry with
two teeth on tbe right side." The figure is correct.

p. 281, 15th line from bottom. Delete " and perhaps all."

p. 382. For "W. H. Benham" read "W. B. Benham."

p. 429. For " Banyul's " read " Banyuls."

p. 473, 4th and 6th lines from bottom. For " Tornaria" read " Balanoglossus"

p. 526. Delete the heading " (1) Clear cases of Extra Parts in Secondary
Symmetry."

Note to p. 461, Note 718. As to union of eyes in Bees, see further, Ditteich,
Zeit. f. Ent., Breslau, 1891, xvi. p. 21, and Cook, A. J., Proc. Amer. Ass., 1891,
p. 327.

Note to p. 468, Note 2. In connexion with Giard's observation the following
fact should be given. Since this Chapter was printed I have had an opportunity of
examining a sample of Flounders taken in the shallow water off Bournemouth. Of
23 specimens seen alive, all but about half a dozen were more or less blotched with
shades of brown on the " blind " side. In five the brown was more extensive than
the white. The eyes and dorsal fins were normal. The fishmonger who shewed
them to me said that the Flounders in that place were generally thus blotched, and
that those seen were a fair sample. In estimating the significance of Cunningham's
experiment (p. 467) this fact should be remembered.

INTRODUCTION.

All flesh is not the same flesh : but there is one kind of flesh of men, another
flesh of beasts, another of fishes, and another of bird?.

SECTION I.

The Study of Variation.

To solve the problem of the forms of living things is the aim
with which the naturalist of to-day comes to his work. How
have living things become what they are, and what are the laws
which govern their forms ? These are the questions which the
naturalist has set himself to answer.

It is more than thirty years since the Origin of Species was
written, but for many these questions are in no sense answered
yet. In owning that it is so, we shall not honour Darwin's
memory the less ; for whatever may be the part which shall be
finally assigned to Natural Selection, it will always be remem-
bered that it was through Darwin's work that men saw for the
first time that the problem is one which man may reasonably
hope to solve. If Darwin did not solve the problem himself, he
first gave us the hope of a solution, perhaps a greater thing.
How great a feat this was, we who have heard it all from child-
hood can scarcely know.

In the present work an attempt is made to find a way of
attacking parts of the problem afresh, and it will be profitable
first to state formally the conditions of the problem and to examine
the methods by which the solution has been attempted before.
This consideration shall be as brief as it can be made.

The forms of living things have many characters: to solve the
problem completely account must be taken of all. Perhaps no
character of form is common to all living things; on the
contrary their forms are almost infinitely diverse. Now in those
attempts to solve the problem which have been the best, it is this
diversity of form which is taken as the chief attribute, and the
attempt to solve the general problem is begun by trying to trace
the modes by which the diversity has been produced. In the
shape in which it has been most studied, the problem is thus the

Fftor *AFY l

B.

ii n n i\\\\ooo

2 THE PROBLEM OF SPECIES. [ixtrod.

problem of Species. Obscurity has been brought into the treat-
ment of the question through want of recognition of the fact that
this is really only a part of the general problem, which would still
remain if there were only one species. Nevertheless the problem
of Species is so tangible a part of the whole that it is perhaps the
best point of departure. For our present purpose we cannot
begin better than by stating it concisely.

The forms of living things are diverse. They may neverthe-
less be separated into Specific Groups or Species, the members of
each such group being nearly alike, while they are less like the
members of any other Specific Group. [The Specific Groups may
by their degrees of resemblance be arranged in Generic Groups
and so on.]

The individuals of each Specific Group, though alike, are not
identical in form, but exhibit differences, and in these differences
they may even more or less nearly approach the form characteristic
of another Specific Group. It is true, besides, that in the case of
many Specific Groups which have been separated from each other,
intermediate forms are found which form a continuous series of
gradations, passing insensibly from the form characteristic of one
Species to that characteristic of another. In such cases the
distinction between the two groups for purposes of classification is
not retained.

The fact that in certain cases there are forms transitional
between groups which are sufficiently different to have been
thought to be distinct, is a very important fact which must not
be lost sight of; but though now a good many such cases are
known, it remains none the less true that at a given point of
time, the forms of living things may be arranged in Specific
Groups, and that between the immense majority of these there
are no transitional forms. There are therefore between these
Specific Groups differences which are Specific.

No definition of a Specific Difference has been found, perhaps
because these Differences are indefinite and hence not capable of
definition. But the forms of living things, taken at a given
moment, do nevertheless most certainly form a discontinuous
series and not a continuous series. This is true of the world as
we see it now, and there is no good reason for thinking that it has
ever been otherwise. So much is being said of the mutability of
species that this, which is the central fact of Natural History, is
almost lost sight of, but if ever the problem is to be solved this
fact must be boldly faced. There is nothing to be gained by
shirking or trying to forget it.

The existence, then, of Specific Differences is one of the
characteristics of the forms of living things. This is no merely
subjective conception, but an objective, tangible fact. This is the
first part of the problem.

sect. I.] INTRODUCTION. 3

In the next place, not only do Specific forms exist in Nature,
but they exist in such a way as to fit the place in Nature in
which they are placed; that is to say, the Specific form which an
organism has, is adapted to the position which it fills. This again
is a relative truth, for the adaptation is not absolute.

These two facts constitute the problem :

I. The forms of living things are various and, on the whole,
are Discontinuous or Specific.

II. The Specific forms, on the whole, fit the places they
have to live in.

How have these Discontinuous forms been brought into exist-
ence, and how is it they are thus adapted ? This is the question
the naturalist is to answer. To answer it completely he must find
(1) The modes and (2) The causes by which these things have
come to pass.

Before considering the ways in which naturalists have tried to
answer these questions, it is necessary to look at some other
phenomena characteristic of Life. We have said that at a given
moment, or point of time, the specific forms of living things com-
pose a discontinuous series. The element of time thus intro-
duced is of consequence, and leads to important considerations.
For the condition of the organized world is not a fixed condition,
but changes from moment to moment, and that which can be pre-
dicated of its condition at one moment may not at any other point
of time be true. This process of change is brought about partly by
progressive changes in the bodies of the individuals themselves,
hut chiefly by the constant succession of individuals, the parents
dying, their offspring succeeding them. It is then a matter of
observation that the offspring born of parents belonging to any
one Specific Group do as a rule conform to that Specific Group
themselves, and that the form of the bodv, the mechanisms and
the instincts of the offspring, are on the whole similar to those
which their parents had. But like most general assertions about
living things this is true not absolutely but relatively only. For
though on the whole the offspring is like the parent or parents, its
form is perhaps never identical with theirs, but generally differs
from it perceptibly and sometimes materially. To this pheno-
menon, namely, the occurrence of differences between the structure,
the instincts, or other elements which compose the mechanism of
the offspring, and those which were proper to the parent, the name
Variation has been given.

We have seen above that the two leading facts respecting the
forms of living things are first that they shew specific differen-
tiation, and secondly that they are adapted. To these we may
now add a third, that in the succession from parent to offspring
there is, or may be, Variation. It is upon the fact of the exist-
ence of this phenomenon of Variation that all inductive theories
of Evolution have been based.

1—2

4 A POSTULATE. [introd.

The suggestion which thus forms the common ground of these
theories is this : — May not the Specific Differences between Species
and Species have come about through and be compounded of the
individual differences between parent and offspring ? May not
Specific Differentiation have resulted from Individual Variation ?
This suggestion has been spoken of as the Doctrine of Common
Descent, for it asserts that there is between living things a
community of descent.

In what follows it will be assumed that this Doctrine of
Descent is true. It should be admitted from the first that the
truth of the doctrine has never been proved. There is never-
theless a great balance of evidence in its favour, but it finds its
support not so much in direct observation as in the difficulty of
forming any alternative hypothesis. The Theory of Decent in-
volves and asserts that all living things are genetically connected,
and this principle is at least not contrary to observation ; while
any alternative hypothesis involves the idea of Separate Creation
which by common consent is now recognized as absurd. In favour
of the Doctrine of Common Descent there is a balance of evidence:
it is besides accepted by most naturalists ; lastly if it is not true
we can get no further with the problem : but inasmuch as it is
unproven, it is right that we should explicitly recognize that it is
in part an assumption, and that we have adopted it as a pos-
tulate.

The Doctrine of Descent being assumed, two chief solutions of
the problem have been offered, both starting alike from this
common ground. Let us now briefly consider each of them.

A. Lamarck's Solution. So many ambiguities and pitfalls are
in the way of any who may try to re-state, in a few words, the
theory propounded in the Philosoplvie Zoologique, that it is with
great diffidence that the following account of it is given.

Lamarck points out that living things can in some measure
adapt themselves both structurally and physiologically to new
circumstances, and that in certain cases the adaptability is present
in a high degree. He suggests that by inheritance and perfection
of such adaptations they may have become what they are, and that
thus specific forms and mechanisms have been produced, as it were,
by sheer force of circumstances. On this view it is assumed that
to the demands made on it by the environment the organism
makes an appropriate structural and physiological response ; in
other words, that there is in living things a certain tension, by
which they respond to environmental pressure and fit the place
they are in, somewhat as a fluid fits a vessel.

This is not, I think, a misrepresentation of Lamarck's theory.
It amounts, in other words, to a proposal to regard organisms as
machines which have the power of Adaptation as one of their
fundamental and inherent qualities or attributes.

sect, l] introduction. 5

Without discussing this solution, we may oote that it aims at
being a complete solution of both

(1) The existence and persistence of differing forms,
{'!) The fact that the differing forms are adapted fco
different conditions ;
and (3) The causes of the Variation by which the diversity baa
occurred.

B. Darwin's Solution. Darwin, without suggesting causes of
Variation, points out that since (1) Variations occur — which they
are known to do — and since (2) some of the variations are in tin-
direction of adaptation and others are not — which is a necessil v —
it will result from the conditions of the Struggle for Existence
that those better adapted will on the whole persist and the less
adapted will on the whole be lost. In the result, therefore, there
will be a diversity of forms, more or less adapted to the states
in which they are placed, and this is very much the observed
condition of living things.

We may note that this solution does not aim at being a com-
plete solution like Lamarck's, for as to the causes of Variation it
makes no suggestion.

The arguments by which these several solutions are supported,
and the difficulties which are in the way of each, are so familiar
that it would be unprofitable to detail them. On our present
knowledge the matter is talked out. Those who are satisfied with
either solution are likely to remain so.

It may be remarked however that the observed cases <<t" adap-
tation occurring in the way demanded on Lamarck's theory are
very few, and as time goes on this deficiency of facts begins to be
significant. Natural Selection on the other hand is obviously a
• true cause,' at the least.

In the way of both solutions there is one cardinal difficulty
which in its most general form maybe thus expressed. Aco.rding
to both theories, specific diversity of form is consequent upon
diversity of environment, and diversity of environment is thus
the ultimate measure of diversity of specific form. Mere then we
meet the difficulty that diverse environments often shade into
each other insensibly and form a continuous series, whereas the
Specific Forms of life which are subject to them on the whole
form a Discontinuous Series. The immense significance of this
difficulty will be made more apparent in the course of this work
The difficulty is here put generally. Particular instances have
been repeatedly set forth. Temperature, altitude, depth of water.
salinity, in fact most of the elements which make up the physical
environment are continuous in their gradations, while, as a rule,
the forms of life are discontinuous1. Besides this, forms which

1 It may be objected that to any organism tbe other organisms coexisting with
it are as serious a factor of tbe environment as the strictly physical components;
and that inasmuch as these coexisting organisms are discontinuous Bpecies, the

6 METHODS OF ATTACKING THE PROBLEM. [ixtrod.

are apparently identical live under conditions which are apparently
very different, while species which though closely allied are con-
stantly distinct are found under conditions which are apparently
the same. If we would make these facts accord with the view
that it is diversity of environment which is the measure of
diversity of specific form, it is necessary to suppose either (1)
that our estimate of similarity of forms, or of environment, is
wholly untrustworthy, or else (2) that there is a wide area of
environmental or structural divergence within which no sensible
result is produced : that is to say, that the relation between en-
vironment and structure is not finely adjusted. But either of these
admissions is serious ; for if we grant the former we abrogate the
right of judgment, and are granting that our proposed solutions
are mere hypotheses which we have no power to test, while if we
admit the latter, we admit that environment cannot so far be either
the directing cause or the limiting cause of Specific Differences,
though the first is essential to Lamarck's Theory, and the second is
demanded by the doctrine of Natural Selection.

Such then, put very briefly, are the two great theories, and this
is one of the chief difficulties which beset them. We must now
pass to our proper work.

We have to consider whether it is not possible to get beyond
the present position and to penetrate further into this mystery
of Specific Forms. The main obstacle being our own ignorance,
the first question to be settled is what kind of knowledge would
be of the most value, and which of the many unknowns may
be determined with the greatest profit. To decide this we must
return once more to the ground which is common to all the induc-
tive theories of Evolution alike. Now all these different theories
start from the hypothesis that the different forms of life are re-
lated to each other, and that their diversity is due to Variation.
On this hypothesis, therefore, Variation, whatever may be its cause,
and however it may be limited, is the essential phenomenon of
Evolution. Variation, in fact, is Evolution. The readiest way,
then, of solving the problem of Evolution is to study the facts of
Variation.

SECTION II.

Alternative Methods.

The Study of Variation is therefore suggested as the method
which is on the whole more likely than any other to give us the
kind of knowledge we are wanting. It should be tried not so
much in the hope that it will give any great insight into those

element of discontinuity may thus be introduced. This is true, but it does not
help iu the attempt to find the cause of the original discontinuity of the coexisting
organisms.

sect, ii.] INTRODUCTION. 7

relations of cause and effect of which Evolution is the expression,
but merely as an empirical means of getting at the outward and
visible phenomena which constitute Evolution. On the hypothesis
of Common Descent, the forms of living things are succeeding each
other, passing across the stage of the earth in a constant proces-
sion. To find the laws of the succession it will be best for us to
stand as it were aside and to watch the procession as it passes by.
No amount of knowledge of individual forms will tell us the laws or
even the manner of the succession, nor shall we be much helped by
comparison of forms of whose descent we know nothing save by
speculation. To study Variation it must be seen at the momenl
of its beginning. For comparison we require the parent and the
varying offspring together. To find out the nature of the progres-
sion we require, simultaneously, at least two consecutive terms of
the progression. Evidence of this kind can be obtained in no other
way than by the study of actual and contemporary cases of Varia-
tion. To the solution of this question collateral methods of re-
search will not contribute much.

Since Darwin wrote, several of these collateral methods have
been tried, and though a great deal has thus been done and a vast
number of facts have been established, yet the advance towards a
knowledge of the steps by which Evolution proceeds has been
almost nothing. It will not perhaps be wandering unduly if we
consider very shortly the reason of this, for the need for the Study
of Variation will thereby be made more plain.

Before the publication of the Origin of Species the wrork of
naturalists wras chiefly devoted to the indiscriminate accumulation
of facts. By most the work was done for its own sake in the strict-
est sense. In the minds of some there was of course a hope that
the gathering of knowledge would at last lead on to something
more, but this hope wras for the most part formless and vague.
With the promulgation of the Doctrine of Descent the whole course
of the study was changed. The enthusiasm of naturalists ran
altogether into new channels ; a new class of facts was sought and
the value of Zoological discovery was judged by a new criterion.
The change was thus a change of aim, and consequently a change
of method. From a large field of possibilities the choice fell
chiefly upon two methods, each having a definite relation to the
main problem. The first of these is the Embryological Method,
and the second may be spoken of as the Study of Adaptation.
The pursuit of these two methods was the direct outcome of
Darwin's work, and such great hopes have been set on them that
before starting on a new line we shall do well to examine carefully
their proper scope and see whither each of them may reasonably
be expected to lead.

It is besides in the examination of these methods and in ob-
serving the exact point at which they have failed, that the need
for the Study of Variation will become most evident.

8 THE EMBRYOLOGICAL METHOD. [introd.

When the Theory of Evolution first gained a hearing it became
of the highest importance that it should be put to some test which
should shew whether it was true or not. In comparison with this
all other questions sank into insignificance.

Now, the principle which has been called the Law of von Baer,
provided the means for such a test. By this principle it is affirmed
that the history of the individual represents the history of the
Species. If then it should be found that organisms in their de-
velopment pass through stages in which they resemble other forms,
this would be 'prima facie a reason for believing them to be geneti-
cally connected. The general truth of the Theory of Descent
might thus be tested by the facts of development, For this reason
the Study of Embryology superseded all others. It is now, of course,
generally admitted that the Theory has stood this test, and that
the facts of Embryology do support the Doctrine of Community of
Descent.

But the claims of Embryology did not stop here. In addition
to the application of the method to the general Theory of Descent,
it has been sought to apply the facts of Embryology to solve
particular questions of the descent of particular forms. It has
been maintained that if it is true that the history of the individual
repeats the history of the Species, wre may in the study of De-
velopment see not only that the various forms are related, but
also the exact lines of Descent of particular forms. In this way
Embryology was to provide us with the history of Evolution.

The survey of the development of animals from this point of
view is now complete for most forms of life, and in all essential
points; we are now therefore in a position to estimate its value.
It will, I think, before long be admitted that in this attempt to
extend the general proposition to particular questions of Descent
the embryological method has failed. The reason for this is
obvious. The principle of von Baer was never more than a
rough approximation to the truth and was never suited to the
solution of particular problems. It is curious to notice upon how
very slight a basis of evidence this widely received principle really
rests. It has been established almost entirely by inference and
it has been demonstrated by actual observation in scarcely a single
instance.

For the stages through which a particular organism passes
in the course of its development are admissible as evidence of
its pedigree only when it shall have been proved as a general
truth that the development of individuals does follow the lines
on wmich the species developed. The proof, however, of this
general proposition does not rest on direct observation but on
the indirect evidence that particular organisms at certain stages
in their development resemble other organisms, and hence it
is assumed that they are descended from those forms. Thus the
truth of the general proposition is established by assuming it

sect. II.] INTRODUCTION. 9

true in special cases, while its applicability to special cases rests
on its having been accepted as a general truth.

Probably however the apologists of this method would main-
tain that the principle of von Baer, though its truth has nol
been demonstrated directly, yet belongs to the class of "True
Hypotheses." To establish the truth of a hypothesis in a case
like the present in which the number of possible hypotheses is
not limited, it should at least be shewn that its application in all
known instances is so precise, so simple, and in such striking
accordance with ascertained facts, that its truth is felt to be
irresistible.

Nothing like this can be said of the principle of von Baer.
Even if it be generally true that the development of a form is
a record of its descent, it has never been suggested that the record
is complete.

Allowance must constantly be made for the omission of stages.
for the intercalation of stages, for degeneration, for the presence
of organs specially connected with larval or embryonic life, for
the interference of yolk and so forth. But what this allowance
should be and in what cases it should be made has never beeD
determined.

More than this: closely allied forms often develop on totally
different plans; for example, Balanoglossus Kowalevskii has an
opaque larva which creeps in the sand, while the other species of
the family have a transparent larva which swims at the surface of
the sea; the germinal layers of the Guinea-pig when compared with
those of the Rabbit are completely inverted, and so on. These are
not isolated cases, for examples of the same kind occur in almost
every group and in the development of nearly all the systems of
organs. When these things are so, who shall determine which de-
velopmental process is ancestral and which is due to secondary
change ? By what rules may secondary changes be recognized as
such? Do transparent larvae swimming at the surface of the sea
reproduce the ancestral type or does the opaque larva creeping in
the mud shew us the primitive form? Each investigator has
answered these questions in the manner which seemed best to
himself.

There is no rule to guide us in these things and there is no
canon by which we may judge the worth of the evidence. It is
perhaps not too much to say that the main features of the de-
velopment of nearly every type of animal are now ascertained,
and on this knowledge elaborate and various tables of phylogeny
have been constructed, each differing from the rest and all plau-
sible; but it would be difficult to name a single case in which
the immediate pedigree of a species is actually known.

The Embryological Method then has failed not for want of
knowledge of the visible facts of development but through ignor-
ance of the principles of Evolution. The principle of von Baer.

10 THE STUDY OF ADAPTATION. [ixtrod.

taken by itself, is clearly incapable of interpreting the phenomena
of development. We are endeavouring by means of a mass of
conflicting evidence to reconstruct the series of Descent, but of the
laws which govern such a series we are ignorant. In the inter-
pretation of Embryological evidence it is constantly necessary to
make certain hypotheses as to the course of Variation in the
past, but before this can be done it is surely necessary that wre
should have some knowledge of the modes of Variation in the
present. When we shall know something of the nature of the
variations which are now occurring in animals and the steps by
which they are now progressing before our eyes, w7e shall be in
a position to surmise what their past has been ; for we shall then
know what changes are possible to them and what are not. In
the absence of such knowledge, any person is at liberty to pos-
tulate the occurrence of variations on any lines which may suggest
themselves to him, a liberty which has of late been freely used.
Embryology has provided us with a magnificent body of facts,
but the interpretation of the facts is still to seek.

The other method which, since Darwin's work, has attracted
most attention is the study of the mechanisms by which organisms
are adapted to the conditions in which they live. This study of
Adaptation and of the utility of structures exercises an extra-
ordinarv fascination over the minds of some and it is most
important that its proper use and scope should be understood.

We have seen that the Embryological Method owed its import-
ance to its value as a mode of testing the truth of the Theory
of Evolution: in the same way the Study of Adaptation was
undertaken as a test of the Theory of Natural Selection.

Amongst many classes of animals, complex structures are pre-
sent which do not seem to contribute directly to the well-being of
their possessors. By many it has been felt that the persistent
occurrence of organs of this class is a difficulty, on the hypothesis
that there is a tendency for useful structures to be retained and
for useless parts to be lost. In consequence it has been antici-
pated that sufficient research would reveal the manner in which
these parts are directly useful. The amount of evidence collected
with this object is now enormous, and most astonishing ingenuity
has been evoked in the interpretation of it. A discussion of the
truth of the conclusions thus put forward is of course apart from
our present purpose, which is to examine the logical value of this
method of research as a means of attacking the problem of Evo-
lution. WTith regard to the results it has attained it must suffice
to notice the fact that while the functions of many problematical
organs have been conjectured, in some cases perhaps rightly, there
remain wrhole groups of common phenomena of this kind, which
are still almost untouched even by speculation, and structures and
instincts are found in the best known forms, as to the " utility " of

sect, ii.] INTRODUCTION. 1 1

which no one has made even a plausible surmise. All this is fa-
miliar to every one and every one knows the various answers that
have been made.

It is not quite fair to judge such a method by the imperfection
of its results, but in one respect the deficiency of results obtained by
the Study of Adaptation is very striking, and though this has
often been recognized it must be again and again insisted on as a
thing to be kept always in view. The importance of this consider-
ation will be seen when the evidence of Variation is examined.
The Study of Adaptation ceases to help us at the exact point at
which help is most needed. We are seeking for the cause of the
differences between species and species, and it is precisely on the
utility of Specific Differences that the students of Adaptation are
silent. For, as Darwin and many others have often pointed out,
the characters which visibly differentiate species are not as a rule
capital facts in the constitution of vital organs, but more often
they are just those features which seem to us useless and trivial,
such as the patterns of scales, the details of sculpture on chitin or
shells, differences in number of hairs or spines, differences between
the sexual prehensile organs, and so forth. These differences are
often complex and are strikingly constant, but their utility is in
almost every case problematical. For example, many suggestions
have been made as to the benefits which edible moths may derive
from their protective coloration, and as to the reasons why unpalat-
able butterflies in general are brightly coloured ; but as to the
particular benefit which one dull moth enjoys as the result of his own
particular pattern of dullness as compared with the closely similar
pattern of the next species, no suggestion is made. Nevertheless
these are exactly the real difficulties which beset the utilitarian
view of the building up of Species. We knew all along that Species
are approximately adapted to their circumstances; but the diffi-
culty is that whereas the differences in adaptation seem to us to
be approximate, the differences between the structures of species
are frequently precise. In the early days of the Theory of Natural
Selection it was hoped that with searching the direct utility of
such small differences would be found, but time has been running
now and the hope is unfulfilled.

Even as to the results which rank among the triumphant suc-
cesses of this method of study there is need for great reserve.
The adequacy of such evidence must necessarily be a matter for
individual judgment, but in dealing with questions of Adaptation
more than usual caution is needed. No disrespect is intended
towards those who have sought to increase our acquaintance with
these obscure phenomena: but since at the present time the con-
clusions arrived at in this field are being allowed to pass unchal-
lenged to a place among the traditional belief's of Science, it is
well to remember that the evidence for these beliefs is far from
being of the nature of proof.

12 FUTILITY OF THIS METHOD. [introd.

The real objection however to the employment of the Study of
Adaptation as a means of discovering the processes of Evolution is
not that its results are meagre and its conclusions unsound. Apart
from the doubtful character of these inferences, there is a difficulty
of logic which in this method is inherent and insuperable. This
difficulty lies in the fact that while it is generally possible to
suggest some way by which in circumstances, known or hypothe-
tical, any given structure may be of use to any animal, it cannot on
the other hand ever be possible to prove that such structures are
not on the whole harmful either in a way indicated or otherwise.
There is a special reason why the impossibility of proving the
negative applies with peculiar force to the mode of reasoning we
are now considering. This is due to the fact that whereas the
only possible test of the utility of a structure must be a quan-
titative one, such a quantitative method of assessment is entirely
beyond our powers and is likely to remain so indefinitely. The
students of Adaptation forget that even on the strictest applica-
tion of the theory of Selection it is unnecessary to suppose that
every part an animal has, and every thing which it does, is useful
and for its good. We, animals, live not only by virtue of, but also
in spite of what we are. It is obvious from inspection that any
instinct or any organ may be of use : the real question we have to
consider is of how much use it is. To know that the presence of a
certain organ may lead to the preservation of a race is useless if we
cannot tell how much preservation it can effect, how many indi-
viduals it can save that would otherwise be lost; unless we kn<»w
also the degree to which its presence is harmful ; unless, in fact, we
know how its presence affects the profit and loss account of the
organism. We have no right to consider the utility of a structure
demonstrated, in the sense that we may use this demonstration as
evidence of the causes which have led to the existence of the struc-
ture, until we have this quantitative knowledge of its utility and are
able to set off against it the cost of the production of the structure
and all the difficulties which its presence entails on the organism.
X<> one who has ever tried to realize the complexity of the relations
between an organism and its surroundings, the infinite variety of
the consequences which every detail of structure and every shade of
instinct may entail upon the organism, the precision of the correla-
tion between function and the need for it, and above all the mar-
vellous accuracy with which the- presence or absence of a power or
a structure is often compensated among living beings — no one can
reflect upon these things and be hopeful that our quantitative
estimates of utility are likely to be correct. But in the absence of
such correct and final estimates of utility, we must never use the
utility of a structure as a point of departure in considering the
manner of its origin ; for though we can see that it is, or may be,
useful, yet a little reflexion will shew that it is, or may be, harmful,
but whether on the whole it is useful or on the whole harmful,

sect, in.] INTRODUCTION. 1 3

can only be guessed at. It thus happens that we can only gel
an indefinite knowledge of Adaptation, which for the purposes of
our problem is not an advance beyond the original knowledge
that organisms are all more or less adapted to their circumstanc< -.
No amount ot" evidence of the same kind will can-)' us beyond this
point. Hence, though the Study of Adaptation will alwaysremain
a fascinating branch of Natural History, it is not and cannot be a
means of directly solving the problem of the origin of Species.

SECTION III.
Continuity oh Discontinuity of Variation.

What is needed, then, is evidence of a new kind, for do
amount of evidence of the kinds that have been mentioned will
take us much beyond our present position. We need more know-
ledge, not so much of the facts of anatomy or development, as of
the principles of Evolution. The question to be considered is how
such knowledge may be obtained. It is submitted that the
Study of Variation gives us a chance, and perhaps the only one, of
arriving at this knowledge.

But though, as all will admit, a knowledge of Variation lies at
the root of all biological progress, no organized attempt to obtain it
has been made. The reason for this is not very clear, but it
apparently proceeds chiefly from the belief that the subject is ton
difficult and complex to be a profitable field for study. However
this maybe, the fact remains, that since the first brief treatment of
the matter in Animals and Plants under Domestication do serious
effort to perceive or formulate principles of Variation has been
made, and there is before us nothing but the most meagre ami
superficial account of a few of its phenomena. Darwin's firsl
collection of the facts of Variation has scarcely been increased.
These same facts have been arranged and rearranged by each
successive interpreter: the most various and contradictory pro-
positions have been established upon them, and they have been
strained to shew all that it can possibly he hoped that they will
shew. Any one who cares to glance at the works ot' those who
have followed Darwin in these fields mav assure himself ot'
this. So far, indeed, are the interpreters of Evolution from adding
to this store of facts, that in their hands the original -t<><k
becomes even less until only the most striking remain. It is
wearisome to watch the persistence with which these are revived
for the purpose of each new theorist. How well we know the
offspring of Lord Morton's mare, the bitch 'Sappho,' t he Sebright
Bantams, the Himalaya Rabbit with pink eyes, the white Cats
with their blue eyes, and the rest! Perhaps the time has come

14 THE PHYLOGENETIC SERIES I [introd.

when even these splendid observations cannot be made to shew
much more. Surely their use is now rather to point the direction
in which we must go for more facts.

The questions which by the Study of Variation we hope to
answer may be thus expressed. In affirming our belief in the
doctrine of the Community of Descent of living things, we declare
that we believe all living things to stand to each other in definite
genetic relationships. If then all the individuals which have
lived on the earth could be simultaneously before us, we believe
that it would be possible to arrange them all, so that each stood
in its own ordinal position in series. We believe that all the
secondary series together make up one primary series from which
each severally arises. This is the fundamental conception of
Evolution and is represented figuratively by the familiar image of
a genealogical tree. If then all the individual ancestors of any
given form were before us and were arranged in their order, we
believe thev would constitute a series. This view of the forms of
organisms as constituting a series or progression is the central idea
of modern biology, and must be borne continually in mind in the
attempt to apply any principle to the Study of Evolution.

Each individual and each type which exists at the present
moment stands, for the moment, therefore, as the last term of
such a series. The problem is to rind the other terms. In the
case of each type the question is thus stated in a particular
form, and it is a somewhat remarkable circumstance that it is in
its particular forms that this problem has been most studied.
The same problem is nevertheless capable of being stated in the
general form also. Instead of considering what has been the
actual series from which a specified type has been derived, we may
consider what are the characters and attributes of such series in
general. It may indeed be contended that it is scarcely reason-
able to expect to discover the line of descent of a given form, for
the evidence is gone ; but we may hope to find the general
chararacteristics of Evolution, for Evolution, as we believe, is still
in progress. It is really a strange thing that so much enterprise
and research should have been given to the task of reconstructing
particular pedigrees — a work in which at best the facts must be
eked out largely with speculation — while no one has ever seriously
tried to determine the general characters of such a series. Yet if
our modern conception of Descent is a right one, it is a pheno-
menon now at this time occurring, which by common observations,
without the use of any imagination whatever, we may now see.
The chief object, then, with which we shall begin the Study of
Variation will be the determination of the nature of the Series by
which forms are evolved.

The first questions that we shall seek to answer refer to the
manner in which differentiation is introduced in these Series.

sect, in.] INTRODUCTION. 15

All we as yet know is the hist term of the Series. By the
postulate of Common Descent we take it that the hist term
differed widely from the last, which nevertheless is its lineal
descendant: how then was the transition from the first term to
the last term effected? If the whole series were before us, should
we find that this transition had been brought about by very
minute and insensible differences between successive terms in the
Series, or should we find distinct and palpable gaps in the Series
In proportion as the transition from term to term is minimal and
imperceptible we may speak of the Series as being Continuous,
while in proportion as there appear in it lacunae, filled by no
transitional form, we may describe it us Discontinuous. The
several possibilities may be stated somewhat as follows. The
Series may be wholly continuous; on the other hand it may be
sometimes continuous and sometimes discontinuous; we know how-
ever by common knowledge that it is never wholly discontinuous.
It may be that through long periods of the Series the differences
between each member and its immediate predecessor and successor
are impalpable, while at certain moments the series is interrupted
by breaches of continuity which divide it into groups, of which the
composing members are alike, though the successive groups are
unlike. Lastly, discontinuity may occur in the evolution of par-
ticular organs or particular instincts, while the changes in other
structures and svstems may be effected continuous] v. To decide
which of these agrees most nearly with the observed phenomena of
Variation is the first question which we hope, by the Study of
Variation, to answer. The answer to this question is of vital con-
sequence to progress in the Study of Life.

The preliminary question, then, of the degree of continuity
with which the process of Evolution occurs, has never been
decided. In the absence of such a decision there has never-
theless been a common assumption, either tacit or expressed, that
the process is a continuous one. The immense consequence of a
knowledge of the truth as to this will appear from a consideration
of the gratuitous difficulties which have been introduced by this
assumption. Chief among these is the difficulty which has been
raised in connexion with the building up of now organs in their
initial and imperfect stages, the mode of transformation of organs,
and, generally, the Selection and perpetuation of minute variations.
Assuming then that variations are minute, we are met by this
familiar difficulty. We know that certain devices and mechanisms
are useful to their possessors; but from our knowledge of Natural
History we are led to think that their usefulness is consequent on
the degree of perfection in which they exist, and thai if they were
at all imperfect, they would not be useful. Now it is clear that in
any continuous process of Evolution such stages of imperfection
must occur, and the objection has been raised that Natural
Selection cannot protect such imperfect mechanisms so as to lift

16 CONTINUOUS, OR DISCONTINUOUS? [iNTBOD.

them into perfection. Of the objections which have been brought
against the Theory of Natural Selection this is by far the most
serious.

The same objection may be expressed in a form which is more
correct and comprehensive. We have seen that the differences
between Species on the whole are Specific, and are differences of
kind, forming a discontinuous Series, while the diversities of en-
vironment to which they are subject are on the whole differences
of degree, and form a continuous Series ; it is therefore hard to
see how the environmental differences can thus be in any sense
the directing cause of Specific differences, which by the Theory of
Natural Selection they should be. This objection of course in-
cludes that of the utility of minimal Variations

Now the strength of this objection lies wholly in the sup-
posed continuity of the process of Variation. We see all organ-
ized nature arranged in a discontinuous series of groups differing
from each other by differences which are Specific ; on the other
hand we see the divers environments to which these forms are
subject passing insensibly into each other. We must admit, then,
that if the steps by which the divers forms of life have varied
from each other have been insensible — if in fact the forms ever
made up a continuous series — these forms cannot have been
broken into a discontinuous series of groups by a continuous en-
vironment, whether acting directly as Lamarck would have, or
as selective agent as Darwin would have. This supposition has
been generally made and admitted, but in the absence of evidence
as to Variation it is nevertheless a gratuitous assumption, and
as a matter of fact when the evidence as to Variation is studied,
it will be found to be in great measure unfounded.

In what follows so much will be said of discontinuity in Varia-
tion that it will not be amiss to speak of the reasons which have
led many to suppose that the continuity of Variation needs no
proof. Of these reasons there are especially two. First there
is in the minds of some persons an inherent conviction that all
natural processes are continuous. That many of them do not
appear so is admitted: it is admitted, for example, that among
chemical processes Discontinuity is the rule ; that changes in the
states of matter are commonly effected discontinuously, and the
like. Nevertheless it is believed that such outward and visible
Discontinuity is but a semblance or mask which conceals a real
process which is continuous and which by more searching may
be found. With this class of objections we are not perhaps con-
cerned, but they are felt by so many that their existence must not
be forgotten. Secondly, Variation has been supposed to be always
continuous and to proceed by minute steps because changes of
this kind are so common in Variation. Hence it has been inferred
that the mode of Variation thus commonly observed is universal.
That this inference is a wrong one, the facts will shew.

sect, iv.] INTRODUCTION. 17

To sum up :

The first question which the Study of Variation may be ex-
pected to answer, relates to the origin of that Discontinuity of
which Species is the objective expression. Such Discontinuity
is not in the environment; may it not, then, be in the living
thing itself?

The Study of Variation thus offers a means whereby we may
hope to see the processes of Evolution. We know much of what
these processes may be: the deductive method has been tried,
with what success we know. It is time now to try if these things
cannot be seen as they are, and this is what Variation may shew
us. In Variation we look to see Evolution rolling out before our
eyes. In this we may foil wholly and must fail largely, but it.
is still the best chance left.

SECTION IV.
Symmetry and M eristic Repetition.

Having thus indicated some of the objects which we may
hope to reach by the Study of Variation, we have next to consider
the way in which to set about this study.

The Study of Variation is essentially a study of differences
between organisms, so for each observation of Variation at Leasl
two substantive organisms are required for comparison. It is
proposed to confine the present treatment of the subject to a
consideration of the integral steps by which A^ariation may pro-
ceed; hence it is desirable that the two organisms compared
should be parent and offspring, and if, as is often the case, the
actual parent is unknown, it is at least necessary that the normal
form of the species should be known and that there must be
reasonable evidence that the varying offspring is actually de-
scended from such a normal. For this reason, evidence from a com-
parison of Local Races, and other established Varieties, though a
very valuable part of the Study, will for the most part not be here
introduced. For the belief that such races are descended from i ln-
putative normal scarcely ever rests on proof, and still more rarely
is there evidence of the number of generations in which the
change has been effected.

For our purpose we require actual cases of Variations occurring
as far as possible in offspring of known parentage: and if, foiling
this, we make use of cases occurring in the midst of normal indi-
viduals of known structure, it must in such cases be always
remembered that we cannot properly assume that the varying form
is the offspring of such individuals, though special reasons may
make this likely in special cases.

Since the structure of the offspring is perhaps in no case
b. 2

1 8 HETEROGENEITY. [introd.

identical with that of the parent, observation of any parent and
its offspring is to the point ; but such a field as this is plainly too
wide to be studied with profit as a whole, and it is necessary from
the first, that attention should be limited to certain classes of such
phenomena. With this object certain limitations are proposed,
and though confessedly arbitrary, they will be found on the whole
to work well.

The first limitation thus introduced concerns the magnitude
of Variations. We have seen above that the assumption that
Variation is a continuous process lands us in serious difficulties
in the application of a hypothesis which, on general grounds,
we nevertheless are prepared to receive. If then we can shew
that Variation is to some extent discontinuous, a road will be
opened by which these difficulties may perhaps be in part avoided.

Species are discontinuous ; may not the Variation by which
Species are produced be discontinuous too ? It may be stated at
once that evidence of such Discontinuous Variation does exist,
and in this first consideration of the subject attention will be con-
fined to it. The fact that Continuous Variation exists is also none
the less a fact, but it is most important that the two classes of
phenomena should be recognized as distinct, for there is reason to
think that they are distinct essentially, and that though both may
occur simultaneously and in conjunction, yet they are manifesta-
tions of distinct processes. The attempt to distinguish these two
kinds of Variation from each other constitutes one of the chief
parts of the study. It will not perhaps be possible to find any
general expression which shall accurately differentiate between
Variations which are Discontinuous and those which are Con-
tinuous, but it is possible to recognize attributes proper to each
and to distinguish changes which are or may be effected in the one
way from other changes which are or may be effected in the other.

For the present wre shall treat only of the evidence of Dis-
continuous Variation.

In order to explain the second limitation wThich is to be intro-
duced it is necessary to refer to some phenomena which are
characteristic of the forms of organisms, and to separate from them
the group with which we shall deal first.

It was stated above that perhaps no character of form is
common to all living things, but nevertheless there is one feature
which is found in the great majority.

In the first place, the bodies of organisms are not homo-
geneous but heterogeneous, consisting of organs or parts which
in substance and composition differ from each other. This
heterogeneity in composition is of course an objective expression
of the process of Differentiation, and it is further recognized
that such structural heterogeneity of material corresponds with
a physiological Differentiation of function. This Differentiation

-sect, iv.] INTRODUCTION. 19

or Heterogeneity is found in the bodies of all organisms, even
in the simplest.

Now in a wide survey of the forms of living things there is
a fact with regard to the presence of this Heterogeneity which bo
the purpose of our present consideration is of the highest con-
sequence. This may perhaps be best expressed by the state-
ment that in the bodies of living things Heterogeneity is generally
orderly and formal ; it is cosmic, not chaotic. Not only are the
bodies of all organisms heterogeneous, but in the great majority
the Heterogeneity occurs in a particular way and according to
geometrical rule. This character is not peculiar to a few
organisms, but is common to nearly all. We will now examine
this phenomenon of geometrical order in Heterogeneity and try
to see some of the elements of which it is made up.

Order of form will first be found to appear in the fact that in
any living body the Heterogeneity is in some degree symmetri-
cally distributed around one or more centres. In the great
majority of instances these centres of symmetry are themselves
distributed about other centres, so that in one or more planes the
whole body is symmetrical.

The idea of Symmetry which is here introduced is so familiar
that it is scarcely necessary to define it, but as all that follows
depends entirely on the proper apprehension of what is meant by
Symmetry it may be well to call attention to some of the phenomena
which the term denotes.

In its simplest form the Symmetry of a figure depends on the
fact that from some point within it at least two lines may be
taken in such a way that each passes through parts which are
similar and similarly disposed. The point from which the lines
are taken may be called a centre of Symmetry and the lines may
be called lines of Symmetrical Repetition.

Commonly the parts thus symmetrically disposed are related
to each other as optical images [in a plane mirror passing through
the centre of Symmetry and standing in a plane bisecting the
angle which the lines of Symmetrical Repetition make with each
other]. For a figure to be symmetrical, in the ordinary sense of
the term, it is not necessary that the relation of optical images
should strictly exist, and several figures, such as spirals, &c.,
are accordingly described as symmetrical. But since the relation
of images exists in all cases of bilateral and radial symmetry, which
are the forms most generally assumed in the symmetry of organ-
isms, it is of importance to refer particularly to this as one of
the phenomena often associated with Symmetry.

In the simplest possible case of Symmetry there is a series
of parts in one direction corresponding to a series of parts in
another direction. Perhaps there is no organism in which such an
arrangement does not at some time and in some degree exist.
For even in an unsegmented ovum or a resting Amoeba there is

20 MERISTIC REPETITION. [introd.

little doubt that Symmetry is present, though owing to the slight
degree of Differentiation, its presence may not be clearly
perceived. In the manifestations, however, in which it is most
familiar, Symmetry is a decided and obvious phenomenon.

Symmetry then depends essentially on the fact that structures
found in one part of an organism are repeated and occur again in
another part of the same organism. Symmetrical Heterogeneity
may therefore be present in a spherical body having a core
of different material, and it is possible that in an unsegmented
ovum for example a Symmetry of this simple kind may exist.
But Symmetry, as it is generally seen in organisms, differs from
that of these simplest cases in the fact that the organs repeated
are separated from each other by material of a nature different
from that of the organs separated. Repetitions of this kind are
known in almost every group of animals and plants. The parts
thus separated may belong to any system of organs. There is no
known limit to the number of Repetitions that may occur.

This phenomenon of Repetition of Parts, generally occurring
in such a way as to form a Symmetry or Pattern, comes near to
being a universal character of the bodies of living things. It will
in cases which follow be often convenient to employ a single term
to denote this phenomenon wherever and however occurring.
For this purpose the term Merism will be used. The introduc-
tion of a new term is, as a practice, hardly to be justified; but in
a case like the present, in which it is sought to associate divers
phenomena which are commonly treated as distinct, the employ-
ment of a single word, though a new one, is the readiest way of
giving emphasis to the essential unity of the phenomena comprised.

The existence of patterns in organisms is thus a central fact
of morphology, and their presence is one of the most familiar
characters of living things. Anyone who has ever collected
fossils, or indeed animals or plants of any kind, knows how in
hunting, the eye is caught by the formal regularity of an organized
being, which, contrasting with the irregularity of the ground, is
often the first indication of its presence. Though of course not
diagnostic of living things, the presence of patterns is one of their
most general characters.

On examining more closely into the constitution of Repetitions,
they may be seen to occur in two ways ; first, by Differentiation
within the limits of a single cell, as in the Radiolaria, the sculpture
of egg-shells, nuclear spindles, &c, to take marked cases ; and
secondly, by, or in conjunction with, the process of Cell-Division.
The Symmetry which is found in the Serial Repetitions of Parts in
unicellular organisms does not in all probability differ essentially
from that which is produced by Cell-Division, for, though suffi-
ciently distinct in outward appearance, the two are almost cer-
tainly manifestations of the same power.

sect, iv.] INTRODUCTION. 21

Such patterns may exist in single cells or in groups of cells, in
separate organs or in groups of organs, in solitary tonus or in
colonies and groups of forms. Patterns which arc completed in the
several organs or parts will be referred to as Minor Symmetries.
These may be compounded together into one single pattern, which
includes the whole body: such a symmetry will be called a Major
Symmetry. In most organisms, whether colonial or solitary,
there is such a Major Symmetry ; on the other hand organisms
are known in which each system of Minor Symmetry is, at least
in appearance, distinct and without any visible geometrical relation
to the other Minor Symmetries. Examples of this kind are not
common, for, as a rule, the planes about which each Minor
Symmetry is developed have definite geometrical relations to
those of the other Minor Symmetries. It is possible, even, that in
some if not all of these, the planes of division by which the tissues
composing each system of Minor Symmetry are originally split off
and differentiated, have such definite relations, though by sub-
sequent irregularities of growth and movement these relations are
afterwards obscured.

The classification of Symmetry and Pattern need not now be
further pursued. The matter will be often referred to in the
course of this work, when facts concerning Variations in number
and patterns are being given, for it is by study of Variations in
pattern and in repetition of parts that glimpses of the essential
phenomena of Symmetry may be gained.

That which is important at this stage is to note the almost
universal presence of Symmetry and of Repetition of Parts among
living things. Both are the almost invariable companions of divisi- m
and differentiation, which are fundamental characters without which
Life is not known.

The essential unity of the phenomenon of Repetition of Parts
and of its companion-phenomenon, Symmetry, wherever met with,
has been too little recognized, and needless difficulty has thus been
introduced into morphology. To obtain a grasp of the nature of
animal and vegetable forms, such recognition is of the first eon
sequence.

To anyone who is accustomed to handle animals or plants, and
who asks himself habitually — as every Naturalist must — how they
have come to be what they are, the question of the origin and
meaning of patterns in organisms will be familiar enough. They
are the outward and visible expression of that, order and complete-
ness which inseparably belongs to the phenomenon of Life.

If anyone will take into his hand some complex piece of living
structure, a Passion-flower, a Peacock's feather, a Cockle-shell, or
the like, and will ask himself, as I have said, how it has come to
be so, the part of the answer that he will find it hardest to give, is
that which relates to the perfection of its pattern.

And it is not only in these large and tangible structures that

22 VARIATION MERISTIC AND SUBSTANTIVE. [introd.

the question arises, for the same challenge is presented in the most
miuute and seemingly trifling details. In the skeleton of a Diatom
or of a Radiolarian, the scale of a Butterfly, the sculpture on a
pollen-grain or on an egg-shell, in the wreaths and stars of nuclear
division, such patterns again and again recur, and again and again
the question of their significance goes unanswered. There are
many suggestions, some plausible enough, as to why the tail
of a Peacock is gaudy, why the coat of a pollen-grain should be
rough, and so forth, but the significance of patterns is untouched
by these. Nevertheless, repetitions arranged in pattern exist
throughout organized Nature, in creatures that move and in those
that are fixed, in the great and in the small, in the seen and in
the hidden, within and without, as a property or attribute of Life,
scarcely less universal than the function of respiration or meta-
bolism itself.

Such, then, is Symmetry, a character whose presence among
organisms approaches to universality.

SECTION V.
Meristic Variation and Substantive Variation.

It is to the origin and nature of Symmetry that the first
section of the evidence of Variation will relate. That a knowledge
of the modes of Variation of so universal a character is important
to the general study of Biology must at once be evident, but to
the particular problem of the nature of Specific Differences this
importance is immense. This special importance comes from two
reasons. As it is the fact first that Repetition and Symmetry are
among the commonest features of organized structure, so it will be
found next that it is by differences in those features that the various
forms of organisms are very commonly differentiated from each other.
Their forms are classified by all sorts of characters, by shape and
proportions, by size, by colour, by habits and the like ; but perhaps
almost as frequently as by any of these, by differences in number
of parts and by differences in the geometrical relations of the parts.
It is by such differences that the larger divisions, genera, families,
&c. are especially distinguished. In such cases of course the
differences in number and Symmetry do not as a rule stand
alone, but are generally, and perhaps always, accompanied by
other differences of a qualitative kind ; nevertheless, the differ-
ences in number and Symmetry form an integral and very definite
part of the total differences, so that in any consideration of the
nature of the processes by which the differences have arisen,
special regard must be had to these numerical and geometrical,
or, as I propose to call them, Meristic, changes.

sect, v.] INTRODUCTION. 23

In the present Introduction I do not propose to forestall the
evidence more than is absolutely necessary for the purpose of
making clear the principles on which the facts are grouped, but
it will do the evidence no wrong if at the present stage it is stated
that Meristic Variation is frequently Discontinuous, and that in
the case of certain classes of Repetitions is perhaps always so.

The nature of Merism and the manner in which Meristic
Variations occur will be fully illustrated hereafter, but it Is
necessary to say this much at the present stage, since it is from
this Discontinuity in the occurrence of Meristic Variations that
the phenomena of Symmetry and Repetition derive their special
importance in the Study of Variation.

The importance of the phenomena of Merism to the Study of
Variation is thus, in the first instance, a direct one, for the Varia-
tions which have resulted in the production of Meristic Systems
are a direct factor in Evolution. In addition to this direct relation
to the Study of Variation, the phenomena of Merism have also an
indirect relation, which is scarcely less important ; for they are a
factor in the estimation of the magnitude of the integral steps by
which Variation proceeds. This will be more evident after the
second group of Variations has been spoken of.

We have thus far spoken only of the processes by which the
living body is divided into parts, and we have thus constituted a
group which is to include Variations in number, Division, and geo-
metrical position. From these phenomena of Division may be
distinguished Variations in the actual constitution or substance
of the parts themselves. To these Variations the name Substan-
tive will be given. Under this head several phenomena may be
temporarily grouped together, which with further knowledge will
doubtless be found to have no real connexion with each other.
For the present, however, it will be convenient to constitute such
a temporary group in order to bring out the relative distinctness of
Variations which are Meristic.

These two classes of Variation, Meristic and Substantive, may
be recognized at the outset of the study. There can be no doubt
that they are essentially distinct from each other, and the proof
that they are thus distinct will be found in the evident f Varia-
tion, for it will be seen that either may occur independently of the
other. An appreciation of this distinction is a first step towards
a comprehension of the processes by which the bodies of organisms
are evolved.

A few simple illustrations may make the nature of these two
classes of Variations more clear. For example, then, the flower of
a Narcissus is commonly divided into six parts, but through
Meristic Variation it may be divided into seven parts or into only
four. Nevertheless there is in such a case no perceptible change

24 ILLUSTRATIONS. [introd.

in the tissues or substance of which the parts are made up. All
belong to and are recognizable as belonging to the same sort of
Narcissus. On the other hand many Narcissi, i\r. corbularia, for
example, are known in two colours, one a dark yellow and the other
a sulphur-yellow, though the number of parts and pattern of the
flowers are identical. This is, therefore, an example of a Sub-
stantive Variation.

Again, the foot of a Pig may, through Meristic Variation, be
divided into five or six toes instead of into four ; or, on the other
hand, the number may, by absence of the median division between
the digits III and IV, be reduced to three, though the tissues
composing the toes may not in structure differ from the normal.

Again, the tarsus of a Cockroach (Blatta) may, through Me-
ristic Variation, be divided into only four joints instead of into
five, the normal number, but the joints are still in substance or
quality those of a Cockroach.

I am aware that Meristic and Substantive Variations often
occur together, and that there is a point at which it is not possible
to separate satisfactorily the changes which have come about by
the one process from those which have come about by the other.
Instances of this kind occur especially in the case of series of
parts such as Teeth or Vertebrae, in which individual members
or groups of members of the series are differentiated from the
others. For example, we may see that it is through Meristic
Variation that the vertebral column of a Dog may be divided into
a number of Vertebra? greater or less than the normal ; and
though in such cases all the Vertebrae have distinctively canine
characters, yet there are nearly always Substantive Variations
occurring in correlation with the Meristic Variations, manifesting
themselves in a re-arrangement of the points of division between
the several groups of Vertebrae, and causing individual Vertebrae
to assume characters which are not proper to their ordinal
positions.

Further inquiry into the questions thus raised cannot at this
stage be profitably undertaken, though when the evidence has
been considered it will perhaps be advisable to recur to them ; all
that is now intended is to indicate broadly the general scope of
Meristic and Substantive Variation respectively.

As has already been stated, it is proposed to begin the Study
of Variation by an examination of Variations which are Meristic,
leaving the consideration of Substantive Variation to be under-
taken hereafter. But nevertheless in the consideration of Meristic
Variation it will be necessary to refer to phenomena of Substantive
Variation in so far as their occurrence or distribution in the body are
affected by Meristic phenomena. For in the determination of the
magnitude of the integral steps by which Variation proceeds, the
existence of Merism plays a conspicuous part, and it is in con-

;.

M

sect, v.] INTRODUCTION. 25

sequence of this that the subject of Symmetry and Repetition of
Parts has a second and indirect bearing on the Study of Variation
which is scarcely less important than the direct bearing of which
mention has been made above.

This indirect bearing on the manner of origin of Specific
Differences arises from a circumstance which in treatises on
Evolution is commonly overlooked. In comparing a species in
which parts are repeated, with an allied species in which the same
parts are repeated, it commonly occurs that each of the repeated
parts of the one have some character by which they are dis-
tinguished from the like parts of the other. This differentiating
character may be a qualitative one, or a numerical one, or both.
In such cases it very frequently happens that this character occurs
in each member of the series of Repetitions. For example, the
tarsi of the Weevils have only four visible joints, while those
of the majority of beetles have five ; but the characteristic
division into four joints occurs in each of the legs. Before the
four-jointed character as seen in the Weevils could be produced
it was necessary that not one but all of the legs should vary from
the five-jointed form, and in this particular way. The leaves on a
beech tree are all beech leaves, and if the tree is a fern-leaved
beech, they may, and generally speaking do, all shew the charac-
ters of that variety; and so on with other particular species ami
varieties.

The limbs of a bilaterally symmetrical animal, in which the
right side is the image of the left, are of course alike, and any
specific character which is present in the limbs of the one side
must in such an animal be normally present in those of the other
side.

The same is true of many forms in which appendages are
repeated in series, as for example, the fore-legs and hind-legs
of the Horse, the fore- and hind-wings of the Brimstone Butterfly
(Gonepteryx rhamni); of the patterns on several segments of many
caterpillars ; of the patterns of the segmental setae of many worms,
and so forth. In series whose members are differentiated from each
other, it of course frequently happens that the same specific
characters are not present in all the members of the series, and in
nearly all such cases these characters are not presented by all in
equal degree; nevertheless substantially the phenomenon remains
that similar characters often are presented by the several members
of a series of repeated organs.

To many this will seem little better than a truism, neverthe-
less I offer no apology for its introduction; for though, as a
common and obvious fact, it is a truism, it is besides a truth, I la-
far-reaching significance of which is scarcely appreciated For, in
the consideration of the magnitude of the integral steps by which
Variation proceeds, we shall have this to remember : that to
produce any of the forms of which we have spoken, by V ariation

26 SIMILAR VARIATION OF PARTS IN SERIES, [introd.

from another form, it is not enough that the particular Variation
should occur and become fixed in one member of the series, but it
is necessary that the character should sooner or later be taken on
by each member of the series which exhibits it. In such cases
therefore, this question is raised. Did the Variation come in first
in one member of the Series and then in another ? Did it occur,
for example, simultaneously on the two sides of the body? Did
the right and left fore-legs of the Horse cease to develop more
than the present number of digits simultaneously or separately?
Was the similar form of the hind-legs assumed before, after, or
simultaneously with that of the fore-legs ? Were the orange
markings which are present on both fore- and hind- wings of the
Brimstone, or the ocellar markings of the Peacock ( V. Io), and of
the Emperor (Saturnia carpini), assumed by both wings at once?
Were the four wrings of the Plume Moths split simultaneously into
the characteristic " plumes " ? Did the brown spots on the three
leaflets of Medicago, the fimbriation of the petals of Ragged Robin
(Lychnis flos-cuculi), the series of stripes on the Zebra, the pink
slashes on the segments of Sphinx larvae, the eyes on the scutes
of Chitons, and the thousand other colour-marks, sense-organs,
appendages and structural features, wThich throughout organized
Nature occur in Series, vary to their present state of similarity
by similar and simultaneous steps, or did each member of
such Series take these characters by steps which were separate
and occurring independently? To this question, which lies at
the root of all progress in the knowledge of Evolution, the
Study of Variation can alone reply. That in the facts which
follow, the answer to this question will be found, cannot of course
be said ; but these facts, few though they are, do nevertheless
answer it in part, and they suggest that more facts of the same
kind would go far towards answering it completely. But beyond
this, the facts are of value as an indication of the part wrhich the
phenomenon of Merism may play in determining the magnitude of
Variations and the manner of their distribution among the several
parts of the body. On examining the evidence it will be found
that between parts related to each other in the wray that has been
described, there is a certain bond or kinship, by virtue of which
they may and often do vary simultaneously and in similar ways,
though the fact that they may also vary independently, and in
different ways, will of course also appear.

The phenomenon of the Similar Variation of parts which are
repeated Meristically in Series is a fact which will be found to
have important bearings on several distinct departments of
biological study.

As was shewn above, it is by recognition of the existence
of such similar and simultaneous Variation that the manner of
origin of the similar complexity of several organs belonging to the
same system or series becomes comparatively comprehensible ; for

sect, v.] INTRODUCTION. 27

it is not then necessary to conceive a separate origin for the com-
plexity of each member of the series. For example, it is difficult
to conceive the manner of evolution of an eye of a vertebrate ;
nevertheless, for each vertebrate tiuo eyes have been evolved. If
it were necessary to suppose that each arose by separate selections
of separate variations, the difficulty would be thus doubled. If,
however, it is recognized that the complexity of both arose simul-
taneously, the phenomenon becomes the more intelligible as the
number of integral variations and selections demanded is reduced.

The case chosen, of paired organs in bilateral symmetry, ifi
a very simple one, but it will be found that similar relations hold
between other parts repeated in series. For in the same way it is
not necessary to suppose an independent evolution for each of the
tail-feathers of the Peacock, for the legs of the Horse, and the like,
since in the light of the facts of Variation it is as easy for all t«>
take on the new characters as for one.

If the manner of development of Repeated Parts is considered,
this fact will not seem surprising. For all these parts arise from
the undifferentiated tissues by a process of Division, and what-
ever characters were potentially present in the undifferentiated
tissues may appear in the parts into which it subsequently divides.
A somewhat loose illustration will perhaps make this more clear.
Everyone knows the rows of figures which children cut out from
folded paper. There are as many figures as folds, each figure being
alike if the folds coincide. If the paper is pink, all the figures are
pink ; if the paper is white, all the figures are white, and so on.
If blotting-paper is used, and one blot is dropped on the folded
edges, the blot appears symmetrically in all the figures. So also
any deviation in the lines of cutting appear in all the figures ;
a whole row of soldiers in bearskins may be put into helmets by
one stroke of the scissors. Of course it is not meant to suggest
that the process of division by which parts of the body are pro-
duced bears any resemblance to that by which the figures are cul
out, but merely to illustrate the fact that since it is by a proc- ss
of Division of an undifferentiated mass that the Repeated Parts
are produced, so the characters of these Repeated Parts depend
upon the characters which were present in the original mass and
upon the modes by which the parts were divided out from it.

Summary of Sections I to I

r

At this point it will be well briefly to recapitulate the pre-
ceding Sections.

We are proposing to attack the problem of Species by studying
the facts of Variation. Of the facts of Variation in general we have
selected a particular group upon which to begin this study. The
group of variations thus chosen are those which relate to Number
of parts, Division, Repetition, and the other phenomena which are

28 METAMERIC SEGMENTATION. [introd.

to be included under the term Meristic. With variations in
quality and Substance it is not at present proposed to deal, except
in so far as it is necessary to refer to them in their relation to the
phenomena of Merism, and in illustration of the structural possi-
bilities or necessities which in the body follow as corollaries upon
the existence of Meristic Repetition.

It has also been proposed to limit the consideration to Varia-
tions which are Discontinuous. As has been already stated, Dis-
continuous Variations may belong to the Meristic Group or to the
Substantive, but it is to the former that attention will first be
directed.

SECTION VI.
Meristic Repetition and Homology.

In what has gone before, the two conceptions now introduced,
namely the distinction of Variations into Meristic and Substan-
tive, and into Continuous and Discontinuous, have been sketched
in outline. The significance of the facts which follow will be
made more evident if these two conceptions are now more fully
developed in some of their aspects.

Under the name Merism I have proposed to include all pheno-
mena of Repetition and Division, whenever found and in whatever
forms occurring, whether in the parts of a body or in the whole.
The consequences of the admission of this proposition are con-
siderable and should be fully realized ; for on recognition of the
unity of these phenomena it is possible to group together a number
of facts whose association will lead to simplification of some
morphological conceptions, and to other results of utility.

That the phenomena of Merism form a natural group is in
some respects a familiar idea, but in its fullest expression it is as
yet not generally received, still less have the consequences which
it entails been properly appreciated. Every one who has gone
even a little way into morphological inquiry has met some of the
difficulties to which we shall now refer.

It is with respect to the phenomena of Segmentation that
these difficulties are most familiar, and it is in this connexion that
they may be best discussed. Segmentation is a condition which
reaches its highest development in Vertebrates, the Annelids,
and the Arthropods, and it is in these groups that it has been
most studied. In them it appears as a more or less coincident
Repetition of elements belonging to most of the chief systems
of organs along an axis corresponding to the long axis of the body.
To segmentation of this kind the name ' Metameric ' has been
given, and by many morphologists the attempt has been made,
either tacitly or in words, to separate such Metameric Segmen-
tation from other phenomena of Repetition elsewhere occurring.

sect, vi.] INTRODUCTION. 29

It has thus been attempted to distinguish the Repetitions which
occur along the long axis of the body from those occurring
along the long axis of appendages, such as for example the joints
of antennae or of digits, and some have even gone so far as to
regard the Segmentation of the Vertebrate tail as a thing different
in kind from that of the trunk itself. It would be apart from our
present purpose to recur to these subjects, were it not that this
suggestion of the existence of a difference in kind between Meta-
meric Segmentation and other Repetitions has led to several
notable errors in the interpretation of the facts of morphology and
in the application of these facts to the solution of the problems of
Descent. In order to lay a sound foundation for the study of
Meristic Variation these errors must be cleared away, and to do
this it is necessary to break down the artificial distinction between
the phenomena of Metameric Segmentation and other cases of
Repetition of Parts, so that the whole may be seen in their true
relations to each other. When this is done, the mutual relations
of the facts of Meristic Variation will also become more evident.

The first difficulty which has been brought into morphology
by the suggestion that Metameric Segmentation is a phenomenon
distinct in kind, is one which has coloured nearly all reasoning
from the facts of Morphology to problems of phylogeny. For the
existence of Metameric Segmentation in any given form is thus
taken to be one of its chief characters, and, as such, is allowed pre-
dominant weight in considering the genetic relations of these
forms. By the indiscriminate though logical extension of this
principle the conclusion has been reached that Vertebrates are
immediately connected with, or have arisen by Descent from
Annelids, or from Crustacea and the like, for the Repetition in
these forms is closely similar. Others again, being struck with
the resemblance between the Repetition of Parts along the radial
axes of Starfishes and those which occur along the long axes ot"
Annelids have hazarded the conjecture that perhaps this resem-
blance may indicate the actual phylogenetic history of these
Repetitions. Though such speculations as these are little better
than travesties of legitimate theory, some of them still command
interest if not belief.1 All alike are founded on the assumption
that resemblances between the manner and degree in which Repe-
tition occurs are unlikely to have arisen save by community oi
Descent. A broader view of Meristic phenomena will shew that

1 These modern "Instances" recall many that once were famous but are now-
forgotten. For example : Item non absurda est similitudo et conformitas ilia, ut
homo sit tanquam planta inversa. Nam radix nervorum et facultatum animalium
est caput; parte* autem seminales sunt infima, nan computatis < .rtremitatibus tihi-
arum et brachiorum. At in planta, radix [qua irutar capitis est) regulariter infimo
loco collacatur ; scmitia autem supremo. BACON, Nov. Org. Lib. II. 27. In «0fl
computatis extremitatibus, amateurs of Instantije Confohmes may still find matter
for warning.

30 HOMOLOGY. [istrod.

this assumption is unfounded ; for so far are the expressions of it
which are called Metamerism from standing alone, that it is
almost impossible to look at any animal or vegetable form without
meeting phenomena of Repetition which differ from Metamerism
only in degree or in extent. Between these Repetitions and
Metameric Repetitions it is impossible to draw any line, and the
Meristic Variations of all will therefore be treated together.

This error in the estimate of the value of Metamerism as a
guide to phylogeny is one by which the evidence of Variation is
only indirectly affected. The other errors now to be mentioned
are of a much more serious nature, for they concern the general
conception of the nature of Homology which is the basis of all
morphological study.

In introducing the method of the Study of Variation I have
said that it can alone supply a solid foundation for inquiry into
the manner by which one species arises from another. The facts
of Variation must therefore be the test of phylogenetic possibility.
Looking at organs instead of species, we shall now see that the
facts of Variation must also be the test of the way in which organ
arises from organ, and that thus Variation is the test of Homo-
logy. For the statement that an organ of one form is homologous
with an organ of another means that there is between the two
some connexion of Descent, and that the one organ has been
formed by modification of the other, or both by modification of a
third. The precise way in which this connexion exists is not
defined, and indeed has scarcely ever been considered, though
such a consideration must sooner or later be attempted. We
must for the present be content with the belief that in some un-
defined way there is a relationship between ' homologous ' parts,
and that this is what we mean when we affirm that they are
homologous.

We have however assumed that the transition from one form
to another takes place by Variation. If therefore we can see the
variations we shall see the precise mode by which the descent is
effected, and this must be true of the parts or organs as it is true
of the whole body. In like manner then as the Study of Variation
may be hoped to shew the way by which one form passes into
another, so also may it be hoped that it will shew howr the organs
of one form take on the shape of the homologous organs of
another.

In the absence of the evidence of Variation reasoning as
to Homology rests solely on conjecture, and assumptions have
thus been made respecting the nature of Homology which have
coloured the whole of morphological study. Of these, two demand
attention now.

I. As to Homology between the Members of one Series. We
saw above (page 29) how the resemblance between Repetitions

sect, vi.] INTRODUCTION. 31

occurring in divers forms has led to the belief that those forms
had a common descent: in a somewhat similar way it has hap-
pened that the resemblance between individual members of a
series of Repeated Parts has led to the belief that they must
originally have been alike, and that they have been formed by
differentiation of members originally similar. Many who would
hesitate thus to formulate such a belief nevertheless have taker
part in inquiries which can succeed only on the hypothesis that
this has been the history of such parts. Of this nature are the
old attempts to divide the skull into vertebrae, recognizing the
several parts of each ; the modern disquisitions on the segmenta-
tion of the cranial nerves ; the attempts to homologize the several
phalanges of the vertebrate pollex and hallux with the several
phalanges of the other digits ; similar attempts to trace the
precise equivalence of the elements of the carpus and tarsus, and
many other quests of a like nature. In all these it is assumed
that there is a precise equivalence to be found with enough
searching, and that all the members of such series of Repetitions
were originally alike. If the series of ancestors were before us it
is expected that this would be seen to have been the case. In the
light of the facts of Variation this assumption will be seen to be a
wrong one, and these simple views of the Repetition and Differen-
tiation of members in Series must be given up as inadequate and
misleading, even though there be no other to substitute.

II. As to the individuality of Members of Series. In seeking
to homologize a series of parts in one form with a series of parts in
another, cases often occur in which the whole series of the one is
admittedly homologous with the whole series of the other. In
such cases the question arises, can the principle of Homology be
extended to the individual members of the two Series? If the
two Series each contain the same number of members this question
is a comparatively simple one, for it may be assumed that each
member of the Series is the equivalent or Homologue of the
member which in the other Series occupies the same ordinal
position. If however the number of members differs in the tw<>
Series, how is the equivalence to be apportioned ? This is a
question again and again arising with regard to Meristic Series
such as teeth, digits, phalanges, vertebrae, nerves, vessels, mammae,
colour-markings, the parts of the flower, and indeed in almost every
system whether of animals or plants. To decide this question
there are still no general principles. But though we yel know
nothing as to the steps by which Meristic Variation proceeds,
there is nevertheless a received view by which the interpretation
of the phenomena is attempted, and though in the case of each
system of organs the application of the principle is different, yel
the principle applied is essentially the same.

Thus to compare the members of Series containing different
members it is first assumed that the series consisted ancestrally of

32 INDIVIDUALITY OF MEMBERS OF SERIES, [introd.

some maximum number, from which the formula characteristic of
each descendant has been derived by successive diminution. Here,
again, I do not doubt that many who employ this assumption
would hesitate to make it in set terms, but nevertheless it is the
logical basis of all such calculations.

Now this hypothesis involves a definite conception of the
mode in which Variation works, and it is most important that
this should be realized clearly. For if it is true that each member
of a Series has in every form an individual and proper history, it
follows that if we had before us the whole line of ancestors from
which the form has sprung, we should then be able to see the
history of each member in the body of each of its progenitors. In
such a Series the rise of an individual member and the decline of
another should then be manifest. Each would have its individual
history just as a Fellowship in a College or a Canonry in a
Cathedral has an individual history, being handed on from one
holder to his successor, some being suppressed and others founded,
but none being merged into a common fund. In other words,
according to the received view of the nature of these homologies,
it is assumed that in Variation tlie individuality of each member
of a Meristic Series is respected.

The difficulty in applying this principle is notorious, but when
the evidence of Variation is before us the cause of the difficulty
will become evident. For it will be found that though Variation
may sometimes respect individual homologies, yet this is by no
means a universal rule; and as a matter of fact in all cases of
Meristic Series, as to the Variation of which any considerable
body of evidence has been collected, numerous instances of Varia-
tion occur, in which what may be called the stereotyped or tra-
ditional individuality of the members is superseded.

This error in the application of the principle of Homology to
individual members of Meristic Series has arisen almost entirely
through want of recognition of the unity of Meristic Repetition,
wherever found. In the case of a series of parts among which
there is no perceptible Differentiation, no one would propose to
look for individual Homologies. For example, no one consid* rs
that the individual segments in the intestinal region of the Earth-
worm have any fixed relations of this kind ; no one has proposed
to homologize single leaves of one tree with single leaves on
another ; it is not expected that the separate teeth of a Roach
have definite homologies with separate teeth of a Dace, for such
expectations would be plainly absurd. But in series whose mem-
bers are differentiated from each other the existence of such in-
dividuality is nevertheless assumed. To take only one case: a
whole literature has been devoted to tin- attempt to determine
some point in the vertebral column or in the spinal nerves from
which the homologies of the segments may bo reckoned. This is a
problem which in its several forms has been widely studied. Some

sect, vi.] INTRODUCTION. 33

have attempted to solve it by starting from the lumbar plexus,
while others have begun from the brachial. In the case of Birds
this question is reduced to an absurdity. Which vertebra «>f a
Pigeon, which has 15 cervical vertebrae, is homologous with the
first dorsal of a Swan which has 26 cervicals ? To decide these
questions the only possible appeal is to the facts of Variation, and
judged by these facts the whole inquiry comes to an end, for it is
seen at once that the expectation is founded on a wrong con-
ception of the workings of Variation. No one, as has been said
above, would attempt such an inquiry if the series were un-
differentiated, for this individuality would not be expected in such
a Series ; but to suppose that it does exist in a differentiated
Series of parts, is to suppose that with Differentiation the ordinal
individuality of the members has become fixed beyond revision.
This supposition the Study of Variation will dispel.

Here, as in the preceding case of the theoretical doctrine of
Serial Homology, the current view is far too simple and far too
human. Though the methods of Nature are simple too, yet
their simplicity is rarely ours. In these subjective conceptions of
Homology and of Variation, we have allowed ourselves to judge
too much by human criterions of difficulty, and we have let our-
selves fancy that Nature has produced the forms of Life from each
other in the ways which we would have used, if we had been
asked to do it. If a man were asked to make a wax model of the
skeleton of one animal from a wax model of the skeleton of
another, he would perhaps set about it by making small additions
to and subtractions from its several parts; but the natural process
differs in one great essential from this. For in Nature the body
of one individual has never been the body of its parent, and is no1
formed by a plastic operation from it; but the new body is made
again new from the beginning, just as if the wax model had gone
back into the melting-pot before the new model was begun.

SECTION VII.
Meristic Repetition and Division.

Before ending this preliminary consideration of ftferism it is
right that we should see other aspects of the matter. What fol-
lows is put forward in no sense as theory or doctrine but simply as
suggesting a line of thought which should be in the minds of any
who may care to pursue the subject further or to study the
evidence. It is perhaps only when it is seen in connexion with its
possible developments that the magnitude of the subject can be
fully felt.

b. 3

34 ASEXUAL REPRODUCTION. [introd.

Iii the treatises on Comparative Anatomy which belong especi-
ally to the beginning of this century, the idea constantly recurs that
the series of segments of a metamerically segmented form do in
some sort represent a series of individuals which have not detached
themselves from each other. Seen in the light of the Doctrine
of Descent this resemblance or analogy has been taken as a pos-
sible indication that the segmented forms may actually have had
some such phylogenetic history as this. By similar reasoning the
Metazoa have been spoken of as " Colonies " of Protozoa. Now
though we need not allow ourselves to be drawn away into these
and other barren speculations as to phylogeny, we may still note
the substance of fact which underlies them. For it is now
recognized that between the process by which the body of a Kais
is metamerically segmented, and that by which it divides into a
chain of future " individuals," no line can be drawn : that the
process of budding, or of stabilization, by which one form gives
rise to a number of detached individuals, is often indistinguishable
from the process by which a near ally gives rise to a connected
colony, and that the two processes may even be interchangeable in
the same form; finally that the process of division of a fertilized
ovum by the first cleavage plane may be in some essentials com-
parable with the division of a Protozoon into two new individuals.
All these are now commonplaces of Natural History.

With what justice these considerations may have been applied
to the problems of phylogeny we need not now inquire, but to the
interpretation of the facts of Variation they have an application
which ought not to be neglected.

If, then, as is admitted, there is a true analogy between the
process by which new organisms may arise asexually by Division,
and the process by which ordinary Meristic Series are produced, it
follows that Variation, in the sense of difference between offspring
and parent, should find an analogy in Differentiation between the
members of a Meristic Series. Applied to the case of asexual re-
production there seems no good reason for denying this analogy.
It is of course an undoubted fact that in the asexual reproduction
of many forms Variation is rare, though the sexually produced
offspring of the same forms are very variable. In plants this is
familiar to everyone, though the extension of the same principle
to animals rests chiefly on inference. Nevertheless in plants bud-
variation, both Meristic and Substantive, happens often, and the
division of a plant into two dissimilar branches may well be coin-
pared to the production of dissimilar offspring by one parent : in-
deed, if the processes of Division are admitted to be fundamentally
the same, this conclusion can scarcely be escaped.

In one more aspect this subject may be considered with profit.
It is, as we have seen, believed that the division of an ovum into
two segmentation-spheres is not a process essentially different

SECT, vii.] INTRODUCTION. 35

from the division of certain Protozoa into two " individuals." In
conceiving the manner of Variation in such Protozoa we have
little or no fact to guide us, but this much is obvious : that for the
introduction of a variety as the offspring of a given species, ii La
necessary either that the two parts into which the unicellular
organism divided should have varied equally, and that the
division should thus be a symmetrical division (in the full sense of
qualitative as well as formal symmetry); or that the division
should be asymmetrical, the resulting parts being dissimilar, in
which case one may conceivably belong to the type and the other
be a Variety. If Variation has ever occurred in the reproduction
of animals of this class it must have occurred on one or both of
these plans.

Returning to the segmentation of the Metazoan ovum we have
the well-known results of Roux and others, shewing that, in
certain species, the first1 cleavage-plane divides the body into the
future right and left halves. In such cases then on the analogy
of the Protozoon, the right and left halves of the body are in a
sense comparable with the two young Protozoa, and though each
half is hemi-symmetrical, it is in this way the equivalent of a
separate organism. This suggestion, which is an old one. receives
support from many facts of Meristic Variation, especially from the
mode of formation of homologous Twins and "double Monsters
which are now shewn almost beyond doubt, to arise from the
division of one ovum2. But besides the evidence that each
half of the body may on occasion develop into a whole, evidence
will be given that one half may vary in its entirety, independently
of the other half. Such Variation may be one of sex. taking the
form of Gynandromorphy, so well-known among Lepidoptera, in
which the secondary sexual characters of one side are male, those
of the other being female; or it may happen that the difference
between the two sides is one of size, the limbs and organs of one
side being smaller than those of the other; or lastly the Variation
between the two sides may be one that has been held characteristic
of type and variety or even of so-called species and species3.

These matters have been alluded to here as things which a
student of the facts of Variation will do well to bear in mind. I'
is difficult to see the facts thus grouped without feeling the

1 Often it is the second cleavage-plane (if any) which corresponds with the
future middle line.

- The well-known evidence relating to this subject will be spoken of later. The
view given above, which is now very generally received, finds BUpporl in the striking
observations of Diuesch, lately published (Zt. f. w. ZooL, L891, Lin. p. 160).
Working with eggs of Echinus, Driesch found that if the first two segmentation-
spheres were artificially separated, each grew into :i Beparate Pluteut; if tin-
separation was incomplete, the result was a double-monster, united by homologous
surfaces. Similar experiments attended by similar results have since been made on
Ampkioxus by E. B. Wilson, Anat. An:., vn. 1892, p. 732.

:} Evidence of such abrupt Variation between the two sides of the body belongs
for the most part to the Substantive group.

3—2

36 SUBSTANTIVE VARIATION : EXAMPLES. [introd.

possibility that the resemblance between the two sides of a
bilaterally symmetrical body may be in some essentials the same
as the resemblance between offspring of the same parent, or to
use an inclusive expression, that the resemblance between the
members of a Meristic Series may be essentially the same as the
resemblance and relationship between the members of one family ;
that the members of a row of teeth in the jaw, of a row of peas
in a pod, of a chain of Salps, or even a litter of pigs, all resulting
alike from the processes of Division, may stand to each other
in relationships which though different in degree may be the
same in kind.

If reason shall appear hereafter for holding any such view as
this, the result to the Study of Biology will be profound. For
if it shall ever be possible to solve the problem of Symmetry,
which may well be a mechanical one, we shall thus have laid a
sure foundation from which to attack the higher problem of
Variation, and the road through the mystery of Species may thus
be found in the facts of Symmetry.

SECTION VIII.
Discontinuity in Substantive Variation: Size.

From the subject of Merism and the thoughts which it suggests,
we nowr pass to another matter. The first limitation by which we
proposed to group Variations was found in the characters which
they affect : the second relates to the magnitude, or as I shall call
it, the Continuity of the variations themselves. And though
for many a conception has no value till it be cast in some finite
mould, my aim will be rather to describe than to define the
meaning of the term Continuity as applied to Variation. In
dealing writh a subject of this obscurity, where the outlines are
doubtful, an exact mapping of the facts cannot be made and
ought not to be attempted; but I trust that from the present
indications, vague though they are, some larger and more definite
conception of Discontinuity in Variation may shape itself hereafter
by a process of natural growth. For this reason I shall as far as
possible avail myself of examples rather than of general expres-
sions, whether inclusive or exclusive.

To those who have studied the recent works of Galton, the
conceptions here outlined will be familiar. In the chapter on
" Organic Stability " in Natural Inheritance, the matter has been
set forth with charming lucidity, and what follows will serve
chiefly to illustrate the manner in which the facts of Natural
History correspond with the suggestions there made.

In the ease of most species it is a matter of common knowledge

sect, viii.] INTRODUCTION. 37

that though no two individuals are identical, there are many which
in the aggregate of their characters nearly approach each other,
constituting thus a normal, from which comparatively few differ
widely. In such a species the magnitude of these differences is
proportional to the rarity of their occurrence. Now this, which is
a matter of common experience, has been shewn by Galton to be
actually true of several quantities which in the case of Man are
capable of arithmetical estimation. In the cases referred to it has
thus been established that these quantities when marshalled in
order give rise to a curve which is a normal curve of Frequency of
Error. Taking for instance the case of stature, Galton's statistics
shew that for a given community there is a mean stature, and the
distribution of the statures of that community around the mean
gives rise to a Curve of Error. In this case the individuals of that
community in respect of stature form one group. Now in the case
of a collection of individuals which can be separated into two
species, there is some character in respect of which, when arranged
by their statistical method, the individuals do not make one group
but two groups, and the distribution of each group in respect of
that character cannot be arranged in one Curve of Error, though
it may give rise to two such curves, each having its respective
mean. For example, if in a community tall individuals were
common and short individuals were common, but persons of medium
height were rare, the measurements of the Stature of such a
community when arranged in the graphic method would not form
one Curve of Error, though they might and probably would form
two. There would thus be a normal for the tall breed, and a
normal for the short breed. Such a community would, in respect
of Stature, be what is called dimorphic. The other case, in which
the whole community, grouped according to the degrees in which
they display a given character, forms one Curve of Error, may
conveniently be called monomorphic in respect of that character.
By considering the possible ways in which such a condition of
dimorphism may arise in a monomorphic community, one of the
uses of the term Discontinuity as applied to Variation will be
made clear.

Considering therefore some one character alone, in a specie
which is monomorphic in respect to that character, individuals
possessing it in its mean form are common while the extremes
are rare; while if the species is dimorphic the extremes are
common and the mean is rare. Now the change from the mono-
morphic condition to the dimorphic may have been effected with
various degrees of rapidity: for the frequency of the occurrence of
the mean form may have gradually diminished, while that <>f the
extremes gradually increased, through the agency of Natural
Selection or otherwise, in a long series of generations; or on the
other hand the diminution in the relative numbers of the mean
individuals may have been rapid and have been brought about in

38

HORNS OF BEETLES.

[iNTROD.

a few generations by a few large and decisive changes, whether of
environment or of organism.

Referring to the curve of Distribution formed in the graphic
method of displaying the statistics, during the monomorphic period
the curve has one apex corresponding with the greatest frequency
of one normal form, but in the dimorphic period the curve has two
apices, corresponding with the comparative frequency of the two
extremes, and the comparative rarity of the mean form. The
terms Continuous or Discontinuous are applicable to the process
of transition from the monomorphic to the dimorphic state according
as the steps by which this change was effected are small or large.

The further meanings of Discontinuous Variation will be
explained by the help of examples. The first cases refer to Sub-
stantive Variation1, and we may conveniently begin by examining
a case of Variation in a character which is easily measured arith-
metically.

Among beetles belonging to the Lamellicorn family there are
numerous genera in which the males may have long horns arising
from various parts of the head and thorax2. These horns may be

n

in

Fig. 1. Side-views of the Lamellicorn beetle, Xylotrupe* gideon. Legs not
represented. I, High male, II, Medium male, III, Low male.

1 In referring thus to evidence as to Substantive Variation, I find myself in tin-
difficulty mentioned in the Preface. For it is necessary to allude to matters which
cannot be properly treated in this first instalment of facts. In order, however, that
the one introductory account may serve for all the evidence together, such allusion
is inevitable and I can only trust that full evidence as to Substantive Variation may
be produced before long.

2 For particulars of this subject with illustrations, see Descnit of Man, 1st ed..
vol. i. pp. 309 — 372. A detailed account of this and the succeeding example in the
case of the Earwig was given by Mr Brindley and myself in P. Z. N.. 1893.

SECT. VIII.]

INTRODUCTION.

39

of very great size, as in the well-known Hercules beetle ( Dynastes
here ales) and others. The females of these forms are usually
without horns. In such genera it is commonly found that the
males are not all alike, but some are of about the size of the
females and have little or no development of horns, while others
are more than twice the size of the females and have enormous
horns. These two forms of male are called " low ' and " high '
males respectively.

In many places in the Tropics such beetles abound, both
" high ': and "low" males occurring in the same locality. An
admirable example of this phenomenon is seen in Xylotrujpes
gideon, of which a " high," " low," and medium male are shewn
in profile in Fig. 1. Of this insect a very large number were
kindly given to me by Baron Anatole von Hiigel, who collected
them at one time, in one locality, in Java. In this species there is
one cephalic and one thoracic horn, placed in the positions shewn
in the figure. Fig. 1, I shews a "high' male, II is a medium,
and in a "low': male. In the gathering received there were
342 males. My friend, Mr H. H. Brindley, has made careful
measurements of the lengths of the horns of these specimens and
has constructed the diagram, Fig. 2. In this each dot represents
an individual, and the abscissae shew the measurements of the
length of the cephalic horn. For clearness these measurements
are represented as of twice the natural size. So far as the
numbers go the result shews that the most frequent forms are

Fig. 2. Diagram representing the frequency of the lengths of cephalic horn in
male Xylotrupea gideon. M, the mean case ; M' the mean value. The abscissas
give lengths of cephalic horn in lines.

40 FORCEPS OF EARWIGS. [introd.

the moderately low and the moderately high, the forms of mean
measurement being comparatively scarce. It is true that the
numbers are few, but so little heed is paid to phenomena of this
kind that material is difficult to obtain and the present oppor-
tunity was indeed wholly exceptional1. But taking the evidence
for what it is worth, the comparative scarcity of " medium " males
in that particular sample is clear, and so far the form is dimorphic,
and has two male normals.

Now such a condition may have arisen in several ways. First,
in the past history of the species there may have been a time
when the males were horned and were monomorphic, the " medium"
form being the most frequent, and the present dimorphic condition
may have been derived from this, either continuously or discon-
tinuously as described above for the case of Stature. Secondly,
the dimorphism may date from the first acquisition of the horns,
and this character may perhaps have always been distributed in
the dimorphic way. In this case the term Discontinuous would
be applicable to the Variation by which the groups of "high" and
"low' males have been severally produced. I am not acquainted
with evidence as to the course of inheritance in these cases, and I
do not know therefore whether both " high" and " low" males may
be produced by one mother. If this should be shewn to be the
case, it would suggest that the separation of the males into two
groups was a case of characters which do not readily blend,
and are thus exempt from what Galton has called the Law of
Regression2.

In the case of a somewhat similar structure found in the Common
Earwig (Forjicula auricularia) the dimorphism is
still more definite. In the autumn of 1892 on a
visit to the Fame Islands, a basaltic group off the
coast of Northumberland, it was found that these
islands teem with vast quantities of earwigs. The
abundance of earwigs was extraordinary. They
lay in almost continuous sheets under every stone
and tussock, both among the sea-birds' nests
1 * and by the light-keepers' cottages. Among them

Fig. 3. I, High were males of the two kinds shewn in Fig. 3 ; the

male, II, Low male one or high male having forceps of unusual length,
of Common Earwig th Qther Qr j j b- the common form.

{horticula auricu- x . . . . ' . ° . , P

laria) from the It appears that the high male is known trom many

Fame Islands. places in England and elsewhere and that it was

made into a distinct species, F. forcipata, by

1 In the Lucanidffi, of which the Stagbeetle (L. cervus) is an example, a similar
phenomenon occurs, the "high" and "low" males being distinguished by the
degree of development of the mandibles. No suihcient number of male Stagbeetles
has yet been received to warrant any statement as to the frequency of the various
types of males.

2 Natural Inheritance, pp. 88 — 110.

SECT. VIII.]

INTRODUCTION.

41

Stevens1 though by later authorities*2 the species has not been
retained. A large sample of Earwigs collected in a Cambridge
garden contained 163 males of which 5 would come into the
high class, but the great abundance of high males at the Fames
seems to be quite exceptional.

With a view to a statistical determination of the frequency of
the high and low forms 1000 of these Earwigs were collected 1»\
Miss A. Bateson, the whole being taken at random on one day
from three very small islands joined to each other at low tide.
Of the 1000 specimens 583 proved to be mature males with elytra
fully developed, no specimen with imperfect elytra being included
in this number3. On measuring the length of the forceps to the
nearest half mm. and grouping the results in the graphic method
the curve shewn in Fig. 4 was produced. The figures on the

Fig. 4. Curve shewing frequency of various lengths of forceps of male Earwigs
{F. auricularia) from the Fame Islands. Ordinate*, numbers of individuals \
abseissie, lengths of forceps in mm.

ordinates here shew the numbers oi individuals, those on the
abscissae giving the length of the forceps in millimetres. As there

1 Stevens, Brit. Ent. 1835, vi. p. 6, PI. xxvm. fig. 4.

2 Fischer, Orthop. Euro})., 1853, p. 74; Bkunnek von Wattinwyj, Prodr. d.
europ. Orthop., 1882, p. 12.

1 For particulars in evidence of the maturity of these specimens see /'. '/.. Sf.,
1893.

42 COLOUR. [iNTROD.

shewn the smallest length of forceps was 25 mm., and the greatest
9 mm., the greatest frequency being grouped about 3*5 mm. and
7 mm. respectively. The mean form having forceps of moderate
length is comparatively rare. The size of the forceps of the
females scarcely varies at all, probably less than 1 mm. in the
whole sample.

The number of cases is enough to fairly justify the acceptance
of these statistics and it is not likely that a greater number of
cases would much alter the shape of the curve. Here, therefore,
is a group of individuals living in close communion with each
other, high and low, under the same stones. No external circum-
stance can be seen to divide them, yet they are found to consist
of two well-marked groups.

Before leaving these examples special attention should be di-
rected to the fact that the existence of a complete series of indivi-
duals, having every shade of development between the "lowest" and
the " highest " male, does not in any way touch the fact that the
Variation may be Discontinuous ; for we are concerned not with
the question whether or no all intermediate gradations are possible
or have ever existed, but with the wholly different question
whether or no the normal form has passed through each of these
intermediate conditions. To employ the metaphor which Gal ton
has used so well — and which may prove hereafter to be more than
a metaphor — we are concerned with the question of the positions
of Organic Stability; and in so far as the intermediate forms are
not or have not been positions of Organic Stability, in so far is
the Variation discontinuous. Supposing, then, that the "high" and
" low " males should become segregated into two species — a highly
improbable contingency — these two species would have arisen by
Variation which is continuous or discontinuous according to the
answer which this question may receive.

SECTION IX.

Discontinuity in Substantive Variation : Colour

and Colour-Patterns.

From the consideration of Discontinuity in the Variation of a
character, size, which may be readily measured arithmetically, we
pass to the more complex subject of Discontinuous Variation in
qualities which are not at once capable of quantitative estimation.
In this connexion the case of colour- variation may be profitably
considered. Nature abounds with examples of colour-polymor-
phism, and in numerous instances such Variation is discontinuous.
Of such discontinuous Variation in colour I shall speak under two
heads, considering first variations in colours themselves and

sect, ix.] INTRODUCTION. }:>

secondly variations in colour-patterns. As it is not proposed to
give the evidence as to Substantive Variation in this volume, a
few examples must suffice to shew the use of the term Dis-
continuity as applied t<> these Colour- variations.

I. Colours. The case of the eye-colour of Man may well be
mentioned first, as it has been studied statistically by Galton In
this case the facts clearly shewed that certain types of eye-colour
are relatively common and that intermediates between th< se
types are comparatively rare. The statistics further shewed that
in this respect inheritance was alternative, and that the different
types of eye-colour do not often blend in the offspring. " If one
parent has a light eye-colour and the other a dark eye-colour,
some of the children will, as a rule, be light and the rest dark ;
they will seldom be medium eye-coloured, like the children of
medium eye-coloured parents.1"

Colour dimorphism of this kind is very common among animals
and plants. It is well known, for example, among beetles. Several
metallic blue beetles have bronze varieties of both sexes, living
together in the same locality. A familiar instance of this dimor-
phism occurs in the common Pliratora vitellince. Again in the
Elaterid beetle, Corymbites cupreus, there is a similar dimorphism
in both sexes, the one variety having elytra in larger part yellow-
brown, while the elvtra of the other are metallic blue. This blue
variety was formerly reckoned a distinct species, G. ceruginosus.
In the latter case I am informed by Dr Sharp, who has had a
large experience of this species, that no intermediate between
these two varieties has been recorded, and in the case of the
Phratora the occurrence of intermediates is very doubtful. An-
other common example of colour dimorphism is seen in Telephorus
livid us y the "sailor" of "soldiers and sailors." This beetle inav
be found in large numbers, about half being slaty in colour ( var.
disj)ar), while the remainder have the yellowish colour which
coleopterists call "testaceous." Such instances may be multi-
plied indefinitely. When the whole evidence is examined it will
be found that different colours are liable to different discontinuous
variations; as instances may be mentioned black and tan in dogs ;
olive-brown or green and yellow in birds, &c.'J; grey and cream-

1 Natural Inheritance, p. 1H9.

2 A specimen of the green Ring Parakeet [PaUeornU torquatua) at the Zoological
Society's Gardens was almost entirely canary-yellow in 1890. Since that date it
has become more and more "ticked" with green feathers. A Green Woodpecker
(Picas riridis) is described, having the feathers of the runi]> edged with red instead
of yellow, the normally green feathers of the three lower rows of wing-coi
and the back were pointed with yellow. J. H. Gubnby, Zoologist, xi. p. •"■-

I am indebted to Mr Gnrney for the loan of a coloured drawing of this specimen.
Another example is described as being entirely canary-yellow, with the exception <>t
a few feathers on the cap, which were purple-red. Dk Bktta, Mater. i<> r una fauna
Veronese, p. 174. For this reference I am indebted to Prof. Newton. Specimen <>f
Common Bunting whitish yellow. Edwabo, ZawL, 6492 ; Sedge Warbler canary-
yellow. Bird, Zool., 3G32. The Canary itself is a similar case. An Eel gamb<>
yellow. Gurnet, Zool., 3599.

44 RED AND YELLOW. [introd.

colour in mice and cygnets1 ; red and blue in the eggs of many
Copepoda2, the tibiae of Locusts3, the hind wings of the Crimson
Underwing (Catocala nupta)4, &c. Another case of blue as a
variety of scarlet is the familiar one of the flower of the Pim-
pernel (Anagallis arvensis). Discontinuous colour-variation of
this kind is one of the commonest phenomena in nature, but to
advance the subject materially it is necessary for a large mass of
evidence tc^be produced. This cannot now be attempted, but in
order to bring out the close relation between these facts and the
problem of Species I propose to dwell rather longer on one special
section of the evidence which must serve to exemplify the rest.
The case which I propose to take is that of certain yellow, orange,
and red pigments. For brevity I shall present the chief facts in
the first instance without comment.

1. Colias edusa (Clouded Yellow) is usually orange-yellow, having
a definite pale yellow female variety, helice, which is not recognized as
occurring in the male form. A specimen is figured having the right
side helice and the left edusa. Fitch, E. A., Entomologist, 1878, xli.
p. 52, PI. fig. 11. This was an authentic specimen, for Mr Fitch tells
me that it was taken by his son and seen alive by himself.

A specimen having one wing white and the rest orange is recorded
by Morris, Brit. But., p. 13.

Intermediates between edusa and helice must be exceedingly rare.
Oberthur records two such specimens and says that Staudinger took
a similar one at Cadiz. For this intermediate he proposes a new name,
helicina. Bull. Soc. Ent. Fr. (5), x. p. cxlv.

1 In this case I can affirm the alternative character of the inheritance. For
several years a pair of swans kept by St John's College, Cambridge, have produced
cygnets, some of which have been of the normal grey, while others have been fawn-
colour, a condition which Prof. Newton tells me has been thought characteristic of
the " Polish " swan, a putative species. None of these cygnets are intermediate in
colour, and all accmire the full white adult plumage, but the feet of the fawn-coloured
cygnets remain pale in colour. Now the father of these has pale feet and was
doubtless himself a fawn-coloured cygnet ; the hen is normal. The cock formerly
belonged to Dr Clifford, who kindly told me that the cygnets of this bird by a different
hen were also thus diverse. A pair of these were given to Sir John Gibbons, who
informs me that "from these there has been a brood every year, and always I think
one of the cygnets has been white or nearly so, the others being of the usual colour."
One of Dr Clifford's birds was also given to the late Mrs Gosselin of Blakesware,
to whom I am indebted for descriptions of and feathers from several fawn-coloured
cygnets which were its offspring. A similar case on the Lake of Geneva is re-
corded by Fauvel, Rev. ZooL, 1869, p. 334, and another in the Zool. Gardens at
Amsterdam, by Newton, Zool. Rec, 1869, p. 99.

2 This is well known to collectors of fresh-water fauna, and I have repeatedly
seen the same phenomenon in species of Diaptomue, especially D. asiaticus, in the
lakes of W. Siberia. Among thousands of individuals with red-brown egg-sacs, will
often occur a few specimens having the egg-sacs of a brilliant turquoise-blue. In
this connexion compare the case of the Crayfish [Astacus fluviatilis), which turns
scarlet on being boiled, and which, like the Lobster, not uncommonly appears in a
full blue variety.

3 Caloptemu spretus with hind tibia? blue instead of red, Dodge, Can. Ent., 1878,
x. p. 105 ; Melanoplus paekardii, having hind tibia? red instead of bluish, Bruner,
Can. Ent., 1885, xvn. p. 18. For reference to these observations I am indebted to
Cockereel, Ent. , 1889, xxii. p. 127.

4 Win ik. Ent., 1889, xxn. p. 51. Compare the fact that in another species of
Catocala (C. fraxini), the Clifden Nonpareil, the hind wings are normally bluish.

sect, ix.] INTRODUCTION. 45

A curious specimen, apparently a male, having the colour of hdice
was kindly shewn me by Mr F. H. Waterhouse. The light marks
which in the female are present on the dark borders of the fore-wing
are only represented by one minute light mark on each fore-wing.

In most if not all of the edusa group of Colias, there is a pale
aberration of the female, corresponding to the helice variety of < zdusa.
Elwes, Tr. Ent. Soc, 1880, p. 134. In the same paper is a full account
of the geographical distribution of the several species and colour-varieties
of Colias.

Colias hyale (Pale Clouded Yellow) is normally sulphur-coloured.
Nearly white varieties and a variety with the field rich sulphur colour,
and the apical marginal patches red, are recorded in several works.

2. Gonepteryx rhamni (The Brimstone) is sulphur-yellow in the
male, and greenish-white in the female. There is a spot in each wing,
and the scales covering this on the upper side are bright orange.

Gonepteryx cleopatra, a S. European species, is like the above
in the hind-wings, while the field of the fore-wings is flushed with
orange of exactly the tint of that on the spots of G. rhamni.

There are several records in entomological literature alleging the
capture of "G. cleopatra" in Britain, e.g. Proc. Ent. Soc., 1887, p. xliii.

In addition to these there are records of specimens of G. rhamni
more or less flushed with orange ; e.g., a specimen at Aldershot with
orange spots on fore-wings as in cleopatra, Proc. Ent. Soc, 1885,
p. xxiv. Mr Jenner "Weir said he had seen a specimen in Ingall's
collection, intermediate between rhamni and cleopatra. ibid.

A male of G. rhamni taken at Beckenham had the costal margin
of each fore-wing broadly but unequally suffused with bright rose-
colour or scarlet, and the right posterior wing was marked in like
manner. The insect was thus marked when captured. Bicknell,
Proc. Ent. Soc, 1871, p. xviii.

3. Anthocharis (Euchloe) cardamines (The Orange Tip), in the male
has the fore-wings tipped with orange on both sides, while in the
female these orange tips are absent. The field in both is white In
entomological literature are many records of variations in the extent
and depth of the orange markings on upper or under side, or both
(cp. Zoologist, xiii. 4562; Proc Ent. Soc, 1S70, p. ii. ; Mosley,
Illustrations of British Lepidoptera ; Haworth ; Boisduval ami many
others), but with these we are not immediately concerned.

A specimen is figured in which the orange spots were completely
represented by yellow. Mosley, Illustrated Brit. Lep.

The white of the field is replaced by primrose or lemon yellow in
several Continental forms. These have been described as species
under the names eupheno, belia, euphenoides, gruneri, &c.

A local variety of A. eupheno is described from Mogador, where it
was found common at a little distance from the town. The female
was much larger than the type, resembling the male in markings and
in shape of the fore-wings. The orange blotch, instead of being con-
fined to tip of the fore-wing as normally, extends to the discoidal spot
and is usually bounded by a black band, sometimes suffusing the whole
tip of the wing. The colour of the field varies from pure white to pale
lemon: the hind-wings are always yellower than in the type, in some

46 RED AND YELLOW. [ixtrod.

specimens being nearly as yellow as those of the male. Mr M. C.
Oberthiir supplied a specimen from Central Algeria which was inter-
mediate between the type and this variety. Leech, J. H., P. Z. S.,
1886, p. 122.

4. Amongst Lepidoptera the change from red to yellow is very
common. A case of Vanessa atalarda, having the red partially replaced
by yellow, is figured in Entom., 1878, xi. p. 170, Plate. Varieties of
Arctia caja, Callimorpha dominula, C. hebe, C. hera, C. jacoboece,
Zygcena filipendulce, Z. minos, tfcc, with yellow instead of red, are to
be seen in many collections. See especially Ochsexheimer, Schm.
v. Europa, 1808, n. p. x, also p. 25, and many other authors. A
chalk-pit at Madingley, Cambridge, has long been known to collectors
as a locality for the yellow Z. filipendulce (Six-spot-Burnet); see Eat.
Mo. Mag. xxv. p. 289. In some of these the yellow is tinged with
red, but it is commonly a very distinct variety. A variety of the Red
Underwing (Catocala nupta) with brownish-yellow in the place of the
red, is figured by Exgramelle, Papill. d'Eur., PL cccxxn. The evidence
relating to this subject is very extensive, and concerns many genera and
species besides those named above.

5. Pericrocotus flammeus (an Indian Fly-catcher) is grey and
yellow in the female, and black and orange-red in the male. The young
male is grey and yellow like the female. An adult male is described in
which the grey had been fully replaced by black, but the yellow
remained, not having been replaced by red. R. G. "Wardlaw Ramsay,
P. Z. S., 1879, p. 765. See also Legge, Birds of Ceylon, I. p. 363, for
description of male in transitional plumage.

Curiously enough the change from red to yellow and from light
yellow to dark is no less common among plants, though it can
scarcely be supposed that the substances concerned are similar.

1. y<ircissus corbularia and other species are known in sulphur-
yellow and in full yellow1.

2. The Iceland Poppy (P. nudicaule) is very common in gardens
under three forms, white, yellow and orange. Intermediate and flaked
varieties occur, but are less common than the three chief forms.
Respecting this species Miss Jekyll of Munstead, who first brought
out the varieties, kindly gives me the following information. She
writes : — " I began with one plant of the yellow colour that I take to
be the type-colour. It was then new as a garden plant, so I saved the
seed. The first sowing gave me various shades of orange, as well as the
type, in different shades. In the 3rd and 4th years I got buffs, whites,
and very pale lemon colourings. As there was only one plant to begin
with there was no question of cross-fertilization. A white appeared in

the 3rd year of sowing and I kept on selecting for 2 or 3 years and

gave it to a friend in Ireland, who returned it to me 2 years later still
more improved. This strong white seems now to be fixed and quite
unwilling to revert to the yellow colourings, and is a rather stouter and

1 Mr P. Barr, who has collected these forms in Portugal, tells me that he believe3
the pale (" citrina") varieties of N. ajax and X. corbularia to be confined to
calcareous soils.

SECT. IX.] INTRODUCTION. 47

handsomer plant altogether." In seedlings from the orange or yellow

form grown in separate beds the proportion of seedlings true to their
parent colour would not be nearer than about 60 or 70 per cent., but
in the case of the white form Miss Jekyll considers that 95 per cent.
may be expected to come true.

The yellow Horned Poppy (Glauciiun hUcinn) is normally of a
lemon yellow very like that of P. nudicaule. Of this species also 1 here
is an orange cultivated variety. The varieties of the tomato offer a
similar series of colour- variations.

3. Fruits of many kinds are known in red and yellow forms.
For instance the yellow berried Yew is well known. It is described
under the name Taxus baccata fructu-luteo. Loud. "It appears to
have been discovered about 1817 by Mr Whitlaw of Dublin, growing
in the demesne of the Bishop of Kildare, near Glasnevin; but it
appears to have been neglected till 1833 when Miss Blackwood dis-
covered a tree of it in Clontarf churchyard near Dublin. Mr Mackay
on looking for this tree in 1837 found no tree in the churchyard, but
several in the grounds of Clontarf Castle, and one, a large one, with its
branches overhanging the churchyard, from which he sent us specimens.
The tree does not differ, either in its shape or foliage, from the common
yew, but when covered with its berries it forms a very beautiful
object, especially when contrasted with yew trees covered with berries
of the usual coral colour." Loudon, Arb. et Frut JJrif., iv. 1S38,
p. 2068.

4. The Raspberry {Rub us idceus) is another fruit which is known
wild in both the red and yellow forms, though the latter is less common.
According to Babington, it has pale prickles, and leaflets rather obovate.
Brit. Rubi, p. 43. (See Rivers, Gard. Chron., 1867, p. 516.)

Any person who has opportunities of handling animals and
plants in numbers can add many similar cases. These few are
taken more or less at random, as illustrations of the frequency
with which red, orange, and yellow may vary to each other. It is
of course not necessary to say that in numerous instances both
among animals and plants, the same parts which in one species
are yellow, in an allied species or in a geographically distinci race
are represented by orange or by red. To an appreciation of the
rapidity with which such changes may have come about, facts like
the foregoing contribute.

The frequency of such variations suggest that many of these
yellow and red pigments are either closely allied bodies or dim' lent
forms of the same body. Until the chemistry of these substances
has been properly investigated nothing can be definitely stated
as to this, but the fact that vegetable yellows are very sensitive to
reagents is familiar. The lemon variety of the Iceland Poppy
treated with ammonia turns to a colour almost identical with
that of the orange variety, while the white variety so treated g<
primrose yellow. The lemon variety when boiled, (»r treated with
alcohol yields an orange solution, which is of the same tint. This
returns to lemon-colour if treated with ammonia or acids. The

48 COLOUR-PATTERNS. [introd.

wings of G. rhamni when boiled yield a soluble yellow, which
according to Hopkins (Proc. Chem. Soc, reported Nature, Dec. 31,
1891) is a derivative of mycomelic acid, allied to uric acid. This
substance turns orange with reagents. The wings of G. rhamni
turn orange-red when exposed to wet potassium cyanide {Proc.
Ent. Soc, 1871, p. xviii) as may be easily seen.

When these facts, meagre though they are, are considered
together with the evidence of variability, the suggestion is very
strong that the discontinuity between these several charac-
teristic colours is of a chemical nature, and that the transitions
from one shade of yellow to another, or from yellow to orange or
red is a phenomenon comparable with the changes of litmus and
some other vegetable blues from blue to red or of turmeric from
yellow to brown. If such a view of these phenomena were to be
accepted, it would, I think, be simpler to regard the constancy of
the tints of the several species and the rarity of the intermediate
varieties as a direct manifestation of the chemical stability or
instability of the colouring matters, rather than as the con-
sequences of environmental Selection for some special fitness as
to whose nature we can make no guess. For we do know the
phenomenon of chemical discontinuity, whatever may be its ulti-
mate causes, but of these hypothetical fitnesses we know nothing,
not even whether they exist or no.

II. Colour-patterns. Thus far I have spoken only of dis-
continuous variations in colours themselves, but there are no less
remarkable instances of discontinuous variations in the distri-
bution of colours in particoloured forms. By a combination of
these modes, variations of great magnitude may occur.

One of the most obvious cases of this phenomenon is that of
the Cat. In European towns cats are of many colours, but they
nevertheless foil very readily into certain classes. The chief of
these are black, tabby, silver-grey and silver-brindled, sandy, tor-
toiseshell, black and white, and white. Of course no two cats
have identical colouring, but the individual variations group very
easily round these centres, and intermediate forms which cannot at
once be referred to any of these groups are immediately recognized
as something out of the common and strange. Yet it is almost
certain that cats of all shades breed freely together, and there is
no reason to suppose that the discontinuity between the colour-
groups is in any way determined by Natural Selection.

Another example may be seen in the Dog-whelk {Purpura
I a pill us). This animal occurs on nearly the whole British coast,
wherever there are rocks or even clay hard enough to form
definite crevices. Like most littoral animals, the Dog-whelks of
each locality differ more or less from those of other localities, and
these differences may be differences of size, texture of shell,
degree of calcification, amount of " frilling," kc. The peculiarities

SECT, ix.] INTRODUCTION. 49

may be so striking that each individual can at once 1>'' n -cognized
as belonging to a given locality, or they may be trifling, and
appreciable only when a large number of individuals arc gathered
But apart from these differences of form and texture there are a
great number of colour-varieties of which the following are the
three chief whole-coloured forms, viz. white, dark purple-brown,
and yellow. In addition to these there are banded forms, and the
bands may be coloured with any two of the three colours men-
tioned above. Among the banded forms there are two distinct
sorts of banding, in the one there are very many fine bands and in
the other there are a few broad bands. In most localities these
colour- varieties may all be found ; though in some places, especi-
ally where the water is foul, as at Plymouth, the shells are greatly
corroded and the colours, if originally present, are obscured.
Speaking however of localities in which colour- varieties are to be
seen at all, several may generally be found together. If any one
will take the trouble to gather a few hundreds of these shells and
will set himself to sort them into groups according to their
colours, he will find that the majority fall naturally into groups of
this kind ; and that those which cannot be at once assigned to
groups but fall intermediately between the groups are com-
paratively few. I have seen this at many places on the English
coast; in Yorkshire, Norfolk, Suffolk, Kent, Sussex, Dorsetshire.
Devonshire, Cornwall, &c. In several localities I have found
pairs belonging to different colour-varieties breeding together,
and there is therefore no reasonable doubt that these colour-
variations do not freely blend, but are discontinuous.

The statements here made with regard to P. lapillus hold in
almost the same way for Littorina rudis, but in this case the
number of colour-types is larger. In L. rudis I have occasionally
seen specimens of which the upper part belonged to one colour-
type, and the lower to another, the transition occurring sharply at
one of the varices. In these cases the shell appears to have been
injured and is possibly renewed.

One of the commonest British Lady-birds (Coccuwlla decern -
■punctata) is an extremely variable form. A great number <>f its
varieties may be found together, ranging from forms with small
black spots on a red field to forms in which the field is black with
a few red spots. But in spite of the great diversity there are
certain types which are again and again approached, while the
intermediates are comparatively scarce.

The following case, well known to entomologists, may he mentioned here. The
Painted Lady (Pyrameis cardui) is found in the typical form over the i utile extent
of every continent, with the exception of the Arctic regions and possibly 8. America.
A special form of it (var. kerakawi) is found in Australia an 1 New Zealand, bnt the
other large islands south of Asia possess the normal type. The Latter is also found
in the Azores, Canaries, Madeira and St Helena. This butterfly lias been taken on
the snowdevel in the Alps; and in X. America, though it may he regarded as one
of the commonest butterflies in the elevated centra] district, it is most abundant at
a level of 7000—8000 feet. It has been taken on Arapahoe Teak, between 11,000

B. 4

50

COLOUR-PATTERNS.

[INTEOD.

and 12,000 feet (from Scxdder, Butterflies of X. America, i. pp. 477 — 480). Of this
insect, which is a very constant one, a certain striking aberration has been found,
always as a great rarity, in many lands. In this aberration the markings are
almost entirely rearranged. It is said to have been first described by Eambur under
the name var. Elymi, but this description I have never found. (The reference
quoted is Annales des Sci. d' observation, Paris, 1829, Vol. n. PL v.) As often happens
with Variation, without coloured figures description is almost useless, but tbe
figures referred to are very accessible. In a British specimen of this aberration
the white bars are absent from the anterior costae and a series of white fusiform
blotches are present along the marginal border; two abnormal white spots are
also present near the anal angle, thus continuing the series down the wing (fig.
5, a.). The hind- wings are equally aberrant. The two large dark spots which are
usually on the disk between the median nervure and the inner margin are altogether
wanting. Between each of the nervures of the hind-wing is a white spot, whereas
in the normal form there is no white spot at all on the hind-wings. These white
spots on the hind-wings form a row parallel to the border of the wing and, as it

Fig.

5.

A. Clark's specimen of P. cardui, var. ehjmi from I'.ut. 1880.

B. Newman's specimen. Brit. But., p. 64.

C. P. cardui, normal, also from Newman, Brit. But., p. 64.

SECT, ix.] INTRODUCTION. 51

were, continue the series of white spots borne by the anterior rings. [Underside
not described.] This specimen was reared from a larva found near the river I
Clapton Park. Clark, J. A., Entomologist, 1880, xm. p. 73, fig. A coloured
figure of the same specimen, Mosley, S. L., PI. 8, fig. H.

A form very closely similar to the above is figured in black and white by
Newman from a specimen in IngalFs collection (fig. 5, n). [This is apparently the
specimen given in Zoologist, p. H304.] Newman, British Butterflies, p. 01, liji. A
British specimen which nearly approaches this aberration in the absence of the
white bars on the costae and in the absence of the black transverse bar i- recorded.
In it each of the sub-marginal rows of black spots on the posterior wings is drawn,
containing a white spot. In this specimen the In-own-red of the type v.
presented by rose-colour. Newman, Entomologist, 1*73, p. 345, fig.

Another specimen closely resembling this aberrant form is described from New
South Wales. Olliff, A. S., Proc. Linn. Hoc, N. 8. W., S. 2, in. p. L250.

Another specimen closely resembling the above was taken at Graham's Town,
S. Africa, and is mentioned by Jenner Weir, Entomologist, 1889, xxn. p. 7:;.

Another specimen is figured in which the hind-wings are marked as in tie-
above, but the anterior wings, though strongly resembling this aberration in the
general disposition of the colours, yet differ in details, the chief points of difference
being that the white costal bar is only partially obliterated and the white spots on
the anal angles of the fore- wings are not developed.

[This specimen was in Kaden's collection and was presumably European. J
Heurich-Schaffer, Bd. i. p. 41, PI. 35, tigs. 157 and 158.

A description is given of an aberrant form taken at King William's Town,
S. Africa, which " closely resembled that figured by Herrich-Schaffer."' Tbimen,
R., South-African Butterflies, i. p. 201.

A specimen (British) resembling the above, but lacking the white spots on the
anal angles of the fore- wings and having the marginal row on the hind-wing light-
coloured, but not quite white, is figured by Mosley, Pt. in. PI. 3, fig. 3.

Two specimens were taken in New Jersey, U.S.A., which are stated to have
conformed to this aberration. Si'reckkr, Cat. N. Amer. Macrolepidop., p. 187.

Another British specimen generally resembling Herrich-S chaffer's figure is
represented by Mosley, PI. 8, fig. 4.

In all the above specimens the resemblance, as far at least as the upper surface
is concerned, is considerable. With the exception of Herrich-Schaffer's example,
the undersides are not figured, but from the descriptions it may he gathered that
they also resembled each other though probably not so closely as the upper surfaces.
The resemblance between the underside of the Australian specimen an I that figured
by Herrich-Schaffer must have been very close.

"Intermediate between these extreme sports and the normal form are tin
examples taken at Cape Town in 1866, 1878 and 1874 — the first by myself in
which the fore-wing markings are scarcely affected, hut the hind-wing spots are
minutely ocellate and externally prolonged, so as to be confluent with tie
ing row of lunules." Tkimen, ibid. pp. 201, 202.

Another aberration, a Belgian specimen, resembles •* Elijmi" in kind but differs
from it in degree. In it also the while bars are absent from the costflB, and tin-
brown and black markings of the anterior wings are rearranged in almost exactly
the same manner. The posterior wings are modified u> a much less extent and the
normal row of black spots between the nervines remains, while only the first and
second of the series of white spots is present, the former being very slight. In this
individual the markings of the underside also resemble the alienation generally,
but it retains the four ocelli of the type. Die DoNCEEL, II. Doni kikk. Ann. S
oVEnt. Beige, 1878, xxi. p. 10, Plate.

A specimen, also Belgian, is described in which the two anterior win J8 n -liihle
Herrich-Schaffer's figure in lacking the white bars on the costal and in the arran
nient of the black and ground colour. In neither of them are the whit. of the

anal angles (found in the British ami Australian sp scimens) present. The white
markings at the apex of the anterior wings differ on the two sides, being in both
of them unlike the type and an approach v> the aberrations in question, hut the
degree to which they are developed differs markedly, being greatesl on the right si
The left posterior wing resembles the aberration in having the -ix abnormal white
spots, but less emphasized than in the figures quoted above; in general colour this wine
is darker than the type. The right posterior wing, however, has Qone of the white
spots of the aberration, and differs from the type only in being more suffused with

4- 2

52 COLOUR-PATTERNS. [iNTBOD.

black. To recapitulate, the two anterior and the left posterior wing resemble generally,
though not entirely, the aberration, while the right posterior wing is nearly normal.
A specimen is described from Ekaterinoslav, S. Russia, which resembles this
aberration in wanting the black transverse band and in the disposition of the apical
white spots. A trace of the white costal bar remains on the costal border. On the
underside of this specimen the ocelli were placed in a pale rose-coloured band.
(Name proposed, aberration, inornata). Bramsox, K. L., Ann. Soc. Ent. France,
S. 6, vi. 1886, p. 284.

Besides the rare aberration " var. Elymi" there is a variety sometimes found in
Europe, which in Australia is so constant and definite that it has been regarded as
a species. The following may be quoted respecting its occurrence in Australia,
where it is common :

" There is in abundance about Melbourne and in many other parts of Australia
a Cynthia with the general appearance and habit of G. cardui, so closely represented
that every entomologist I know refers it to that species. The Australian species
differs from the European one constantly, however, in having the centres of the
three lower round spots on the posterior wings bright blue, and having two other
blue spots on the posterior angles of the same wings, the corresponding parts of
the European form being black." For this form the name C. kershawi is proposed.
M'Cot, F., Ann. and May. of Nat. Hist., Ser. 4, i. 1868, p. 76. See also Olliff,
A. S., Proc. Linn. Soc, N. S. W., Ser. 2, in. p. 1251. The notices of its occurrence
in Europe are as follows. In 1884 Mr Jenner Weir exhibited a specimen of P.
cardui, taken in the New Forest. Three of the five black spots in the disk of the
upper side of the hind-wings had blue pupils ; he pointed out that the specimen
thus approached the Australian form, P. kershawi. Proc. Ent. Soc, 1884,
p. xxvii.

Olliff, loc. cit., states that he has taken a specimen having these blue
markings at Katwijk, in Holland.

In the case given, the evidence certainly suggests that these
various forms of aberration are grouped round a normal form of
aberration, just as the individuals of the type are grouped round
its normal.

One example of a similar discontinuity in a melanic varia-
tion may profitably be given. I have taken this opportunity
of referring to such a case, as the general evidence of melanic
variations goes on the whole to shew that they are not commonly
discontinuous, and further evidence on this point would be most
valuable. To appreciate the evidence Butler's coloured plate
should be referred to.

Terias. A well-marked group of butterflies of this genus allied to
T. hecabe, is found in Japan. It contains forms of great diversity in
amount of black border which occurs on the outer margins of the fore-
and hind-wings. The remainder of the wings is lemon-yellow. The
black border may be confined to the tip of the fore-wings, or may there
occupy a considerable area and be extended along the whole outer
margin of both wings. The form with the least black is called T. man-
ihirina, that with the most, is called T. mariesii, and the intermediate
form is called T. anemone. Upwards of 150 specimens, all from Nikko,
were examined; these ranged between the two extremes, and were
found to form a continuous series. Butler states that "the absence of
six of them, referable only to two gradations, would at once leave the
three species as sharply defined as any in the genus."

[In the case of these butterflies, there are thus three groupsof va net ies,
two extreme groups and one mean group ; intermediates between these

sect, ix.] INTRODUCTION. 53

are comparatively rare. Butler suggests that these intermediate forma
should be regarded as hybrids, even in the absence of experimental
evidence. This view is of course dependent on the truth of the belief
that such a discontinuous occurrence of variations is anomalous.]

Twenty specimens of the species T. bethesaba and thirty-nine of
T. jaegeri (both from Japan), were also examined. The former pre-
sented no variations whatever, and the latter only vary in the yellower
or redder tint on the under surface of the secondaries. Butler, A. G.,
Trans. Ent. Sob, 1880, p. 197, PL vi.

Compare the following :

Terras constantia. Twenty-five pupae, all found together on the same
twigs at Teapa, Tabasco, Mexico, by Mr H. H. Smith. The butterflies
from these are in Messrs Godman and Salvin's collection, who kindly
allowed me to examine them. The amount of black border on both wings
varies much, nearly though not quite so much as in the cases figured
by Butler. In the lightest the apex of the fore-wing alone is black,
and there is no black on the hind-wing in 9 specimens ; of the remaining
16 some have a well-defined black border to the hind-wing, while in
the rest (about 6) this border is slight. This case is a particularly
interesting one, as the specimens were associated and presumably
belonged to one brood.

ev

For another beautiful case of discontinuous Variation in
pattern I am indebted to Dr D. Sharp. The Cambridge Univer-
sity Museum lately received a series of 38 specimens of Kallima
inachys, the well-known butterfly whose folded wings resemble a
dead leaf with its mid-rib and veinings. The underside of this
butterfly is sometimes marked with large blotches and flecks of
irregular shape, which, as has often been noted, resemble the
patches of discoloration caused by fungi in decaying Leaves.
Dr Sharp pointed out to me that the specimens examined fell
naturally into four groups according to the coloration of the
underside. In the first group the field is nearly plain, though
the tint varies in individuals. The "mid-rib" is strongly marked
in this and all the groups, but the "veinings" are absent or very
slightly marked in the first group : 18 specimens. In the second
group the ground is almost plain, but it bears numerous strongly
marked black-speckled spots, of forms which though irregular in
outline are closely alike, and occupy the same positions in all the
six specimens, being scarcely if at all represented in any of the
others. In the third group the dark bars representing "veins'
are strong, but the field is nearly uniform : 10 specimens. In the
fourth group, of four specimens, the ground-colour is darkened in
such a way as to leave large and definite blotches of light colour
in particular places. Of these specimens three have the veinings
very strongly marked, while the fourth is without them.

Into these four groups the specimens could be unhesitatingly
separated, though in each group many individual differences

54 MISCELLANEOUS EXAMPLES. [iNTBOD.

occurred. Xo marked variation in the upper-sides was to be seen.
These specimens were all from the Khasia hills, Assam, but there
was of course no evidence that all were flying together.

One of the most interesting examples of discontinuous Variation in
colour-patterns is the case of ocellar markings or eye-spots. Upon
this subject nothing need here be said as the evidence will be given in
detail in the course of this volume (see Chap. XIII.).

SECTION X.

Discontinuity in Substantive Variation. — Miscellaneous

Examples.

Of the discontinuous occurrence of Substantive Variation, the
manifestations are many and diverse. We have seen that in such
features as size, colour, and colour-patterns, Variations may be
discontinuous, and a form may thus result, differing markedly
from the type which begot it. Variation in the proportions or
the constitution of essential parts may no less suddenly occur.
The range of these phenomena is a large one, but for the purposi -
of this Introduction a few examples must suffice in general
illustration of their scope.

A discontinuous variation which is familiar to all is that of
" reversed" varieties, especially of Molluscs and Flat-fishes. Such
varieties are formed as optical images of the body of the type. In
both of the groups named, some species are norm ally right-handed,
others being normally left-handed, while as individual variations
reversed examples are found. In Molluscs this is not peculiar to
Gasteropods with spiral shells, but may occur also both in Lima-
cidse (slugs)1 and in Lamellibranchs"2. Such variation is commonlj
discontinuous, and the two conditions are alternative. The fact
that the reversed condition may become a character of an estab-
lished race is familiar in the case of Fnsus antiquus. This shell
is found in abundance as a fossil of the Norwich Crag, such
specimens being normally left-handed, though the same species at
the present day is a right-handed one. Of the left-handed form a
colon)- was discovered by MacAndrew on the rocks in Vigo Bay8.
It was there associated with certain ether shells proper to the
Norwich Crag. This discovery seemed to Edward Forbes to be so
remarkable that he looked on it as corroborative evidence of a
special connexion between the fauna of Vigo Bay and the Crag
fossils3. Jeffreys had the same variety from Sicily4.

1 For example, a sinistral Avion, Baudon, Jour. <!<■ Conch., xxxn. 1884, p. 320,
and many otheis.

- Sinistral Tellina, Fischbb, P., Jour, dc Conch., xxvm. 1880, p. 234. The
same is recorded in several other genera.

;< Seven specimens, Ann. X. H., 1849, p. 507.

4 Brit. Conch., i. p. 3'2»i.

SECT. X.] INTRODUCTION. 55

That they may the better serve to bring out the significance
of Discontinuity in Variation to the general theory of Descent, it
may be well to choose some examples with reference to characters
which when seen in domestic animals are looked on as especially
the result of Selection.

In exoskeletal structures several of this kind are known.
From time to time there have been records of captures of the
" hairy variety " of the Moorhen (Gallinula chloropus), in which the
feathers were destitute of barbules and consequently had a hairy
texture, greatly changing the general appearance of the bird.

Of the " hairy " variety twelve specimens were recorded, five from
Norfolk, and the rest from Cambridgeshire, Hampshire, Sussex (2),
Suffolk, Nottinghamshire and Athlone in Ireland. The tips of the
barbs and shafts of the feathers have been broken off and the barbules
are entirely wanting, giving a hairy appearance. This appearance was
found in the whole of the plumage. Owing to the absence of barbules,
the general coloration is tawny. A few feathers of this kind have
been found in Hawks and Gulls, and in the case of a Parra (a bird
which bears considerable resemblance to a Moorhen), lent to Mr Gurney
by Professor Newton, a great portion of the body feathers were in this
condition. The feathers of the Apteryx and Cassowary are also partially
destitute of barbules. Mr Gurney was informed of a single case of a
Grey Brahma hen which shewed the same peculiarity which appears
otherwise to be without parallel. The case of the Silky Fowl is
similar in the absence of most of the barbules, but in it the point of
the shaft is produced to a delicate point, and the barbs are tine and
sometimes bifid or tritid at the apex. From J. H. Gurney, Trans.
Norwich Nat. Soc, in. p. 581, Plate. [Bibliography given.] [Tf
another " hairy " Moorhen is found, note of the colour of the skin and
bones should be made, for, as is well known, in the Silky Fowl they are
purplish blue.]

The following may be compared : " Cochins are now and then met
with in which the webs of the feathers having no adhesion, the whole
plumage assumes a silky or flossy character like that of the Silky Fowl.
It usually occurs quite accidentally, and in every case we have met
witli, the variety has been Buff. By careful breeding the character
can be transmitted, but we have only known <>,<>> case in which there
had been this hereditary character, the others having been of accidental
occurrence. Such bircls are sometimes called 'Emu' fowls." Lkwis
Wright, IllvM. Book of Poultry, 1886, p. 230.

Of many domestic animals, for example, the goat, eat and

rabbit, varieties with long, silky hair are familiar under the name

of "Angoras." Very similar breeds of guinea-pigs are kept, to

which the name " Peruvian " is given. In this connexion the

capture of a mouse {Mm musculus) with long, black, silk-like hair

is interesting1, as shewing that such a total variation may occur

as a definite phenomenon without Selection.

1 Cocks, W. P., Tram. Cornwall Polytech. Soc, L852. Like other animals,
mice have of course often been found black. For instance, a number of black mice
were found in Hampstead-down Wood. Hkwktt, Y\\. '/.oo\. Jour. iv. p. 348.

56 HAIR. [iNTROD.

As to the partial nakedness of the skin of many animals
(Man, &c.), several suggestions have been made. It has been
variously supposed that the covering of hair has been gradually
lost by Man, in correlation with the use of clothes ; with the heat
of the sun ; for ornamental purposes under sexual selection l ; or
perhaps as a protection from parasites2. Various suggestions
Have also been made to explain the persistence of hair at the
junction of the limbs and on the head and face. To a con-
sideration of the origin of nakedness, the evidence of Variation in
some measure contributes, and though the bearing is not very
direct, it may illustrate the futility of inquiries of this kind made
without regard to the facts of Variation.

Mouse (Mus musculus) : male and pregnant female found in a
straw-rick at Taplow ; both were entirely naked, being without hairs
at all, excepting only a few dark-coloured whiskers. The skin was
thrown up into numerous prominent folds, transversely traversing the
body in an undulating manner. This condition of the skin obtained
for them the name of " Rhinoceros mice." The ears were dark or
blackish, the tail ash-coloured, and the eyes black, indicating that they
were not albinos. The exfoliations from the skin were examined
microscopically but no trace of hair-follicles was found, nor any
suggestion of disease. The animals were active and healthy.

The young ones, when born, were similar to the parents. The
teeth were normal.

In the Museum of the College of Surgeons is a precisely similar
specimen which was found in a house in London. Gaskoix, Proc.
Zool. Soc, 1856, p. 38, Plate.

Three specimens of the common Mouse ( Mus musculus) were caught
in the town of Elgin. The whole bodies of these three creatures "were
completely naked — as destitute of hair and as fair and smooth as a
child's cheek. There was nothing peculiar about the snout, whiskers,
ears, lower half of the legs and tail, all of which had hair of the usual
length and colour. They had eyes as bright and dark as in the common

variety At least two others were killed in the same house where

these were found." Gordon, G., Zoologist, 1850, viii. p. 2763.

Shrew. (Sorex sp.) "whole of upper surface of head and body
destitute of hair, and skin corrugated like that of Naked Mice figured
in P. Z. S., 1856 ;" sent to Brit. Mus. by Mr P. Garner. Gray, J. E.,
Ann. and Mag. of X. II., 1869, S. 4, iv. p. 360.

In connexion with these cases, the following fact is interesting :
Heterocephalus is a genus of burrowing rodent from S. Africa. It contains two
species, of which one is about the size of a mouse and the other is rather larger.
They are characterized by possessing an apparently hairless skin which is on the
head and body of a wrinkled and warty nature. On closer inspection the skin is
seen to be furnished with tine scattered hairs, but there is no general appearance of
a hairy covering. There is no external ear in these animals. Oldfikld Thomas,
P. Z. S., 1885, p. 845, Plate LIV.

Naked horses have often been exhibited. Such a horse caught in a

1 C. Darwin, Descent of Man, i. p. 142.

2 Belt, Naturalist in Nicaragua; see also Hudson, Naturalist in La Plata, 1892.

sect, x.] INTRODUCTION. 57

semi-feral herd in Queensland was described by Tegetmeikr, Field,
xlviii. 1876, p. 281. The skin was black and like india-rubber. Careful
examination shewed no trace of hair, or any opening of a hair-follicle.
In Turkestan, in the year 1886, I heard of one thus travelling, but failed
to see it. ' Hairless' dogs in S. America remain distinct (Belt, I. c. ).

Of discontinuous Substantive Variation in bodily proportions a
single example must suffice. Among domestic animals of many
kinds, races are known in which the bones of the face do not grow
to their full size, while the bones of the jaw are, or may be, of
normal proportions. Familiar examples of this are the bull-dog,
the pug, the Japanese pug, the Niata cattle of La Plata1, some
short-faced breeds of pigs, and others. In the case of these
domestic animals the part which Selection has taken in their pro-
duction is unknown, and the magnitude of the original variations
cannot be ascertained. It is nevertheless of interest to notice
that parallel variations have occurred in distinct forms, and I
think that this is to some extent evidence that the variations
were from the first definite and striking. As regards the dogs
even, there is a presumption that the short face of at least the
Japanese pug arose independently from that of the common, or
Dutch pug (as it used to be called), but as to this the evidence is
insufficient. Among the dogs' skulls found in ancient Inca inter-
ments, a skull was found having the form of the bull-dog.
Nehring, Kosmos, 1884, xv. As these remains belong to a
period before the European invasion, it is most probable that
this bull-dog breed arose independently of ours.

Apart however from domestic animals there is evidence as to
the origin of short-faced breeds. This evidence, which is not so
well-known as it deserves to be, is provided by the occurrence of a
similar variation in fishes. Darwin in speaking of the evidence as
to Niata cattle makes allusion to the case of fishes in a note2,
quoting Wyman as to the cod, which occurs in a form known to
fishermen as the " bull-dog " cod. The interest of this obser-
vation is increased by the fact that it does not stand alone, but
similar variations have been seen in the carp, chub, minnow, pike,
mullet, salmon and trout. In the last-named there is even
evidence of the establishment of a local race having this singular
character.

Carp (Ci/prinus carpio). " Bull-dog"-headed Carp have often boon
described. The face ends more or less abruptly in front of the eyes,
while the lower jaw has almost its normal length. The front part of
the head is bulging and prominent, giving the fish an appearance which
several authors compare to that of a monumental dolphin. A ufood
figure of such a specimen is given by G. St Hilaibe, Hist, des Anom.,
ed. 1837, i. p. 9G, where a full account of the older literature of the

1 C. Darwin, Animals and Plants under Domestication, 2nd edition, i. p. 92.
- Ibid., p. 93, note.

58

BULL-DOG HEADS.

[iNTROD.

subject may be found. Inasmuch as carp are largely bred in ponds on
the continent, there is in this case some suggestion that unnatural
conditions may be concerned, but this suggestion does not apply to other
cases of the same Variation. Otto, Lehrb. path. Anat., I. § 129, states
that in the ponds of Silesia such fish are not rare. See also Voigt,
Mag. f. d. Naturk., ill. p. 515.

Cyprinus hungaricus : specimen from the Danube similarly formed.
The forehead was protuberant and bulged in front of the eyes so that
its anterior border was almost vertical. The attachments of the
mandible are carried forward in such a manner that the mandible
itself was directed upwards almost at right angles to the body. [Good
figure.] Steindachner, Verh. zool.-bot. Ges. Wien, 1863, xm. p. 485,
Plate.

[Several other types of Variation in the heads of Cyprinoids occur,
but cannot be described here.]

Chub {Leuciscus dobula = cephalus) : specimen having anterior part
of head rounded "like a monumental dolphin/' The body was normal,
measuring 33 cm. in length. Landois, Zoo/. Garten, 1883, XXIV.
p. 298.

Minnow (Phoxinus ton's) specimen having a snout like a pug
("mnsratt <ln mopsp,'y) [no description]. LuNEL, Pois*. du lac Lemon,
p. 96.

Mullet (Mugil capito) : specimen having both jaws directed
upwards, and the upper and anterior parts of the skull greatly
elevated and protuberant : the appearance of the head was like that
of a pug dog. Full measurements given. Canestrini, R., Atti deUa
soc. Ven. — Trent, di. sci. vat. in Padova, 1884, ix. p. 117 [Bibliography
given].

Pike (Esox lucius) described as like a pug, ibid., p. 124; see also
Vrolik's Atlas, 1849, Tab LXI. Jiff. 6.

Salmon (Salnio solar) : specimen having front part of face little
developed, the supi •a-maxillaries being asymmetrical. Lower jaw
projects far in front of upper jaw. Animal of fair size, and not
meagre. Van Lidth di-: Jeude, Notes from Leyden Mus., vn. p. 259,
Plate. [Curious malformation of S. trutta ibid], see also Jahrb. Ver.
vaterl. Nat. Wiirtt. xlii. p. 345.

Trout (*Sf. fario) : several specimens having bull-dog heads were
taken in Lochdow, near Pitmain, Inverness-shire. Heads short and
round ; upper iaw truncated like a bull-dog. This variety does not

Fig. 6. Bull-dop-headed Trout after Caklet.

sect, x.] INTRODUCTION. 59

occur in neighbouring lochs. None weighed more than \ 11». Yarbell,
Brit. Fishes, i. p. 286, figure given.

Another specimen (Fig. G), agreeing closely with Yarn-ll's figure,
was taken in a lake at an altitude of over 6000 ft. in the valley of
Sept-Laux (Isere). Saving the head it was in all respects normal.
This specimen is described and figured by CARLET, M. G., Journ.
de VAnat. et Phys., 1879, XV. p. 154. [It is declared that the
fishermen who took it, having previously met with similar speci-
mens, supposed that they had found a new species, but it is nut
expressly stated that these other specimens were from the same
locality.]

Before ending this preliminary glance at Discontinuity in
Substantive Variation, allusion must be made to a case which is
at once more famous and more instructive than any other. I refer
to the celebrated phenomenon of the production of nectarines Im-
peaches, or conversely. Upon the subject of almond, peach and
nectarine, Darwin produced a body of facts which, whether as an
example of a method or for the value of the facts themselves,
form perhaps the most perfect and the most striking of all that he
gave.

The evidence which is there collected is known to all. and
though similar observations have been made since by many, there
is I believe nothing of importance to add to Darwin's statement.
The bearing of these phenomena on the nature of Discontinuity in
Variation is so close that Darwin's summary may with profit be
given at length.

'To sum up the foregoing facts; we have excellent evidence <>f
peach-stones producing nectarine-trees, and of nectarine-stones
producing peach-trees — of the same tree bearing peaches and
nectarines — of peach-trees suddenly producing by bud-variation
nectarines (such nectarines reproducing nectarines by seed), as
well as fruit in part nectarine and in part peach, — and, lastly. of
one nectarine-tree first bearing half-and-half fruit and subsequent ly
true peaches"1. After disposing of alternative hypotheses he
concludes that "we may confidently accept the common view
that the nectarine is a variety of the peach, which may be pro-
duced either by bud- variation or from seed."

In this case the evidence is complete. The variation from peach
to nectarine or from nectarine to peach may be total. If less than
total, the fruit may be divided into either halves or quarters
so that for each segment the Variation i> total -till. Of inter-
mediate forms other than these divided ones, we have in this case

1 Animals and Plants under Dom€8ticationt cd. 2, i. p. 362.

2 Ibid., p. 362, quoting from Loudon's Hard. Mag, L828, p. •">:>. The case of a
Royal George peach which produced a fruit. " three parts of it being peach and one
part nectarine, quite distinct in appearance as well a< in flavour." The lin« ~ of
division were longitudinal.

60 RADIAL REPETITION. [introd.

no evidence : it is therefore a fair presumption that they are
either rare or non-existent; and that the peach-state and the
nectarine-state are thus positions of " Organic Stability," between
which the intermediate states, if they are chemical ami physical
possibilities, are positions of instability.

These examples of Discontinuity in Substantive Variation
must suffice to illustrate the nature of the phenomena. It will be
seen that the matters touched on cover a wide range, and the
evidence relating to them must be considered separately and at
length. Such a consideration I hope in a future volume to
attempt.

SECTION XI.

Discontinuity ix Meristic Variation: Examples.

Inasmuch as the facts of Meristic Variation form the substance
of this volume, it is unnecessary in this place to do more than refer
to the manner in which they exhibit the phenomenon of Dis-
continuity. One or two instances must suffice to give some sug-
gestion of this subject, detailed consideration being reserved.

Parts repeated meristically form commonly a series, which is
either radial or linear, or disposed in some other figure derived
from or compounded of these. For the purpose of this preliminary
treatment an instance of Discontinuous Variation in each of these
classes may be taken.

1. Radial Series.

Variations in the number of petals of actinomorphic flowers
exhibit the Discontinuity of Meristic Variation in perhaps its
simplest form.

Phenomena of precisely similar nature will hereafter be de-
scribed in animals, but such variations in flowers are so common
and so accessible that reference to them may with profit be made.
In Fig. 7 such an example is shewn.

It represents a Tulip having the parts of the flower formed in
multiples of four, instead of in multiples of three as normally.
Variation of this kind may be seen in any field or hedgerow1.

Meristic Variation is here presented in its greatest simplicity.
Such a case may well serve to illustrate some of the phenomena of
Discontinuity.

1 For full literature and lists of cases see especially Masters, Vegetable
Teratoid;/ //. s. v. PolyphyUy. It is perhaps unnecessary to refer to the fact tbat
the numerical changes here spoken of are quite distinct from those which result
from an assumption by the members of one series or whorl of the form and
characters proper to other whorls.

SECT. XI.]

INTRODUCTION.

61

A form with four segments occurs as the offspring of a form
with three segments. Such a Variation, then, is discontinuous

Fig. 7. Diagram of the flower of a Tulip having all the parts in -4.

because a new character, that of division into four, has appeared in
the offspring though it was not present in the parent. This new
character is a definite one, not less definite indeed than that of
division into three. It has come into the strain at one step of
Descent. Instances in which there is actual evidence of such descenl
are rare, but there can be no question that these changes do
commonly occur in a single generation, and, indeed, in many
plants, as for example Lysimachia (especially L. nemorum), flowers
having all the parts in -4 or in -6 may be frequently seen on
plants which bear likewise normal flowers with the parts in -5.

Now such a variation as this of the Tulip illustrates a pheno-
menon which in the Study of Variation will often be met.

We have said that the variation is discontinuous, meaning
thereby that the change is a large and decided one, but it is more
than this ; it is not only large, it is complete.

The resulting form possesses the character of division into four
no less completely and perfectly than its parent possessed the
character of division into three. The change from three to four is
thus perfected : from the form with perfect division into three La
sprung a form with perfect division into four. This is a case of a
total or perfect Variation.

This conception of the totality or perfection of Variation is one
which in the course of the study will assume great importance,
and it may be best considered in the simple case of numerical and
Meristic Variation before approaching the more complex questioo
of the nature of totality or perfection in Substantive Variation.

The fact that a variation is perfect at once leads to the (pus-

62 RADIAL REPETITION. [introd.

tion as to what it might be if imperfect. Between the form in -3
and the form in -4 are intermediates possible? and if possible, do
they exist ? Now by choosing suitable species of regular flowers,
individual flowers may no doubt be found in which there are three
large segments and one small one ; or two normal segments and a
third divided into two, making four in all. Such flowers are firstly
rare, while cases of perfect transformation are common. But be-
sides their rarity there is, further, a grave doubt whether they are
in any true sense intermediate between the perfect form in -3 and
the perfect form in - 4. After this again it must be asked whether
or no they do as a matter of fact occur as intercalated steps in the
descent of the form in -4 from the form in -3 '. To the last ques-
tion a general negative may at once be given ; for though there is
abundant evidence that Meristic Variations of many kinds and in
several degrees of completeness may be seen in the offspring of the
same parent, yet any one member of such a family group may
shew a particular Variation in its perfection, and the occurrence of
an}- intermediate in the line of Descent is by no means necessary
for the production of the perfect Variation.

To answer the former question, whether or no forms imperfectly
divided into four parts are in reality intermediate between those
in -3 and those in -4, a knowledge of the mechanics of the
process of Division is required. Such knowledge is as yet entirely
wanting, and discussion of this matter must therefore be prema-
ture. With much hesitation I have decided to make certain
reflexions on the subject, which will be found in an Appendix to
this work. These may perhaps have a value as suggestions to
others, though from their theoretical nature they can find no place
here.

There is however another class of cases which are intermediate
in a different way. In the Tulip described above the quality of
division into 4 was present in all the floral organs. This is not
always the case, for a Meristic Variation may be present in one
series of organs, though it is absent in some or all of the others,
and this is a phenomenon frequently recurring. Nevertheless,
though only partially distributed, a Variation may still be dis-
played in its totality in the parts wherein it is present. The
parts of a single whorl, the calyx for example, may undergo a
complete Variation, while the corolla and other parts are un-
changed. In the same way single members of a radial series, as a
petal for example, may undergo a complete Variation while the
other members of the series are unchanged. The same will be
shewn hereafter to be true of animals also.

For instance, the normal number of the parts in the disc of
Aurelia is four, but the whole body may be divided instead into
Bix or some other number of parts. Examples are also found in
which the parts of one-half or of one quadrant are arranged in the
new number, while the remainder is normal; and. as in flowers,

SECT. XI.]

INTRODUCTION.

<;:;

this new Dumber may prevail in some or in all of those systems of
organs which are disposed around the common centre.

2. Linear Series.

Before speaking further of the totality or perfection of Varia-
tion it will be well to give an illustration of Discontinuous Meristic
Variation as it occurs in the case of a linear series of parts. AlS
such an illustration the case of the variation in the number of
joints in the tarsus of the Cockroach (Blatta) may be taken. This
variation has been the subject of very full investigation l>v Mr
H. H. Brindley. The tarsus of the Cockroach is normally divided
into five joints, but in about 25 per cent, of B. americana (and in
a smaller proportion of several other species) the tarsus of one or
more legs is divided into only four joints, though the total length
may be the same as that of the corresponding leg of the other side,
Fig. 8. Between the five-jointed form of tarsus and the four-jointed
form no single case in any way intermediate was seen. The whole

11

Fig. 8. Tarsi of the third pair of legs in a specimen of Blatta americana,
I. the left tarsus, having the normal, or 5- jointed form; II. the right tarsus,

having the 4-jointed form.

evidence will be given in full in the proper place and raises many
questions of great interest; but that which is important to our
present consideration is the fact that the Variation is hero un-
doubtedly discontinuous, arising suddenly as a total or perfect
Variation, from the rive-jointed form to the four-jointed, ffere
the variation, though total as regards the limb in which it is
present, is not total as regards all the legs taken together. For
commonly only a single leg had a four-jointed tarsus, and only one
specimen was met with in which all six legs thus varied, and one
specimen only shewed the variation in five legs.

In speaking of such a Variation as a perfect Variation several
things are meant.

First, it is meant that the tarsus of the new pattern is as
distinctly divided into four joints as the normal is into five. In

64 LINEAR REPETITION. [ixtrod.

addition to this the statement that the varying limb is perfect
conveys a number of ideas that cannot be readily formulated ; for
example, that the joints are to all appearance properly proportioned
and serviceable, shewing no sign of unfitness: they have in fact
much the same appearance as they have in those of the Orthoptera
in which the tarsus is normally four-jointed. But besides these
attributes, which though useful enough for ordinary description
are still in their nature formless and of no precise application,
there is another which in the case of these varying legs we are
entitled to make. We have said that these four-jointed tarsi are
to all appearance normal, save for the number of the joints. Now
the measurements which, at my suggestion, Mr Brindley has been
kind enough to make, entitle us to go beyond this, and to assert
that the four-jointed, tarsus has another character bv reason of
which it is actuallv in a sense a "normal" form. A brief considera-
tion of this will clearly illustrate the meaning of the term "per-
fection" applied to Variation.

We saw above that in a monomorphic form, the frequency with
which, in respect of any given character, it departs from its mean
condition follows a curve of Frequency of Error. This is, indeed,
what is meant by the statement that the mean condition is a
normal.

Taking the five-jointed tarsus, measurements shewed that the
ratio of the length of any given joint to the length of the whole
tarsus varied in this way about a moan value. Measurement of
the joints of the four-jointed form shewed that the ratios which
they bear to the total length of their respective tarsi vary in a
similar way about their mean values, and that there is thus a
"normal" four-jointed condition just as there is a "normal" five-
jointed condition. In the same way, then, that the ratio of the
length of each of the five joints to that of the whole tarsus is not
always identical but exhibits small variations, so the ratios of the
several joints of the four-jointed tarsus to the length of the whole
tarsus also vary, but in each case the ratio has a mean value
which is approached with a frequency conforming to a curve of
Error.

The measurements established also another fact which is of
consequence to an appreciation of the nature of totality in
Variation. It not only appeared that the departures from the
mean value of these ratios in the four-jointed variety were dis-
tributed about the mean in the same way as those of the five-
jointed form, but it was also shewn that the absolute varia-
tions from the mean values of these ratios were not on the
whole greater in the four-jointed tarsi than in the five-jointed
tarsi. In other words, the four-jointed tarsus occurring thus
sporadically, as a variety, is not less definitely constituted than
the five jointed type, and the proportions of its several joints
are not less constant. It is scarcely necessary to point out that

sect, xi.] INTRODUCTION. 65

these facts give no support to the view that the exactness or
perfection with which the proportions of the normal \m\i\ are
approached is a consequence of Selection. It appears rather, that
there are two possible conditions, the one with five joints and the
other with four, either being a position of Organic Stability. Int.*
either of these the tarsus may fall; and though it is still conceivable
that the final choice between these two may have been made by
Selection, yet it cannot be supposed that the accuracy and com-
pleteness with which either condition is assumed is the work of
Selection, for the "sport" is as definite as the normal.

This interesting case of Meristic Variation in the tarsus of the
Cockroach illustrates in a striking way the principle which is
perhaps the chief of those to which the Study of Variation at the
outset introduces us. We are presented with the phenomenon of
an organ existing in two very different states, between which no
intermediate has been seen. Each of these states is definite and
in a sense perfect and complete ; for the oscillations of the four-
jointed form around its mean condition are not more erratic than
those of the normal form. Now when it is remembered that just
such a four-jointed condition of the tarsus is known as a normal
character of many insects and especially of some Orthoptera, it is,
I think, difficult to avoid the conclusion that if the four-jointed
groups are descended from the five-jointed, the Variation by which
this condition arose in them was of the same nature as that seen
as an individual Variation in Blatta ; that as the modern pheno-
menon of the individual Variation which we see, so thai pasl
phenomenon of the birth of a four-jointed race, was definite and
complete, and that the change whose history is gone, like the
change to be seen to-day, was no gradual process, but a Discon-
tinuous and total Variation1.

1 Since this Section was written it has seemed possible that the account Riven
above may be found to need an important modification. It is well known that
Blatta, in common with many other Orthoptera, has the power of reproducing the
antennae and legs after amputation or injury, and we have made 80me observations
shewing that the tarsi of these regenerated legs sometimes, if not always, contain
four joints. The question therefore arises whether the 4-jointed tarsus la a truly
congenital variation, and not rather a variation introduced in the process of
regeneration, somewhat after the manner of a bad- variation. To determine this
point a considerable number of immature specimens were examined, and it was
found that the percentage of individuals with 4-jointed tarsi is considerably Less
in the young than in the adult. These facts lend support to the view that the
4-jointed condition is not congenital. A quantity of individuals were also hatched
from the egg-cocoons, and among them there has thus far been found no ease of
4-jointed tarsus. On the other hand the total number thus hatched is not yet
sufficient to create any strong probability that none are ever batched in the
4-jointed state. We have also seen the 4-jointed tarsus in three very young in-
dividuals, which, to judge from their total length, must have been newly hatched.
The statistics shew besides that the abnormality is distinctly commoner p females
than in males, and that it is commoner in the legs of the 2nd pair than in the 1st,
and much more common in the 3rd pair of legs than in the 2nd. These facts some-
what favour the view that the variation may be congenital. It seems also ex-
ceedingly improbable that in the specimen with all the tarsi 4-jointed. the six legs
could each have been lost and renewed. There seems on the whole to be a pre-

B. 5

66 SEX AND VARIETY. [introd.

SECTION XII.

Parallel between Discontinuity of Sex and Discontinuity

in Variation.

The application of the term Discontinuity to Variation must
not be misunderstood. It is not intended to affirm that in dis-
continuous Variation there can be between the variety and the
type no intermediate form, or that none has been known to occur,
and it is not even necessary for the establishment of Discontinuity
that the intermediate forms should be rare relatively to the
perfect form of the variety, though in cases of discontinuous
Variation this is generally the case ; but it is rather meant that
the perfect form of the variety may appear at one integral step
in Descent, either without the occurrence of intermediate grada-
tions, or at least without the intercalation of such graduated forms
in the pedigree.

In the case of the tarsus of Blatta we have seen an example
of a total and complete Variation affecting single members of a
series of repeated parts, not collectively, but one or more at a
time1. Such an instance of a Meristic Variation occurring in
a state which is total as regards members of a series but not
total as regards the whole series finds many parallels among
Substantive Variations, as, for example, that of the Crab (Cancer
par/ ants) bearing the right third maxillipede fashioned as a chela,
while the left third maxillipede was normal. Variations of this
nature in plants are of course well known to all.

At a previous place (Section vn.) allusion was made to the
familiar but very curious analogy between members of a series of
Meristic parts and separate organisms. The facts of Variation bring
out this analogy in many singular ways, and in speaking of the
totality of Variation it is necessary to bear these facts in mind.
Not only are there abundant instances of independent division
or multiplication of single members of Meristic series, but as
has been said, single members of such series may thus inde-
pendently and singly undergo qualitative or Substantive Variation,
being treated in the physical system of the body as though they
were separate units. In Variation, therefore, though it will be

sumption that the variation may at least sometimes be congenital. Supposing
however that this shall be found hereafter not to be the case, I do not thiuk that
the deductions drawn from the facts will be less valid. The conclusions as to
the definiteness of the two types, and the relationships of the several parts of each
to the several parts of the other, would still hold good. There are besides in other
forms, instances of similar numerical Variation, as for example, in the number of
joints in the antennae of Prionidae, where the hypothesis of change on renewal is
impossible, from which a similar argument might be drawn ; but on the whole I
have preferred to leave the account as it stands, taking the case of Blatta as an
example, because it is easily accessible and because, from the fewness of the joints
concerned, the issues are singularly clear.
1 See Note at the end of Section xi.

sect, xii.] INTRODUCTION. G7

found that members of Meristic series may vary simultaneously
and collectively — and this is one of the most important generaliza-
tions which result from the Study of Variation — yet it is also
true that in Variation single members of such series may vary
independently and behave as though they possessed an " in-
dividuality" of their own. If ever it shall be possible to form
a conception of the physical processes at work in the division
and reproduction of organisms, account must be taken of both of
these phenomena.

I know no way in which the nature of Discontinuity in Varia-
tion and the position of intermediate forms may be so well illus-
trated as by the closely parallel phenomenon of Sex. In the case
of Sex in the higher animals we are familiar with the existence
of a race whose members are at least dimorphic, being formed
either upon one plan or upon the other, the two plans being in
ordinary experience alternative and mutually exclusive. Between
these two types, male and female, there are nevertheless found
intermediate forms, "hermaphrodites," occurring in the higher
animals at least, as great rarities. Now though these inter-
mediate forms perhaps exist in gradations sufficiently fine to
supply all the steps between male and female, it cannot be
supposed that the one sex has been derived from the other, and
still less that the various stages of hermaphroditism have been
passed through in such Descent. Besides this, even though there
is an accurate correspondence or homology between the several
organs which are modified upon the one plan in the male and
upon another in the female, and though this homology is such
as to suggest, were we comparing two species, that the one had
been formed from the other, part by part, yet by the nature of
the case such a view is here inadmissible: for firstly it is im-
possible to suppose that either sex has at any time had the organs
of the other in their completeness, and secondly it is clear that
any hypothetical common form, by modification of which both
may have arisen, must have been indefinitely remote and could
certainly not have possessed secondary sexual organs bearing any
resemblance to those now seen in the higher forms. All this
has often been put, but the application of it to Variation is of
considerable value. For in the case of Sex there is an instance
of the existence of two normals and of many forms intermediate
between them, occurring in a way which precludes the supposition
that the intermediates represent stages that have ever occurred
in the history of the two forms.

In yet another way Sex supplies a parallel to Variation. As
we know, the sexes are discontinuous and occur commonly in their
total or perfect forms. Now just as members of a Meristic seri« -
may present total variations independently of each other, so may
single members of such a series present opposite secondary sexual
characters, which may nevertheless be in each case complete.

68 NATURE OF DISCONTINUITY. [introd.

The best known instance of this is that of gynandromorphic
insects, in which the characters of the whole or part of one side
of the body, wings and antennae, are male, while those of the
other side are female. Remarkable instances of a similar pheno-
menon have been recorded among bees and will be described later.
As is well known, the organs and especially the legs of the sex-
less females or workers are formed differently from those of the
drones, but there are cases of individuals having some of the
parts and appendages formed on the one plan arid some on the
other. Thus in these individuals, which are in a sense inter-
mediate between workers and drones, the characters of the two
sexes may still be not completely blended, the male type pre-
vailing in some parts, and the female in others. In the Dis-
continuity of Substantive Variation will be found examples of
imperfect blending of variety and type closely comparable with
this case of the imperfect blending of Sex.

SECTION XIII.
Suggestions as to the natuke of Discontinuity in Variation.

The observations at the end of Section XI, regarding the Dis-
continuity of Meristic Variation lead naturally to certain reflexions
as to the nature of Discontinuous Variation in general. In tin-
case of the Cockroach tarsus, there given, it appeared that just as
the structure of the typical form varies about its mean condition,
so the structure of the variety varies about another mean condition.
This fact, which in the given instance of Meristic Variation is so
clear, at once suggests an inquiry whether this is not the usual
course of Discontinuous Variation, and, indeed, whether Discon-
tinuity in Variation does not mean just this, that in varying the
organism passes from a form which is the normal for the type to
another form which is a normal for the variety. Such transitions
plainly occur in many cases of Meristic Variation, and in a consider-
able number of Substantive Variations there will be found to be
indications that the phenomenon is similar. It is true that at the
present stage of the inquiry the evidence has the value rather of
suggestion than of proof, but the suggestion is still very decided
and it is scarcely possible to exaggerate the importance of even
this slender clue.

In stating the problem of Species at the beginning of this
inquiry it was said that the forms of living things, as we know
them, constitute a discontinuous series, and it is with the origin
of the Discontinuity of the series that the solution of the main
problem is largely concerned. Now the evidence of Discontinuous
Variation suggests that organisms may vary abruptly from the

sect, xiii.] INTRODUCTION. G9

definite form of the type to a form of variety which has also in
some measure the character of definiteness. Is it not then possible
that the Discontinuity of Species may be a consequence and ex-
pression of the Discontinuity of Variation \ To declare at the
present time that this is so would be wholly premature, but the
suggestion that it is so is strong, and as a possible light on the
whole subject should certainly be considered.

In view of such a possible solution of one of the chief parts
of the problem of Species it will be well to point out a line of
inquiry which must in that event be pursued. If it can be shewn
that the Discontinuity of Species depends on the Discontinuity of
Variation, we shall then have to consider the causes of the Dis-
continuity of Variation.

Upon the received hypothesis it is supposed that Variation is
continuous and that the Discontinuity of Species results from the
operation of Selection. For reasons given above (pp. 15 and 1G) there
is an almost fatal objection in the way of this belief, and it cannot
be supposed both that all Variation is continuous and also that the
Discontinuity of Species is the result of Selection. With evidence
of the Discontinuity of Variation this difficulty would be removed.

It will be noted also that it is manifestly impossible to suppose
that the perfection of a variety, discontinuously and suddenly
occurring, is the result of Selection. No doubt it is conceivable
that a race of Tulips having their floral parts in multiples of four
might be raised by Selection from a specimen having this character,
but it is not possible that the perfection of the nascent variety
can have been gradually built up by Selection, for it is, in its very
beginning, perfect and symmetrical. And if it may be seen thus
clearly that the perfection and Symmetry of a variety is not the
work of Selection, this fact raises a serious doubt that perhaps
the similar perfection and Symmetry of the type did not owe its
origin to Selection either. This consideration of course touches
only the part that Selection may have played in the first building
up of the type and does not affect the view that the perpetuation
of the type once constituted, may have been achieved by Selection.

But if the perfection and definiteness of the type is not due
to Selection but to the physical limitations under which Variation
proceeds, we shall hope hereafter to gain some insight into the
nature of these limitations, though in the present state of zoological
study the prospect of such progress is small. In the observations
which follow I am conscious that the bounds of profitable specu-
lation are perhaps exceeded, and I am aware that to many this
may seem matter for blame; but there is, in my judgment, a
plausibility in the views put forward, sufficient at least to entitle
them to examination. They are put forward in no sense as a
formulated theory, but simply as a suggestion {'or work. It is,
besides, only in foreseeing some of the extraordinary possibilities

70 MECHANICAL. [introd.

that lie ahead in the Study of Variation, that the great value of
this method can be understood.

It has been seen that variations may be either Meristic or
Substantive, and that in each group discontinuous and definite
variations may occur by steps which may be integral or total.
We are now seeking the factors which determine this totality and
define the forms assumed in Variation. In this attempt we may,
by arbitrarily confining our first notice to very simple cases, recog-
nize at least two distinct factors which may possibly be concerned
in this determination. Of these the first relates to Meristic
Variation and the second to Substantive Variation.

1. Possible nature of the Discontinuity of Meristic Variation.

Looking at simple cases of Meristic Variation, such as that of
the Tulip or of Anrelia, or of the Cockroach tarsus, there is, I think,
a fair suggestion that the definiteness of these variations is deter-
mined mechanically, and that the patterns into which the tissues
of animals are divided represent positions in which the forces that
effect the division are in equilibrium. On this view, the lines or
planes of division would be regarded as lines or planes at right
angles to the directions of the dividing forces ; and in the lines of
Meristic Division we are perhaps actually presented with a map
of the lines of those forces of attraction and repulsion which
determine the number and positions of the repeated parts, and
from which Symmetry results. If the Symmetry of a living bod}
wore thus recognized as of the same nature as that oi any sym-
metrical system of mechanical forces, the definiteness of the sym-
metry in Meristic Variation would call for no special remark, and
the perfection of the symmetry of a Tulip with its parts divided
into four, though occurring suddenly as a " sport," would be recog-
nized as in nowise more singular than the symmetry of the type.
Both alike would then be seen to owe their perfection to me-
chanical conditions and not to Selection or to any other gradual
process. If reason for adopting such a view of the physics of
Division should appear, the frequency with which in any given
form a particular pattern of Division or of Symmetry recurs,
would be found to be determined by and to be a measure of the

%J

stability of the forces of Division when disposed in that particular
pattern. It will of course be understood that in these remark-
no suggestion is offered as to the causes which determine whether
a tissue shall divide into four or into three, but merely as to the
conditions of perfection of the division in either case. It will also
be clear that though the symmetry of a flower or of any other
tissue depends also on symmetrical growth, it is primarily dependent
on the symmetry of its primary divisions, upon which symmetrical
growth and secondary symmetrica] divisions follow.

•sect, xiii.] INTRODUCTION. 71

It would be interesting and I believe profitable to examine
somewhat further the curiously close analogy between the sym-
metry of bodily Division and that of certain mechanical systems
by which close imitations both of linear and of radial segmentation
can be produced ; and though to some this might seem overdaring,
the possibility that the mechanics of bodily Division are in their
visible form of an unsuspected simplicity is so far-reaching that it
would be well to use any means which may lead others to ex-
plore it.

And even if at last this suggestion shall be found to have in it
no other element of truth, it would still be of use as a forcible
presentation of the fact, which when realized can hardly be
doubted, that among the factors which combine to form a living
body, the forces of Division may be distinguished as in their mani-
festations separable from the rest and forming a definite group.
For, already (Section V.) it has been pointed out that the patterns
of Division or Merism may be changed, while the Substance of the
tissues presents to our senses no difference. The recognition of
this essential distinctness of the Meristic forces will, I believe, be
found, to supply the base from which the mechanics of growth will
hereafter be attacked.

The problems of Morphology will thus determine themselves
into problems in the physiology of Division, which must be
recognized together with Nutrition, Respiration and Metabolism,
as a fundamental property of living protoplasm.

To sum up : there is a possibility that Meristic Division may
be a strictly mechanical phenomenon, and that the perfection
and Symmetry of the process, whether in type or in variety, may
be an expression of the fact that the forms of the type or of the
variety represent positions in which the forces of Division are
in a condition of Mechanical Stability.

2. Possible nature of the Discontinuity of Substantive Variation.

Passing from the phenomena of Division and arrangement to
those of constitution or substance we are, as has been said, again
presented with the phenomenon of discontinuous or total Varia-
tion, and we must seek for causes which may perhaps govern
and limit this totality, and in obedience to which the Variation
is thus definite. Now as in the case of Meristic Variation, by
arbitrarily limiting the examination to those cases which seem
the simplest it appears that there is at least an analogy be-
tween them and certain mechanical phenomena, bo by similarly
restricting ourselves to very simple cases there will be seen to
be a similar analogy between the discontinuity of some Sub-
stantive Variations and that of chemical discontinuity. It is
on the whole not unreasonable to expect that the definitem —
of at least some Substantive Variations depends ultimately on
the discontinuity of chemical affinities. To take but one instance,

72 CHEMICAL. [introd.

that of colour, we are familiar with the fact that the colours of
many organic substances undergo definite changes when chemi-
cally acted on by reagents, and it is not suggested that the
defmiteness and discontinuity of the various colours assumed is
dependent on anything but the defmiteness of the chemical
changes undergone. The changes of litmus and many vegetable
blues to red on treatment with acids, of many vegetable yellows
to brown on treatment with alkalies, the colours of the series
of bodies produced by the progressive oxidation of biliverdin are
familiar examples of such definite colour-variations.

With facts of this kind in view, the conclusion is almost
forced on us that the defmiteness of colour-variation is a conse-
quence of the defmiteness of the chemical changes undergone.
No one doubts that the orange colouring matter of the variety
of the Iceland Poppy (P. nudicaule) is a chemical derivative
from the yellow colouring matter of the type. It is not ques-
tioned that in such cases a definite alteration in the chemical
conditions in which the pigment is produced determines whether
the flower shall be orange or yellow ; and I think it is reasonable
to expect that the frequency with which the flowers are either
yellow or orange as compared with the rarity of the intermediate
shades is an expression of the fact that the yellow and orange forma
of the colouring matter have a greater chemical stability than the
intermediate forms of the pigment, or than a mixture of the tun
pigments. If then it should happen, as we may fairly suppose it
might, that the orange form were to be selected and established
as a race, it would owe the defmiteness of its orange colour and
the precision of its tint, not to the precision with which Selection
had chosen this particular tint, but to the chemical discontinuity of
which the originally discontinuous Variation was the expression.

To pass from the case of a sport to that of Species, it is well
known that of the man}* S. African butterflies of the genus
Euchloe ( = Anthocharis, Orange-tips), some have the apices or
tips of the fore-wings orange-red (for example, E. danae), while
in others they are purple (for example, E. ione). Upon the
view that the transition from orange to purple, or vice verm,
had been continuously effected by the successive Selection of
minute variations, we are met bv all the difficulties we know so
well. Why is purple a good colour for this creature ? If purple
is a good colour and red is a good colour, how did it happen that
at some time or other all the intermediate shades were also good
enough to have been selected ? and so on. These and all the
cognate difficulties are opened up at once, and though they have
been met in the fashion we know, they have scarcely been over-
come. But at the outset this view assumes that every inter-
mediate may exist and has existed, an assumption which i-
gratuitous and hardly in accordance with the known fact thai
chemical processes are frequently discontinuous. When besides

sect, xiil] INTRODUCTION. 73

this it is known that Variation may be discontinuous, I submit
that it is easier to suppose that the change from red to purple
was from the first complete, and that the choice offered to Selec-
tion was between red and purple ; and that the tints of the purple
and of the red were determined by the chemical properties of
the body to which the colour is due. This case is a particularly
interesting one in the light of the fact that, as Mr F. G. Hopkins
has lately shewn me, this purple colour, dissolved in hot water,
leaves on evaporation a substance which gives the murexide
reaction and cannot as yet be distinguished from the substance
similarly derived from the orange or yellow colouring matters
of Pieridae in general. As was stated above, Mr Hopkins has
shewn that these yellows are acids, allied to mycomelic acid, a
derivative of uric acid, and therefore of the nature of excret-
ory products. Whether the purple body is related to the yellow
or to the orange as a salt is to an acid, or otherwise, cannot yel
be affirmed ; but if the difference between them is a chemical
difference, which can hardly be doubted, there is at least a pre-
sumption that the discontinuity of these colours in the several
species, is an expression of the discontinuity of the chemical
properties of this body. The possibility that from such bodies
a series of substances might perhaps by suitable means be pre-
pared in such a way as to represent many or even all intermediate
shades, does not greatly affect the suggestion made; for even in
such series it is almost certain that points of comparative stability
would occur, and Discontinuity would be thus introduced.

The case of Colour has been taken in illustration because it
is the simplest and most intelligible example of the possibility
that the Discontinuity of some Substantive Variations is d. 'tor-
mined by the Discontinuity of the chemical processes by which
the structures are produced. It is true that perhaps no Bpecies
has been rightly differentiated by colour alone, but colour is
still one of the many characters which go to the distinguishing
of a species, and it is precisely one of the characters whi s
significance and delimitation by Natural Selection is most
obscure. Moreover by the fact that in the case of these yellow
and red Pieridye the colours are of an excretory nature, we are
reminded that Variation in colour may be an index of serious
changes in the chemical economy of the body, and that when an
animal is said to be selected because it is red or because it is
purple, the real source of its superiority may be not its red colour
or its purple colour, but other bodily conditions of which th<
colours are merely symptoms. By those who have attempted to
reconcile the phenomena of Colour with the hypothesis of Natural
Selection this fact is too often overlooked.

But though it may reasonably be supposed that much of the
Discontinuity of Variation and some of the Discontinuity of

74 ANALOGY OF DISEASE. [introd.

Species arise through discontinuous transition from one state of
mechanical or chemical stability to another state of stability, there
nevertheless remain large classes of discontinuous variations, and
of Specific Differences still more, whose Discontinuity bears no
close analogy with these. To these phenomena inorganic Nature
offers no parallel. We may see that they are discontinuous and
that their course is in some way controlled, but as to the nature
of this control we can make no guess.

Though the resemblance may be misleading, it is neverthe-
less true that in living Nature there are other phenomena, those
of disease, which present a Discontinuity closely comparable with
that of many variations. In problems of disease we meet again
the same problem which we meet in Variation, namely, changes
which may be complete or specific, though occurring so suddenly
as to exclude the hypothesis that Selection has been the limiting
cause. All this is familiar to everyone who has considered the
problem of Species.

For though, like discontinuous variations, the manifestations
of specific disease are not always identical, but differ in intensity
and degree, varying about a normal form, still these manifestations
maybe specific in the sense in which the term is used with reference
to the characters of Species. If we exclude those diseases whose
specific characters are now known to be the result of the invasion
of specific organisms, there still remain very many which are known
and recognized by definite and specific symptoms produced in the
body, though there is as yet no evidence that they are due to
specific organisms. [Of course if it were shewn that these diseases
also result from the action of specific organisms, they then only
present to us again the original problem of Species ; for if the
definiteness, or Species, of a disease is due to the definiteness, or
Species, of the micro-organism which causes it, the cause of that
definiteness of the micro-organism remains to be sought, and we
are simply left with a particular case of the general problem of
Species.] But in the meantime we can see that the manifestations
are specific ; and while we do not know that they result from causes
themselves specific, the nature of the control in obedience to which
they are specific is unknown.

The parallel between disease and Variation may be mis-
leading, but this much at least may fairly be learned from it :
that the system of an organized being is such that the result
of its disturbance may be specific. And in the end it may well
be that the problem of Species will be solved by the study of
pathology ; for the likeness between Variation and disease goes
far to support the view which Virchow has forcibly expressed,
that " every deviation from the ty pe of the parent animal must
have its foundation on a pathological accident1."

1 E. Virchow, Journal of Pathology, I. 1892, p. 12.

sect, xiv.] INTRODUCTION. 75

SECTION XIV.

Some current conceptions of Biology in view of the facts

of Variation.

Enough has now been said to explain the aim of the Study
of Variation, and to shew the propriety of the choice of the facts
of Meristic Variation as a point of departure fur that study.
Before leaving this preliminary consideration, reference to some
cognate subjects must be made.

It has been shewn that in view of the facts of Variation,
some conceptions of modern Morphology must be modified, while
others must be abandoned. With the recognition of the sig-
nificance of the phenomena of Variation, other conceptions of
biology will undergo like modifications. As to some of these a
few words are now required, if only to explain methods adopted in
this work.

1. Heredity.

It has been the custom of those who have treated the subject
of Evolution to speak of " Heredity ': and "Variation" as two
antagonistic principles ; sometimes even they are spoken of as
opposing "forces."

With the Study of Variation, such a description of the pro-
cesses of Descent will be given up, even as a manner of speaking.
In what has gone before I have as far as possible avoided any
use of the terms Heredity and Inheritance. These terms which
have taken so firm a hold on science and on the popular fancy,
have had a mischievous influence on the development of bio-
logical thought. They are of course metaphors from the descent
of property, and were applied to organic Descent in a time when
the nature of the process of reproduction was wholly mis-
understood. This metaphor from the descent of property is
inadequate chiefly for two reasons.

First, by emphasizing the fact that the organization of the
offspring depends on material transmitted to it by its parents,
the metaphor of Heredity, through an almost inevitable confusion
of thought, suggests the idea that the actual body and consti-
tution of the parent are thus in some way handed on. No one
perhaps would now state the facts in this way, but something
very like this material view of Descent was indeed actually de-
veloped into Darwin's Theory of Pangenesis. From this sugges-
tion that the body of the parent is in some sort remodelled into
that of the offspring, a whole series of errors arc derived Chief
among these is the assumption that Variation must necessarily
be a continuous process; for with the body of the parent to start
from, it is hard to conceive the occurrence of discontinuous
change. Of the deadlock which has resulted from the attempt

76 REVERSION. [introd.

to interpret Homology on this view of Heredity, I have already
spoken in Section VI.

Secondly, the metaphor of Heredity misrepresents the essential
phenomenon of reproduction. In the light of modern investiga-
tions, and especially those of Weismann on the continuity of the
germ-cells, it is likely that the relation of parent to offspring,
if it has any analogy with the succession of property, is rather
that of trustee than of testator.

Hereafter, perhaps, it may be found possible to replace this
false metaphor by some more correct expression, but for our
present purpose this is not yet necessary. In the first exami-
nation of the facts of Variation, I believe it is best to
attempt no particular consideration of the working of Heredity.
The phenomena of Variation and the origin of a variety must
necessarily be studied first, while the question of the perpetua-
tion of the variety properly forms a distinct subject. Whenever
in the cases given, observations respecting inheritance are forth-
coming they will be of course mentioned. But speaking of dis-
continuous Variation in general, the recurrence of a variation
in offspring, either in the original form or in some modification
of it, has been seen in so many cases, that we shall not go far
wrong in at least assuming the possibility that it nun/ nappear
in the offspring. At the present moment, indeed, to this state-
ment there is little to add. So long as systematic experiments
in breeding are wanting, and so long as the attention of naturalists
is limited to the study of normal forms, in this part of biology
which is perhaps of greater theoretical and even practical im-
portance than any other, there can be no progress.

2. Reversion.

Around the term Reversion a singular set of false ideas have
gathered themselves. On the hypothesis that all perfection and
completeness of form or of correlation of parts is the work of
Selection it is difficult to explain the discontinuous occurrence
of new forms possessing such perfection and completeness. To
account for these, the hypothesis of Reversion to an ancestral
form is proposed, and with some has found favour. That this
suggestion is inadmissible is shewn at once by the frequent occur-
rence by discontinuous Variation, of forms which though equally
perfect, cannot all be ancestral. In the case of Veronica and
Liiuiria, for example, a host of symmetrical forms of the floral
organs may be seen occurring suddenly as sports, and of these
though any one may conceivably have been ancestral, the same
cannot be supposed of all, for their forms are mutually exclusive.
On Veronica buxbaumii, for instance, are many symmetrical
tlowers, having two posterior petals, like those of other Scrophu-
larinese : these may reasonably be supposed to be ancestral, but

sect, xiv.] INTRODUCTION. 77

if this supposition is made, it cannot be made again for the
equally perfect forms with three petals, and the rest1.

The hypothesis of Reversion to account for the Symmetry
and perfection of modern or discontinuous Variation is made
through a total misconception of the nature of Symmetry.

There is a famous passage in the Descent of Man, in which
Darwin argues that the phenomenon of double uterus, from its
perfection, must necessarily be a Reversion.

"In other and rarer cases, two distinct uterine cavities are formed, each

having its proper orifice and passage. No such stage is passed through during the
ordinary development of the embryo, and it is difficult to believe, though perhaps
not impossible, that the two simple, minute, primitive tubes could know how (if
such an expression may be used) to grow into two distinct uteri, each with a well-
constructed orifice and passage, and each furnished with numerous muscles, nerves,
glands and vessels, if they had not formerly passed through a similar course of
development, as in the case of existing marsupials. No one will pretend that bo
perfect a structure as the abnormal double uterus in woman could be the result
of mere chance. But the principle of reversion, by which Long-lost dormant
structures are called back into existence, might serve as the guide for the full
development of the organ, even after the lapse of an enormous interval of time-."
Descent of Man, vol. I. pp. 123 and 124.

This kind of reasoning has been used by others again and
again. It is of course quite inadmissible; for by identical reason-
ing from the perfect symmetry of double monsters, of the si ugh-
eye of the Cyclopian monster, and so on, it might be shewn th.it
Man is descended from a primitive double vertebrate, from a
one-eyed Cyclops and the like. For other reasons it is likely
enough that double uterus was a primitive form; but the per-
fection and symmetry of the modern variation to this form is
neither proof nor indication of such an origin. Such a belief
arises from want of knowledge of the facts of Meristic Variation,
and is founded on a wrong conception of the nature of symmetry
and of the mechanics of Division. The study of Variation shews
that it is a common occurrence for a part which stands in the
middle line of a bilaterally symmetrical animal, to divide into
two parts, each being an optical image of the other: and thai
conversely, parts which normally are double, standing as optical
images of each other on either side of such a middle line may

1 For a full account of such facts, see a paper by Miss A. Bateson and myself
On Variations in Floral Symmetry. Journ. Linn. Soc, xxvui. p, 386.

2 This extraordinary passage is scarcely worthy of Darwin's penetration. If
read in the original connexion it will seem strange that it should have been allowed
to stand. For in a note to these reflexions on Reversion [Descent, i. i>. L25) Darwin
refers to and withdraws his previously expressed view that supernumerary digits
and mamma? were to be regarded as reversions. This view had been based on I
perfection and symmetry with which these variations reproduce the structure of
putative ancestors. It was withdrawn because Gegenbaur had shewn that poly*
dactyle limbs often bear no resemblance to those of possible ancestors, and I
extra mammae may not only occur symmetrically and in places where they are
normal in other forms, but also in several quite anomalous situations. In the light
of this knowledge it is strange that Darwin should have continued to regard the
perfection and symmetry of a variation as evidence that it is a Reversion.

78 CAUSES OF VARIATION. [introd.

be compounded together in the middle line forming a single,
symmetrical organ.

It would probably help the science of Biology if the word
'Reversion' and the ideas which it denotes, were wholly dropped,
at all events until Variation has been studied much more fully
than it has yet been.

In the light of what we now know of the process of repro-
duction the phrase is almost meaningless. We suppose that a
certain stock gives off a number of individuals which vary about
a normal ; and that after having given them off, it begins to
give off individuals varying about another normal. We want
to say that among these it now and then gives off one which
approaches the first normal, that shooting at the new mark it
now and then hits the old one. But all that we know is that
now and then it shoots wide and hits another mark, and we
assume from this that it would not have hit it if it had not
aimed at it in a bygone age. To apply this to any other matter
would be absurd. We might as well say that a bubble would
not be round if the air in it had not learned the trick of round-
ness by having been in a bubble before : that if in a bag after
pulling out a lot of white balls I find a totally red one, this
proves that the bag must have once been full of red balls, or that
the white ones must all have been red in the past.

Besides the logical absurdity <»n which this use of the theory
of Reversion rests, the application of it to the facts of \ a nation
breaks down again and again. I have already mentioned some
cases of this, but there are manv others of a different class. For
instance, it will be shewn that the percentage of extra molars
in the Anthropoid Apes is almost the highest reached among
mammals. On the usual interpretation, such teeth are due to
Reversion to an ancestral condition with 4 molars, and on less
evidence it has been argued that a form frequently shewing such
" Reversion " is older than those which do not. From this reason-
ing it should follow that the Anthropoids are the most primitive
form, at least of monkeys. It is surely time that these brilliant
and facile deductions wore no more made in the name of science.

3. Causes of Variation.

Inquiry into the causes of Variation is as yet, in my judgment,
premature.

4. The Variability of" useless" Structu?*es.

The often-repeated statement that "useless" parts are
especially variable, finds little support in the facts of Variation,
except in as far as it is a misrepresentation of another principle.
The examples taken to support this statement are commonly
organs standing at the end of a Meristic Series of parts, in which

sect, xiv.] INTRODUCTION. 79

there is a progression or increase of size and degree of development,
starting from a small terminal member. In such cases, as that of
the last rib in Man, and several other animals, the wisdom-teeth of
Man, etc., it is quite true that in the terminal member Variation is
more noticeable than it is in the other members. This is, I
believe, a consequence of the mechanics of Division, and has no
connexion with the fact that the functions of such terminal parts
are often trifling. Upon this subject something will be said later
on, but perhaps a rough illustration may make the meaning more
clear at this stage. If a spindle-shaped loaf of bread, such as a
" twist," be divided with three cuts taken at equal distances, in
such a way that the two end pieces are much shorter than the
middle ones, to a child who gets one of the two large middle
pieces the contour-curves of the loaf will not matter so much ; but
to a child who gets one of the small end bits, a very slight altera-
tion in the curves of the loaf will make the difference between a
fair-sized bit and almost nothing, a difference which the child will
perceive much more readily than the complementary difference in
the large pieces will be seen by the others. An error in some
measure comparable with this is probably at the bottom of the
statement that useless parts are variable, but of course there are
many examples, as the pinna of the human ear, which are of a
different nature. It is unnecessary to say that for any such case
in which a part, apparently useless, is variable, another can be
produced in which some capital organ is also variable ; and
conversely, that for any case of a capital organ wrhich is lit t If
subject to Variation can be produced a case of an organ, which
though trifling and seemingly "useless," is equally constant.
With a knowledge of the facts of Variation, all these trite generali-
ties will be forgotten.

o.

Adaptation.

In examining cases of Variation, I have not thought it neces-
sary to speculate on the usefulness or harmfulness of the variations
described. For reasons given in Section II, such speculation,
whether applied to normal structures, or to Variation, is barren and
profitless. If any one is curious on these questions of Adaptation,
he may easily thus exercise his imagination. In any case of
Variation there are a hundred ways in which it may 1»' beneficial,
or detrimental. For instance, if the " hairy" variety of the moor-
hen became established on an island, as many strange varieties
have been, I do not doubt that ingenious persons would invite us
to see how the hairiness fitted the bird in some special way tor life
in that island in particular. Their contention would he hard t<>
deny, for on this class of speculation the only limitations are those
of the ingenuity of the author. While the only test of utility is
the success of the organism, even this does not indicate the utility

80 NATURAL SELECTION. [ixtrod.

of one part of the economy, but rather the nett fitness of the
whole.

6. Natural Selection.

In the view of the phenomena of Variation here outlined,
there is nothing which is in any way opposed to the theory of the
origin of Species " by means of Natural Selection, or the preserva-
tion of favoured races in the struggle for life." But by a full and
unwavering belief in the doctrine as originally expressed, we shall
in no way be committed to representations of that doctrine made
by those who have come after. A very brief study of the facts will
suffice to gainsay such statements as, for example, that of Claus,
that "it is only natural selection which accumulates those altera-
tions, so that tliey become appreciable to us and constitute a varia-
tion which is evident to our senses1." For the crude belief that
living beings are plastic conglomerates of miscellaneous attributes,
and that order of form or Symmetry have been impressed upon
this medley by Selection alone ; and that by Variation any of these
attributes may be subtracted or any other attribute added in
indefinite proportion, is a fancy which the Study of Variation does
not support.

Here this Introduction must end. As a sketch of a part of the
phenomena of Variation, it has no value except in so far as it may
lead some to study those phenomena. That the study of Variation
is the proper field for the development of biology there can be no
doubt. It is scarcely too much to say that the study of Variation
bears to the science of Evolution a relation somewhat comparable
with that which the study of affinities and reactions bears to the
science of chemistry: for we might almost as well seek for tin-
origin of chemical bodies by the comparative study of crystallo-
graphy, as for the origin of living bodies by a comparative study of
normal forms.

1 Text-book of Zoology, Sedgwick and Heathcote's English translation, vol. i.
p. 148. In the original the passage runs: " erst die naturliche Zuchtwahl haufi
und verstarkt jew Abweichungen in dem Masse dass sie fur mis wahmehmbar
werden und eine in die Augen fallende Variation bewirken." C. Claus, Lehrb. d.
Zool., Ed. 2, 1883, p. 127, and Grundztige der Zoologie, 1880, Bd. i. p. 90. The
italics are in the original.

PART I.

MERISTIC VARIATION.

B.

CHAPTER I.

ARRANGEMENT OF EVIDENCE.

The cases of Meristic Variation, here given, illustrate only a
small part of the subject. The principles upon which these have
been chosen may be briefly explained. It was originally intended
to give samples of the evidence relating to as many different
parts of the subject as possible, so that the ground to be eventual lv
covered might be mapped out, leaving the separate sections of
evidence to be amplified as observations accumulate. This plan
would be the most logical and perhaps in the end the most useful,
but for several reasons it has been abandoned. I have chosen ;i
different course, first, because during the progress of the work
opportunities occurred for developing special parts of the evidence;
secondly, since isolated observations have no interest for most
persons, it is more likely that the importance of the subject will
be appreciated in a fuller treatment of special sections, than in a
general view of the whole ; and lastly, because as yet the attempt
to make an orderly or logical classification of the phenomena <>f
Merism, however attractive, must be so imperfect as to be alm<»M
worthless. For these reasons I have decided to treat more fullv a
few sections of the facts, hoping that in the course of time similar
treatment may be applied to other sections also. The sections
have been chosen either because there is a fairly large body <>t
evidence relating to them, or on account of the importance or
novelty of the principles illustrated.

As far as possible I have described each case separately, in
terms applicable specially to it, deductions or criticism being kepi
apart. The descriptions are written as if for an imaginary cata-
logue of a Museum in which the objects might be displayed1. This
system, though it entails repetition, has, I believe, advantag -
which cannot be attained when the descriptions are given in a
comprehensive and continuous form. In speaking of subjects, such
as supernumerary mamma1, or cervical Rstulse, where the evidence
has been exhaustively treated by others, and upon which 1 can
add nothing, it has not seemed necessary to follow this system, and
in such cases connected abstracts are given.

1 Cases of special importance are marked by an asterisk.

6—2

84 MERISTIC VARIATION. [part i.

As the evidence here presented consists, as yet, only of speci-
men chapters in the Natural History of Meristic Variation, and
does not offer any comprehensive view of the whole subject, no
strict classification of the facts is attempted. The evidence of
Meristic Variation relates essentially to the manner in which
changes occur in the number of members in Meristic series. Such
numerical changes may come about in two ways, which are in some
respects distinct from each other. For instance, the number of legs
and body-segments in Peripatus edivardsii varies from 29 to 341:
here the variation in number must be a manifestation of an
original difference in the manner of division or segmentation in
the progress of development. The change is strictly Meristic or
divisional. On the other hand, change in number may arise by
the Substantive Variation of members of a Meristic series already
constituted. For example, the evidence will shew that the
number of oviducal openings in Astacus may be increased from one
pair to two or even three pairs. Here the numerical variation has
come about through the assumption by the penultimate and last
thoracic appendages, of a character typically proper to the append-
ages of the antepenultimate segment of the thorax alone. Now
there is here no change in the number <»f segments composing the
Meristic series, but by Substantive Variation the number of
openings has been increased.

The case of the modification of the antenna of an insect into a
foot, of the eye of a Crustacean into an antenna, of a petal into a
stamen, and the like, are examples of the same kind.

It is desirable and indeed necessary that such Variations,
which consist in the assumption by one member of a Meristic
series, of the form or characters proper to other members of the
series, should be recognized as constituting a distinct group of
phenomena. In the case of plants such Variation is very common
and is one of the most familiar forms of abnormality. Masters, in
his treatise on Vegetable Teratology2, recognizes this phenomenon
and gives to it the name "Metamorphy," adopting the word from
Goethe. As Masters says, so long as it is only proposed to use the
word in Teratology, no great confusion need arise from the fact
that the same term and its derivatives are used in a different
sense in several branches of Natural History. But if, as I hope,
the time has come when the facts of what has been called '"Tera-
tology" will be admitted to their proper place in the Study of
Variation, this confusion is inevitable. In this study, besides, this
particular kind of variation will be found to be especially impor-
tant and I believe that in the future its significance and the mod,'
of its occurrence will become an object of high interest. For this
reason it is desirable that the term which denotes it should not
lead to misunderstanding, and I think a new term is demanded.

1 Sedgwick, A., Quart. Jour. Micr. Sri., 1888, xxvm. p. 467.

2 Masters, M. T., Vegetable Teratology, p. 239.

chap. I.] ARRANGEMENT OF EVIDENCE. 85

For the word 'Metamorphy' I therefore propose to substitute the
term Homoeosis, which is also more correct; for the essential
phenomenon is not that there has merely been a change, but that
something has been changed into the likeness of something else

In the cases given above, the distinction between Homceotic
Variation and strictly Meristic Variation is sufficiently obvious,
but many numerical changes occur which cannot be referred with
certainty to the one class rather than to the other. Such cas
are for the most part seen in Vertebrates: for in them what may
be called the fun da mental numbers of the segments are not consti-
tuted with the definiteness found in Arthropods or in the Annelids,
and several Meristic series of organs are disposed in numbers and
positions independent of, or at least having no obvious relation bo
those of the other Meristic series. The number and positions of
mammae, or stripes, for instance, need not bear any visible relation
to the segmentation of the vertebrae &c. The repetition of mem-
bers of such a series may thus not coincide with, or occur in mul-
tiples of the segmentation of other parts in the same region. When
such is the case, when the segmentation of one series of organs
bears no simple or constant geometrical relation to the segmenta-
tion of other systems, it is not always possible to declare whether
a numerical change in one of the systems of organs belongs properly
to the first or the second of the classes described abow. It is
likely enough that in such a case as that of mammas there may
sometimes be an actual Meristic division and subsequent separation
of the tissues already destined to form the mamma?, occurring in
such a way that each comes to take up its final position, and
indeed the numerous cases in which such division has been
imperfectly effected go far to prove that this is the case. But, on
the other hand, it is not possible to know that the division did no1
occur before any tissue was specially differentiated off to form
mammae, and that the separation may be as old even as the
division of the mamma? of the right side from those of the left, a
process which almost beyond question occurs in the segmentation
of the ovum. The distinction between these two alternatives is
thus one rather of degree than of kind, and it is only in such forms
as the Arthropods, the floral organs of some Phanerogams and the
like, where the members of the several Meristic series have definite
numbers, or coincide with each other, that this distinction is easily
recognized. For this reason 1 do not think it well to at tempt
to carry out any classification of the evidence based on this dis-
tinction.

In the foregoing remarks I am aware that a very large question,
which lies at the root of all accurate study of Meristic Variation,
has been passed over somewhat superficially, but I scarcely think
a fuller treatment possible in the present state of knowledge of
the physics of Division, and in the absence of thorough observation
of the developmental history of those tissues which ultimately

86 MERISTIC VARIATION. [PABT I.

become differentiated to form members of such non-coincident or
independent Meristic series.

Some years ago1, in the course of an argument that Balanoglossus
should be considered as representing some of the ancestral characters
of Chordata, I had occasion to refer to some of these difficulties, and
especially to the different characters of the two kinds of segmentation ;
that of the Annelids, in which the repetitions of the organs belonging
to the several systems are coincident, and, on the other hand, that
of the Chordata, for example, in which this coincidence may be
irregular or partial. At that time I was of opinion that these two
sorts of segmentation may, in certain cases, have had a different
phylogenetic history, and have resulted from processes essentially
distinct. It appeared to me that we should recognize that, in the
Annelids on the one hand, segmentation of the various systems of
organs had been coincident from the beginning, while in the Chordata
the segmentation had been progressive and had arisen by segmentation
or repetition of the organs of the several systems independently. The
reasons for this view were derived chiefly from the fact that it is
possible to arrange the lower Chordata in order of progressive segmen-
tation of the several systems. In particular such treatment was shewn
to be applicable to the central nervous system, the vertebral column
and the mesoblastic somites, and in these cases it was maintained that
the evidence of the lower forms of Chordata goes to shew that segmen-
tation had occurred in these systems one after another, and that their
segmentation was not derived from a form having a complete repetition
of each part in each segment : that these forms, in fact, shewed us tin-
history of this progress from a less segmented form to one more fully
segmented.

The views then set forth have met with little acceptance. Those
who are occupied with the search for the pedigree of Vertebrates still
direct their inquiries on the hypothesis, expressed or implied, that in
the ancestral form there was a series of complete segments, each
containing a representative of each system of those organs which in
the present descendants appear in series. It is thus supposed that each
segment of the primitive form must have been a kind of least common
denominator of the segments of its posterity. The possibility that the
segmentation of Vertebrates may have arisen progressively is, indeed,
scarcely considered at all.

Though in the light of the study of Variation, it now seems to
me that the discussion of these questions must be indefinitely post-
poned, and that there are radical objections to any attempt to interpret
the facts of anatomy and development in our present ignorance of
Variation, I have seen no reason to depart from the view expressed
in the paper referred to : that interpreted by the current methods of
morphological criticism, the facts go to shew that the segmentation of
the Chordata differs essentially from that of the Annelids drc, and
that it has arisen by progressive segmentation of the several systems of
an originally unsegmented form. T<> those who hold as Dohrn, Gaskell.
Marshall and others have done, that the evolution of Vertebrates has

1 Quart. Jour. Micr. Set, 1886.

chap. I.] ARRANGEMENT OF EVIDENCE. 87

been a progress from a more fully segmented form to forms less seg-
mented, I would again point out that this view is in direct opposition
to the indications afforded by the lower Chordata, which are less and
not more segmented than the higher forms.

The hypothesis of an ancestor made up of complete segments is
resorted to because it is felt to be difficult to conceive the progressiva
building up of a segmented form, but on appeal to the facts of Variation
the evidence will clearly shew that Repetition of parts previously (wilt-
ing is a quite common phenomenon; that such repetition may occur in
almost any system of organs; and lastly that such new repetitions may
be coincident in the several systems. To argue moreover that these
repetitions, for instance that of oviducal apertures in Astacus, of
mammas or cervical ribs in mammals are "reversions," leads to ab-
surdity, for on the same reasoning, the occurrence, in the Crab, of a
third maxillipede formed as a chela, would shew that these appendages
had been originally chehe, that the occurrence of petaloid sepals shews
that the sepals had originally been petals, and so forth.

These considerations will suffice to illustrate the great difference
of degree, if not of kind, which probably exists between these two
kinds of segmentation, that which arises by the repetition of bud-
like segments, each containing parts of many systems on the one
hand, and the progressive and separate segmentation of the several
systems on the other. For reasons already given, however, I shall
not attempt in this first collection of evidence to separate the facts
on these lines. Though some cases can at once be seen to be
strictly Meristic while others are plainly Homceotic, many cannot
be affirmed to belong to the one group rather than to the other.
There is, besides, a serious doubt whether perhaps after all,
Homceotic Variation even in its most marked forms, may Dot
ultimately rest on and be an expression of a change in the pro-
cesses of Division, and be thus, at bottom, strictly Meristic also.
In our present ignorance of the physics of Division, this doubt
cannot be satisfied, and therefore it will be best to make no
definite separation between the two classes of variations, though
whenever the nature of a given variation is such that it may at
once be recognised as Homceotic, it will be well to specify this.

In the absence of a more natural classification, the material
has been roughly arranged with reference to the geometrical
disposition and relations of the structures concerned. In the
Introduction, Section IV. p. 21, reference was made to the (aft
that the Symmetry of an organism may be such as to include all
the parts into one system of Symmetry, and for such a system the
term Major Symmetry was proposed. Systems of this kind are
seen in the Vertebrates and Echinoderms, for example. On the
other hand systems of Symmetry occur in limbs and other separate
parts of organisms, in such a way that each such system is either
altogether or partially geometrically complete and symmetrical in
itself. For example, the toe of a Horse, the arm of a Starfish, the

88 MERISTIC VARIATION. [part I. \

eye-spots of some Satyrid butterflies, &c, are each in themselves
nearly symmetrical. To these separate systems of Symmetry the
term Minor Symmetry will be applied. Minor Symmetries may
or may not be compounded into a Major Symmetry. Between
these there is of course no hard and fast line.

In each class of Symmetry, Meristic Repetition may occur, and
the repeated parts then stand in either

I. Linear or Successive Series.

II. Bilateral or Paired Series.

III. Radial Series.

Parts meristically repeated may thus stand in one or more
geometrical relations to each other, and the first part of the
evidence of Meristic Variation will be arranged in groups according
as it is in one or other of these relations that the parts are affected.
In each group cases affecting Major Symmetry will be given first,
and those affecting Minor Symmetries will be taken after.

As it is proposed to arrange the facts of Meristic Variation in
groups corresponding with these three forms of Meristic Repetition,
it will be useful to consider briefly the nature of the relation in
which the members of such series stand to each other, and the
characters distinguishing the several kinds of series. Reduced to
the simplest terms, the distinction may be thus expressed.

In the Linear or Successive series the adjacent parts of any
two consecutive members of the series are not homologous, but the
severally homologous parts of each member or segment form a
successive series, alternating with each other. For example, the
anterior and posterior surfaces of such a series of segments may
be represented by the series

A ,AP, AP, AP, P.

The relation of any pair of organs in Bilateral Symmetry differs
from this, for in that case each member of the pair jwesents to its
fellow of the opposite side parts homologous with those which it*
fellow presents to it, each being, in structure and i>osition, an
optical image of the other. The external and internal surfaces of
such a pair may therefore be represented thus :

E 1,1 E.

If the manner of origin of these two kinds of Repetition be
considered, it will be seen that though both result from a process
of Division, yet the manner of Division in the two cases is very
different. For in the case of division to form a paired structure,
the process occurs in such a way as to form a pair of images,
of which similar and homologous parts lie on each side of the
plane of division ; while, in the formation of a chain of successive
fluents, each plane of division passes between parts which are
dissimilar, and whose homology is alternate. The distinction
between these two kinds of Division is of course an expression of
the fact that the attractions and repulsions from which Division

chap. I.] ARRANGEMENT OF EVIDENCE. 89

results are differently disposed in the two cases. It is further to
be observed that the distinction, though striking, is nevertheli &
one of degree, for the two kinds of Division pass gradually into
each other. By one or other of these two modes, or by a combin-
ation of both, all Meristic Series of Repetitions are formed

In Radial series, the Major Symmetry is built up by radial
divisions of the first kind, producing segments whose adjacent
parts are homologous, and related to each other as images. Each
of these segments is therefore bilaterally symmetrical about a
radial plane. There is no succession between the segments, and
in a perfectly symmetrical series, Successive or Linear repetitions
can only occur in Minor Systems of Symmetry.

The considerations here set forth, though well known, have an
importance in the interpretation of the evidence, for the connexion
between the geometrical relations of organs and their Meristic
Variations is intimate.

An arrangement of the facts with reference to these geometrical
relations cannot, of course, be absolute, for it is clear that a Bilateral
Symmetry, containing Linear Repetitions may be derived from a
Radial Symmetry, and that these figures cannot be precisely
delimited from each other; nevertheless this plan of arrangement
has still several advantages. Chief among these is this : that it
brings out and emphasizes the fact that the possible, or at least
the probable Meristic Variations of such parts depend closely on
the r/eometrical relation in which they stand. This is, perhaps, in a
word, the first great deduction from the facts of Meristic Variation.
The capacity for, and manner of Meristic Variation appear to
depend not on the physiological nature of the part, on the system
to which it belongs, on the habits of the organism, on the Deeds
or exigencies of its life, but on this fact of the geometrical position
of the parts concerned. Linear series are liable to certain sorts of
Variation, Bilateral Series are liable to other sorts of Variation,
and Radial Series to others again. As 1 have ventured to hint
before, the importance of all this lies in the glimpse which is thus
afforded us of the essential nature of Meristic Division and
Repetition. Such interdependence between the geometrical re-
lations, or pattern, in which a part stands, and the kinds of
Variation of which it is capable, is, I think, a strong indication
that in Meristic Division we are dealing with a phenomenon
which in its essential nature is mechanical. Since this is a thing
of the highest importance, it will be useful to employ a system
which shall give it full expression.

Evidence as to Meristic Variation in cell-division and in the
segmentation of ova will bespoken of in connexion with the Varia-
tion of Radial and Bilateral series.

The second section of evidence is less immediately relevant to
the problem of Species; nevertheless it bears bo closely on the
nature of Merism and on the mechanics of Physiological Division,

90 MERISTIC VARIATION. [part i.

that in any study of this subject reference to it cannot be omitted.
The evidence in question relates first to abnormal repetition of
limbs or other peripheral structures, (which in the normal form are
grouped into and form part of a system of Symmetry,) such ab-
normal repetitions occurring in such a way as to lie outside tin's
normal system of Symmetry and unbalanced by any parts within
it. This phenomenon occurs in many forms, especially in bilateral
animals, and may be exceptionally well studied in the case of
supernumerary limbs in Insects and in supernumerary chelte in
Crabs and Lobsters. It will be shewn that such extra parts
generally, if not always, make up a Secondary system of
Symmetry in themselves ; and the way in which such a
Secondary system is related to the normal or Primary system
of Symmetry of the body from which they spring, constitutes
an instructive chapter in the study of Meristic Variation.

More extensive repetitions of this class, when affecting the
axial parts of the body, give rise to the well-known Double and
Triple Monsters, which, as has often been said, reproduce in tin-
higher animals phenomena which, under the name of fission,
are commonly seen in the lower forms. The general evidence as
to these abnormalities is so accessible and familiar that it need
not be detailed here, and it will therefore be enough to give an
outline of its chief features and to point out the bearing of this
class of evidence on the subject of Meristic Variation in general.

CHAPTER II.

meristic variation of parts repeated in linear ob

successive series.

Segments of Arthropoda.

Individual Variation in the fundamental number of members
constituting a Linear Series of segments can only be recognized in
those forms which at some definite stage in their existence cease
to add to the number of the series. Hence in a large proportion
of the more fully segmented invertebrates this phenomenon cannot
be studied, for in many of these, as for instance in Chilognatha
and in most of the Chaetopoda the formation of new segments is
not known to cease at any period of life, but seems to continue in-
definitely. On the other hand, while in Insecta, and in Crustacea
excepting the Phyllopods, the fundamental numbers are definite,
no case of individual Variation in them has been observed.

Between these two extremes, there are animals in certain
classes, for example, Peripatus, some of the Chilopoda among
Myriapods, Aphroditidae among Annelids, and sonic of tin- Hran-
chiopoda among Crustacea, in which the number of segments do< a
not increase indefinitely during life, but is nevertheless not so
immutable as in the Insects and the majority of Crustacea. In
the forms mentioned, certain numbers of segments, though not the
same for the whole family, are characteristic of certain genera, as
in the case of the Chilopoda (excepting I reophilidae), or of certain
species, as in some of the Peripati. But besides this, in some oi
the forms named, e.g., the Geophili and Peripatus edwardsii, indi-
vidual Variation has been recorded among members of the same
species. It is unfortunate that for many of the forms in which
Variation of this kind possibly takes place no Bufficienl observa-
tion on the point has been made, but as examples of a phenomenon
which, on any hypothesis, must have played a chief part in the
evolution of these animals, the few available instances are oi in-
terest.
*1. Peripatus. The number of segments which have claw-bearing
ambulatory legs differs in different species of this genus. Y\ hile,

92 MERISTIC VARIATION. [part i.

moreover, in some of the species the number appears to be very
constant for the species, in the case of others, great individual
variation is seen to occur. Sedgwick's observations in the case of
P. edwardii shew conclusively that these variations cannot be
ascribed to difference in age. There is besides no ground for sup-
posing that increase in the number of legs occurs in any species
after birth, and it is in fact practically certain that this is not the
case. In Peripatus capensis, which was exhaustively studied by
Sedgwick, the appendages arise in the embryo successively from
before backwards, the most posterior being the last to appear, and
the full number is reached when the embryo arrives at Sedgwick's
Stage G. The following is taken from the list constructed by
Sedgwick from all sources, including his own observations. As
the bibliography given by him is complete and easily accessible
it is not repeated here, and the reader is referred to Sedgwick's
monograph for reference to the original authorities.

Sedgwick, A., Quart. Jour. Micr. Sci. xxviii., 1888, pp. 431 —
493. Plates.

South African Species.

P. capensis : 17 pairs of claw-bearing ambulatory legs (Table
Mountain, S. Africa).

P. balfouri : 18 pairs of legs, of which the last pair is rudiment-
ary (Table Mountain, S. Africa).

Sedgwick has examined more than 1000 specimens from the
Cape, and has only seen one specimen with more than 18 pairs of
legs. This individual had 20 pairs, the last pair being rudiment-
ary. It closely resembled P. balfouri, but differed in the number
of legs and in certain other details (q. v.); Sedgwick regarded this
form provisionally as a variety of P. balfouri.

P. mosleyi : 21 and 22 pairs of legs: near Williamstown, S.
Africa. The specimens with 22 legs were two in number and were
both females. They differed in certain other particulars from the
form with 21 legs, but on the whole Sedgwick regards them as a
variety of the same species.

P. brevis (DE Blainville): 14 pairs of legs. (This species not
seen by Sedgwick.)

Other species from S. Africa which have been less fully studied
are stated to have 19, 21 and 22 pairs of legs respectively.

In all South African forms, irrespective of the number of legs,
the generative opening is subterminal and is placed behind the
last pair of fully developed legs (between the 18th or rudimentary
pair in P. balfouri). Sedgwick, pp. 440 and 451.

Australasian Species.

P. v one- Zealand ice. 15 pairs of legs. New Zealand.
P. leuckartii. 15 pair of legs. Queensland.
In both of these species the generative opening is between the
last pair of legs. (Sedgwick, p. 486.)

chap, il] SEGMENTS OF ARTHROPOD A. 93

Neotropical Species.

In all the Neotropical Species which have been at all fully ex-
amined, the number of legs varies among individuals of the same
species.

P. edward&ii: number of pairs of legs variable, the smallest
number being 29 pairs, and the greatest number being 34. Males
with 29 and 30 pairs of legs. The females are larger, and have a
greater number of legs than the males.

The new-born young differ in the same way. From 4 females
each having 29 legs, seven embryos were taken which were practi-
cally fully developed. Of these, 4 had 25) legs, 2 had 34, 1 had 32.
An embryo with 29 and one with 30 were found in the same mother.
An embryo, quite immature, but possessing the full number of legs,
was found with a larger number of legs than one which occupied
the part of the uterus next to the external opening. (Caracas. |

Peripatus demeraranus : 7 adult specimens had 30 pairs of
legs; 6 had 31 pairs; 1 had 27 pairs. Out of 13 embryos ex-
amined, 7 have 30 pairs and 6 had 31. (Demerara.)

Peripatus trinidadensis : 28 to 31 pairs of ambulatory legs.
(Trinidad.)

Peripatus torquatus : 41 to 42 pairs. (Trinidad.)

Specimens of other less fully known species are recorded as
having respectively, 19, 28, 30, 32, 36 pairs of legs, &c.

In the Neotropical Species, irrespective of the number of legs,
the generative opening is placed between the legs of the penulti-
mate pair. (Sedgwick, p. 487.)

Peripatus (jidiformis?) from St Vincent: six specimens ex-
amined. Of these, 1 specimen had 34 pairs of legs, 2 had 32 pairs.
1 had 30 pairs, and 1 had 29 pairs. Pocock, R. I., Nature} 1892,
xlvi. p. 100.

In connexion with the case of Peripatus, the following evidence
may be given, though very imperfect and incomplete.

2. Myriapoda. Chilognatha. Variation in the number of segments
composing the body in this division of Myriapoda cannot be observed
with certainty; foritisnotpossibletoeliniin.it.' changes in number due
to age, nevertheless the manner in which this increase occurs has a
bearing on the subject.

In Jidus terrestris the number of segments is increased al each
moult by growth of new segments between the lately formed antepen-
ultimate segment and the permanent penultimate segment At each
of the earlier moults six new segments are here added: in Blaniulua
the number thus added is four, and in Polydesmus? two fresh segments
are formed at each of the earlier moult-. In each of these forms the
number added is the same at each of the earlier moults. Newport,
G., Phil. Trans., 1841, pp. 129 and 130.

Chilopoda. The number of Leg-bearing Begments differs in the
several genera of Chilopoda, but except in the Gkophilidse the number
proper to each genus is a constant character. For instance in Lithobiw

94 MERISTIC VARIATION. [part i.

this number is 15; in Scolopendra it is 21; in Scolopendrops, 23; in
Cryptops 21, &c.

In Geophilidse, however, the total number of moveable segments is
much larger, ranging from about 35 to more than 200. Though not
characteristic of genera, the number seems within limits to mark each
particular species. It was found that male Geophili have fewer segments
than the female. The males of Arthronomalus longicornis have 51 or
52 leg-bearing segments, while females usually have 53 or 54. Full-
grown females of Geophilus terrestris have 83 or 84 pairs of legs and
segments, and the males of the same species have 81 or 82. In a
large Neapolitan species, Geophilus Icevigatus Bruhl. 1 the variation
is rather greater. In eight males the number varied between 96
and 99; in eleven females, between 103 and 107. Of two female
Geophilus sulcatus one individual had 136 and the other 140. Newport,
G., Trans. Linn. Soc, xix. 1845, p. 427, &c.

[In some of the Chilopoda1 an increase in the number of segments
takes place after the larva hatches, but the variations mentioned above
are recorded as occurring in fully formed specimens independently of
changes due to age.]

In the foregoing cases, a fact which is often met in the Study
of Variation is well seen. It often happens that in particular
genera or in particular species, a considerable range of Meristic
Variation is found, while in closely allied forms there is little or
none. Examples of this are seen in the variability of the Geophi-
lidae as compared with the other Chilopoda, and in the neo-tropical
species of Peripatus which vary in the number of legs, while P.
balfouri, for instance, is very constant. It will !».• noticed that in
both these cases, the absolute numbers of parts repeated are con-
siderably higher in the variable than in the constant forms. But
though such cases have given rise to general statements that series
of organs containing a small number of members are, as such, less
variable than series containing more members, these statements
require considerable modification ; for it is not difficult to give
instances both in plants and in animals, where series made up of
a small number of members, shew great meristic variability.

The bearings of these cases on the nature of Meristic Repetition
and the conception of Homology will be considered hereafter.
Here, however, it may be well to call attention to the fact that we
have now before us cases in which various but characteristic num-
bers of legs or segments differentiate allied species or genera ; that
in assuming the truth of the Doctrine of Descent, we have ex-
pressed our belief that in each case the species with diverse num-
bers are descended from some common ancestor. In the evolution
of these forms, therefore, the number has varied : this on the one
hand. On the other hand, in GeopJtilus and in Peripatus, we see

1 According to Newport (Trans. Linn. Soc. xix. 1845, p. 268), all Myriapoda
.acquire a periodical addition of segments and legs, but according to later observi i a
this is not true of all the Chilopodu.

chap. II.] SEGMENTS OF ARTHROPODA. 95

contemporary instances of the way in which such a change at its
origin may be brought about. Though there are several things to
be gained by study of these instances, one feature of them calls for
attention now, namely, the definiteness of the variations recorded.
The change from a form with one number to a form with another
number here shews itself not as an infinitesimal addition or sub-
traction, but as a definite, discontinuous and integral change, pro-
ducing it may be, as in Peripatus edwardsti, a variation amounting
to several pairs of legs, properly formed, at one step of Descent.
This will not be seen always to be the case, but it is none the less
to be noted that it is so here.

Among Insects I know no case of such individual variation in
the fundamental number of segments composing the body. Among
Crustacea two somewhat remarkable examples must be mentioned,
though it will be seen that both of them belong to categories very
different from that with which we are now concerned. But in-
asmuch as they relate to the general subject of Meristic Variation
they should not be omitted.

3. Carcinus maenas. The abdomen of these crabs consists normally of seven
segments, including the last or telson. In the female the divisions between all
these seven are very distinct. The abdomen of the normal male is much narrower
than that of the female, and in it the divisions between the 3rd, 4th and 5th
segments are obliterated. Males, however, which are inhabited by the Rhizo-
cephalous parasite Sacculina do not acquire these sexual characters, and in them
there are distinct divisions between the 3rd, -4th and 5th segments. (Fig. '.• c. I

Fig. 9. A. Abdomen of Carcinus mamas, female, normal.

B. Abdomen of male, normal.

C. Abdomen of male infested by Sacculina. After Giabb and

Bonnier.

In male Carcinus mamas inhabited by the Entoniscian parasite, Fori union, a similar
deformity may occur, but is often very much less in extent, sometimes being only
apparent in a slight alteration in the contour of the sixth abdominal Bomite. In
specimens of Portunus, Platyonyckus, Pilummu and Xantho inhabited by Knto-
niscians, no change was observed. Giahd and Bonne b comment on the remarkable
fact that the change in the sexual characters effected by Sacculina is greater than
that resulting from the presence of Entoniscian- ; for since the latter are more
internal parasites, preventing the growth of and actually replacing generative
entirely or in part, it might have been expected that the conseqnenoes of their
presence would be more profound. <im:i>. A., and Bonnibb, J., Contrib. a L'e'tnde
des Bopyriens, Travaux de Vinst. zool. de Lille et <lu laboraioire tool. </<■ Wimereux,
1887, torn. V. p. 184.

96 MERISTIC VARIATION. [PART i.

4. Branchipus and Artemia. As it has been alleged that variation may be pro-
duced in the segmentation of the abdomen of these animals by changes in the
waters in which they live, it is necessary here to give the facts on which this state-
ment rests. The further question of the relation of Artemia salina to A. mil-
hausenii is so closely connected with this subject, that though not strictly cognate,
some account of the evidence on this point also must be given.

Some years ago Schmankewitsch 1 published certain papers on variations of
Artemia salina induced by changes in the salinity of the water in which the animals
lived. The statements there made excited a great deal of interest and have often
been repeated botb by scientific and popular writers. The facts have thus at times
been somewhat misrepresented, and so much exaggeration has crept in, that before
giving any further evidence it will be well to give Schmankewitsch's own account.
It is frequently asserted that Schmankewitsch observed the conversion of Branchipus
into Artemia and of Artemia salina into A. milhausenii following upon the pro-
gressive concentration of the waters of a salt lake. Strictly speaking however this is
not what was stated by Schmankewitsch. His story is briefly this: That the Bait
lagoon, Kuyalnik, was divided by a dam into an upper and a lower part; the waters
in the latter being saturated with salt, while the waters of the upper part were less
salt. By a spring flood in the year 1871 the waters of the upper part of the lake
swept over the dam and reduced the density of the lower waters to 8° Beaume
( = about sp. g. 1-051), and in this water great numbers of A. salina then appeared,
presumably having been washed in from the upper part of the lake, or from the
neighbouring salt pools. After this the dam was made good, and the waters of the
lower lake by evaporation became more and more concentrated, being in the summer
of 1872 14° B (about sp. g. 1-103) ; in 1873, 18° B (about sp. g. 1-135); in August 1874,
23-5° B (about sp. g. 1-177) and later in that year the salt began to crystallize out.
In 1871 the Artemia had caudal fins of good size, bearing 8 to 12, rarely 1 5, l'Hstles,
but with the progressive concentration of the water the generations of Artemia
progressively degenerated, until at the end of the summer of 1871 a large part of
them had no caudal fins, thus presenting the character of A. miliums, mi Fischer
and Milne Edw. The successive stages of the diminution of the tail-fins and of the
numbers of the bristles are Bhewn in the figures, with which all are now familiar.

A similar series was produced experimentally by gradual concentration of water,
leading to the extreme form resembling A. milhausenii. It was found also that if
the animals without caudal tins were kept in water which was gradually diluted,
after some weeks a pair of conical prominences, each bearing a single bristle, ap-
peared at the end of the abdomen.

It is further stated that the branchial plates- of the animals living in the more
highly concentrated water were materially larger than those of animals living in
water of a less concentration.

Schmankewitsch next goes on to say that by artificially breeding Artemia salina
in more and more diluted salt water he obtained a form having the characters of
Si ii a i Fi'.n's genus Branchipus, and that he considers this form as a new species of
Branchipus. He explains this statement thus: In the normal Artemia, the last
Begment of the post-abdomen is about twice as long as each of the other segments,
while the corresponding part in Branchipus is divided into two segments. He states
that in his opinion the condition of the last segment of the post-abdomen consti-
tutes the essential difference between Artemia and Branchipus, and that such
division of the last segment occurred in the third generation of the form produced
by him from Artemia by progressive dilution of the water. A second distinction
between the genera is found in the fact that Artemia is reproduced partheno-
genetically, while Branchipus is not known to be so reproduced. As to the
condition of his new form in this respect, Schmankewitsch had no evidence.

In a subsequent paper, '/.. f, w. '/.. . 1877, further particulars are given, re-
specting especially the natural varieties of A. salina. Of these he distinguishes two,
var. a and var. b. The first of these i^ distinguished by its greater size (8 lines
instead of 6 lines, the average for the type) and by the greater length of the post-
abdomen. In the type the bristles on each caudal fin are generally 8 — 12, and in

1 Z. f. w. Z., xxv., 1875, 2, p. 103 and xxix., 1*77. p. 42«J ; also in several
Russian publications, to which references will be found /. <•.

Upon this point a good deal of interesting evidence is given in Schmanke-
witsch's papers, but as it does not bear immediately on the question of the specific
differences, it has not been introduced here.

chap, ii.] SEGMENTS OF ARTHHOPODA. 97

var. a, 8 — 15, rarely more. Amongst specimens of var. a, as also among those of
the type, specimens maybe found having three, two, or even only one bristle on the
caudal fin. The second antennae of the male are less wide in var. a than in the
type, and the knobs on the inner border are rather larger than in the type.

The variety b was found in pools of a concentration of 4° Beaume. It differs
from the type in having the post-abdomen shorter in proportion, though the whole
length is about the same. The number of bristles on the caudal fins is greater in
the variety. The second antenna? of the male are narrower in the variety than in
the type, and bear a tooth and a thickening of the skin internal to the rough knob-
like projections. But the most important difference characterizing var, b is the
appearance of transverse segmentation in the last (8th) post-abdominal segment.
This, according to Schmankewitsch, does not amount to an actual segmentation,
but is really a transverse annulation, which may be more or less conspicuous, and
suggests an appearance of segmentation. Schmankewitsch looks on this second
variety as a transitional form between Artemia and Branchipus,

Before going further it may be remarked that Schmankewitsch gives no figures
of these varieties, except in so far as they are represented in the well-known Beriefl
of sketches of the caudal forks with varying numbers of bristles. No analysis of the
waters is given.

It will be seen that two principal and distinct statements are made :

(1) That A. milhausenii may be reared from A. salina by gradually raising the
concentration of the water.

(2) That by diluting the water a division is produced in the last (8th) segment
of A. salina: that this is a character, or, as Schmankewitsch says, the chiei
character, of the genus Branchipus.

First as to the relation of A. salina to A. milhausenii. The species milhausi nix
was made by G. Fischer de Waldheim1 on spirit specimens sent to him, and the
absence of caudal fins and bristles was taken as the diagnostic character. Fischi
figures are very poor, and indeed are scarcely recognizable : they are also incorrect
in several points, giving for instance 12 pairs of swimming feet instead of 11. The
description is also very imperfect. In the course of this he speaks of the malt-.
saying that its second antennae are larger than those of the female, in which he
declares the second antennae may be sometimes absent. From Fischer's account it
is quite clear that his material was badly preserved, and indeed, as Schmankewitsch
says, specimens of these animals preserved with spirit only are of little use.

In 1837 Rathke2 gave a better figure of A. milhausenii l from the original
locality of Fischer's specimens. The tail, ending in two plain lobes, is shown. Tin-
male is not mentioned. The following analysis of the water is given :

Potassium Sulphate 0*7453
Sodium Sulphate 2*4439

Magnesium Chloride 7*5500
Calcium Chloride 0*2760

Sodium Chloride 16*1200

271352

in 100 of the water.

Other authors mention A. milhausenii, but there i-. so far as 1 am aware, no
special account of the male, or any material addition to the above.

I will now give an abstract of such further evidence on this subject a- I have
been able to collect.

In the course of a journey in Western Central Asia and Western Siberia
I collected samples of Branchiopods from a great variety of localities, of tl.
two consist of Branchipus ferox (Milne Edwards), one of Branchipus spinostu .Milne
Edwards), three of a species of Branchipus not dearly corresponding with any >p. .
of which a description is known to me, and the remainder of Artemia. All the sp*
of Branchipus collected are quite clearly defined both in the male and the female,
and have certainly nothing to do with the Artemia. Of the latter some preliminary
account may now be given, as the tacts bear on Schmankewitsch'a problem.
Omitting those which were badly preserved and those which do not contain adults,
there remain twenty-eight samples, satisfactorily preserved with corrosive Bublima
from as many localities. Of these, eight contain males, all of them having the

1 Bull. Imp. Soc. Sat. Moscou, 1834, vxx. p. 152.

2 Mem. Ac. Sci. P€t.t 1837. in. p. 395.

B. 7

98

MERISTIC VARIATION.

[part I.

distinctive characters of A. salina. It is difficult to speak with confidence as to the
species of an Artemia from the female alone, but by careful comparison I can find
no point of structure which differentiates any of the remainder from the females
found with males, and I therefore regard them as all of the same species, A. salina.
The waters were of many kinds, some being large salt lakes, while others were small
salt ponds or even pools. The specific gravities of these waters varied from 1-030 to
1-215, and judging from the results of the analysis of six samples, the composition of
the waters is also very different. The specific gravities were measured in the field
with a hydrometer reading to -005, and on comparing these readings with the de-
terminations of the Sp. G. of the samples brought home it appears that they were
approximately correct, and I think therefore that these rough readings are fairly
trustworthy. As to the composition of the waters not analyzed, nothing can be said
with much confidence. As the analyses shew, some of these lakes contain chiefly
chlorides, others chiefly sulphates, and so on. In a few {e.g. xxix) there is a great
quantity of sodium carbonate, so much that the water was strongly alkaline and
felt soapy to the hands. This can generally be recognized on the spot in various
ways.

The first point raised by Schmankewitsch's work is that of the caudal fins.
Among my samples I have every stage between the large fins with some twenty
bristles, down to the condition with no distinct fin or bristles. The following table
gives the results as regards the number of bristles on the caudal fins, and this

Bristles

on single

No. in
Catalogue

Sp. G.

caudal fin.

Eggbearing

? ? only

Remarks

XXIX.

1-030

10 to 24

Analyzed. Strongly alkaline. <? s present.

LI.

1

050

11—13

XXXIV.

1

056

9—17

SS present.

XXV.

1

065

2— 7

Si present.

XLII.

?1

070

XXXVII.

1

075

8—13

XXXIX.

1

075

5— 7

XLI.

1

085

13—15

IV.

1

095

20—28

SS present. This and III. both pools in
one dry stream -bed.

XIV.

1

100

8—14

Analyzed.

XLV.

1

100

8—12

XXVII.

1

100

4—10

XXXI.

1

105

5— 9

<T<? present.

XXXV.

1

105

4— 8

XLIII.

1

115

1— 6

Analyzed.

XIX.

1

115

5— 9

XL.

about 1

130

12—16

Pool in a stream-bed. <?<? present

LII.

1

140

3— 7

XXXVI.

?1

150

4—10

XLIV.

1

150

7— 8

Analyzed.

XVI.

1

150

0— 1

III.

1

160

16—19

<? $ present. This and IV. both pools in
one dry stream-bed.

XII.

1

165

1— 3

XXII.

1

165

1— 5

XVIII.

1

170

6— 8

XXIII.

1

175

1— 5

XXVI.

1

179

4— 9

Analyzed.

XXIV.

1

204

2— 5

Analyzed.

XXXII.

1

215

2— 4

XXXIII.

1-215

2— 7

CHAP. II.]

SEGMENTS OF ARTHROPODA.

99

number is a fair guide to the size of the fins, large fins for the most part havin»
many bristles and small fins having few. In the third column the range of this
number in several individuals is shewn, and for this purpose only adult females
bearing eggs in the ovisac are reckoned, as with sex and age there are changes in
respect of the number of bristles.

ANALYSIS OF WATER FROM SIX LOCALITIES CONTAINING

ARTE MIA SALINA.

Catalogue Number

Chlorine Cl2

Sulphuric

anhydride S03 . . .
Carbonic

anhydride C02 ...

Lime CaO

Magnesia MgO

Soda and Potash

Na20, K,0

Total"

Oxygen equivalent

to the Chlorine...
Total solids in 1000

grams

Sp. G. compared

with Water at 20°

XXIX.

2-6950

5-9105

7-0125
•0311
•0384

16-7471
32-4346

•6082

31-8264

1-03074

XIV. XLIII.

24-8646

13-3585

•3185

•2256

3-3561

27-4589 i
69-5822

5-6112

63-9710

1-05196

54-7793

30-3797

•3926

•0678

6-0367

63-6088
155-2649

12-3620

142-9029

1-11787

XXVI.

70-8130

53-8150

•2398

•2266

4-7514

96-7906
226-6364

15-9804

210-6560

1-17999

XLIV.

57-6653

71-8775

•3231

•1466

4-5115

100-0803
234-6043

13-0133

221-5910

1-19586

XXIV.

61-0830

74-4463

•2451

•5175

9-8394

97-2084
243-3397

13-7846

229-5551

1-20441

These analyses were undertaken for me by Mr H. Robinson, of the Cambridge
University Chemical Laboratory, and my best thanks are due to him for the care
-with which he has conducted them.

The table shews the great variability in the development of the tails and bristles.
In specimens from the same locality there is generally great difference, and even the
numbers on the two fins of the same individual are rarely the same. It will be seen
that on the whole the forms with few bristles came from waters of high specific
gravity, thus generally agreeing with Schmankewitsch's statement. This relation
to the salinity is not however very close, but Schmankewitsch never asserted
that it was. He fretmently refers to the existence of individuals with tails in several
conditions of degeneration in the same water, and especially (Z. f. w. Z., 1877,
p. 482) he expressly states that in the original locality of A. milhausenii he found
this form and with it several others intermediate between it and A. salina.

It will also be seen in the Table, that the three samples, IV, XL and III stand
•out as having far more bristles than other samples from waters of ecpial specific
gravity. Each of these localities was exceptional, and all belong to one class.
Ill and IV were pools in the dry bed of a stream in the Kara Kum, near the Irghiz
river. They were close together, and must be joined in each spring. XL. was a
pool in a somewhat similar dried stream-bed, coming down to the lake Tulu Bai in
the district of Pavlodar. The conditions in these pools must be very different from
those of the large, shallow, permanent salt lakes from which the other samples
mostly came, and it is only fair to Schmankewitsch's case to remember that the
water in such pools must be almost fresh during the early part of each summer.

On the whole, then, it seems satisfactorily shewn that the tailless form is con-
nected by intermediate stages with the fully-tailed A. salina, and that this transition
is at all events partly connected with the degrees of salinity of the water in which
it lives. Almost each locality has its own pattern of Arte mi a, which differs from
those of other localities in shades of colour, in average size, or in robustness, and
in the average number of spines on the swimming feet, but none of these differences
seem to be especially connected with the degree of salinity.

7—2

100 MERISTIC VARIATION. [part I.

Passing now to the question of the distinctness of A. milhausenii, it seems clear
that, as Eathke said, it should never have been considered a distinct species. The
character of the finless tail, which is now seen to be one of degree, does not differ-
entiate it satisfactorily, and, as Schmankewitsch found, it is to be seen swimming
with tin-bearing individuals. It has never been shewn that there is a male A. mil-
hansenii, with distinctive sexual characters, and among the Branchiopoda the
various sexual characters of the second antennas in the male are most strikingly
distinctive of the several forms. While being in no sense desirous of disparaging
the value of Schmankewitsch's very interesting observation, I think it is misleading
to describe the change effected as a transformation of one species into another.
Schmankewitsch himself expressly said that he did not so consider it, and it is-
unfortunate that such a description has been applied to this case.

The question of the division of the 8th post-abdominal segment of Artemia,
stated to occur on dilution of the water, directly concerns the subject of Meristic
Variation. As to the facts, there is no doubt that the tail of Branchipus appears to
be made up of seven segments besides the two which bear the external generative
organs, in all, nine, while in the commonest forms of A. salina there are only
eight such segments ; and that the difference lies in the fact that in the long
terminal segment of A. salina there is generally no appearance of division. But as
Claus1 has shewn, the last apparent division in Branchipus is of a different
character from that of the other abdominal segments. This is indeed easily seen
in B. ferox, B. stagnalis, B. spinosus, &c, in which the appearance of the last
division is very different from that of the other divisions. It appears, in fact, to be
rather an annulation than a segmentation. In longitudinal sections the distinction
is quite clear. Such a division, according to Schmankewitsch, appears in the third
generation of A. salina bred in diluted salt water.

Among my own specimens an appearance of division in the last segment occurs
in a considerable number, and these are not by any means from the most dilute
waters alone, some of them being from waters of great concentration. For instance,
the specimens in XXIX, LI, XXXVII, XXXIX and XIV, all have no trace of such
division. On the other hand, it was found in several specimens from XXVI (Sp. G.
1*179) and XLIII (Sp. G. 1'115), while others from these localities did not shew it.
These facts relate to adult females bearing eggs. I do not think, therefore, that the
relation of this appearance of division to the salinity of the water is a constant one.

Lastly, as regards the relation of Artemia to Branchipus, Schmankewitsch has
maintained that the division of the last abdominal segment is the only structural
character really differentiating Branchipus. Claus (I. c.) pointed out that there are
many other points of difference, and that the supposed division is not a structural
character of great moment. But above all these, it should be remembered that by
the sexual characters of the males, Branchipus is absolutely separated from Artemia.
No Branchipus has any structure at all resembling the great leaf-like second antennae
of the male A. salina or A. gracilis- Verrill. Schmankewitsch remarks (Z. f. iv. Z.,.
1877, p. 492) that there are species of Branchipus (e.g. B. ferox) without the
appendages characterizing the second antennas of B. stagnalis s , &c, and that the
males of Artemia bear on the second antennas a knob, which is possibly the repre-
sentative of the appendages of Branchipus, but nevertheless there is no resemblance
whatever between the males of B. ferox or of any other Branchipus and those of
Artemia, and there is no reason to suppose that these sexual characters are modified
by the degree of concentration of the water. The statement that the descendants
of an Artemia can be made to assume the characters of Branchipus Schaffer, depends
entirely on the acceptance of Schmankewitsch's criterion of that genus, which is set
iip in practical disregard of the far more distinctive sexual characters. It is, besides,
as has already been stated, only an irregular and possibly misleading relation which
subsists between this appearance of segmentation and the salinity of the water3.

1 Anz. Ak. Wiss. Wien, 1886, p. 43 ; see also idem, Abhandl. Gdttingen, 1873,
Taf. in. Fig. 10, Taf. v. Fig. 16.

2 For two samples of this American form I am indebted to Dr A. M. Norman,
who received them from Professor Packard.

3 I cannot leave this subject without expressing astonishment at the com-
paratively slight and evasive differences in the structure of Artemice and other
Crustacea inhabiting waters of different salinity and composition. It is not a little

chap.il] segments of arthropoda. 101

surprising that the animals living in No. XIV, for example, are scarcely dis-
tinguishable from those in No. XXIX, though the water in the latter was so strongly
alkaline as to feel soapy. The conditions of animal life in these two waters must
surely be very different, and yet no visible effect is produced. It is of course certain
that there are great differences in the physiology of these forms, for, as I have often
seen, animals (Copepoda, Cladocera, &c.) transferred from one water to another of
materially different composition, die in a few minutes, though the second water may
be inhabited by the same species; but in visible structure, the differences are for the
most part trifling and equivocal.

CHAPTER III.

Linear Series — continued.
Vertebrae and Ribs.

The Meristic Variations of the vertebral column constitute a
subject of some complexity. In considering them it must be
remembered that numerical change may be brought about in the
series of vertebrae by two different processes : first, by Variation in
the total number of segments composing the whole column, in which
case the variation is truly Meristic ; and secondly by Variation in
the number or ordinal position of the vertebra? comprised in one
or more regions of the column, not necessarily involving change in
the total number of segments forming the whole series, and in this
case the variation is Homceotic. Though Homceotic Variation is
often associated with change in the total number of segments,
from the nature of the case it is rarely possible in any given
instance to distinguish clearly whether such change has occurred
or not. This arises largely from the fact that while to find the
total number of vertebra? it is necessary to know the exact number
of caudal vertebra?, in many specimens these are incomplete, and
even if present their number cannot often be given with con-
fidence. For these reasons the chief interest of this section of the
facts arises in connexion with Homceotic Variation, and the modes
in which it occurs ; but it must be constantly borne in mind that
in almost any given case there may be Meristic Variation also, though
the evidence of this may be obscured.

True Meristic Variation in Vertebrae and Ribs.

I. Vertebrce.

True Meristic Variation, that is to say, change in the total
number of segments composing the whole column, may neverthe-
less be plainly recognized in certain animals. Among some of the

CHAP. III.]

VERTEBRAE AND RIBS.

103

5.

lower vertebrates, Fishes and Snakes, for example, the range of
such Variation may be very great. Among Mammals the following
may be given as an example of considerable Variation in the
number of presacral vertebrae in a wild animal, and such evidence
may be multiplied indefinitely.

Erinaceus europaeus (the Hedgehog).

No. 1

C

D

L

S
4

C

Total

7

14

6

11

42

2

7

15

6

3

10 +

3

7

16

6

3

9 +

4

7

15

6

4

12

44

5

7

15

6

4

11

43

6

7

14

6

3

9 +

7

7

15

6

3

11 or 12

8

7

15

6

3

13

44

9

7

15

6

3

12 or 13

Nos. 1—5 in Mus. Coll. Surg., see Catalogue, 1884, pp. 645 and 646; No. 6 in
Cambridge Univ. Mus. ; Nos. 7 — 9 in British Museum.

6. Man. The simplest form of true Meristic Variation in the
total number of vertebrae may occur in Man by the formation of
an extra coccygeal vertebra, making five coccygeals in addition to
five sacrals, i.e. ten pelvic vertebrae in all. Instances of this are
rare (Struthers), though in many tailed forms such Variation
is common. Two cases, in both of which the sixth piece (1st
coccygeal) was partially ankylosed to the sacrum, are fully de-
scribed by Struthers, J., Journ. Anat. Phys., 1875, pp. 93 — 96.

In the presence of cases like that last given, there is a strong
suggestion that the number of vertebrae has been increased by
simple addition of a new segment behind, after the fashion of a
growing worm : the variation of vertebrae thus seems a simple
thing. But there is evidence of other kinds which plainly shews
this view of the matter to be quite inadequate. Some of these
facts may now be offered, and in them we meet a class of fact
which will again and again recur in other parts of the study of
Repeated Parts.

Imperfect Division of Vertebrae.

*7. Python tigris K This is a case of great importance as illus-
trating several phenomena of Meristic Division. In a skeleton of
Python in the Mus. Coll. Surg., No. 602, the following peculiarities
of structure are to be seen. Up to the 147th inclusive the ver-
tebrae are normal, each having a pair of transverse processes and a

1 This and the following cases of Pelamis and Cimoliasaurus are discussed by
Baur, G., Jour, of Morph., iv. 1891, p. 333.

104

M ERISTIC VARIATION.

[part i.

pair of ribs. The appearance of the next vertebra is shewn in the
figure (Fig. 10, I.). Anteriorly, and as far as the level of the
posterior surface of the transverse processes, it is normal, save that
its neural spine is rather small from before backwards. The trans-
verse processes bear a pair of normal ribs. But behind this pair
of transverse processes the parts, so to speak, begin again, rising
again into a neural spine, and growing outwards into a second pair
of transverse processes, with a second pair of normal ribs. Poste-
riorly again the parts are normal. This specimen is described
in the Catalogue of 1853, as " 148th and 149th vertebrae anky-
losed," but upon a little reflexion it will be seen that this account
misses the essential point. For the bone is not two vertebrae
simply joined together as bones may be after inflammation or the
like, but it is two vertebrae whose adjacent parts are not formed,

K

Fig. 10. Two examples of imperfect division of vertebrae in one specimen of
Python tigris. I. The vertebras 147 — 150 seen from the right side, shewing the
imperfect division between the 148th and 149th. The condition on the left side is
the same. II. View of dorsal surface of vertebra? 165 — 167, shewing duplicity of
166th vertebra on the right side. On this side it bears two ribs. The left side is
normal. (From a skeleton, in Coll. Surg. Mus., No. 602.)

chap, in.] VERTEBRAE AND RIBS. 105

and between which the process of Division has been imperfect.
With more reason it may be spoken of as one vertebra partly divided
into two, but this description also scarcely recognizes the real
nature of the phenomenon.

Further on, in the same specimen, at the 166th vertebra, there
is an even more interesting variation. This vertebra is represented
in Fig. 10, II. As there seen, it is normal on the left side, bearing
one transverse process and one rib, while on the right side there
are two complete transverse processes and two ribs. The 185th
vertebra is also in exactly the same condition, being double on the
right side and single on the left.

8. Python sebs : a precisely similar case (Brussels Museum, No.
87, I. G.), in which the 195th vertebra is single on the right side
and double with two ribs on the left, is described by Albrecht, P.,
Bull. Mies. Nat. Hist. Belg., 1883, n. p. 21, Plate II.

9. Python sp.: a precisely similar case of duplicity in the 168th
vertebra, on the left side, in a mounted skeleton in the Camb.
Univ. Mus.

It is to be especially noticed that in each of these four cases of
lateral duplicity, the degree to which the process of reduplication
has gone on is the same.

10. Pelamis bicolor [ = Hydrophis]. The 212th vertebra simple
on the left side, and double on the right. It bears one rib on the
left side and two ribs on the right side. Yale Univ. Mus., No. 763.
Batjr, G., Jour. ofMorph., IV. 1891, p. 333.

11. Cimoliasaurus plicatus (a Plesiosaur). " Centrum of a small
and malformed cervical vertebra from the Oxford Clay near Oxford.
This specimen is immature, and on one side is divided into two
portions, each with its distinct costal facet." Lydekker, R., Cat.
Fossil Rept. and Amph. in Brit. Mus., Pt. II. 1889, p. 238, No.
48,001.

A case somewhat similar to the above is recorded in the Rabbit by Bland Sutton,
Trans. Path. Soc, xli., 1890, p. 3-41. See also certain cases of a somewhat com-
parable variation in Man, considered in connexion with the variations of Bilateral
Series.

II. Bibs.

12. Man. Partial division of ribs is more common than that of
vertebras. Five cases are given by Struthers. 1. Fourth rib
becoming broad, and bifurcated in front. Male, aged 93. From
about middle of shaft these ribs gradually increase in length from
7 lines to 1^, inch on the left side, 1} on right. They then fork,
the left 1^ inch, the right J inch from where they join their
cartilages. Cartilage of right forks close to rib, enclosing a space
which admits little finger ; cartilage of left lost, but the diverging
bony divisions, each of good breadth for a rib (6 to 7 lines) enclose
an intercostal space 1^ inch long, attaining a breadth of J inch,
which was probably continued forwards by the division of the

106 MERISTIC VARIATION. [part i.

cartilage or by two cartilages. The cartilage of the left 7th rib is
also double for H inch, all the others are normal. 2. Left fourth
rib becoming very broad and bifurcating in front ; two large spaces,
one in the bone, one at the bifurcation. 3. Left fourth rib becoming
broad towards sternal end, where it joins bifurcated cartilage. In
these three cases the division affected the 4th rib. Three others
are given in which the rib affected was probably the 4th or 5th.
Struthers, J., Jour. Anat. Phys., Ser. 2, VIII. 1875, p. 51. Such
cases are often recorded and preparations illustrating them may
be seen in most museums.

Besides these cases of obviously Meristic Variation, there are
many which are combined with Homceosis so as to produce far
greater anatomical divergence. Though in some of these examples
there may be change in the total number of vertebra? shewing
that true Meristic change has occurred, they cannot well be treated
apart from the more distinctly Homceotic cases.

Homceotic Variation in Vertebrae and Ribs.

Homceosis in vertebrae may be best studied in Mammals,
and the following account in the first instance relates chiefly to
them. Before considering the details of such variations in vertebrae,
it may be useful to describe briefly the ordinary system of nomen-
clature which is here followed. In treating this subject it is im-
possible to employ a terminology which does not seem to imply
acceptance of the view that there is a true homology between the
individual vertebrae of two spines containing different total num-
bers, for all the nomenclature of Comparative Anatomy is devised
on this hypothesis. This difficulty is especially felt in regard to
vertebrae, and at this point it should be expressly stated that in
using the ordinary terms no such assent is intended. This matter
has already been referred to in Section VI. of the Introduction,
and will be discussed in relation to the facts to be given.

The vertebral column1 is divided into five regions: — cervical, dorsal, lumbar,
sacral and caudal. None of these regions can be absolutely defined, but the following
features are generally used to differentiate them.

Cervical vertebrae are those of the anterior portion of the column, which either
have no moveable ribs, or else have ribs which do not reach the sternum. Dorsal
vertebrae are those which lie posterior to the cervicals and have moveable ribs.
Lumbar vertebras are those which succeed to the dorsals and have no moveable ribs.
Sacral vertebrae cannot be defined in terms applicable even to the whole class of
mammals, but, for the purpose of this consideration, it will be enough to use the
term in the sense ordinarily given to it in human anatomy, to mean those vertebra?
which are ankylosed together to form a sacrum. Caudal vertebrae are vertebra?
posterior to the sacrum.

The characters thus defined are distributed among the several
vertebrae according to their ordinal positions. Among mammals
the number of vertebrae which develop the characters of each re-

1 Abridged from Flower, W. H., Mammals, Living and Extinct, 1891, p. 41.

chap, in.] VERTEBRA AND RIBS: MAN. 107

gion, though differing widely in different classificatory divisions,
are as a rule maintained with some constancy within the limits of
those divisions, which may be species, genera or larger groups, so
that vertebral formulae are often of diagnostic importance. Changes
in the numbers of vertebrae composing the several regions must
therefore have been an important factor in the evolution of the dif-
ferent forms.

Homceotic Variation in the spinal column consists in the as-
sumption by one or more vertebrae of a structure which in the
type is proper to vertebrae in a different ordinal position in the
series. Examples of this are seen in the case of the development
of ribs on a vertebra which by its ordinal position should be lum-
bar ; or in the occurrence of a vertebra, normally lumbar, in the
likeness of a sacral vertebra, having its transverse processes modi-
fied to support the pelvic girdle, &c. Variations of this kind have
one character in common, which though at first sight obvious, will
help us in interpreting certain other cases of Homoeosis. In all
cases of development of a vertebra normally belonging to one region,
in the likeness of a vertebra of another region, this change always
takes place in vertebrae adjacent to the region whose form is as-
sumed. For example, if one vertebra, normally cervical, bears ribs,
it is always the last cervical ; if two cervicals bear ribs, they are the
last two, and so on. No gaps are left.

Homceotic Variation in the spinal column may occur by the
assumption of

(1) dorsal characters by a vertebra in the ordinal position of a
cervical,

(2) lumbar characters by a vertebra in the ordinal position of a
dorsal,

(3) sacral characters by a vertebra in the ordinal position of
a lumbar,

(4) coccygeal characters by a vertebra in the ordinal position of
a sacral,

or by the reverse of any of these. Since almost any of these
changes may occur either alone or in conjunction with any of the
others, it is not possible to group cases of such Homoeosis under
these heads, but the consideration of the more complex cases will
be made easier if simple examples of each class are first described
as seen in Man.

I. Simple cases. — Man.

(1) Homoeosis between cervical and dorsal vertebrce.

(a) From cervical towards dorsal type.

The chief character distinguishing dorsal vertebrae is the pos-
session of moveable ribs. This character may to a greater or less
extent be assumed by cervicals.

108 MERISTIC VARIATION. [part i.

13. Cases of the development of ribs on the 6th cervical seem
to be extremely rare. One is given by Struthers in a young
spine, set. 4. The ribs were present as rudiments only, being
the same on both sides in the 6th vertebra, and on the left side
in the 7th. Each of these rib-elements was -^ inch long. In the
6th the ribs rested on the body of the vertebra, but in the 7th the
rib did not reach so far. Full details, q. v., Struthers, J. Anat.
Phys., 1875, p. 32.

Cervical ribs on the 7th vertebra are comparatively common,
being sometimes moveable and sometimes fixed. The literature of
this subject up to 1868 is fully analyzed by Wenzel Gruber,
Mem. Ac. Sci. Pet, Ser. vn. T. xiil, 1860, No. 2, who refers to 76
cases of such ribs, occurring in 45 bodies, being all that were known
to him in literature or seen by himself. In addition to these 12
cases are described (10 in detail) by Struthers (I. c.\. Some of
the results of an analysis of these cases are important to the study
of Variation.

Of 57 cases, the ribs were present on both sides in 42 cases
and on one side only in 15.

According to the degree of completeness with which the cervi-
cal ribs are developed, Gruber divided them into four classes \

1. Lowest development. Cervical rib not reaching beyond the
transverse process ; corresponding to the vertebral end of a true
rib with capitulum and tnberculum, and articulating by both of
them. Rare form.

2. Higher development. Cervical rib reaching beyond the
transverse process for a greater or less extent, either ending freely
or joining with the first true rib. Commonest form.

3. Still higher development. Cervical rib reaching still further,
and joining the cartilage of the first true rib either by its cartila-
ginous end or by a ligament continued from this. Hardest form.

4. Complete development. Cervical rib resembling a true rib,
having a cartilage (generally for a greater or less part of its length
united with the cartilage of the first true rib) connecting it with
the sternum. Less rare form.

Gruber states, as the result of an analysis of 47 cases, that the
third of these states is very rare, that the second condition is the
common one, and that the fourth or complete condition is commoner
than the first or least state of development, which is also rare.
Of Struthers' cases the majority seem to belong to Gruber's second
class, while that on the left side in Struthers' Case 4 must have
approached Class 1, and that on the left side in Case 10 belonged
to Class 3.

Two features in this evidence are of especial consequence : first

1 Gruber considered that cervical ribs in Man are probably of two kinds, the
one arising by development of an "epiphysis" on the superior transverse process,
and the other by development of the "rib-rudiment" contained in the inferior
transverse process. It is of cases of the latter kind that he is here speaking.

chap, in.] VERTEBRAE AND RIBS: MAN. 109

that the variation is more common on both sides than on one side ;
secondly, that it is not in its lowest development that it is most fre-
quent, but rather in a condition of moderate completeness, having
the proper parts of a true rib.

(b) From dorsal towards cervical type.

14. Reduction of ribs in the first dorsal is described by Struthers
in a specimen in the Path. Mus. of Vienna. " The whole of the
cervical vertebrae being present 1 there is no doubt as to the case
being one of imperfect first rib. On left side rib goes about §
round, and articulates with a process of the second rib. On right
side it joins second rib at from -J- to 1 inch beyond tubercle, but
again projects as a curved process where the subclavian artery has
passed over it. The manubrium sterni first receives a broad car-
tilage, as if from one rib only, and secondly a cartilage at the junc-
tion of the manubrium and body which is the cartilage of the third
thoracic rib." Struthers, J. Anat. Phi/s., 1875, p. 47, Note. (See
also Nos. 24 and 25.)

(2) Homoeosis betiveen dorsal and lumbar vertebras.

15. (a) From dorsal towards lumbar type. The characters chiefly
distinguishing dorsal vertebras from lumbars are the presence of
ribs attached to the former, and of long, flat transverse processes in
the latter. Secondly, the articular processes of lumbar vertebrae
generally differ from those of most of the dorsal series, each pair of
articular surfaces facing inwards and outwards respectively instead
of upwards and downwards as they do in the dorsal region. The
transition from the one type of process to the other, in passing down
the column, is generally an abrupt and not a gradual one. In Man
it occurs between the 12th dorsal and 1st lumbar, but in most
Mammals it takes place more or less in front of the last dorsal.
leaving several dorsal vertebrae with articular processes of the
lumbar type. (Struthers, /. c, p. 59.)

Cases of rudimentary 12th rib in Man are not rare. When the
last dorsal in this respect approaches to the lumbar type, the
change of the articular process from dorsal to lumbar may take
place higher than normally, as in Struthers' Cases 1 and 2 (/. c.
p. 54 and p. 57). In both of these the change was symmetrical,
and in the first case it was abrupt and completed between the 11th
and 12th dorsals, but in the second it was less complete. Though
the place at which the change of articular processes takes place
here varies in correlation with the diminution of the last ribs, bo1 li
being higher than usual, such correlation is not always found,
change in respect of either of those characters sometimes occurring
alone.

1 Struthers points out that unless the cervical vertebras above the rudimentary
ribs are counted there can be no certainty that in any given case these ribs are not
extra cervical ribs.

110 MEMSTIC VARIATION. [part i.

(b) From lumbar towards dorsal type.

16. The formation of moveable ribs upon vertebrae normally be-
longing to the lumbar groups is in Man rarer than reduction of the
12th ribs. In these cases the ribs may or may not coexist with
transverse processes of considerable size. In a case of 13th rib in
Man, given by Struthers (I. c, p. 60), the change of articular pro-
cesses occurred a space lower than usual, being thus correlated with
the appearance of ribs at a lower point.

(3) and (4). Homoeosis between lumbar, sacral and coccygeal

vertebrae.

17. The differences between the vertebrae of these regions are far
more matters of degree than those between the members of other
vertebral regions. By detachment of the 1st sacral (25th vertebra)
the lumbars may become 6, and in this case the 2nd sacral wholly
or partially takes the characters proper to the 1st sacral, but this
change is not necessarily accompanied by union between the last
sacral and the 1st coccygeal (see, for example, Struthers, I.e.,
p. 68). On the other hand, the last lumbar may unite with the
1st sacral, and such union may be either symmetrical or unilateral
only. The amount to which the ilium articulates with these ver-
tebrae and the degree to which their processes are developed to
support it also present many shades of variation. Similarly the
last sacral may be free, or the 1st coccygeal may be united to the
sacrum.

Since all these changes are manifestly questions of degree it
would be interesting to know whether any particular positions in
the series of changes are found more frequently than others, but I
know no body of statistics from which this might be determined.
In the absence of such determination there is no reason to suppose
the existence of Discontinuity in these variations.

Homceotic Variation, Vertebrae and Ribs.

II. More Complex Cases. — Man.

From examples of the occurrence of Homoeosis between mem-
bers of the several regions we have now to pass to the more
interesting question of the degree to which Homoeosis in one part
of the column may be correlated with similar Homceotic variation
in the other parts. For, though each of the particular changes in
the various regions may occur without correlated change in other
regions, such correlation nevertheless often occurs, and in any con-
sideration of magnitude of Variation it is a factor of importance.
In several of the examples to be given it will be seen that the re-
distribution of regions is also associated with Meristic change in
the total number of segments in the column. It is obvious that in

*

chap, in.] VERTEBRA AND RIBS : MAN. ] 1 1

the present place only the most summary notice of the various cases
can be given.

Amongst them can be recognized two groups, the first in
which the Homceosis is from before backwards, the second in
which it is from behind forwards.

A few words in explanation of the use of these terms are perhaps
needed.

In describing cases of such transformation in the series, it is
usual to speak of structures, the pelvis for example, as " travelling
forwards" or "travelling backwards." These modes of expression
are to be avoided as introducing a false and confusing metaphor
into the subject, for there is of course no movement of parts in
either direction, and the natural process takes place by a develop-
ment of certain segments in the likeness of structures which in
the type occupy a different ordinal position in the series. In
using the expression, Homceosis, we may in part avoid this con-
fusion, and we may speak of the variation as occurring from before
backwards or from behind forwards, according as the segment to
whose form an approach is made stands in the normal series
behind or in front of the segment whose variation is being con-
sidered. The formation of a cervical rib on the 7 th vertebra is
thus a backward Homceosis, for the 7th vertebra thus makes an
approach to the characters of the 8th. On the other hand de-
velopment of ribs on the 20th vertebra (1st lumbar), is a forward
Homceosis, for the 20th vertebra then forms itself after the pattern
of the normal 19th1.

A. Backward Homososis.

If each segment in the series of vertebras were to be developed
in the likeness of that which in the normal stands in the position
next posterior to its own, we should expect the whole series to be
one less than the normal. The following case makes an approach
to this condition.
18. Skeleton of old woman. C 7, D 11, L 5, S 5, C 4 (5th and 6th
cervicals partially ankylosed). The 7th cervical bore a pair of cervical
ribs [of Gruber's class 2, see p. 108], that on the left being ankylosed
to the 7th cervical. There were only 11 pairs of thoracic ribs.
The 1st lumbar was a true lumbar. Gruber, Wexzel, Mem. Ac.
Set. Pet, 1869, Ser. vil, xiil, No. 2, p. 23. Here the 7th vertebra
resembles a dorsal in having ribs, the 19th, which in the type is
the last dorsal, resembles a lumbar in all respects, the 24th is the
1st sacral, and there is no 33rd vertebra.

1 The same terminology may conveniently be adopted in the case of the parts of
flowers. Development of petals in the form of sepals being an outward Homceosis,
while the formation of sepaloid petals would be thus called an inward Homoeosis,
and so forth.

112 MERISTIC VARIATION. [part i.

Male, in Cambridge Univ. Mus., No. 78. Preparation shews
C 7, D 11, and the 19th vertebra formed as the 1st lumbar: re-
mainder not preserved, but Professor A. Macalister kindly informs
me that there were 5 lumbars and 5 sacrals, giving C 7, D 11, L 5,
S 5. The 7th vertebra has cervical ribs, the left being large and
articulating with a tuberosity on 1st thoracic rib, the right being
considerably smaller, but now broken at the end. Only 11 pairs
of thoracic ribs. Change of articular process from dorsal to lumbar
begins partially on the left side between 17th and 18th vertebra
(instead of between 19th and 20th) and is complete on both sides
between 18th and 19th. The 19th bears no rib. [Backward
Homoeosis, greater on left side than on right, as seen in the
greater size of the left rib on the 7th vertebra, and in the change
of processes beginning at a higher level on this side. As the
coccyx is not preserved it cannot be seen whether there is one
segment less in the whole column, which would be the case were
the backward Homoeosis complete.]

Female, cet. 40. C 7, D 12, L 5, S 6, C 3. The 7th vertebra bore
cerv. ribs, free on left, ankylosed to vertebra on right. Change of
artic. processes partially on left side between 18th and 19th (instead of
between 19th and 20th). Twelfth thoracic ribs short, being l^in. long
on left, If in. on right. Struthers, J., J. Anat. Phys., 1875, pp. 53
and 35. [There is therefore backward Homoeosis, greater on the left
side than on the right.]

Vertebrae C 7, D 11 or 12, L 5 or 4, S 6, C lost. Eleven pairs of ribs.
The 19th vertebra having a transverse process on the left side re-
sembling that of the vertebra next below it, as regards place of origin
and its upward slope, but is longer than it by iin. and is nearly a
third broader and also thicker. On right side corresponding part is in
two pieces. Change of articular processes complete between 18th and
19th (instead of between 19th and 20th). The 24th vertebra is united
to sacrum, but is of unusual shape, differing greatly from a normal
1st sacral (25th vertebra). The 29th vertebra is nevertheless not
detached from sacrum. Struthers, I. c, pp. 70 and 57.

Adolescent subject. 7th cervical, 12 dorsals and ribs, and 3 lumbars
preserved. 11th ribs reduced, 4 in. long, 4^- in. with cartilage. 12th
ribs rudimentary, left 1 in., right f in. long, breadth of each about |-in.
Artic. processes change chiefly between 18th and 19th vertebrae.
Struthers, I. c, p. 55.

Male, cet. 47. C 7, D 12, L 5, S 5, C 4. Twelfth ribs very unequal;
right scarcely 2 in., left 34 in. The 5th lumbar ankylosed to sacrum
by its right transverse process. Struthers, I. c, p. 57. [Backward
Homoeosis on right side in respect of reduction of 12th rib and union
of 24th vertebra to sacrum on that side.]

B. Forward Homoeosis.

As was remarked in the case of backward Homoeosis, if each
vertebra were to be developed in the likeness of the one which in

*

chap, in.] VERTEBRAE AND RIBS: MAN. 113

the normal stands next behind it in ordinal sequence, we should
expect such backward Homoeosis to be accompanied by reduction
in the total number of vertebrae ; so, conversely we should expect
forward Homoeosis to be accompanied by an increase in total
number. This will be found to be sometimes the case (e.g.
No. 26).

24. Male. C 7, D 13, L 5, S 5 [C not recorded]. 13 ribs on each
side. The right side differed considerably from the left.

Right side. 1st rib resembled the usual supernumerary cervical,
being moveable and extending j- in. from its tubercle. Greater
part of ixth nerve crossed the neck of the rib ; just before doing so
it was joined by large branch of xth. The 2nd rib, borne by ninth
vertebra, in all respects resembled a normal 1st rib. The 3rd rib
articulated with sternum like a normal 2nd rib. In all, 8 ribs
articulated with sternum on right side, as usual. The 13th rib
(on 20th vertebra) was 4^ in. long.

Left side. The 1st rib articulated with body and transverse
process of 8th vertebra, connecting with sternum in normal position,
but differing much from a normal 1st rib, being nearly straight
with very slight horizontal curve. 2nd rib normal in form and
direction; articulates with sternum J in. higher than right 3rd rib,
owing to the lower margin of manubrium being directed slightly
obliquely upwards and to the left. In all, 8 ribs articulated with
sternum, all below the first being at a level slightly higher than
that of the right ribs. ■ The 13th rib (on 20th vertebra) was 4f in.
long. Lane, W. Arbuthnot, J. Anat. Phys., 1885, p. 267 [full
description and discussion].

In this remarkable case, by the reduction of the 1st rib on the
right side, the 8th vertebra shews a forward Homoeosis so far as
that side is concerned. The 20th vertebra, bearing a pair of 13th
ribs, also shews a forward Homoeosis, but this seems to have been
a little greater on the left than on the right (cp. No. 20), the right
rib being a \ in. less in length. The fact that a large branch of
the xth nerve on the right side joined the brachial plexus instead
of the usually minute fibre is specially noteworthy, as shewing a
forward Homoeosis in the brachial plexus on the right side in
correlation to the similar Homoeosis appearing in the reduction of
the 1st rib on the same side. (Compare Nos. 14 and 25. )

25. Skeleton C 7, D 12, L 6 [S and C not recorded]. First pair
of ribs rudimentary, about 1|- in. long, exactly alike, as small
horns attached to 8th vertebra. Scalene muscles were inserted
into 2nd rib. The 25th vertebra was free, but the first lumbar
(20th vertebra) had no trace of a rib. Bellamy, E., J. Anat. Phys.,
1885, p. 185.

[In this case there is forward Homoeosis in the reduction of
the first ribs and in the formation of the 25th vertebra as a
lumbar, but there were no ribs on the 1st lumbar, which would

B.

8

114 MERISTIC VARIATION. [part i.

have been expected had there been an even Homceosis throughout
the dorso-lumbars.]

Male, cet. 50. C 7, D 12, L 6, S 5, C "3 or 4, probably 4."
Thirteen pairs of ribs, 13th ribs on 20th vertebra, nearly sym-
metrical, right 2 in. long; left 1J, and in breadth a little less than
the right. The 6th lumbar, 25th vertebra, had the characters of
a normal last lumbar (sc. 24th vertebra), including normal trans-
verse processes. Coccyx in 3 moveable pieces, the 3rd apparently
composed of two. There is therefore probably one more than
the normal number in the whole series. Struthers, J. Anat.
Phys., 1875, p. 62.

27. Male, cet, 56. C 7, D 12, L 6, S 5, C 3. Dorsal vertebrae and
ribs normal. 20th vertebra normal, except that it has no trace
of transverse processes ; ribs have perhaps been present on it.
25th vertebra quite free from sacrum, but articulating with ilium
by small facet on each side. The 1st coccygeal joined to sacrum.
Struthers, I. c, p. 66 and p. 91. [Homceosis in absence of trans,
processes in 20th vertebra, in separation of 25th from sacrum, and
in union of 30th with sacrum.]

28. Skeleton C 7, D 12, L6, S 5, C lost. The 25th vertebra is separate
from the ilium and the sacrum, but the 30th is united to the latter.
Struthers, I.e., p. 69.

29. Male, cet. 29. C 7, D 12, L6 (1st bearing ribs — 6th partially joined
to sacrum), S 5 (exclusive of 5th lumbar), C 4. 20th vertebra bearing
ribs ; 25th partially free from sacrum but partly supporting the ilium,
and one extra vertebra in the series. Struthers, I. c., p. 64 and p. 92.

30. Skeleton D 12, L 6, S 4, C 4. The 25th vertebra by right trans-
verse process articulates with sacrum and on the same side with the
ilium ; the 30th, however, though moveable on the sacrum, has charac
ters transitional between those of a 5th sacral and a 1st coccygeal.
Struthers, I.e., p. 68 and p. 91.

31. Male. C 7, D 13, L 5, S and C ankylosed together of uncertain
number. Articular processes change between 20th and 21st, i.e. a space
lower than usual, but the processes between 19th and 20th are smaller
than those higher up and are not quite symmetrical. The 20th vertebra
bore rib on left side and rib has apparently been present on right, but
probably not so much developed. Struthers, /. c., p. 64, note. [For-
ward Homceosis in development of ribs on 20th and in detachment
of 25th.]

But though the variations of the vertebrae may thus in great
measure be reduced to system, there remain other cases, rare in
Man but not very uncommon in lower forms, which cannot be
brought into any system yet devised. Such cases shew that the
limits imposed by a system of individual homologies, between which
we conceive the occurrence of Variation, are not natural limits,
and that they may be set aside in nature. In the following case it
may be especially noted that Variation in the segmentation of the

chap, in.] VERTEBRAE AND RIBS : MAN. 115

spinal nerves does not necessarily coincide with that of the ver-
tebrae. This fact will be more fully illustrated in the section of
evidence respecting the spinal nerves.
'32. Female, cet. 40. As it stands, the grouping is C 6, D 12, L 6,
S 5, C 3; in all 32, viz. one less than usual. The vertebral artery
did not enter till 5th cervical (instead of 6th) on left side. The
7th vertebra bore a pair of ribs, left small, ceasing at middle of
shaft ; right has been sawn off, but has all the appearance of a rib
that would have reached the sternum. The 19th vertebra bore
no ribs, and has transverse processes like those of a normal 1st
lumbar. 23rd has transverse processes triangular and sloping
upwards, like those of normal last lumbar but one (sc. 23rd),
though in a less degree : pedicle thicker than usual for this
vertebra.

The articular processes change in the normal space, between
19th and 20th vertebrae. Sacrum 5 ; Coccyx represented by 3
pieces ankylosed together.

Two entire lumbar nerves went down from the lumbar region
to the sacral plexus. [Bones described in detail, q. v.] Struthers,
J. Anat. Phijs. 1875, p. 72 and p 29.

Here then the 7th vertebra shews backward Homceosis, im-
perfect on left side, but more complete on right. 19th having no
ribs, shews the same, and this also appears in the absence of a
4th coccygeal. The fact that two entire lumbar nerves join the
sacral plexus is also a variation of the same kind. But if the
backward Homceosis were complete, the 24th vertebra should be
the 1st sacral, and the 29th should be joined to the coccygeal.
The change of articular processes moreover is in the normal place.

An example like this brings out the difficulty that besets the
attempt to find an individual homology for each segment. If the
characters proper to each segment in the type may be thus re-
distributed piecemeal amongst a different total number of seg-
ments, the question, which in this body corresponds to any given
vertebra, say the 25th, in a normal body, cannot be answered.
The matter is thus clearly summed up by Struthers (I. c. p. 75):

" The variation in this case presents some complexity. To which
region is the suppression of the vertebra to be referred 1 The lumbo-
sacral nerves would seem to indicate that the lowest lumbar vertebra
is the usual 1st sacral set free, thus accounting for the seemingly
deficient pelvic vertebra, and leaving 23 instead of 21 vertebrae above.
The appearance of suppression of a vertebra in the neck, is met by
the consideration that the 7th vertebra carries ribs, imperfectly de-
veloped on one side, like cervical ribs.

"Then, although only 11 ribs remain, the next vertebra below,

though rib-less, has the normal articular processes of a 12th dorsal

(19th vertebra). If it is to be regarded as such, and not as the

1st lumbar, then the suppressed vertebra would be really a lumbar,

.although there are six free vertebrae between the thorax and the

8—2

116 MERISTIC VARIATION. [part r.

pelvis. Whichever view be taken, this case is an interesting one,
as exhibiting variation in every region of the spine, and as shewing
the importance of examining the entire spine before deciding as to
a variation of any one part of it."

To the question, which vertebra is missing, there is no answer ;
or rather the answer is that there is no segment in this body
strictly corresponding to the normal 7th, 20th, 25th, &c; that the
characters of these several segments are distributed afresh and
upon no strict, consistent plan among the segments of this body,
and that, therefore, there is no one segment missing from the
body. Surely further efforts to answer questions like these can
lead to no useful result.

Attempts to interpret Variation by the light of simple arith-
metic serve only to obscure the real nature of Repetition and
segmental differentiation ; for by constantly admitting to the
mind the fancy that this simple, subjective representation of these
processes is the right guide, and that the tangible complexity in
which they present themselves is a wrong one, we only become
used to an idea which is not true to the facts and the real difficulty
is shirked.

Anthropoid Apes.

Though adding little that is new in kind to the foregoing speci-
men-cases occurring in Man, the following instances of Variation
in the vertebrae of the Anthropoid Apes are of some interest if only
as illustrations of the fact that the frequency of such Variation
has no necessary relation to the conditions of civilization or domesti-
cation. (On the subject of Variation in the vertebrae of Anthropoids,
see especially Rosenberg's list, Morph. Jahrb. I. p. 160.)

Troglodytes niger (the Chimpanzee).

[In considering cases of variation in the Chimpanzee it should
be borne in mind that there are several races and perhaps species
included under this name, which have not been clearly distinguished.
It is possible, therefore, that some of the variations recorded may
be characteristic of these races and not actually individual varia-
tions.]

C 7, D 13, L 4, S 5.

This is the formula in the great majority of Skeletons (v. auctt.).
33. An adult female having C 7, D 12, L 4, S 5, C 5, viz. one
vertebra and one pair of ribs less than usual. This is a specimen
of du Chaillu's T. calvus. It was received united by the natural
ligaments and no vertebra therefore is lost. Gat. Coll. Surg., 1884, n.
No. 4.
34# Specimen having rudimentary ribs unequally developed on the
21st vertebra. The 25th vertebra was transitional or lumbo-sacral in
character. The 26th — 30th formed the sacrum and there were 6
caudals, while other specimens had from 2 to 4. For the lumbo-
sacral plexus of this specimen, see No. 71. Rosenberg, Morph.

chap, iil] VERTEBRAE AND RIBS: GORILLA. 117

Jahrb., I. p. 160. Tables, Note 19. This case therefore shews forward
Homoeosis in the presence of ribs on the 21st, also in the transitional
character of the 25th, together with increase in total number. This
increase is however not always found when the 25th is lum bo-sacral,
for, on the contrary one such case quoted by Rosenberg had only
4 caudals (q.v.).

In this form the number of vertebrae articulating with the ilium
varies, and the number uniting with the sacrum is also liable to
alterations probably connected with age. Rosenberg, I. c. : Cat. Coll.
Surg., 1884, n. p. 3.

Gorilla savagii. C 7, D 13, occur in all skeletons of which I
have found descriptions, making therefore one pair of ribs more
than in Man1.

The number of vertebra? articulating with the ilium and the
number joining with the sacrum vary, perhaps with age. Cf.
Rosenberg, I.e.; Cat. Coll. Surg.; Struthers, J.Anat. Pliys., 1875,
p. 79 note, &c.
'35. Adult female. C 7, D 12, L 4, S 5, C 3. This is a remarkable
case. There is one rib-bearing vertebra less than usual, while the
number of lumbo-sacrals is nine, as in the normal cases collected
by Rosenberg. In a normal skeleton in the Camb. Mus. the
articular processes change from the dorsal to the lumbar type
between the 20th and 21st, but in this abnormal specimen the
change is completed on the right side between the 19th and 20th
as in Man, and on the left side, though the change has there also
taken place, there is a curious irregularity in the fact that the
posterior zygapophysis of the 19th is divided to form two processes
which fit into two similar processes of the left anterior zygapo-
physis of the 20th vertebra. The rest is normal. Cambridge Univ.
Mas., 1161, F. [There is here, therefore, a backward Homoeosis of
all vertebrae from the 19th onwards; perhaps also an absolute
diminution in the total number of segments. The simultaneous
variation of both the number of ribs and the position of the

1 Since this account was written, Struthers has published a valuable paper
(Journ. Anat. Phys., 1892, xxvn. p. 181), giving particulars of twenty Gorilla
skeletons. Of these the following are especially remarkable.

Female, C 8, D 13, L 3. The seventh cervical is formed like a sixth, and the eighth
is formed as a seventh, bearing no rib. The vertebrre 9 to 21 bear ribs, those of the
21st being well formed and coming close to iliac crest. The change of articular
processes from dorsal to lumbar type occurred between 21st and 22nd, namely, one
vertebra lower than usual. There is thus a forward Homoeosis in absence of ribs on
8th, in presence of ribs on 21st, and in the variation of position of the articular
change.

Out of 20 skeletons 3 have 11 pairs of ribs (on 8th to 21st) instead of 13 pairs.
In one of these the articular change also occurred one vertebra lower than usual.
On p. 136 a case is described in which there was a remarkable asymmetry in the
structure of the articular processes, which as Dr Struthers lias pointed out to me, is
in some respects like that here described as No. 35 in the text.

Struthers points out that it would be better in all cases to speak of the change of
processes as from lumbar to dorsal instead of from dorsal to lumbar. I regret that
this suggestion comes too late for me to adopt.

118 MEMSTIC VARIATION. [part I.

change of articular processes to the human numbers is especially
worthy of notice.]

* Simia satyrus (Orang-utan). Out of eight skeletons in the
Mus. Coll. Surg., C 7, D 12, L 4 occurs in seven. In young
specimens the distinction between the last lumbar and the first
sacral is clearly shewn by presence of pleurapophysial ossifications in
the transverse processes of the latter. Thus though Simia resembles
Man in the number of ribs, it differs in the total number of prae-
sacral vertebra?. Cat. Mus. Coll. Surg., 1884, n. p. 10.

The arrangement C 7, D 12, L 4, S 5 occurs in a great number
of specimens (for cases quoted, see Rosenberg, Morph. Jahrb., i.
p. 100, Tabellen ; Cat. Mus. Coll. Surg, ttc.)

36. Adult male, Sumatra. C 7, D 11, L 5, S 5, C 2. Mus. Coll
Surg.f No. 37.

37. Foetal skeleton. C 7, D 11, L 5, S 5, C 2. Trinchese, S.,
Ann. Mus. civ. Storia nat. Genova, 1870, p. 4.

38. Adult. C 7, D 11, L 4, S + C, ankylosed together, containing
8 ? pieces. Camb. Univ. Mus., 1160, a.

39. Adult, C 7, D 12, L 4, S 4, C 3. The last lumbar shared
in supporting iliac bones, de Blainville, Osteogr., Primates, Fsc. I.
p. 29.

40. A young specimen, well preserved : there were certainly L 4, S 3.
C 4, but in the adult mentioned above, one of the coccygeal was
joined to the sacrum, de Blainville, ibid.

41. Young specimen in spirit, C 7, D12, L 4, So, C 2. Rosenberg,
E., Morph. Jahrb. I. p. 160.

42. Specimen in spirit, not full grown, C 7, D 12, L 4, S 5, CI.
There was no doubt that only one coccygeal was present. Rosenberg,
ibid.

43 [Hylobates. Considerable differences in the number of vertebrae
and ribs found in this genus are recorded in the Catalogue of the
Museum of the College of Surgeons, &c. ; since however the specific-
divisions of the genus are very doubtful (see Catalogue, II. p. 15),
it is not possible to consider these as necessarily individual variations.
See also Rosenberg, I.e., Tables.]

Bradypodid^e.

To the study of Variation of the vertebral regions the pheno-
mena seen in the Sloths are of exceptional importance, and in
attempts to trace the homologies of the segments special attention
has always been paid to them. The following table contains brief
particulars of 11 specimens of Brady pus and 11 of Cholcepus seen
by myself in English museums, and of a few others of which
descriptions have been published. To these is added a summary
of 40 specimens of Bradypus and 9 of Cholcepus in German
museums1 examined by Welcker. His account is unfortunately
not given in detail, but I have tabulated his results so far as is

1 viz. Gottingen, Tubingen, Marburg, Leipzig, Frankfurt, Berlin, Giessen, Jena
and Halle.

CHAP. III.]

VERTEBRA AND RIBS : BRADYPUS.

119

*

possible. Welcker's list does not, I believe, include any of the
specimens separately given in No. 44.

The determination of the species is quite uncertain. Welcker
in his analysis does not divide the species of Brady pas. In the
other cases I have simply taken the name given on the labels. As
regards Gholoepus the confusion of species is much to be regretted,
for according to the received account1 the more northern species,
G. hoffmanni, has only 6 cervicals, while G. didactylus has 7. In
the table it will be seen that four specimens in different places
have C 6, though generally marked G. didactylus. Possibly
some or all of these are G. hoffmanni, and I have therefore entered
them as Gholoepus sp. In the case of Bradypus it has not been
alleged that the number of cervicals characterizes particular
species, so the fact that the species are confused is of less con-
sequence.

44. Bradypus.

B. tridactylus

5»
) >

5 >

sp.

5 >
5 >

sp.?

B. cuculliger
B. torquatus

ditto
Bradypus sp.

sp.

sp.

C

9

9
9
9
9

9

9
9

8

9

9
9

9
9

8
8
8

D

L

15

4

15

4

15

4

15

4

15

45

14

4

14

4

16

3

15

3

15

4

s

6

6
6
5
5

5

6

7

Struthers3

6

6

15

4

14

4

5

15

15

C

5 +

8 +
9?
12
10

11

9

11

9?

11

Coll. Surg. 3428.

9
10

C8 minute c. r. rt.

C9 large c. r. both sides (one lost).

jD15 moveable r. rt., fixed on 1.

Camb. Mus.
C9 no rib. Coll. Surg. 3427.
Brit. Mus. 919 a.
Brit. Mus. 52. 9. 20. 5.
C9 c. r. h in. long. Univ. Coll. Loud.

frt. ^ n
Oxford Mus.
Coll. Surg. 3422.
7th sacral onlv ankylosed in part.

Brit. Mus. 46. 10. 16. 14.
C9 small rib-like horn on 1. Mus.

Med.-Chir. Acad. Petersb. Gruber2.
Gruber's private collection'2.
C8 may have borne rib on rt.

il. free c. r. 1st thoracic complete,
rt. c. r. ankylosed. 1st thor. A in.
long, like a c. r. ; ankylosed.
C9 has pair short c. r. Brit. Mus. «>21 b.
Gruber2.

Brit. Mus. 47. 4. 6. 5.
j 3 specimens from Brazil said to have
8 cervicals. No detailed account

\

given.

I)E BliAINVILLE4.

1 Flower, W. H., Mammals, Living and Extinct, 1891, p. 183.

2 Gruber, Mem. Imp. Ac. Sci. Pet. Ser. vn., xiii. 1869, no. 2, p. 31.

3 Struthers, Jour. Anat. Phys., 1875, p. 48 note.

de Blainville, Osteogr., Psc. v., pp.

27, 28 and 64. In the place cited,

de Blainville gives C 9, D 16, L 3, S 6, C 9—11 as the normal, but he does not say
in how many specimens this formula was seen. I have therefore been unable to
tabulate this observation. It will be seen that D 16 is quite exceptional, but as it
occurred in the Coll. Surg, specimen no. 3422 it was described by Owen as the
normal, and this statement has been copied by many authors, perhaps by de Blainville.
5 Fourth lumbar ankylosed to sacrum by tr. proc.

120

MERISTIC VARIATION.
SUMMARY OF 40 CASES: Welcker1.

[part i.

Brady pus

C

D

L

10

14
(14

4
4 )

C10 no c. r. 2 cases2, *

10

< or

or >

C10 with c. r. of fair size.

On C9 c. r. very

(15

3 )

3 cases.

y small or absent.

(15

4 )

29th is 1st sacral.

9

1 or

or }

9 cases.

16

3 )

/

9

15

3

15 cases, j C° usually with) 28th fa x L

9

14

4

o cases. \ c. r. 21 cases. \

9

14)

si

C9 has either large c. r. or complete r. ) 27th

or

or >

5 cases. (This normal in B. tor- > is 1st

8

15)

i

quatus: once in B. cuculliger.) ) sacral.

(c. r., cervical rib. C6, C7, &c, sixth, seventh cervical vertebra, &c.)

45. Choloepus.

C

7

D
23

L

3

S
8

4

C. didactylus

CoZi. Surg. 3435.

it

7

24

3

7

Oxford.

ii

7

23

4

5

CoZZ. Swrp. 3427 {Catalogue).

ii

7

23

3

7

6

Coll. Surg. 3424.

sp.

6

24

3

6

5

Cambridge.

sp.

6

23

3

9

3or4

Brit. Mm. 65. 3. 4. 5.

sp.

6

22

4

8

5

CZmv. CoZZ. Bond.

sp.

6

21

3

8

5?

Brit. Mm. 1510 o.

C. hoffmanni

6

22

5

8

5?

JBrZf. Mus. 1510 c.

ii

6

21

4

7

5

CoZZ. S»r#. 3439.

C. hoffmanni ?

63

23

2

7

4?

Brit. Mus. 80. 5. 6. 84.

SUMMARY OF 9 CASES: Welcker4.

C

D + L

C. didactylus

ii
C. hoffmanni

ii

7
7
6
6
6C

27
26
27
26
25

1st sacral is the 35th. 2 cases.
1st sacral is the 34th. 2 cases.
1st sacral is the 34th. 1 case.
1st sacral is the 33rd. 1 case.
1st sacral is the 32nd. 3 cases.

1 Welcker, Zool. Anz. 1878, i. p. 294.

2 This includes the celebrated specimen (in natural ligaments) described by
Rapp, Anat. Unters. d. Edent., Tubingen, ed. 1843, p. 18.

3 This specimen is labelled C. didactylus, but coming from Ecuador and having
this formula is probably C. hoffmanni. (Compare Thomas, O., P. Z. S., 1880, p. 492.)
In it C6 bears cervical rib articulating with shaft of the first thoracic rib.

4 Zool, Anz. 1878, i. p. 295.

5 In a specimen in Leipzig Museum, no. 459, the 6th cervical bears large ribs, of
which the right nearly reaches the sternum, so that Welcker says that there are
only 5 true cervical vertebras. In another of these specimens there is a cervical rib
on C6 measuring 19 mm.

chap, iil] VERTEBRA AND RIBS : BRADYPODID^E. 121

On this evidence several comments suggest themselves. First
it should be noted that the Bradypodidae strikingly exemplify the
principle which Darwin has expressed, that forms which have an
exceptional structure often shew an exceptional frequency of
Variation. Among Mammals the Sloths are peculiar in having a
number of cervicals other than 7, and from the tables given it will
be seen that both the range and the frequency of numerical
Variation is in them very great, not only as regards the cervicals,
but as regards the vertebra? generally.

As concerning the correlation between Variation in the several
regions, Welcker points out that his results go to shew that there
is such a relation, and that when the sacrum is far back, the ribs
also begin further back, or at least are less developed on the
cervicals. As he puts it. with a long trunk there is a long neck.
This is a very remarkable conclusion, and it must be admitted
that it is, to some extent, borne out by the additional cases given
above. The connexion, however, is very irregular. For instance,
the Cambridge specimen of Brady pus, though the 29 th is the 1st
sacral, has had cervical ribs of good size on the 9th vertebra, and
even has a small one on the 8th. But taking the whole list
together, Welcker's generalization agrees with the great majority
of cases. Expressed in the terms defined above, we may therefore
say that backward Homoeosis of the lumbar segments is generally,
though not quite always, correlated with backward Homoeosis of
the cervicals, and vice versa.

It will be seen further that this Variation concerns every region
of the spine, and that even in the total number of prae-sacral
vertebrae there is a wide range of variation, viz. from 27 to 29 in
Bradypus (52 specimens) and from 30 to 34 in Cholozpus (20
specimens). Perhaps no domestic mammal shews a frequency
of variation in the fundamental number of segments com-
parable with this. In this connexion it may be observed that the
absolute number of dorso-lumbars in Clwl&pus (25 — 27) is ex-
ceptionally large amongst mammals ; but this is not the case in
Bradypus.

If the case of Bradypus stood alone, some would of course
recognize the occurrence of cervical ribs on the 9th and 8th ver-
tebrae as an example of atavism, or return to the normal mam-
malian form with 7 cervicals. The occurrence of normal ribs on
the 7th in Gholoepus and the occasional presence of cervical ribs on
the 6th vertebra in this form, even reaching nearly to the sternum
as in Welcker's Leipzig case, obviate the discussion of this hypo-
thesis.

We have, then, in the Bradypodidae an example of mammals in
which the vertebrae undergo great Variation as regards both their
total number and their regional distribution. As the tables shew
this is no trifling thing, concerning merely the number of the
caudal vertebrae, the detachment of epiphyses which may then be

122 MERISTIC VARIATION. [part i.

called ribs, or some other equivocal character, but on the contrary
it effects besides changes in the number of pras-sacral segments,
that is to say, of large portions of the body, each with their proper
supply of nerves, vessels and the like, producing material change
in the mechanics and economy of the whole body : this moreover
in wild animals, struggling for their own lives, depending for their
existence on the perfection and fitness of their bodily organiz-
ation.

Carnivora.

The following cases, though few, have an interest as exemplifying
vertebral Variation in another Order.

Felis domestica. In all the skeletons of Felidje that I have
examined the formula is C 7, D 13, L 7, S 3. A specimen of the
domestic Cat having C 7, D 14, L 7 is described by Struthers. The
change of articular processes from dorsal to lumbar was completed
between the 18th and 19th vertebra? but the posterior zygapophyses of
the 17 th, though of the dorsal type, have to some extent the characters
of a transition-joint. As is stated below, the change in the domestic
Cat normally occurs between the 17th and 18th. In this case therefore
with increase in numbers of ribs the position of the articular change
has varied. This case is described by Struthers, J. Anat. Phys., 1875,
p. 64, Note, but the description there given differs in some respects
from that stated above, which is taken from a letter kindly written
by Professor Struthers in answer to my inquiries.

There is here forward Homceosis in the development of ribs on the
21st vertebra, in the alteration in position of the articular change,
and in the fact that the 28th is not united to the sacrum.

As seen in some other cases, therefore, with forward Homceosis the
number of presacral vertebrae is increased ; but as usual owing to the
equivocal nature of caudal vertebra? it is not possible to state that
the total number of vertebra? is greater.

Canis vulpes. Normally, C 7, D 13, L 7 ; articular change from
dorsal to lumbar between 17th and 18th.

Specimen having C 7, D 14, L 6, in which further the articular
change occurs partly between the 17th and 18th. and partly between
the 18th and 19th. In Mus. Coll. Sure/. Edin. Information as to
this specimen was kindly sent me by Professor Struthers.

Jackal. Specimen having C 7, D 13, L 8 instead of 7. Articular
change as usual between 17th and 18th. Struthers in litt.

Canis familiaris. Case of cervical rib on left side borne by 7th

cervical. This rib was lh in. long and articulated with a tubercular

elevation on the 1st thoracic rib of the same side. The remaining

ribs and vertebra? were normal, [fully described] Gruber, W., Arch.

f. Anat. Phys., u. wiss. Med., 1867, p. 42, Plate.

[In connexion with the foregoing observations it may be mentioned
that the articular change does not take place in the same place in all
Felida?. In 4 specimens of F. leo, 2 of F. tigris and 2 of F. pardus, in
Edinburgh, and in one Lion and one Tiger in Cambridge the lumbar
type begins between the 18th and 19th as in Struther's abnormal Cat

chap, in.] vertebrae: reptilia. 123

above described ; but in 4 F. domestica, and 2 F. catus in Edinburgh,

I F. domestica, 1 F. catus, 1 F. concolor and 1 Cyncelurus jubatus
in Cambridge the change is between the 17th and 18th. For informa-
tion as to the Edinburgh specimens, I am indebted to Professor
Struthers.]

50. Galictis vittata. Specimen from Parana had 16 pairs of ribs,

I I true and 5 false ; 5 lumbar, 2 sacral and 2 1 caudal vertebra?.

A specimen from Brazil had only 15 pairs of ribs and the same
number of lumbar and sacral vertebra?. Burmeister, Heise durch d. La
Plata-Staaten, Halle, 1861, II. p. 409.

[This is therefore another case of forward Homceosis, (as manifested
in the presence of an additional pair of ribs) associated with an increase
in the number of pra?sacral vertebra?.]

51. Halichcerus grypus. Phocida? generally have C 7, D 15, L 5.
Specimen of H. grypus having C 7, D 15, L 6 at Berlin. The an-
terior of the six lumbars bears a rudimentary rib about 5 cm. in length
on the left side. The 28th vertebra is here detached from the sacrum
giving S 3, but generally it is united to it, giving S 4. Nehring, A.,
Sitzb. naturf. Fr. Berlin, 1883, pp. 121 and 122. There is here
therefore a forward Homceosis in the development of a rib on the
23rd, and also in the detachment of the 28th from the sacrum.

Reptilia.

52. Mr Boulenger kindly informs me that though the number of
ventral shields (which is the same as that of the vertebra?) is as a
rule very variable in the several species of Snakes as a whole, there
is nevertheless great difference in the degree of variability. A case
of maximum variation is that of Polyodontophis subpunctatus, in
which the number of ventral shields has been observed to vary from
151 to 240 (Boulenger , Fauna of Brit. India; Reptilia ko,. 1890,
p. 303).

53. On the other hand the range of variation in Tropidonotus natrix
is unusually small. Among 141 specimens examined the number of
ventral shields varied from 162 to 190 (Straucii, Mem. Ac. Sci. Pet.,
1873, xxl, No. 4, pp. 142 and 144).

*54. Gavialis gangeticus. In this animal there are normally present
24 presacral vertebra? and 2 sacrals, the first caudal being the 27th.
This vertebra has a peculiar form, being biconvex. Specimen de-
scribed having 25 presacrals, 2 sacrals, the 28th being the first
caudal. Baur, G., J. of Morph., IV., 1891, p. 334. In this case
Baur argues that since the first caudal is clearly recognizable by
its peculiar shape, this vertebra must be "homologous" in the
two specimens and he considers that a vertebra must have been
"intercalated" at some point anterior to the first caudal by a process
similar to that seen in Python (see No. 7). In liis judgment this
has occurred between the 9th and 10th vertebra1, but no reason for
this view is given. On the system here adopted, this would be spoken
of as a case of forward Homoeosis.
55. Heloderma. The first caudal in the normal form may be dis-
tinguished by having a perforation in the small rib connected with

124

MERISTIC VARIATION.

[part I.

it. In this it is peculiar. Four specimens shewed the following
arrangements : —

II. horridum Xo. 1. First caudal is the 36th vertebra (Troschel).

ditto No. 2 37th (Baur).

//. suspectum No. 1 38th (Shufeldt).

ditto No. 2 39th (Baur).

Baur, G., J. of Morph. iv. 1891, p. 335.

Batrachia.1

Rana temporaria. In the normal frog there are nine
separate vertebrae in addition to the urostyle. A specimen is
described by Bourne having 10 free vertebras (Fig. 11, III.). The
axis and third vertebra bore tubercles upon the transverse pro-
cesses, perhaps representing a partial bifurcation of the kind
described in No. 58. The ninth vertebra was abnormal in having
zygapophyses, and in that its centrum presented two concavities

Figure 11. Vertebral columns of Frog (Rana temporaria), after Bourne.

I. Specimen having transverse processes borne by the atlas, together with
other abnormalities described in text No. 58.

II. Normal Vertebral Column.

III. Specimen having ten free vertebra?, described in text, No. 56.

1 I regret that the paper bearing on this subject lately published by Adolphi,
Morph. Jahrb., 1892, xix. p. 313, appeared too late to permit me to incorporate
the valuable facts it contains.

chap, ill.] VERTEBRAE: BATRACHIA. 125

for articulation with a tenth vertebra. The right zygapophysis
was well formed and articulated with the tenth, but the left was
rudimentary. The tenth vertebra itself had an imperfect centrum
and the neural arch though complete was markedly asymmetrical.
Posteriorly its centrum presented two convexities for articulation
with the urostyle. [For details see original figures.] Bourne,
A. G., Quart. J. Micr. Sci., xxiv. 1884, p. 87.

This is a case of some importance as exhibiting Meristic
Variation in a simple form. Of course, as Bourne says, we may
say that in this specimen the end of the urostyle has been
segmented off and that it is composed of " potential " vertebra?,
and as he also remarks, it is interesting in this connexion to
notice that some Anura, e.g. Discoglossus, present one or two pairs
of transverse processes placed one behind the other at the proximal
end of the urostyle. But this description is still some way from
expressing all that has happened in this case ; for beyond the
separation .of a tenth segment from the general mass of the
urostyle there is Substantive Variation in the ninth vertebra in
correlation with this Meristic Variation. For the ninth has devel-
oped a zygapophysis and has two concavities behind, like the
vertebra? which in the normal frog are anterior to the ninth.
There is therefore a forward Homoeosis, associated with an increase
in number of segments, just as there is in such a case as that of
Man (No. 20) or in that of Galictis vittata (No. 50).

It is also interesting in this case to see that the actually last free
vertebra here, though it is the 10th, has two convex articular sur-
faces behind like the 9th, which is the last in the normal frog, thus
shewing a similar forward Homoeosis. Now applying the ordinary
conception of Homology to this case, we may, as Bourne says.
prove that the 9th in it is homologous with the 9th in a normal
frog for its transverse processes are enlarged in the characteristic
manner to carry the pelvic girdle. But similarly we may prove
also that the tenth in this case is homologous with the ninth of the
normal, for its centrum has the peculiar convexities characterizing
the last free vertebra. Baur's proof that the first caudal was
homologous in the two specimens of Gavialis (see No. .54) rested
on the same class of evidence, and for the moment is satisfying,
but as here seen this method though so long established leads
to a dead-lock. Upon this case it may be well to lay some stress,
for the issues raised are here so easily seen. Besides this the
imperfect condition of the extra vertebra enables us to sec the
phenomenon of increase in a transitional state, a condition rarely
found. In the instances recorded in Gavialis (No. 54), owing to
the perfection and completeness of the variation, the characters of
the 1st caudal are definitely present in the 28th though normally
proper to the 27th, and therefore it may be argued that the 28th
here is the 27th of the type. The frog here described shews that
in this conclusion other possibilities are not met. On the analogy

126 MERISTIC VARIATION. [part i.

of several cases already given, it is not impossible that if the
variation seen in this frog had gone further, the 10th vertebra
might alone support the ilium (cp. Nos. 57 and 60) and thus
present the characters of the normal 9th in their completeness. If
this change had taken place, we should have a case like that of
Gavialis, and there would be nothing to shew that the new 10th
vertebra was not the 9th of the normal. The truth then seems to
be that owing to the correlation between Meristic Variation pro-
ducing change in number, and simultaneous Substantive Variation
producing a change of form or rather a redistribution of characters,
the attempt to trace individual homologies must necessarily fail ;
for while such determination must be based either on ordinal
position or on structural differentiation, neither of these criterions
are really sound. As I have tried to shew, the belief that they are
so depends rather on preconception than on the facts of Variation.

'57. A male specimen of It. temporaria <£ with ten free vertebras is
described by Howes. In this case the 9th had a posterior
zygapophysis on the left side only. Upon the left side the
transverse process of the 9th wras not larger than that of the 8th
and did not support the ilium, which on the left side was entirely
borne by the large transverse process of the 10th. On the light
side the transverse processes of both 9th and 10th were developed
to support the ilium, neither being in itself so large as that of the
10th on the left side. The 9th was concave in front instead of
convex as usual, and thus the 8th which is normally biconcave is
convex behind. The posterior faces of both 9th and 10th bore two
convexities such as are normal to the 9th. The urostyle was
normal, having well-developed apertures for exit of the last pair
of spinal nerves. Howes, G. B., Anat. Ariz., I. 1886, p. 277,
figures.

In this case the departure from the normal, exemplified by
No. 56, has gone still further, and the new 10th vertebra bears the
ilium wholly on the left side and in part on the right. The con-
dition is thus again intermediate between the normal and a com-
plete transformation of the 9th into a trunk vertebra and the
introduction of a 10th to bear the ilium (as in No. 60). As
regards the homologies of the vertebras, the same issues are
ao-ain raised which were indicated in regard to No. 56.

58. Rana temporaria: Case in which transverse processes were present
in the atlas vertebra and the transverse processes of several of the
vertebra? were abnormal (Fig. 11, I.). The atlas possessed well-
developed transverse processes.

In the axis the transverse processes are directed forwards instead
of backwards, and that of the left side presents an indication of bifur-
cation at its extremity.

The third vertebra possessed two pairs of transverse processes
which are joined together for two-thirds of their length. The fourth

chap, in.] vertebrae: recapitulation. 127

vertebra presents a transverse process on the right side which is bifur-
cated at its extremity.

The remaining vertebra, though slightly asymmetrical, present no
special peculiarity, except that the neural arch of the ninth vertebra is
feebly developed. Bourne, A. G., Quart. Jonrn. Micr. Sci., 1884, xxiv.,
p. 86, Plate.

There is here backward Homoeosis of the atlas, the only case
of the kind I have met with1. The reduplication of the transverse
processes of the third vertebra should be studied in connexion with
the cases of double vertebrae in Python (No. 7) and the cases of
bifid rib (in Man, No. 12), for they present a variation perhaps inter-
mediate between these two phenomena.

Bombinator igneus. In this form there is a considerable range
of variation in the development of the transverse processes for the
attachment of the pelvic girdle.
59. Gotte figures a specimen in which the flat expanded transverse
processes have a similar extent on the two sides, but while that on
the right side is made up of the processes of the 9th and 10th vertebne
(in about the proportions of two to one), that on the left side is
entirely formed by the transverse process of the 10th vertebra. Gotte,
Entiv. d. Unke, Atlas, PI. xix., fig. 346.
*60. Sardinian specimen figured in which the processes for the attach-
ment of the pelvic girdle seem to be composed entirely by those
of the 10th vertebra while those of the 9th are not developed. Gene, J.,
Mem. Reale Ac. cli Torino, S. 2, i., PI. v., fig. 4.

61. Specimen figured in which both transverse processes of 9th and
of the 10th are almost equally developed to carry the pelvic girdle.
Camerano, L., Atti R.Ac. Sci. Torino, 1880, xv.,fg. 3.

62. Specimen in which the left transverse process of the 9th bears
the pelvic girdle on the left side, and the right transverse process
of the 10th bears it on the right side, while the corresponding processes
of the opposite sides were not developed. Similar case recorded in
Alytes obstetricans by Lataste, Rev. int. des Sci., m., p. 49, 1879
[not seen, W.B.] ; ibid. Jig. 4.

63. Specimen in which the transverse processes of the 9th alone
were developed to carry pelvic girdle, but the proximal end of the
urostyle was laterally expanded more than usual, ibid. p. 7, Jig. 3.

[Case of hypertrophy of coccyx, ibid. Jig. 6; ad hoc v. Bedriaga.
Zool. Anz., 1879, il, p. 664; Camerano, Atti R. Ac. Sci. Torino, xv„
p. 8.]

Recapitulation of important features of Variation as seen in the
vertebral column.

I. As regards fact.

1. The magnitude of the variations.

2. The rarity of imperfect vertebne.

3. The phenomenon of imperfect Division of vertebras and

ribs.

Adolphi, I. c, p. 352, PI. xn. fig. 3 gives an account of a specimen of Bufo
variabilis in which the atlas bore a transverse process on the left side only. In
this specimen the first two vertebrae were united and their total length was reduced.

128 MERISTIC VARIATION. [part i.

4. The frequency of substantial if imperfect bilateral sym-

metry in the variations, but the occasional occurrence
of asymmetry also.

5. The special variability of some types, e.g. Simia satyrus ;

the Bradypodida? ; Bombinator igneus.

6. The evidence that this variability may occur without

the influence of civilization or domestication.

II. As regards principle.

1. The occasional, though not universal, association of for-

ward Homceosis with increase in number and of back-
ward Homoeosis with reduction in number.

2. The frequent correlation between Variation in several

regions, such correlated Variation being sometimes
unilateral.

3. The impossibility of applying a scheme of Homology

between individual segments.

CHAPTER IV.

Linear Series — continued.
Spinal Nerves.

The spinal nerves compose a Meristic Series in many respects
similar to that of the vertebrae. As between the vertebra*, so
between the spinal nerves, there is differentiation according to the
ordinal succession of the members, certain distributions and func-
tions being proper to nerves in certain ordinal positions. The study
of the way in which Variation occurs in this series is one of great
interest, but unfortunately it is extremely complicated. For while
as regards vertebrae the distribution of structural differentiation
can be recognized on inspection, in the spinal nerves to obtain a
true knowledge of the arrangement in any one case physiological
investigation or at least elaborate and special methods of dissection
are needed. Though it is therefore impossible to introduce any
account which should at all adequately represent the great diver-
sity of possible arrangements, it is nevertheless necessary to refer
briefly to the chief results attained by these methods and to the
principles which have been detected in the Variation of the nerves.
It must of course be foreign to our purposes to examine the many
diversities of pattern produced by the divisions and anastomoses of
nerve-cords in the formation of plexuses, &c, and we must confine
our consideration to cases of Variation in the distribution of dif-
ferentiation among the spinal nerves, that is to say, in the segmen-
tation of the nervous system in so far as it may be judged from
the arrangement of spinal nerves.

Some conception of the magnitude and range of Variation found
in single species of Birds may be gained by reference to the beau-
tiful researches of Furbringer1. A table is given by Fiirbringer,
shewing the number and serial position of the spinal nerves which
take part in the formation of the brachial plexus in 07 species of

1 Fiirbringer's memoirs are of such magnitude and completeness that I have felt
it to be somewhat of an impertinence to attempt to make selection from them : and
it must be remembered that from the isolated and typical cases here given, only
a distorted view of the evidence can be gained. As regards this subject, therefore,
reference to the original work is especially needed.

B. 9

130

MERISTIC VARIATION.

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CHAP. IV.]

SPINAL NERVES! BIRDS.

131

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132 MERISTIC VARIATION. [part l

Birds investigated by himself. He also gives particulars of the
individual variations which were found in certain cases. From
this table the following statement is compiled, shewing the most
important diversities met with and the instances of individual Va-
riation. In the majority of cases the most posterior spinal nerve
of the cervical region was the most posterior nerve of the brachial
plexus, but in a certain number of cases it does not join the plexus
at all ; in some other cases the anterior spinal nerve of the dorsal
region also takes part in forming the plexus. As the table shews,
each of these plans has been likewise met with as an individual
variation.

Fiirbringer's table shews 3 as the minimum number of spinal
nerves found taking part in the formation of the plexus of any bird
(Bucoi'vus abyssinicus) : the same number has been found as a
minimum by other observers in other birds (v. Furbrixger, p. 242,
note). The maximum number wTas 6, found in Gharadrius and
some specimens of Columba. The plexus is generally formed by 4
or 5 spinal nerves.

In cases where several individuals were examined, individual
variation wras generally found, as in Anser, Podargus, Picas, Geci-
nus and Garrulus ; in these cases the number of spinal nerves
which took part in forming the brachial plexus varied between 4
and 5, while in Columba, the number even varied between 4 and 6.

Variations also occurred in this respect between the two sides
of the body. For example, in a specimen of Anser cinereus the
plexus was formed on the right side by the nerves XVI, XVII,
XVIII and XIX. while on the left side it received a strand from
the XXth nerve in addition to these.

As has been stated, the last cervical nerve is generally the last
nerve supplying the brachial plexus but deviations from this plan
occur in both directions. These deviations may occur as individual
variations and they may even be unilateral, owing to the transition
between the cervical and dorsal vertebras being effected at different
points on the two sides of the body.

Particulars are given respecting the average proportions of the
several roots in the different arrangements, but the arrangement
or size of the roots relatively to each other was not found to bear
any constant relation either to the systematic position of the bird,
or to its size, or to its capacity for flight. It was however generally
found that there was a certain relation betwreen the relative size of
the roots and the length of the neck in birds with a plexus com-
posed of four roots. In this case the greatest thickness was gener-
ally either in or anterior to the middle roots of the plexus in short-
necked birds, but posterior to the middle of the plexus in long-
necked birds, but even this rule was not at all closely observed and
many exceptions occurred. Furbrixger, I. c. p. 243.

In Variation in the ordinal positions of the spinal nerves com-
posing the plexus, the pattern of the plexus as newly constituted

CHAP. IV.]

SPINAL NERVES : BIRDS.

133

commonly bore a resemblance to the original pattern of the plexus,
a phenomenon which Furbuinger has called "imitatory Homo-
dynamy" or u Parhomology " of the plexus1 (I. c. p. 245).

Correlation between the constitution of the brachial plexus and
the position and number of moveable cervical ribs.

Anser cinereus, var. domestica. Upon this point Furbrin-
ger has made a series of important observations, especially in the
Goose, which enabled him to state that there is, within limits, a
certain correlation between the composition of the brachial plexus
and the development of the ribs of this region. Speaking gener-
ally, those individuals in which the plexus was formed in a more
anterior position usually shewed a fairly developed cervical rib on
the 18th vertebra (Anser) t and even as in Fig. 12, I, a very short
but moveable rib on the 17th vertebra ; and in such cases the 19th
vertebra generally bore the first true sternal rib. On the other
hand, examples with a more posterior development of the brachial
plexus shewed not only an entire absence of moveable ribs on the
17th, but even a considerable reduction in the size of the ribs of
the 18th and 19th vertebrae, so that these became "transitional'
in character, leaving the 20th vertebra as the first vertebra bearing

xv xv7 xMic^^CrXisst1 xx x\i xvn xwcrXixcr xx

Fig. 12. Diagrams of brachial plexus and cervical ribs in two Geese {Anser
cinereus, var. domestica) after Furbringer (being his specimens D, left, and G, right).

I. Case in which the 17th and 18th vertebrae bear cervical ribs and the 19th
bears the first sternal rib. II. Case in which the 17th and 18th vertebra bear
cervical ribs, and the 20th bears the first sternal rib.

ax axillaris, bri brachialis longus inferior, brs brachialis longus superior,
cbri coraco-brachialis internus, ci cutaneus brachii inferior, c-x cutaneus brachii
superior, ic intercostals, Id latissimus dorsi, p pectoralis, rh rhomboideus, sbse sub-
scapulars, srpr nerves to levator scapula? and serratus profundus, srsp nerves to
serratus superficialis, stc sterno-coracoideus.

1 The principle denoted by these expressions is nearly the same as that here
expressed in the term Homceosis, which is perhaps more convenient as being a more
inclusive expression.

134

MERISTIC VARIATION.

[part I.

true sternal ribs (Fig. 12, II.). The measurements are given by
Furbringer for 7 specimens, of which those relating to two ex-
treme cases (here figured) are appended.

Eibs of

17th vert.,

length in mm.

Eibs of

18th vert.,

length in mm.

Eibs of

19th vert.,

length in mm.

Eibs of
20th vert.

I. { rt.
23 cm. long \ 1.

II. 1 rt-
51 cm. long 1 .

2-5
2-75

20
21

7
12-5

23-5 (sternal)
23-75 (sternal)
51 + 13-5 ligt.
and cartilage
51 + 15-5 ligt.
and cartilage

(sternal)
(sternal)

59 (sternal)

60 (sternal)

Furbringer, M., Morph. Jahrb., 1879, v. pp. 386 and 387.

66. By comparison of specimens of the Pigeon, Columba livia, var.
domestica, a similar correlation was found to occur, as shewn in
Fig. 13, 1, and II. (Furbringer's specimens A and E).

XI XV Cr XW Cr XI\r Cr XV St'

XB XW Cr XIV Cr XV Cr

Fig. 13. Diagrams of brachial plexus and cervical ribs in two Pigeons (C. livia,
var. domestica) after Furbringer.

I. Case in which the 12th, 13th and 14th vertebrae bore cervical ribs. II. Case
in which the 13th, 14th and loth bore cervical ribs. Letters as in Fig. 12.

The measurements of the ribs of these individuals were as fol-

lows

Eibs of

Eibs of

Eibs of

12th vert.,

13th vert.,

14th vert.,

Eibs of

Eibs of

length in

length in

length in

15th vert.

16th vert.

mm.

mm.

mm.

I.

( rt.

3

18
20

25
26

1st sternal
1st sternal

2nd sternal
2nd sternal

II.

1 rt.
(1-

—

3

18 .
18

(damaged)
23

1st sternal
1st sternal

CHAP. IV.]

SPINAL NERVES : MAN.

135

67. The same correlation was established in the case of the Jay
Garrulus glandarius, but an actual variation in the number of
moveable cervical ribs is not recorded in this species (see Fig. 14,
I. and II., Furbringer' s specimens A and D). Furbringer, M.,
Morph. Jahrk, 1879, v. p. 375.

XI

XII Xm Cr XTV Cr XV St1 X* XU XW CrXIVCr xv st'

Fig. 14. Diagrams of the cervical ribs and brachial plexus in two Jays
(Garrulus glandarius) after Fiirbringer.

I. Case in which the brachial plexus began from the xith nerve, the cervical
ribs of 13th and 14th vertebra? being longer than in II, a case in which the xnth is
the first nerve contributing to the brachial plexus. Letters as in Fig. 12.

The measur
follows :

ements of the two specimens here figured were

as

Ribs of 13th vert.,
length in mm.

Ribs of 14th vert.,
length in mm.

Ribs of loth vert.

(with sterno-costal parts),

length in mm.

I- If

5
7

3-5
3-5

18-5
20-5
17-25
16-5

24-5
26
22
23

Furbringer, M., Morph. Jahrb., 1879, v. p. 363.

But though this correlation between the nerves and the ribs is
on the whole decided and unequivocal, it should be explicitly
stated that it only occurs within certain limits and is not universal,
and this statement of correlation is far from covering the whole
ground. Furbringer, I c. p. 387.

Brachial Plexus.

*68. Man and other Mammals. By minute dissection of the
brachial plexus in fifty-five subjects (32 fcetal and 23 adult)
Herringham obtained important evidence as to the parts sup-
plied by the fibres of the several spinal roots forming the plexus,
and as to the considerable variation which occurs in respect of this
supply. Of the facts thus arrived at, two examples may be quoted

136 MERISTIC VARIATION. [part r.

in illustration, concerning the composition of the median and ulnar
nerves respectively.

The median is formed by two heads from the plexus ; into the
outer head the Vlth and Vllth spinals enter, while the inner is
formed by branches of the Ylllth and IXth, sometimes with the
addition of some bundles of the Vllth. The presence of fibres
from the Vllth depends on whether the anterior branch of the
Vllth bifurcates, or goes wholly to the anterior (outer) cord of the
plexus. In order to see whether both Vlllth and IXth contribute
to the median, twenty-eight dissections were made, fourteen in
infants, fourteen in adults. In one foetus and in one adult no
branch from the IXth was found, these being the only exceptions
to the rule that both Vlllth and IXth send fibres to the median
nerve. The median is then made of the Vlth, Vllth, Vlllth and
IXth, but these roots do not send to it a constant proportion. The
bundle from the Vlth varies little, that from the Vllth varies
considerably, that from the Vlllth is sometimes equal to, some-
times smaller, and sometimes larger than the bundle from the IXth.

The origin of the ulnar nerve was traced in thirty-two cases,
fourteen being adults. It was found to arise in four different ways.
Most commonly it arose from the Vlllth and IXth : this occurred
in twenty-three cases. With the Vlllth and IXth is sometimes
combined a strand from the Vllth, as shewn in five cases (four
foetal, one adult). In three foetal cases it arose from the Vlllth
only, and in one foetal and one adult case from the Vllth and
Vlllth. The Vllth is only added to the ulnar in some of those
cases in which it gives a branch to the posterior (inner) cord of the
plexus. In several cases the branch from the Vlllth was much
larger than that from the IXth, but the reverse w7as never met
with.

Evidence similar to the above is given respecting other nerves
from the brachial plexus.

From the results of the investigation generally, it appeared that
the range of Variation though considerable was not extravagant,
and that when parts, usually supplied by some given nerve root,
are supplied by some other root, this other root is then either the
one anterior or the one posterior to the root from which the supply
normally comes. Some muscles seemed to bear definite relations
to each other and their nerve supply seemed also " to vary solidly,"
their nerve supplies remaining the same relatively to each other,
though derived from a different root. " The best example of this
is in the three muscles which are attached along the inner side of
the bicipital groove, the subscapularis, teres major, and latissimus
dorsi. The first is usually supplied by the Vth and Vlth, the
second by the Vlth, and the last by the Vllth, and however much
they may vary above and below their typical place, they do not
change their relations to each other. A similar relation exists
between the two supinators and the two radial extensors. These

chap, iv.] SPINAL NERVES: MAN. 137

last are sometimes supplied by the Vlth, sometimes by the Vllth,
but they are never in any case placed above the supinators. These
are always supplied by the Vlth alone. The flexor group in the
forearm show a similar fixed relation." Herringham concludes
that " the nerve roots are not always composed of the same fibres,
but that what is in one case the lower bundle of the Vth may be
in another the upper bundle of the Vlth, and what is now the
upper bundle of the VHIth will at another time be the lower of
the Vllth root." Hence the following principle is enuntiated :
" Any given fibre may alter its position relative to the vertebral
column, but ivill maintain its position relative to other fibres."

Herringham, W. P., Proc. Boy. Soc, xll, 1886 pp. 423, 427,
430, 435.

By physiological methods, Sherrington working chiefly on
Macacus, but on other animals also, found that this principle sub-
stantially holds good for the outflow of fibres throughout consider-
able regions of the cord, but that it is not always applicable to
great lengths of the cord, for the brachial plexus may be consti-
tuted in a region which is near the head end in comparison with
the place of origin in other individuals, while in the same individual
the sciatic plexus may be constituted in a region which is for it
comparatively far back. No exception to the principle was found
in the sense that a given efferent fibre which in one individual is
anterior to some other particular fibre is ever in any individual of
the same species posterior to it. Sherrington, C. S., Proc, Boy.
Soc, LI. 1892, p. 76. This principle of Herringham's is analogous
to that which in the much simpler case of Variation in vertebrae
was pointed out on p. 107. It was stated that in such Homceotic
variation no gaps are left. If a vertebra assumes a cervical cha-
racter, it is the 1st dorsal, and so on.

*09, The following noteworthy case is described by Herringham in
an infant. It should be borne in mind that to a normal brachial
plexus the I Vth nerve gives a small communication, the Vth, Vlth,
Vllth, VIII th and IXth give large cords, while the Xth (or Hnd
dorsal) gives a minute fibre only. In this abnormal specimen, on
the left side the part from the Xth was as large as that from the
IXth, and this was as large as the Vlllth, whereas the natural
proportion of VIHth to IXth is about 2 to 1. The musculo-cuta-
neous received from the Vllth, instead of from the Vth and Vlth
only as more commonly found ; the median received no Vlth ( v.
supra); the teres major was supplied by the Vllth alone, instead
of by the Vlth; the circumflex received from the Vllth, instead
of Vth and Vlth alone as seen in' 43 cases without any other ex-
ception; the musculo-spiral was formed by the Vllth, VIHth and
IXth, instead of by the Vlth, Vllth and VIHth (and sometimes
even Vth) ; the deep branch in the hand received from both VIHth

138 MERISTIC VARIATION. [part i.

and IXth (instead of Vlllth alone, as seen in five cases out of six).
But though in all these respects the nerve-supply of the plexus was
in ordinal position posterior to the normal, nevertheless the IVth
sent a communication to the Vth (as it does normally) and the
suprascapular and subscapular were given off normally. Here, then,
the supply to the plexus began at the normal place, though it ex-
tended further back than it normally does. On the right 'side the
branch from the Xth was slightly bigger than usual, but otherwise
the only abnormality noted was that the IXth sent a branch to the
musculo-spiral. Herrixgham, W. P., Proc. Boy. Soc, 1886, xli.
p. 435. In view of Furbrixger's evidence (see Nos. 65 and 67),
it might be expected that the first rib would be reduced in corre-
lation with the irregular forward Homceosis of the nerves. In
reply however to a question on the subject, Dr Herringham has
kindlv informed me that no abnormality in the ribs was seen, but
that this point was not specially considered.

Compare also Laxe's case, No. 24, in wdiich similarly a large
branch from the Xth joined the plexus on the right side and the
first rib was rudimentary, both structures thus shewing a correla-
ted forward Homoeosis.

Lumbo-sacral Plexus.

'70. By physiological methods Sherrixgtox found that the supply
to the lumbo-sacral plexus varied considerably with regard to its
origin from the spinal nerves. This wras seen in Macacus, in the
Cat and in the Frog. In none of these animals was any one ar-
rangement found sufficiently often to justify its selection as a "nor-
mal " type. In each case it was found convenient to divide the
different forms of arrangement into two classes, the one in which
the supply to the plexus was in ordinal position more anterior
(" pre-axial," Sherrington), the other being more posterior (" post-
axial," Sherrington). Particulars respecting the distribution of the
several nerves and the movements resulting from their stimulation
in the two classes, are given in detail (q. v.). In Macacus, 31 in-
dividuals belonged to the more anterior class, and 21 to the more
posterior. In the Cat the number of individuals in the two classes
was 22 and 39 respectively. It is stated generally that

" The distribution of the peripheral nerve-trunks is not obviously
different, whether, by its root-formation the plexus belong to the
pre-axial class, or to the post-axial. The peripheral nerve-trunks are,
as regards their muscles, relatively stable in comparison with the spinal
roots. When the innervation of the limb-muscles is of the pre-axial
class, so also is that of the anus, vagina and bladder ; and conversely."
Sherrington, C. S., Proc. Roy. Soc, 1892, li. pp. 70 — 76.

71. Primates. Since in examining the facts of Variation we are
seeking for evidence as to the modes in wrhich specific differences

chap, iv.] SPINAL NERVES: APES. 139

originate, allusion may therefore be made to some facts of normal
structure in differing forms in illustration of the nature of such
differences, and for comparison with the differences which are seen
to occur by Variation. The arrangement of the lumbo-sacral plexus
in the Primates well exemplifies some of these points. In Man,
Chimpanzee and Gorilla the 1st sacral vertebra is the 25th ; in
the Orang it is the 26th ; in the Baboons, e.g. Macacus inuus
(= Inuus pithecus Is. Geoff, the Barbary Ape) it is the 27th.
Now, as Rosenberg says, seeing that in Man the sacral plexus
receives one whole prae-sacral root, the XXVth, and part of the
XXIVth, it might be supposed that this plexus in the Orang
would receive two whole prse-sacral roots and part of a third, or
that in Macacus it would receive three prse-sacral roots and part
of a fourth. But, as a matter of fact, in each of these forms,
Chimpanzee, Orang and Macacus, according to Rosenberg, only
one whole prse-sacral root and part of the next above it enter
the sacral plexus, just as in Man, though the ordinal positions
of the nerve-roots are different.

The Chimpanzee, however, which Rosenberg examined, was
the specimen described (No. 34), having the 25th as a trans-
itional lumbo-sacral vertebra, and rudimentary ribs on the 21st.
In this specimen the prse-sacral nerves received by the sacral
plexus were the XXVIth and part of the XXVth, thus bearing
the same ordinal relations to the sacrum that the nerves of the
lumbo-sacral cord do in the other forms and in Man, though each
is ordinally one lower in the whole series than it is in Man. The
same was true of the spinal roots composing the obturator and
crural. Rosenberg, E., Morph. Jahrb., I. 1876, pp. 148, 149 and
Tables, note 19.

This case is interesting as an example of forward Homu'osis
in the vertebrae associated with forward Homceosis in the sacral
plexus. When compared with the following case of a Chimpanzee1
having normal lumbo-sacral vertebrae, several discrepancies will
be seen beyond those which can be accounted for by the
single change of one in the ordinal position of the roots. No
doubt for the larger nerves Rosenberg's account is correct, but
as he states that the specimen was so badly preserved that
the nerves could not be satisfactorily traced, it is possible that
some of the branches may have been missed. However this may
be, the specimen dissected by Champneys had important features
of difference, notably that the sacral plexus received from the
XXIInd spinal, while the highest recorded as entering it in
Rosenberg's case was the XXVth, a greater difference than can
be accounted for on the simple hypothesis of a change of one
place throughout. Though, speaking generally, Rosenberg is
right in saying that the evidence of the normal condition in
Macacus and Orang as compared with each other and with Man
1 Champneys, F., Joum. Anat. Phys., Ser. 2, v. 1872, p. 17G.

140 MERISTIC VARIATION. [part I.

suggests that the variation of the vertebral regions goes hand
in hand with that of the plexus, and though a comparison be-
tween Rosenberg's abnormal Chimpanzee with that dissected by
Champneys largely bears out this suggestion, yet it is also clear
that this correlation is not a precise one, as indeed has already
appeared in several instances.

In giving the compositions of the several nerves of the lumbo-
sacral plexus in Man and Chimpanzee, I have given the num-
bers of the nerves in the whole series for simplicity of comparison.
It will be remembered that a Chimpanzee has one pair of ribs
more than Man, the XXIst nerve is the 1st lumbar in Man, but
is the 13th dorsal in Chimpanzee, the XXVIth nerve being the
1st sacral in both forms. The table given shews, as Champneys
says, that the general arrangement of the nerves of the lower
limb and lumbar and sacral plexuses was in Chimpanzee very
similar to that in Man, but that the nerves are very differently
composed.

MAX. CHIMPANZEE.

Iliohypogastric} m m

llio-mgumal J

Genito-crural XXL— XXII XXI.

External cutaneous XXII. XXIII XXL, XXII.

Obturator XXIII. XXIV XXL— XXIII.

Anterior crural XXIL— XXIV XXL— XXIV.

Superior gluteal XXIV.— XXVI XXIV.— XXVI.

Sacral plexus XXI V.— XXIX XXIL— XX VII.

Small sciatic XXI V.— XXIX XXI V.— XXVI.

(From Champneys, I.e. p. 210.)

The origin of the nerves is therefore in several cases lower
in Man than in the Chimpanzee, although in the absence of ribs
on the 20th vertebra Man shews a character which, as compared
with the presence of ribs in this position in the Chimpanzee repre-
sents a backward Homceosis.

Man. With the foregoing, compare the case mentioned above
(No. 32) in which two entire lumbar nerves joined the sacral
plexus in a human subject having no ribs on the 19th vertebra,
&c. Struthers, J. Anat. Phi/*., 1875, p. 72 and p. 29.

72. For information as to the variations of the lumbo-sacral plexus in
the Primates see also Rosenberg, Morph. Jahrb., i. 1876, p. 147 et seqq.;
and as to cases in Primates and in other vertebrates compare von
Jhering, Das peripherische N ervensystem der Wirbelthiere, &c, Leipzig,
1878. Of these, two cases of partial backward Homceosis in the
lumbo-sacral plexus of the Dog are perhaps noteworthy, as being
represented and described in greater detail than many of von Jhering's
cases. In one of these the rib of the 13th dorsal (20th vertebra) was
not developed, this vertebra being formed as a lumbar and thus itself
shewing a backward Homceosis in correlation to that of the nerves

CHAP. IV.]

SPINAL NERVES : BRADYPODID^.

141

(von Jhering, I. c. p. 182, pi. iv. fig. 2). Descriptions and diagrams
of similar cases are given throughout the work, but as some of them
represent specimens described by others (e.g. Strutiiers and Rosen-
berg) originally without diagrams, it is difficult to know how far the

accounts given are schematic,
work must be made.

For this reason reference to the original

*

73. Bradypodidae. Brachial plexus. As examples of normal differ-
ences the Sloths are especially interesting, but unfortunately an
extended investigation of the nerves in several individuals has not
been made. The results found by Solger relate to one specimen of
B. tridactylus and one of C. didactylus. The latter was a perfect
specimen, but the former had been partially dissected and the details
of the nerves were largely imperfect. The Cholcepus was a specimen
with seven cervicals, and the Bradypus had nine, the last bearing rudi-

i n

Fig. 15. Diagrams shewing the composition of the brachial plexus in
I. a Cholcepus, II. a Bradypus. vl — 011, the vertebras. IV, VII, X, XII, fourth,
seventh, tenth and twelfth cervical nerves. A, dorsal cord. B, ventral cord.
a, phrenic, b, dorsalis scapulas, c, suprascapular, d, subscapular.

mentary ribs. As the figure shews (Fig. 15), there was a close but not
a perfect resemblance between the composition of the plexus in the
two cases, that of Bradypus being in nearly each case two roots lower
than that in Cholcepus. In the latter the IVth nerve gave a branch
to the Vth, but whether in Bradypus the Vlth gave a branch to the
Vllth was not determined with certainty owing to the condition
of the specimen. [For details see original paper] Solger, B., Morph.
Jahrb., 1875, 1. p. 199, PI. vi.

One more case may be given in illustration of the kind of
difference which normal forms may present.

74. Pipa (the Surinam Toad). In the majority of the Batrachia, the
most anterior pair of spinal nerves leaves the vertebral column between
the first and second vertebrae, no sub-occipital being present. The

142 MERISTIC VARIATION. [part I.

second pair leaves between the second and third vertebrae, and the
third pair leaves between the third and fourth vertebrae. The brachial
plexus is formed by the whole of the second pair together with parts of
the first and third pairs. (The details of the arrangement are compli-
cated and vary greatly in different forms.) In Pipa a different arrange-
ment exists. The most anterior pair of nerves leaves the spinal
column by perforating the first vertebra, and the pair which leaves
between the first and second vertebra? is therefore ordinally the second
pair of spinal nerves in this form; the pair which leaves between the
second and third vertebrae is the third, and so on. The brachial plexus
is made up of the whole of the second nerve, nearly the whole of the
third nerve and of a branch of the first.

If then it were to be supposed that the pair of nerves which leaves
the column between the first and second vertebrae in Pipa is homo-
logous with the pair of nerves which leaves in the same place in Rana,
ifcc, it is clear that between the skull and the 2nd vertebra of Pipa,
there is an extra pair of nerves not found in Rana. The number of
free vertebrae in Pipa is however less than in Rana. For in the former
there are only seven of these, making with the united sacral vertebra
and urostyle eight pieces in all ; but in Rana there are eight pre-
sacrals, one sacral, and counting the urostyle, ten pieces in all. In
Rana only one spinal nerve, the 10th, leaves the urostyle, while in
Pipa two pairs, the 9th and 10th, pass out through the terminal piece
of the vertebral column, suggesting that the diminution in the
number of vertebrae is due to the absence of separation between the
9th vertebra and the urostyle. The whole number of spinal nerves
is therefore- the same in both Rana and Pipa, but in the latter the
1st pair perforate the 1st vertebra in addition to the 2nd pair
which pass out between the 1st and 2nd vertebrae. Furbringer1,
M., Jen. Zt., 1874, vm. p. 181 and Note, PL vn. fig. 37 ; also Jen.
Zt., 1873, vii. PI. xiv. figs. 5 and 6.

It was suggested by Stannius (Lehrb. d. vergl. Anat., p. 130, Note)
that perhaps the 1st vertebra of Pipa represents two coalesced verte-
brae, but in an anatomical examination of two specimens of Pipa,
Furbringer (I.e. 1874, p. 180), found no confirmation of this suggestion,
and developmental evidence also went to shew that no such fusion
occurs in the ontogeny at least2. Kolliker, A., Verh. phys.-med.
Ges. Wilrzburg, 1860, x. p. 236.

As Furbringer says there is no satisfactory way of bringing this case
of Pipa into accord with the condition seen in Rana. In the Urodela
there is of course a suboccipital nerve between the skull and the 1st
vertebra which is not present in Rana, and some resemblance to Pipa
is thus suggested; but in the Urodela the 1st spinal does not actually

1 Compare von Jhering, H., Morph. Jahrb., 1880, vi. p. 297. The statement
made by von Jhering that the nerves of Pipa and Rana correspond nerve for nerve,
though in different positions relative to the vertebras, if established would be
important ; but from the want of detailed description it is not clear whether this
conclusion was arrived at by actual dissection.

2 This is questioned by Adolphi, Morph. Jahrb., xix. 1892, p. 315, note. The
same paper contains much important matter bearing on the variation of the nerves
of Amphibia. I regret that this paper did not appear in time to enable me to
incorporate the facts it contains.

chap, iv.] SPINAL NERVES: BATRACHIA. 143

anastomose with the plexus, though it gives off the superior thoracic
which in both Rana and Pipa comes off at a point peripheral to the
formation of the plexus (Fiirbringer).

If the two spinal nerves which come out of the urostyle in Pipa
may be taken to shew that this bone contains n + 2 vertebrae while the
single pair in liana shews the urostyle to consist of n + 1, there is in
Pipa (as compared with liana), a diminution of one in the total
number of vertebra?, together with a backward Homoeosis, which is
seen in the fact that the 8th vertebra bears the pelvic girdle. Turning
now to the nervous system, the fact that the last spinal nerves to join
the brachial plexus in Pipa are the Illrd, while in Hana they are the
IVth, is again an evidence of backward Homceosis. But if this process
were completely carried out, the pair of nerves which in Pipa pass out
through the 1st vertebra should pass out between this vertebra and the
skull, i.e. in the position of the suboccipital of the Urodela. Beyond
this analysis cannot be carried, and this case is a good illustration of
the fact that the hypothesis of an individual homology between the
segments does not satisfy all the conditions of the problem.

Relation between the ordinal position of spinal nerves and
their distribution to the limbs.

This subject is introduced partly because it further illustrates the
nature of the relations which the spinal nerves maintain towards each
other, and thus bears indirectly on the phenomena of their Variation ;
but chiefly because it presents a view of some of the complexities which
arise in the apportionment of organs centrally disposed in Meristic
Series, to the parts of peripheral appendages having no clear or co-
incident relation to the primary or fundamental segmentation of the
body. The facts have thus a value as furnishing a kind of commentary
on the nature of Meristic Repetitions in vertebrates. In any attempt
to interpret or comprehend Meristic Repetition as a whole, they must
be taken into account.

The principles of the distribution of the spinal nerves to the muscles
of the fore-limb have been thus enuntiated by Herrixoiiau.

1. "Of two muscles, or of two parts of a muscle, that which is
nearer the head-end of the body tends to be supplied by the higher,
that which is nearer the tail-end by the lower nerve.

2. "Of two muscles, that which is nearer the long axis of the
body tends to be supplied by the higher, that which is nearer the peri-
phery by the lower nerve.

3. "Of two muscles, that which is nearer the surface tends to
be supplied by the higher, that which is further from it by the lower
nerve." Herringham, \V. P., Proc. Roy. Soc, xli. 1886, p. 437.

Details are given shewing- the manner in which the innervation of
the muscles in Man bears out these principles.

Forgue and Lanxegrace \ who worked with dogs and monkey*
by physiological methods, arrived at conclusions identical with those
which Herringham came to by human dissection.

1 Distrib. cles racines motrices, &c, Montpellier, 1883, p. 45 [quoted from
Herringham: not seen, W. B.]; also Comptes Rendu*, 1884. cxvm. p. 087.

144 MEBJSTIC VARIATION. [part i.

As regards the sensory nerves in the fore-limb, the following principles
were similarly established by dissection in Man.

1. "Of two spots on the skin, that which is nearer the pre-axial
border tends to be supplied by the higher nerve.

2. "Of two spots in the pre-axial area the lower tends to be
supplied by the lower nerve, and of two spots in the post-axial area the
lower tends to be supplied by the higher nerve."

"Thus, if the limb be seen from the front, the two highest nerves
on the outer and inner sides respectively are the IVth and Xth.
Lower than these the Vth and Vlth take the outer, the IXth and
Xth the inner side. Below the elbow the Vlth alone takes the outer,
and the IXth alone the inner. In the hand, while the Vlth and IXth
continue their positions, the Vllth and Vlllth for the first time join
in the supply." Particulars from which this general statement is made
are given. Herringham, I.e. p. 439.

According to subsequent investigations of Sherrington's on the
hind-limb, the innervation of the muscles of the posterior aspect of the
thigh and leg do not follow the third of Herringham's principles, for in
their case the deep layer of muscles is innervated by roots anterior to
those which innervate the superficial muscles. The same experiments also,
though clearly shewing that the nerve-supply of the skin of the hallux
is anterior to that of the 5th digit, gave only equivocal evidence that
the same was true of the musculatures of these two digits; and in the
thigh the gracilis is not supplied before the vastus externus, whose
relation is rather that of ventral to dorsal than of anterior to posterior.
Sherrington, C. S., Proc. Roy. Soc, 1892, li. p. 77.

Recapitulation.

Some features in the Meristic Variation of the spinal nerves,
as illustrated by the foregoing evidence, may be briefly sum-
marized.

In the first place, as might be anticipated from the compound
nature of a spinal nerve, when Homoeotic Variation takes place, it
does not commonly occur by the transformation of entire nerves,
but rather by change in the distribution and functions of parts of
nerves. In this respect, therefore, there is a difference between
Homceosis in spinal nerves and that in vertebrae, for in the latter,
Homceosis is often complete.

A rough illustration may make this more clear.

Just as in making up the chapters of a book into volumes,
whole chapters may be put into one volume or into the next, and
the following chapters renumbered, so it may be with the Varia-
tion of vertebras, for these inay belong wholly to one region of the
spine or to another. But the nerves are like chapters made up of
sections ; particular sections or groups of sections may come in an
earlier chapter or in a subsequent one, and the places of those that
have been moved on may be filled up consecutively, but it seldom
happens that whole chapters are renumbered. Nevertheless it is
clear from such a case as that of Brady pus and Choloepus, on the

chap, iv.] SPINAL NERVES! RECAPITULATION. 145

hypothesis that both forms are descended from a common ancestor,
that such changes and renumbering of whole nerves must have
happened, though there is evidence to shew that this may happen
piecemeal, as in cases given.

Of course in speaking of such changes among the vertebrae it
will not be forgotten that partial changes occur too, but there
is still greater Discontinuity in their case than in that of the
nerves.

But that there is Discontinuity in the case of nerves also is
clear ; for a given fibre, supplying a given muscle, must leave the
spinal cord either by one foramen and one spinal nerve, or by
another. Conversely the ?ith motor nerve must supply either one
muscle or another, and the transition between the two, however
finely it may be subdivided, must ultimately be discontinuous in
the case of individual fibres. It would be interesting to know to
what extent fibres vary in bundles, but this can hardly be deter-
mined.

There is, however, some evidence that the group of fibres
supplying a limb does to some extent vary up and down the series
as a group, though much rearrangement may occur also within the
limits of the group itself.

Lastly, there is important evidence that Variation in other
parts may be correlated with change in the ordinal positions at
which nerves with given distributions emerge from the spinal
cord. With Variation in the ordinal positions at which the nerves
come out, change in other parts, notably in the ribs, may happen
too ; so that we may say that in a sense there may be, at least
within the limits of single species (see cases Nos. 24, 65 and
71), a correlation between the apportionment of their functions
among the nerves and the contour of the body, both changing
together, the ribs rising and falling with the rise and fall of the
brachial plexus. The nerves do not merely come out through the
foramina like stitches through the welt of a shoe, the shape of the
shoe remaining the same wherever the threads pass out. The
arrangement is, rather, like that of the strings of such an instru-
ment as a harp or piano, in which there is a correlation between
the curves of the frame and the positions of the several notes: so
long as the frame is the same, the strings cannot be moved up or
down, the instrument still retaining the same compass and the same
number of notes.

B.

10

CHAPTER V.

linear series — continued.
Homceotic Variation in Arthropoda.

The occurrence of Homceosis among the appendages of Ar-
thropoda is illustrated by a small but compact body of evidence.
To this evidence special value may be attached, not because it
is likely that in the evolution of the Arthropods variations have
really taken place, in magnitude comparable with those now to
be described, but rather because these cases give a forcible illus-
tration of possibilities that underlie the common and familiar
phenomena of Meristic Repetition. Of these possibilities they
are indeed " Instances Prerogative," salient and memorable ex-
amples, enuntiating conditions of the problem of Variation in
a form that cannot be forgotten. Facts of this kind, so common
in flowering plants, but in their higher manifestations so rare
in animals, hold a place in the study of Variation comparable
perhaps with that which the phenomena of the prism held in the
study of the nature of Light K They furnish a test, an elenchus,
which any hypothesis professing to deal with the nature of organic
Repetition and Meristic Division must needs endure.

Insecta.

*75. Cimbex axillaris (a Saw-fly), having the peripheral parts
of the left antenna developed as a foot. The right antenna is
normal, ending in a club-shaped terminal joint. In the left an-
tenna the terminal joint is entirely replaced by a well-formed
foot, having a pair of normal claws and the plantula between
them (Fig. 16). This foot is rather smaller than a normal foot,
but is perfectly formed. The rest of the antenna, so far as the
point at which the club should begin is normal in form, but is
a little smaller and thinner than the same parts in the right
antenna. Kraatz, G., Lent. ent. Ztschr., 1876, xx., p. 377, PL

1 See the well-known passage in Nov. Org., u. xxii.

chap, v.] HOMCEOSIS IN ARTHROPOD A. 147

This specimen was most kindly lent to me for examination by
Dr Kraatz, but to this description I am unable to add anything1.

HE

^V^

Fig. 16. Cimbex axillaris: right antenna normal; left antenna bearing a foot.
II. the left antenna seen from in front. III. the same from above. After Kraatz.

It should be noted that the plantar surface of the foot was turned
rather forwards as shewn in the figure, and not downwards like
the normal feet.
*76. Bombus variabilis J1 (a Humble-bee). A specimen taken
beside the hedge of a park in Munich, having the left antenna
partially developed as a foot. The first two joints were normal.
They were followed by two joints which were rather compressed
and increased in thickness and breadth. Of these the first was
oblong and somewhat narrowed towards its apex by two shallow
constrictions, giving it an appearance as of three joints united
into one ; below it presented a projecting and tooth-like point.
This joint was only slightly shiny. The next joint to it was al-
most triangular, and was reddish-brown, shiny, and having hairs
on its lower surface. Posteriorly it was prolonged inwards, cover-
ing the previous joint so that both seemed to form one joint :
the posterior edge was somewhat thickly covered with hairs. The
upper part of the first of these two joints and the prolongation
of the second were together covered by a hairy, scale-like third
joint, which seemed to be only attached at its base. From the
apex of the second joint arose a shortened claw-joint, like the claw-
joint of a normal foot. This joint was reddish-brown and shiny,
bearing a pair of regularly formed claws, like the claws of the
foot. Kriechbaumer, Entom. Nadir., 1889, xv. No. 18, p. -281.

1 Some to whom I have spoken of this specimen, being unfamiliar with entomo-
logical literature, and thus unaware of the high reputation of Dr Kraatz among ento-
mologists, have expressed doubt as to its genuineness. I may add therefore that
the specimen, when in Cambridge, was illuminated as an opaque object and submit-
ted to most careful microscopical examination both by Dr D. Sharp, F.R.S., and
myself, and not the slightest reason was found for supposing that it was other than
perfectly natural and genuine. The specimen was also carefully relaxed and washed
with warm water, but no part of it was detached by this treatment.

10—2

148 MERISTIC VARIATION. [part I.

The two following cases must be given here, inasmuch as
they relate to Homoeosis of the appendages in Insects ; but in
the case of the first the evidence is unsatisfactory, and in the
case of the second there is considerable doubt whether the varia-
tion is really of the nature of Homoeosis.

77. Prionus coriarius £ : having elytra represented by legs.
The following is a translation of an announcement in the

Stettin er Ent. Ztg., 1840, vol. I. p. 48, which is copied from the
original communication to the Preussische Provinzial-BloMer, Bd.
XX. [The latter journal not seen, W. B.] : — " One of my pupils
brought me to-day a male Prionus coriarius, Fbr., the thorax of
which is remarkably constructed. The horny covering of the
meso thorax is absent, and in place of the elytra is a pair of
fully developed legs which are directed upwards and backwards.
These legs are inserted at the points of articulation of the elytra.
The metathorax supports the wings as usual and the abdomen
is not hardened more than it usually is. In trying to fly, the
creature moved these upwardly directed legs simultaneously
with its wings. The scutellum is absent and the prothorax has
only two spines ; other parts normally developed." Dr Saage,
Braunsberg, 1839 : — Hagen, in quoting this case, mentions that
the specimen was afterwards seen by von Siebold, but gives no
reference to any writing of von Siebold on the subject.

[If this specimen still exists, it is to be hoped that a de-
scription of it may be published. In the absence of further in-
formation there seems to be no good reason for accepting the case
as genuine.]

78. Zygaena filipendulae £ . Specimen possessing a supernumerary
wing arising in such a position as to suggest that it replaced a leg.
This specimen was originally described by Richardson, N. M.,

Fig. 17. Zygcena Jilipendulce, <? , having a supernumerary wing on the left side.
The upper figure shews the neuration of the supernumerary wing. From drawings
by Mr N. M. Richardson.

Proc. Dorset Field Club, 1891, and was exhibited at a meeting of
the Entomological Society of London, 1891, Proc. p. x. The extra
wing was in general form and appearance like a somewhat folded

chap, v.] HOMCEOSIS IN ARTHROPOD A. 149

hind wing but its colour was rather yellower, though it was more
red than yellow. I have to thank Mr Richardson for allowing me
to examine this specimen in company with Dr Sharp. In compliance
with Mr Richardson's wish we did not strip the wing or remove the
thick hairs which surrounded its base, and it is therefore not
possible to speak with certainty as to its precise point of origin.
The following description of it was drawn up for me by Dr Sharp :
" The supernumerary wing projects on the under side of the body,
and at its base there intervenes a space between it and the dorsal
region of the body about equal to the length of the metathoracic
side-piece. The exact attachment of the base of the supernumerary
wing cannot be seen owing to the hairiness of the body, but so far
as can be seen it is to be inferred that the wing is attached along
the length of the posterior coxa, the outer edge of the point of
attachment may be inferred to extend as far as the suture between
the coxa and thoracic side-piece ; if this view be correct the
abnormality may be described as the absence of the hind femur
and parts attached to it, and the addition of a reduced wing to the
hind-margin of the coxa. It is, however, just possible that if the
parts could be clearly distinguished it might be found that the
real point of attachment of the abnormal wing is the suture
between the metathoracic side-piece and the hind coxa."

It should be distinctly stated that there is no empty socket or
other suggestion that the rest of the leg had been lost, and it was in
fact practically certain that it had never been present. There is
thus a strong prima facie case for the view that the leg has been
developed as a wiug, however strong may be the theoretical
objections to this conclusion. On the other hand, as will be shewn
in a later chapter, supernumerary wings are known in specimens
having a full complement of legs, and it is conceivable that one of
these supernumerary wings may have arisen in such a way as to
prevent the proper development of the leg from the imaginal disc.
If the specimen were carefully stripped of hairs some light might
perhaps be thrown on this question. The figure (Fig. 17) is from
a drawing kindly lent me by Mr Richardson.

Crustacea.

Cancer pagurus. Specimen having the right third maxilli-
pede developed as a chela. This animal was brought by a fisher-
man to the Laboratory of the Marine Biological Association at
Plymouth. It is a male, measuring five inches from one side of
the carapace to the other. All the parts appear to be normal with
the exception of the third maxillipede of the right side. This
structure, however, has the form shewn in Fig. 18, A, differing
entirely from the ordinary condition of the appendage. Fig. 18, B,
is taken from the third maxillipede of the left side and shews the
ordinary structure of the same parts. On comparing the two
figures it will be seen that the protopodite does not differ in the

150

MERISTIC VARIATION.

[part I.

limbs of the two sides; that the exopodite of the right side is

B

Fig. 18. Cancer pagurus $ ; the right and left third rnaxillipedes, that of the
right side having the endopodite in the likeness of the endopodite of a chela.
bp. basipodite, cp. carpopodite, dp. dactylopodite, ep. epipodite, g. groove between
parts representing ischiopodite and meropodite, g'. groove representing the suture
at which a normal chela is thrown off if injured. From P. Z. S., 1890.

essentially like that of the left, but that it lacks the inner process
and the flagellum which are borne by the normal part. There was
some indication that this branch of the limb had been injured, and
perhaps the flagellum may have been torn away, but the appear-
ances were not such as to warrant a conclusion on this point. The
branchial epipodites (not shewn in the figures) were normal in
both cases. The endopodite of the right side was entirely peculiar,
and was, in fact, literally transmuted into the likeness of one of
the great chelae. It consists of a single joint (mi), articulating
with the basipodite centrally and bearing the carpopodite. This
single joint represents, as it were, the ischiopodite and meropodite
of an ordinary chela, but these two parts are ankylosed together
and the articulation between them is only represented by a groove
(g). Another groove (g') represents the groove upon the ischiopo-
dite of the chela, at which the limb is commonly thrown off by
the animal if it is injured. The carpopodite, propodite and dactylo-
podite are freely moveable on each other and hardly differ, save
in absolute size, from those of the normal chelae. The shape, pro-
portions and texture are all those of the chela. Batesox, W.,
Proc. Zool. Soc, 1890, p. 580, fig. 1.
80. A similar case1 of Cancer pagurus $ . 4 inches across carapace,
mature, right pedipalp [i.e. 3rd maxillipede] normal, left pedipalp
modified into a chela having all the joints clearly defined, Coknish,
T., Zoologist, S. 3, vm. p. 349.

*81. Palinurus penicillatus. The left eye bearing an antenna-
like flagellum, growing up from the surface of the eye as shewn
in the figure (Fig. 19). The eye-stalk and cornea, as represented,
appear to have been of the normal shape but reduced in size.

1 Similar cases since published by Eichaed, Ann. Sci. Nat., Zool., 1893.

CHAP. V.]

HOMCEOSIS IN ARTHROPODA.

151

Milne-Edwards, A., Comptes Rendus, lix. 1864, p. 710 ; described
and figured by Howes, W. B., Proc. Zool. Soc, 1887, p. 469.

Fig. 19. Palinurus penicillatus, the left eye bearing an antenna-like flagellurn.
After Howes.

82. Hippolyte fabricii differs from other species of the genus in
being usually without epipodites at the bases of all the cephalo-
thoracic legs except the first pair, while in the other species these
appendages are usually present upon the bases of the first and
second, or upon the first, second and third pairs, and on this
character it was placed by Kroyer in a separate section of the
genus.

Of 52 individuals (18 males varying in length from 27 mm. to
39 mm. and 34 females varying from 16'5 mm. to 50 mm.), from
various localities on the New England coast, 47 had the normal
number of epipodites, while 5 had epipodites on one or both of the
second pairs of legs. Of the latter 3 were from the Bay of Fundy ;
one </, 35 mm. long, has well-developed epipodites on each side of
the 2nd pair of legs ; another J1, 36 mm. long, has a short epipodite
on the left side and none on the right ; the other, $ , 47 mm. long,
has a well-developed epipodite on the left side and none on the
right. The two others were from Casco Bay: a $,36 mm. long,
with a short epipodite on the left side, and a </\ 28 mm. long, with
a rudimentary one on the right side. As the measurements shew,
the presence of these epipodites is not characteristic of the young.
Smith, S. J., Trans. Connecticut Acad., v. 1879, p. 64.

152 MERISTIC VARIATION. [part i.

Variation in the number of generative openings in Crayfishes.

Astacus fluviatilis. A female having the normal pair of
oviducal openings on the bases of the antepenultimate pair of
walking legs, and in addition to them another pair of similar
openings placed upon the corresponding joints of the penultimate
pair of walking legs. On dissection it was found that the ovary
was normal, and that from each side of it a normal oviduct was
given off; but each of these oviducts divided a little lower down
to form two smaller oviducts, one of which went to each of the
four oviducal openings. Desmarest1, E., Ann. Soc. Ent. France,
1848, Ser. 2, vi. p. 479, PI.

Astacus fluviatilis $ , having a supernumerary pair of ovi-
ducal openings placed on the last pair of thoracic legs. The normal
oviducal openings were in the usual position and of the usual
shape and size, but in addition to them there was an extra pair
placed on the last thoracic legs. It should be remarked that
though these are the appendages upon which the openings of the
male organs are placed, the oviducal openings were not in this
case situated at the posterior surface of the joint as the male
openings are, but were placed relatively to the leg in the same
situation as the female openings on the antepenultimate legs. The
penultimate legs and the abdominal appendages were normal. On
dissection it was found that each oviduct after passing for the
greater part of its course as a single tube, divided into two parts,
one of which went to each oviducal opening. The ovary itself
was normal. Benham, W. B., Ann. Mag. N.H., 1891, Ser. 6, vn.
p. 256, PI. ill. fl am greatly obliged to Mr Benham for an oppor-
tunity of examining this specimen. Attention is called to the
fact that in this specimen Homoeosis occurs in an unusual way,
leaving a gap in the series ; for the openings are on the ante-
penultimate and last thoracic legs respectively.]

Desmarest's observation stood apparently alone until lately, when
the specimen just described and several others presenting the same
or similar variations were observed by Benham. Mr Benham was

%J

kind enough to send me the following specimens for examination :
one female having a single extra oviducal opening on the left side
upon the penultimate thoracic leg (Fig. 20 C), and two females
having a similar extra opening in the same place on the right
(Fig. 20, B) ; in both of these the normal oviducal openings were
unchanged. Together with these Mr Benham also sent a female
having only one oviducal opening on the right side and another
having only the left oviducal opening (Fig. 20, A), the correspond-
ing leg of the other side having no trace of an opening.

1 Desmarest had this specimen from Rousseau {I. c, p. 481 note): Faxon
quoting the case (Harv. Bull., viii.) accidentally represents it as two cases, but the
note to Desmarest's paper shews that the description referred to a single specimen
only.

CHAP. V.]

HOMCEOSIS IN ARTHROPODA.

153

*85. After receiving these specimens I made an attempt to ascer-
tain the degree of frequency with which such variations occur in

b.n

ambM

Right.

Left.

Fig. 20. Females of Astacus fluviatilis having an abnormal number of oviducal
openings. N.B. The form with three pairs of openings is not figured.

A. Right oviducal opening absent. B. Extra opening in right penultimate
leg. C. Extra opening in left penultimate leg.

the Crayfish, and though the total number examined is too small
to give a percentage of much value it may be well to record the
result.

In all, 586 female A. fluviatilis have been examined : of these
563 were normal in respect of the number of oviducal openings,
and 23 were abnormal, as follows :

1. Extra oviducal opening on left penult, leg 7

2. ditto right 10

3. ditto on both penult, legs 1

4. ditto on both penult. & last legs 1

5. Single oviducal opening on left side only 3

6. ditto right1 1

Total abnormal specimens 2-'>

1 Mr R. Assheton sends me word of a similar specimen found among 80 of both
sexes; Prof. W. B. Howes of another among 144 of both sexes.

154 MERISTIC VARIATION. [part i.

In all cases of supernumerary oviducal openings the normal open-
ings were also present.

These cases are in addition to those received from Mr Benham.
So far, therefore, the cases of extra opening amount to over 3 per
cent, of females examined.

Of 714 males examined, only one was abnormal, having no
trace of a generative opening on the right side, the vas deferens
ending blindly and hanging free in the thoracic cavity. There
was no female opening in this specimen, and the abdominal appen-
dages had the form characteristic of the male on both sides. The
base of the last thoracic leg on the right side bore no enlargement
for the genital opening, but was plain and like that of the pen-
ultimate leg1.

In cases of females which lacked one of the openings, the basal
joint for the leg which should have been dilated and perforated
for the opening, was undilated and resembled the basal joint of a
penultimate leg. The oviduct upon the imperforate side was
more or less aborted and hung loosely in the thoracic cavity.

In the abnormal females with extra oviducal openings, the
oviduct divides generally into two just before it enters the legs,
the fork being placed at the level between them. In some few
cases no branch of the oviduct could be traced to the extra open-
ing. In one specimen the extra opening led into a short tube
which ended blindly, not communicating with the oviduct. The
specimen (4) with extra openings on the penultimate and last legs
had thus in all six oviducal openings. Those in the normal position
on the antepenultimate legs were of normal size, those on the next
pair were smaller but still of fair size, while those on the last pair
of thoracic legs were very small, that on the left side being the
smallest and admitting only a fair-sized bristle. In this specimen
the single oviduct of each side forked in its peripheral third,
giving a duct to each of the first two pairs of openings, but I failed
to find any connexion between it and the openings on the last
thoracic legs, which were very short blind sacs.

In all cases of extra oviducal opening the basal joint of the leg
is expanded like those of the normal antepenultimate legs, the
degree of expansion being proportional to the size of the opening.
The normal openings are always the largest, but the extra ones
are sometimes almost as large and would easily allow the passage
of ova, but occasionally they are too small to let an egg through.

As regards principles of Homoeotic Variation illustrated by
these cases, three points should be especially remarked :

1 Compare the following : Astacus fluviatilis. Amongst 1500 specimens 3 were
found in which the tubercle through which the green gland opens was entirely-
absent. The opening itself was not formed and the green gland of the same side
was absent. In another specimen the opening was deformed, probably owing to
some mutilation. In this and the previous cases the green gland of the other side
was considerably enlarged. Strahl, C, Midler's Archiv fiir Anat. u. Phys., 1859,
p. 333,^.

chap, v.] HOMCEOSIS IN ARTHROPOD A . 155

1. That this Variation may be bilaterally symmetrical,
but that the evidence goes to shew that it is more often uni-
lateral.

2. That there is a clear succession between the several
oviducal openings, those of the antepenultimate legs being
the largest, the penultimate the next, and those of the last
legs the smallest.

3. That Homceosis may occur between segments which
are not adjacent, as in the case of extra oviducal openings on
the last thoracic legs, none being formed on the penultimate
(No. 84).

4. That the Variation may be perfect.

With the foregoing, the following evidence may be compared,
though it is very doubtful whether it properly belongs here1.

86. Cheraps preissii [an Australian freshwater Crayfish, nearly allied
to Astacusj. Of seven specimens received one was a normal male
and three were normal females. The other three had on the basal
joint of the third [antepenultimate] pair of legs a round opening,
having the size and shape and situation of the normal female openings.
These apertures were closed with soft substance. The fifth legs bore
the usual male openings, from which the ends of the ductus ejacula-
torius protruded. The coiled spermatic ducts were normal ; but no
ovary was found and no internal structure was connected with these
female openings, von Martens, E., Sitzb. Ges. naturf. Fr. Berlhi, 1870,
p. 1.

87. Astacus pilimanus J, a single specimen, and A. braziliensis J,
a specimen collected by Hensel in Southern Brazil, a similar opening
was found on the third pair of legs ; but in other specimens of these
forms there was only a slight though sharply defined depression in
the chitinous covering at this point, von Martens, E., I.e.

1 See also Nicholls, ~R.,Phil Trans., 1730, xsxvi. p. 290, figs. 3 and 4 describing
a Lobster {Homarus vulgaris) having male organs on the left side and female organs
on the right.

CHAPTER VI.

linear series — continued.

Ch^etopoda, Hirudinea and Cestoda.

Imperfect Segmentation \

Though from the circumstance mentioned at the beginning of
Chapter n, that the total number of segments in the Annelids is
generally indefinite, true Meristic Variation cannot be easily re-
cognized in this group, there is nevertheless a remarkable group of
cases of imperfect segmentation, in which by reason of the incom-
pleteness of the process of Division, the occurrence of Variation is
at once perceived. The following cases were all originally described
by Cori, who speaks of them as instances of "intercalation" of
segments. For reasons sufficiently explained in the Chapter on
Vertebras, there are objections to the use of this term, if only as a
mode of expression, and the evidence concerning these cases has
therefore been re-cast.

*88. Lumbricus terrestris : the 46th segment having the form
shewn in Fig. 21, I. being normal on the right side, but double on
the left. Internally a septum divided the two parts a and a from
each other. Each of them contained a nephridium, setae, &c.
Cori, C. J., Z.f. w. Z.t liv. 1892, p. 571, fig. 1.

*89. Specimen having, in the region close behind the clitellum,
three consecutive segments, each resembling that just described.
Of these the first was double on the right side, the second on the
left, and the third on the right again. Fig. 21, II. shews the
internal structure, the nephridia and other jmrts having doubled
in each of the doubled half-segments. Cori, /. c, p. 572, fig. 2.

90. Lumbriconereis : case similar to the first case in Lumbricus,
Fig. 21, III. Cori, C. J., I c, p. 572, fig. 4.

91. Halla parthenopeia. A specimen 50 cm. long presented
numerous abnormalities of which two are represented in Fig. 21, IV.
At the point marked a the lines of division between the segments

1 Numerous facts illustrating this subject are given in a recent paper by
Buchanan, F., Q. J. M. S., 1893.

CHAP. VI.]

ANNELIDS.

157

enclose a small spindle-shaped island of tissue. Three segments
lower a wedge-shaped half-segment is similarly formed. At

Fig. 21. Examples of imperfect segmentation in Annelids (after Com).

I. Lrimbricus terrestris (No. 88). II. L. terrestris (No. 89), as seen when laid
open on the dorsal side. III. Lumbriconereis (No. 90). IV. Halla parthenopeia
(No. 91).

N, nephridium ; Np, nephridial pores; D, alimentary canal; dG, dorsal vessel;
vG, circular vessel.

The letters a, b, c, &c. indicate the parts belonging to the respective segments.

another point in the same animal (not shewn in Fig. 21) one
of the segments was partly divided into two in the right dorso-
lateral region. Com, p. 572, figs. 8 and 9.

Spiral Segmentation \

92. Lumbricus terrestris. Fig. 22, I. A shews a part of an
Earthworm seen from the dorsal side, the ventral side being-
normal in appearance. By following the groove indicating the
plane of the septum between b and c on the right side to the
ventral surface, it could be traced to the left side between b and c,
so across the dorsal surface, between c and d on the right side,
across the ventral surface and between c and d on the left, reach-
ing nearly to the middle dorsal line again. This is shewn dia-
grammatically in Fig. 22, I. B.

93 A simpler case affecting one segment only is shewn in Fig.
' 22, II.

94. Another specimen exhibited a similar arrangement near the
tail-end (Fig. 22, III.). The lettering of the figure sufficiently
explains the course of the spiral septal plane. [Cori does not
state that the septa internally formed a spiral division, but it can
scarcely be doubted that they did so, following the external groove,

1 Further observations on this subject have been lately published by Morgan,
T. H., Journ. of Morph., 1892, p. 245, and by Buchanan, F., Q. J. M. S., 1893.

158

MERISTIC VARIATION.

[part I.

like the spiral valve of an Elasmobranch's intestine.] Cori,
Z.f. w. Z.t Liv. 1892, p. 573, figs. 5, 6 and 7.

*

IB

Fig. 22. Spiral segmentation in Lumbricus terrestris.

I, A, the case No. 92 ; I, B, diagrammatic representation.

II, A, the case No. 93 ; II, B, diagrammatic representation.

III, the case No. 94. (After Cori.)

Two other cases described by Cori may be mentioned here, though
there is a presumption that they are not really examples of Variation
in the segmentation along the axis of a Primary Symmetry, but rather
belong to the class of Secondary Symmetries. They are alluded to
here as it is convenient to illustrate this distinction by taking them
in connexion with the examples just given.
95. Hermodice carunculata. (Fig. 23, III.) Between two normal
segments is what seems at first to be a segment double on the left
side with two complete sets of parapodia, but imperfectly divided
on the right (left of figure), the septal groove stopping short before
it reaches the parapodial region. The lower half on this side is re-
presented with a normal ventral ramus of the parapodium, but the
ventral ramus in the upper was itself partially doubled, having in
particular two cirri Cv. I. and Cv. II. and two branches of setae. The
condition of the dorsal ramus is not described. Of course without
seeing this specimen it is impossible to say more than this, but the
figure strongly suggests that the division between the two halves of
this parapodium was a division into images and not into successive
segments. The figure represents the lower cirrus Cv II. as standing
in the normal position for the cirrus, on the posterior limb of the
parapodium, but the anterior cirrus is distinctly shewn as placed on
the anterior limb of the elevation and anterior to the bristles. If
this were actually the case, this double parapodium must be looked
on as a kind of bud, with a distinct Secondary Symmetry of its
own. Described afresh from Cori, C. J., Z.f. w. Z., liv. 1892, p. 574,
fig. 3.

CHAP. VI.]

ANNELIDS.

159

96. Diopatra neapolitana. In the middle of a specimen 35 cm. long
was an arrangement somewhat similar to the above. The part marked

ci

CM

TIT

Fig. 23. I. The case of Diopatra neapolitana (No. 96) from the side. II, the
same looking upon the parapodia. C I. C II, the two supernumerary cirri.

III. The case of Hermodice carunculata No. 95. Cv, cirrus of ventral branch
of parapodium ; Cd. dorsal cirrus ; Cv. I, Cv. II, the two cirri borne on the super-
numerary parapodium. (After Cobi.)

V was cut off as shewn in Fig. 23, I., it bore a normal cirrus, and
the other part of the segment, marked b, bore two cirri and two
bunches of bristles. The figure does not indicate that there was any
relation of images between these two parts, but this would scarcely
appear in this case unless specially looked for. Described afresh from
Com, C. J., I.e., p. 573, figs. 10 and 11.

In considering the evidence as to Secondary Symmetries reference
to these cases will again be made.

Generative organs of Earthworms1.

The number and ordinal positions of the primary and accessory
generative organs and of their ducts differ in the several classifi-
catory groups of Earthworms. In the evolution of these forms it
may therefore be supposed that Variation in these respects has
occurred. To this subject the following evidence relates. The
difficulty which was mentioned in the case of Variation in ver-
tebrae, that there is no. clear distinction between Homceotic and
strictly Meristic Variation, will here also be met, inasmuch as the
total number of segments in these forms is indeterminate ; but

1 For information and references on this subject I am indebted to Mr F. E.
Beddard and Mr W. B. Benham.

160 MERISTIC VARIATION. [part i.

probably we shall be right in regarding the majority of these
variations as Homceotic.

Lumbricus. Throughout this genus there is normally a
single pair of ovaries, placed in the 13th segment, on the posterior
surface of the septum between the 12th and 13th segments. The
following cases of supernumerary ovaries are recorded :

97. Lumbricus turgldus : specimen having an extra pair of ovaries
in the 14th1 segment.

98. Specimen having an extra ovary on the right side in the 14th
segment.

99. L. purpureus: specimen having an extra ovary on the left
side in the 14th segment.

In all these cases the extra ovaries were in size, form and
position like the normal ovaries. There was no extra oviduct or
receptaculum ovorum, but the normal ovaries and oviducts were
present as usual. Bergh, R. S., Zeit. f wiss. ZooL, XLiv. 1886,
p. 308, note.

100. Allolobophora sp. [partly = Lumbricus, the common Earth-
worm] : specimen having, in all, seven pairs of ovaries ; viz. a pair
in the 12th, 13th, 14th, 15th, 16th, 17th and 18th segments. Of
these all except the pair of the 13th segment are supernumerary.
Each of these ovaries was placed on the posterior face of a septum
in the usual position. The three anterior pairs in shape, structure
and position closely resembled the normal structures. Of these
the most anterior were slightly the largest. The four posterior
pairs were smaller and resembled the ovaries of a very young or
immature worm, but on examination all were found to contain
ova. The normal pair of oviducts were present and no extra ovi-
ducts could be found, though carefully sought for. Woodward,
M. F., P. Z. S.} 1892, p. 184, Plate xiil

•101. Lumbricus herculeus, Savigny (= L. agricola, HofTmeister),
having an asymmetrical arrangement of the generative organs, &c.
On the left side the arrangement was normal ; the ovary being in
the 13th segment, the oviducal opening in the 14th, and the open-
ing of the vas deferens in the 15th segment (Fig. 24).

On the right side each of these structures was placed in the
segment anterior to that in which it is normally found : the right
ovary was in the 12th, the external opening of the right oviduct
was in the 13th, and the external opening of the right vas deferens
was in the 14th segment. The spermathecse were normal on the
left side, being placed in the 9th and 10th segments, but on the
right side one spermatheca only was present, that of the 9th
segment. The vesiculse seminales were present as usual in the
9th and 11th segments, but there was no vesicula in the 12th

1 In Bergh's enumeration the ordinal number of these segments is one less than
in that commonly used : the latter system is adopted above.

CHAP. VI.

ANNELIDS.

161

segment on the right side, while that of the left side was fully

Right

Left (normal)

Fig. 24. Lumbricus herculeus, having the generative organs of the right side one
segment higher than usual. A, external view from below. B, view of the organs
from above, spth, sperrnathecae ; ov, ovary; as, oesophagus ; cat, calciferous
glands. After Ben ham.

formed. It is remarkable that in this case, the calciferous gland
of the 12th segment was absent on the right side. [I am indebted
to Mr Benham for an opportunity of examining this specimen.]
Benham, W. B., Ann. & Mag. N. H., 1891, Ser. 6, VII. p. 257,
PI. in.

Another specimen presented the same variations as the fore-
going, both as regards the asymmetrical arrangement of the genital
pores and the absence of the calciferous gland : but in it there
were vesiculae seminales on the right side in segments 10 and 11,
but none in segment 9 ; and there was a spermatheca on the right
side in segments 8 and 9. [In the normal form the spermatheca?
are in segments 9 and 10, so that, in this individual in the matter
of the spermathecse as well as of the genital pores, structures were
formed in particular segments which are normally found one
segment lower down.] Bexham, W. B., in litt., March, 1891.

11

B.

162

MERISTIC VARIATION.

[part I.

103. Table shewing position of ovaries in forms having two or more
pairs of ovaries, and in the Variations found (slightly altered from
M. F. Woodward, P. Z. S., 1892):

Segments

A canthodrilus

Kclipidrilus

Eudrilus

Lumbricus terrestris (normal)

L. herculeus (? = teirestris) Benham's \ 1.

2 specimens (rt.

I., turgidus Bergh's spec, (abnorm.)

do. do. do. (abnorm.)... J '

L. purpureus do. do. (abnorm.)... J .'

AUolobophora sp. (Common Earthworm,

abnorm.)

Perionyx (two pairs, varying from 9 — 16)..

Phreodrilus

Ph reoryctes l

Vrochceta

9

10

11

12

13

14

15

X

X?

X

X

X

X

!

I

X
X

X

X
X
X
X
X

X

X

X
X

X

X

X

X

16 1 17

X

X
X
X

X
X

18

x

104. AUolobophora sp. [</ pores normally in 15th and $ pores in
14th, as in common Earthworm] : specimen having on the right
side £ pore in 20th and % pore in 19th ; on the left side, <£ pore in
17th and $ pore in 16th. Michaelsen, W., Jahrb. Hamburg,
wiss. Anstalt, 1890, VII. p. 8. In each case the £ pore is in the
segment behind the % pore, as normally. The position of ovaries
not given.

105. Lumbricus agricola Hoffm. (= terrestris L.) : amongst 230 speci-
mens in which the position of the male pores are determined, 6 speci-
mens were found in which these openings were not normally placed (viz.
one on each side in the 15th segment). In two of these specimens,
both pores were in the 14th segment; in one case the left pore
was in the 14th segment and the right was in the 15th: these three
worms were German. One specimen was found in Savigny's collection
in Paris which had two pores on the left side [and none on the
right (?)]. In one English specimen the " vulva" [sc. the two male
pores] was in the 14th segment and in another it was in the 16th.
[The author speaks sometimes of both pores as the " vulva," and at
other times he uses this term for one pore only, but the meaning is
plainly that given above.] Hoffmeister, W., Uebersicht alter bis
jetzt bekannten Arten a. d. Familie Begenvnirmer, Braunschw., 1845,
p. 7.

1 Phreoryctes, a N. Zealand Oligochast, has 2 pairs of testes and 4 vasa deferentia
opening separately; 2 pairs of ovaries and 4 oviducts. Beddard, F. E., Ann. and
May., 1888, i. p. 339, PI.

CHAP. VI.]

ANNELIDS.

163

Perionyx excavatus. In this earthworm a very remarkable
series of variations has been observed by Becldard. The accompany-
ing table shews the varieties in number of spermatheca? and position
of the generative openings which were found. The spermathecae
are generally 4, and are placed in the 7th and 8th segment, but in
several specimens there were 8 and their position varied from the
6th to the 11th segment. In all the varieties, however, they were
in segments adjacent to each other. In four specimens the sper-
mathecse were in the 8th and 9th segment on the right side and in
the 9th and 10th on the left. In normal specimens the male pores
are 2, but individuals with 4 (and perhaps 6) were found. There
are generally 2 pairs of ovaries and oviducts. In Var. No. 11 an
additional ovary was found on the right-hand side in the 11th
segment and in Var. No. 10 there were three pairs of ovaries.

Table of Variations seen in P. excavatus (from Beddard).

Spermatbecfe

? pores

j pores

Clitellum

Normal (412 specs.)

8, 9

14

18

14—17

Var.

1 (1 spec.)

7,8

11

16

12—15

,,

2

13, 14

18

3

8, 9

13, 14

17

13—17

5,

4

15, 16

20

1 J

5 (2 specs.)

8,9

14, 14

18

13—17

,,

6 (1 spec.)

6,7

10

14,15

5,

n

< 11

7, 8, 9, 10

15, 16

18

,)

8

14, 15

18

11

9

7,8,9

14

17

10

8, 9, 10, 11

15, 16

19

15-18

>>

11 „ .

6,7,8

13, 14

16

12 (2 specs.)

8, 9, rt. ; 9, 10, 1.

14

18

1)

13

8, 9, rt.; 9, 10, 1.

14, 15

18

>>

14 (1 spec.)

8, 9

15, 17

21

1)

15

15, 16

18

Though the position of both varied greatly, the male pores
were always posterior to the female ones.

In some specimens certain of the segments were only divided
from each other on one side of the body, being confluent on the
other. For example in Var. No. 14, segments 11 and 12 and also
segments 18 and 19 were only divided from each other on the left
side (cp. Nos. 88—91).

Out of 430 individuals 15 variations in these structures were
seen; of 12 of these variations single specimens only were found,
but two specimens occurred with each of the other three forms oi
variation. In a single case a nephridium was found nearer to the
dorsal line in one segment than in the adjacent segment. Many
of the conditions here occurring as variations are found normally

11—2

164

MERISTIC VARIATION.

[part I.

in other genera and species.
1886, p. 308, figs.

Beddard, F. E., Proc. Zool. Soc,

A

_2

A.

5
j8

_8_

12.
n_

12

13

11
15

16
17
18
10

20

'^

\-v

^

Fig. 25. Perionyx excavatus. Diagrams shewing some of the variations in
respect of the number and positions of the openings of the spermathecre and
generative pores. From Beddard, P. Z. S., 1886.

Perionyx griinewaldi, Michaelsen. Normally a pair of male
genital pores on the 18th segment, and a single oviducal opening
for the two oviducts in the middle line of the 14th segment.

107. In two specimens a different arrangement was found. One of
these had the oviducal opening in the 15th segment [position of male
openings not specified and presumably normal].

108. The other had two oviducal openings, one in the 13th and one
in the 14th segment [not stated whether these openings were median
or lateral, nor whether each of them was a double structure as of
course the normal female opening is]. In this specimen the male
openings also were placed anteriorly to their normal position, being
in the 17th segment. Michaelsen, Jahrb. d. Hamburg, wiss. Anstalt,
1891, viii., p. 34.

Allurus. In Terricolse generally, the £ pores are on the 15th,
and the $ pores on the 14th, as in the common Earthworm.

109. Allurus tetraedrus, a widely distributed form, has £ pores on
the 13th and $ pores on the 14th, the £ pores being thus in front of
the ^ pores as a specific character. Under the name Allurus dubius
Michaelsen described two specimens having the male pores on the
14th instead of on the 13th, and the £ pores on the 15th instead of
on the 14th, each being thus one segment in advance of its normal
place [backward Homceosis]. Michaelsen, W., Jahrb. Hamb. wiss.
Anst., 1890, vie, p. 7 ; see also Arch. f. Naturg., 1892, lviii.,
p. 251. Compare No. 111.

110. Besides these is a batch of 8 specimens of A. tetrdedrus, loc. un-
known, 6 specimens had both £ and $ pores in the 14th. Clitellum
began in 23rd, tuberc. pubert. in 24th. These specimens are thus
intermediate between A. hercynius, which has the pores as in Lum-

CHAP. VI.]

HIRUDINEA.

165

bricus, and A. tetraedrus. Michaelsen, W., Arch. f. Naturg., 1892,

lviil, p. 251,

Allurus putris : specimen having J1 pores on 13th (instead of
15th) as an abnormality; in it the other external generative organs
(and doubtless the internal also) were 2 segments higher than usual,
the J pore being on the 12th instead of 14th. Tuberc. pubert
26 — 28. Michaelsen, Jahrb. Hamburg, wiss. Anst., 1891, vin.,
p. 8. Compare No. 109.

Allurus sp. : specimen having 1. side normal ; right side, £ pore
in 12th, % in 11th, clitellus and tuberc. pubert. one segment higher
than usual. Ibid.

Enchytrceid^e. J1 pore generally in the 12th segment. In
Buchholzia appendicidata (Buch.) it is on the 8th, as a specific
character. In Pachydrilus sphagnetorum (Vejd.) it is either
on the 8th or on the 9th, according to individual variation, the
other parts being then disposed as follows :

cf pore on 8th

S pore on 9th

Ovaries on dissep

Vas def. in front of dissep.

c? pore

7/8
8/9
8/9

9

9/10

10

9 and \ 10

6/7

7/8
7/8

8

8/9
9

8 and \ 9

Oviduct on dissep

? pore

Clitellum

Michaelsen, W., Arch./, mikr. Anal, 1888, xxxr. p. 493 ; see
also Jahrb. Hamb. wiss. Ansl, vii. p. 8.

Perichaeta hilgendorfi, n. sp. Mich. 7 specimens. Variation in number of
spermathecal openings, as follows. 5 specimens had 2 pairs in the groove between
segments 6/7 and 7/8; 1 specimen had 3 pairs, between 5/6, 6/7 and 7/8; 1 specimen
had only one, on the left side between 6/7, which corresponded internally to a single
spermatheca [other variations also observed in these specimens, q.v.]. Michaelskn,
W., Arch. f. Nature/., 1892, lviii. p. 236.

Perichaeta fortoesi (an Earthworm from New Guinea). In this animal a pair
of spermatheca? is placed in the 8th segment and another pair in the 9th. Two
specimens only have been examined and in both of these an additional spermatheca
was found on the left side, internal to the other. In one individual the 5th sperma-
theca was in the 8th segment, and in the other it occurred in the 9th. Beddaki>,
F. E., Proc. Zool. Soc, 1890, p. 65, Plate.

Aiiolobophora lissaensis. Similar variation in spermatheca1, Michaelsen,
W., Jahrb. Hamb. wiss. Anst., vin., 1891, p. 19.

HlRUDINEA.

Hirudo medicinalis. The number of pairs of testes is
variable, but 9 pairs most often found. Of 31 specimens of this
species, 21 had 9 pairs, 6 had 10 pairs, and 4 had 9 on one side
and 10 on the other. Chworostansky, C, Zool. Anz., 1886,
p. 4-AG.

166

MERISTIC VARIATION.

[part I.

118. Hirudo officinalis : of 7 specimens, 5 had 9 pairs of testes,

1 had 10 pairs, and though in the 7th specimen there were

2 pairs, the vas deferens of the last pair of testes ended blindly.
Ibid.

119. Hirudo medicinalis, Fairly often the vas deferens is prolonged beyond the
9th testis, and having passed through rive annuli, ends in a glandular mass of
irregular form. Case given in which the 7 last testes of right side were absent or
only represented by amorphous material, the testes of the left side being abnormally
large. Ebrard, Nouv. monopr. des Sangsues vied., Paris, 1857, p. 9'.).

*120. Hirudo officinalis : an individual having a supernumerary
penis, and vesicula seminalis of the right side, in the 5th somite.

vs2

Fig. 26. Case of Hirudo officinalis, No. 120.

pl, penis in normal position ; p2, supernumerary penis ; vs, the usual vesicula?
seminales ; vs'2, supernumerary vesicula seminalis. (From a diagram sent to me by
Mr Gibson.)

The normal penis in the sixth segment was fully formed and
into it opened on either side a vas deferens, provided with a
vesicula seminalis as usual. But the vesicula of the right side
gave off in addition a vas deferens, which passed forwards into
the fourth segment and there enlarged into another vesicula
seminalis. This additional vesicula was connected by a duct
with a supernumerary penis placed and opening in the middle
of the fifth segment. The parts of the left side as well as the
female organs were normal. [I have to thank Mr Gibson for
furnishing me with a diagram (Fig. 26) supplementing the
published account.] Gibson, R. J. Harvey, Nature, 1887, xxxv.,
p. 392.

Aulastoma gulo (Horse Leech). In this form as is usual
among the Gnathobdellidce there are from 9 to 12 pairs of tes-

chap, vi.] ANNELIDS : RECAPITULATION. 167

ticular sacs which communicate with a tortuous vas deferens
on each side which together enter a single penis. The paired
ovaries are placed behind this and the oviducts unite to form
a common vagina.
121. In a specimen found amongst a large series investigated, each
vas deferens opened by a separate penis, of which the most an-
terior opened in the 20th annulus and the posterior in the 25th.
The female apparatus was similarly divided. One ovary was
placed near the penis in the 25th annulus and from it a vagina
passed down to open with the penis. The other ovary, with a
similar vagina, lay in the 30th annulus. Asper, G., Zool. Anz.,
1878, I, p. 297.

Recapitulation of evidence as to Oligoch^eta and Hirudinea.

Variation in these two groups appears in such similar modes
that points of special consequence in both may conveniently be
spoken of together.

1. As elsewhere seen, so here, there are forms, e.g., Perionyx
excavatus or Pachydrilus sphagnetorum, shewing great variability,
while others, the common Earthworm for instance, rarely vary.

2. Both forward and backward Homceosis may occur ; a form
normally having the </ pores, for instance, on the 15th segment,
may as an individual variation have them on the 16th (No. 105),
while an individual of another genus, starting from the same
normal, may have them on the 13th (No. 111).

3. As in other cases of Homceosis, when a member of a
Meristic Series, in this case a segment, develops an organ proper
to another segment, this organ is formed in a place serially
homologous with its normal place. (To this principle certain
limitations must hereafter be introduced.)

4. Variation may, or may not, be simultaneous and cor-
related in the several systems. The position of the J openings
for example, may or may not vary similarly and simultaneously
with that of the £ openings, though on the whole the evidence
suggests that such correlation is not uncommon. The facts seen
in the genus Allurus, in which one species (A. tetrdedrus) has the
c/1 pore normally in front of the $ pore, sufficiently indicate that
the variation in the position of these two openings is not always
so correlated. It may be further mentioned that variation in
number of ovaries seems to occur generally without correlated
variation in the number of oviducts.

5. Such Variation may or may not be simultaneous on the
two sides of the body. When not thus bilaterally symmetrical,
there may nevertheless be a full correlation between the parts
of the same side.

6. The evidence does not indicate any limit to the number
of segments which may take on a certain character, or approxi-

168 MERISTIC VARIATION. [part i.

mate to a given pattern. The highest number of ovaries, for
instance, recorded, is 7 pairs ; but there is nothing to shew that
more segments might not undergo similar Homceosis. (The pro-
gressive diminution in size of these ovaries from before back-
wards in this case is worth noticing.)

7. The principle so often manifested in the evidence of
Variation, that the magnitude, completeness, and symmetry of
a variation bears no necessary proportion to the frequency of
occurrence of that variation, is here strikingly exemplified.

8. The evidence as to the existence of two varieties of
Paclnjdrilus sphagnetorum, the one with all the organs a segment
higher than their place in the other variety may be well com-
pared with Sherrington's observation, that in the Frog and
in several Mammals (see No. 70) the individuals could be
roughly divided into two classes according as the lumbo-sacral
plexus was formed more anteriorly (" preaxial class ") or more
posteriorly (" postaxial class ").

9. In the evidence as to Perionyx, it was seen that many
of the arrangements found occurred in single specimens only,
suggesting the inference that the systems do not fall into one
of these conditions more easily than into others ; nevertheless
of each of three abnormal arrangements two examples were found,
a circumstance hardly to be expected on the hypothesis of for-
tuitous Variation.

10. It is perhaps unnecessary to point out that the examples
of Variation given are in their several degrees Discontinuous, and
that by the nature of the case the Variation by which the several
specific forms have attained their particular numbers and charac-
teristic disposition of organs, must almost of necessity have been
thus Discontinuous.

Cestoda.

The following facts respecting Variation in Cestoda are chiefly
taken from Leuckart, Parasiten des Menschen1.

Besides the variations here enumerated, abnormalities of several
other kinds (variation in number of suckers, prismatic segments,
bifurcation, &c.) are known in this group, but as these do not directly
illustrate the Variation of Linear Series, consideration of them must
be deferred.

The degree to which the parts bearing sexual organs are
separated from each other differs greatly in the various groups
of Cestodes. In some (Trice nophor us) the segmentation amounts
to an inconsiderable constriction, while in Ligula the generative
organs are repeated several times in a common body. L., p. 347.

1 In what follows the letter L. is used in reference to this work.

chap, vl] CESTODA. 169

122. Even in the groups whose segmentation is commonly perfect,
variations in the degree of separation between the proglottides
are not rare. It frequently happens that specimens of Tcenia
are found in which the external segmentation is partial, being
only found on half of the contour. This abnormality, which
does not affect the internal organs, occurs several times in the
same chain. Moniez, R, Bull. Sci. du Nord, x., p. 200.

123. Taenia saginata. Cases of the "intercalation" of a triangular,
wedge-like segment between two proglottides are recorded. In
such cases the generative opening is on the same side as in an
adjacent segment, not taking part in the alternation. L., p. 572.
Compare with similar phenomena in Chaetopoda (p. 156).

The evidence of abnormal repetition of parts occurring in
single proglottides bears on the question of the relationship of
the perfectly segmented forms to the less fully segmented.
124 Taenia saginata: a specimen 128 mm. long, wanting the
head, without any division into segments. The longitudinal
vessels were seen, but no transverse vessels were discovered. On
the margins were numerous genital openings, of which 41 were
counted, each leading from a genital organ. There was no regular
lateral alternation between the genital papillae, but they were
disposed without uniformity of pattern, and several were closely
approximated to each other. In no part was there any trace of
division into proglottides. From the characters of the genital
openings and from the number and size of the calcareous bodies
together with other histological details, the specimen was deter-
mined without much doubt as Taenia saginata. Grobbex, C,
Verh. zool.-bot. Ges. Wien, 1887, Bd. xxxvu., p. 679, fig.

Such repetition of the generative openings in single segments
is very common, especially in Tcenia saginata, and indeed examples
of it may be seen in most chains of segments. Usually such
repetition is confined to one segment and is not striking. Five
generative papillae have been seen by L. in one segment, and
Colin [ref. not found, W. B.] described 25 — 30 genital pores in
an unsegmented piece measuring 15 cm. L, p. 571.

125. Repetitions are not confined to the generative openings, but
the generative organs themselves are also thus abnormally re-
peated. In cases in which several sets of generative organs occur
in the same segment it is found that those near the middle of
the segment are the least developed. In these cases, though
the different organs frequently cross each other, Leuckarl Pound
no anastomoses between them, but the number of distinct sets
of generative organs was the same as the number of pores.

It was not found that the length of the segments increased
in the same ratio as the number of the pores they contain. I- 1 >r
example, a segment with two pores measured IS mm. in Length

170 MERISTIC VARIATION. [parti.

[instead of about 20 mm.), and one with five pores measured
28 mm. (instead of 50 mm.). L., p. 571.

120. T.-rnia. < [noted by Leuckart from ELelueb of a Tan i a having generative

on the *ur/ace of the Begments. Leuckart himself has never seen
:ui example of this variation. [Original reference not found] L., p. 570, Note.

127. Taenia solium and T. saginata. Specimens are known
having two generative pores opposite each other at the same level.
In such cases each l<a«ls to ;i male and a female duct with cirrus-
Bac and receptaculum seminis; but the organs for preparing the
a are aormal in construction, as the two vaginae lead to a
ommon uterus and shell-gland. Two cases only have been seen
by Leuckakt and he cites another from Werner. L., pp. 529

and ">7 I .

12s. TaDnia solium in which the pores are normally alternating,
may be found with symmetrically developed pores; and on the
contrary, T. elliptica in which they are normally symmetrical,
may occur with an asymmetrical arrangement. L., pp. 353 and
529.

[29 T. saginata: in a chain of about 6'5 metres in length, and

containing some (150 joints, there was found a single, heart-
Bhaped, supernumerary joint like those described; a single joint
was found with two genital pores, one being on each lateral border
about the same level.
The largest number of consecutive joints having the genital
pores on the same side was six. Tuckermax, F., Zool. Anz., xi.,
L888, p. (.»4.

[30 Taenia coenurus. Specimen observed by Leuckart in which
the last s or 10 segments shewed a transposition of the generative
organs, those which usually lie at the distal end being placed
at the proximal. This change of position was especially seen in
the case of organs engaged in the preparation of the ova. The
proximal proglottides of this individual were normal. The trans-
ition segment between these two regions contained two simple
vesiculae Beminales and two marginal papillae which were on
opposite Bides; but in spite of the resemblance of these structures
to genital pores, neither opening, nor cirrus, nor vasa deferentia
could be distinguished. L., p. 504.

131. A.mongst chains of normal proglottides it is not rare to find
a segment containing male organs only. L., p. 504.

Speaking generally, slight abnormalities are far more common
than great ones. Nearly every specimen of Tapeworm has in-
dividual peculiarities, and these generally repeat themselves in
the same chain of proglottides. This repetition of the same
abnormality in different parts of the chain is also the rule for
the greater abnormalities also. L.. pp. 529, 572 and 573.

CHAPTER VII.

linear series — continued.

BRANCHIAL OPENINGS OF CHORDATA AND STRUCTURES IN

CONNEXION WITH THEM.

Under the general heading of Variation of branchial openings
facts will be given relating to the following subjects.

I. Variation in the patterns formed by the bars, vessels and
stigmata of the branchial sac in Ascidians.

II. Variation in the number of gill-sacs in Cyclostomi.

III. Abnormal openings in the cervical region of Mammals,
known as " cervical fistula3," and external appendages called " cer-
vical auricles," or " supernumerary ears," present sometimes in
connexion with such openings.

With reference to the two first subjects the evidence is only
fragmentary, but the instances recorded seem to be of sufficient
consequence to warrant their introduction in illustration especially
of the magnitude and definiteness of Variation.

Variations affecting the opercular opening in Amphibia are mentioned in
connexion with Bilateral Series.

I. Ascidians.

Transverse vessels of Branchial Sac.

132. Ascidia scabra. Branchial sac in one specimen shewing abnormal
and irregular structure owing to branching of transverse vessels. The
resulting appearance is entirely peculiar. Herdmax, W. A., J. Linn.
Soc. (Zool.), 1881, xv., p. 284, PI. xvii., fig. 3; also p. 330.

133. Ascidia virginea (O. F. Miiller): a case of great irregularity
exactly similar to the above. Ibid., p. 330.

134. Ctenicella lanceplani. Branchial sac may present characters due
to variations in disposition of transverse vessels etc., which assume three
distinct patterns or marked varieties. Lacaze-Duthieks, Arch, Zool.
Exp., S. 1, Vol. vi., p. 619, Vol. xxxiii., rigs. 9 — 11.

172 MKIMSTIO VARIATION. [part i.

'13"). Ascidia plebeia (Alder): branchial sac has very characteristic
appearance and Lb very constant in the size of meshes, papillae &c.
One point La liable to variation: as a rule the transverse vessels are of
the same calibre, but in several specimens every fourth vessel is much
wider than the intervening three. Herdmax, p. 331.

Stiqmata and Meshes.

136. Ciona intestinalis : meshes vary but according to no apparent
method: 5 Btigmata in ;i mesb normal; 4 and G met with frequently;
10 the utmost seen. Herdman, p. 332.

1;>>7. Ascidia aspersa. In typical specimens, transverse vessels all same
size, the meshes being square and undivided, but individuals occur in
which many (not all) of these square meshes are divided by delicate
transverse vessels into pairs of oblong areas. Herdmax, p. 332.

L38. Styela grossularia. The genus Styela is characterized by the
presence of branchial folds, normally four on each side, but in this
3pecies the folds are almost obsolete, being entirely wanting on the
left side and reduced to a single slight inward bulging on the right
side, bearing internal longitudinal bars. This fold is separated from
the dorsal lamina by a broad space without internal longitudinal bars.
A similar wide space is present on the left side of the dorsal lamina,
and two others on the vertebral edcje of the sac, one on each side of the
endostyle. These spaces vary in size in individuals. They commonly
contain 1G stigmata, but numbers down to 12 were frequent and in one
case 10 only were present: only once more than 16 observed, and in
that case tliere were 28. Number of internal longitudinal bars on fold
varies from 6 to 9, generally 8 or 9. Herdmax, p. 330.

Id considering the significance of these cases with reference to
the origin of Species it is to be remembered that the characters of
the branchial sac, the sizes of the transverse vessels, shape of
meshes and the number of stigmata they contain are held to be of
the first importance for the classification of Ascidians; but Herd-
man finds that while they are highly characteristic in some species
they are qoI so in others1.

II. Cyclostomi.

L39. Myxine glutinosa. In this genus there are normally six
pairs of branchial pouches. I am indebted to Professor Weldon
for an account of a specimen dissected by him in which there were
seven pairs of these pouches. On the left side all the seven
pouches were distinct and separate, each having a separate open-

1 The olfactory tubercle in Ascidians may have a different form and position in
different individuals of the same species, but the range of variation changes
according to the species. Molgula was found to be the most constant, Ascidia
virginea and A. plebeia the most variable forms. Herdman, Pwc. R. Phys. Soc.
Edin., vi., p. 267, figs.; also id., Proe. Lit. Phil. Soc. Liverpool, xxxvm. p. 313,
Pis. i. and ii. Variation respecting the atrial pore will be considered in connexion
with Bilateral Repetition.

CHAP. VII.]

CYCLOSTOMT.

173

ing from the oesophagus and a separate aortic arch supplying it.
On the right side the sixth and seventh pouches were practically

*

r D asu

Fig. 27- Myxine glutinosa ; specimen having seven pairs of branchial sac-.
Diagram shewing branchial sacs, heart and aortic arches from the dorsal surface.
On the right side the sixth and seventh branchial sacs were partially confluent.

D. oes., ductus cesopJiageus.

(From a drawing kindly lent by Prof. Weldon.)

confluent though each had a separate oesophageal opening and a
separate arch from the aorta. In the drawing, for which I am also
indebted to Professor Weldon, the oesophageal openings are not
shewn.
40. Bdellostoma. In this genus the number of branchial sacs is
variable, different numbers being found in different species and
individual variation also occurring.

The generic name Heptatrema was originally given by Dum£ril
from the presence of seven gill-sacs. In 1834 Joh. MtJLLER, finding
that this character is not constant proposed the name Bdellostoma.
Of three Cape specimens examined by him one had seven gill-sacs
on each side, one had six on each side, and one had six on the right
side and seven on the left. To these he gave the names B. hepta-
trema, B. hexatrema and B. heterotrema respectively (Abh. k. Ah
Wiss. Berlin, 1834, pp. 66, 67 and 79, Taf. VII.). Further observa-
tion has shewn that the number of gill-sacs in the Cape Bdello-
stoma is liable to individual variation, some specimens having six
while others have seven. The name B. cirrhatum (GtJNTHER, Gat.
Brit Mus., viii. 1870, p. 511) includes these and the New Zealand
specimens. As to the relative frequency of specimens with six or
seven pairs or with an asymmetrical arrangement I have no in-
formation. A collection lately brought from the Cape by Sedgwick
includes one specimen with six pairs and several with seven pairs.

174 MEKISTIC VARIATION. [part i.

141. B. polytrema : single specimen from Chili, badly preserved
but apparently having fourteen pairs of gill-openings. GuNTHEJt
I. c, p. 512.

Specimen having 14 gill-openings on left side and 13 on right.
Sciinkii.ki:. A., Arch. f. iWaturg., xnvi. 1S80, p. 115 (cp. Putnam,
Proc. Bost X. 11. &, xvi. L873, p. 1G0).

/;. bischoffii: single specimen, 10 gill-openings on each side.
ibid.

Ammoccetes : having eighl branchial openings on each side instead
of Beven, the normal number. The shape of the mouth of this specimen
was also abnormal, being described as somewhat square. [No satis-
factory description.] Eowabo, Thomas, Zoologist, xvi., p. 60D7.

142. In connexion with individual Variation in the number of gill-
sacs in Myxinoids it should be borne in mind that in Petro-
myzon there are normally seven pairs of gill-sacs. The case of the
Notidanidse may also be mentioned in this connexion. Among
Selachians the Notidanidse are peculiar in having a number of gill-
slits other than rive, and of them liexanchits has six pairs, while
Heptanchus has seven1.

III. Cervical Fistula and Supernumerary Auricles ix
Mammals.

Though the evidence of this subject is well known and has
often been collected, it may be convenient to give here some
abstract of the facts in so far as the phenomena of Variation are
illustrated by them. Since cervical fistula? have been believed to
result from the persistence of the embryonic branchial clefts, they
may properly be considered in relation to the general question of
Variation in the number of gill-slits, while the development of
external appendages, perhaps serially homologous with the external
ears, directly concerns the subject of Meristic Variation.
Man. The subject has been studied by many observers, espe-
cially by Aschersox2, and by Heusixger3, who brought together
and abstracted 4(i cases, being all that had been described in Man
up to LS(j4. G. Fischer4 gives a full list of the literature of the
subject up to 1870, with an analysis of 65 cases. A further paper
by Heusixger5 contains a general account of these structures as
they are found in Man and in the domestic animals. Additional
cases, together with a general discussion of the subject, especially
in relation to fistula? on the external ears, were given by Sir James

1 Balanoglossus. In five species with which I am acquainted, the number
of pill-bars and slits varies in proportion to the size of the body, and as it is not
unlikely that these animals continue to grow throughout life, it is probable that the
number of branchiae is always increasing by formation of new gill-slits at the
posterior end of the branchial region. The same is probably true of Amphioxus.

2 Ascherson, BefistulU colli congenitis, Berlin, 1832.

3 Heusinger, Anh. f. Path. Anat. u. Phys., 1864, xxix.

4 Fischer, G., Dent. Ztsch.f. Chirurg., 1873.
8 Heusinger, Deut. Ztsch. f. Thierm., 1878.

*

chap, vil] CERVICAL FISTULA. 175

Paget1 in 1878. Lastly, the whole evidence as to cervical fistulas
and the structures associated with them has been fully collected
up to 1889 and tabulated by Kostanecki and Mielecki-, who
also discuss in detail the relations of these abnormalities to the
facts of development. The following account is taken from these
sources. For figures the reader is referred to the original memoirs.

143. Cervical fistuke are generally known as orifices placed in the region
of the neck, leading into a sinus of greater or less extent, varying in
size from a mere pit to a duct some inches in length. In the greater
number of cases the sinus ends blindly, but in about a third of recorded
cases (K. and M.) it passes inwards to open into the pharynx, forming
thus a communication between the pharyngeal cavity and the exterior.
Such passages are spoken of as complete cervical fistulas, those which
have an external but no internal opening being external incomplete
fistuke. Besides these there are cases of diverticula from the pharynx
or oesophagus which do not reach the exterior, and these are known as
internal incomplete fistula?.

Cervical fistuke are more commonly present on one side only, but
in a good many cases they have occurred on both sides. According to
Fischer they are more common on the right side than on the left.
The following statistics are given by him. 65 persons had 79 fistuke :
51 unilateral, 14 bilateral: 20 complete, 53 without an opening to the
pharynx: of the unilateral cases 33 were on the right and 13 on the
left : 34 in males, 30 in females. There was evidence of heredity in
21 cases.

The external opening is very small and may either be on the
surface of the skin or elevated on a minute papilla. Sometimes it is
covered by a small flap of skin as with a valve, in other cases it is
placed as a fissure between two lips. The positions in which the ex-
ternal openings of cervical fistula? are found are very variable, but in
the great majority of cases the opening is close to the middle line
in the neighbourhood of the sterno-clavicular articulation, generally
from a few lines to an inch above it, on either the inner or the outer
border of the sterno-cleido-mastoid muscle. In rarer cases the external
opening is placed at the level of the middle of the cricoid cartilage, and
is sometimes just behind the angle of the jaw. These positions are not
however at all precisely maintained, but vary a good deal in different
cases. When the external opening is in the higher situation and the
fistula is complete, a sound may then be passed into the pharynx, but
when the external opening is low, the duct when present passes
upwards covered by skin only, in a straight line so far as the upper
limit of the larynx, at which point it turns at a sharp angle upwards
and inwards. For this reason it is not possible in such cases to follow
the course to the pharynx by means of a sound, but in some of them
the presence of an internal opening has been proved by the injection of
fluids having colour or taste. The position of the internal openings is
also variable, and from the nature of the case has been accurately

1 Paget, Sir J., Trans. Med. Ghir. Soc, lxi., 1878.

- Von Kostanecki und Yon Mielecki, Arch. f. path. Anat. u. Phys., cxx.
and csxi.

176 MEIilSTIC VARIATION. [part i.

determined in comparatively few instances. In a case dissected by
Neuhopek1 there was a fistula on each side, the external opening
of the right was \ in. from the middle line and 7 lines above the
clavicle, that of the left was 3 — 4 lines higher and further from the
middle line. The right internal opening was on the posterior border of
the pharyngo-palatine muscle, behind the cornu of the hyoid near the
tonsil, tin- left internal opening being rather higher than the right.
Internal openings ol such fistulas have also been seen on the edge of
the areas pharyngo-palatinus, also in the neighbourhood of the root of
the tongue. Seidel9 gives a case in which there were two fistulas, the
one on the right side in the upper position, and the other in the middle
line at about the same level, but whether either of these communicated
with the pharynx could not be made out. The twin-brother of the
-ante infant had a single minute fistula.

The ducts of cervical fistulas are usually of greater calibre than the
external openings but they are rarely wider than a fine quill. The
walls are tough and the lining epithelium is sometimes flat and some-
times ciliated. The degree to which the walls are sensitive differs in
different cases. The external opening is described in several instances
as having a reddish colour. In three cases of the presence of branchial
fistulas in female patients, it is recorded that the external openings
became inflamed during the menstrual periods.

From the point of view of the naturalist the chief interest of
cervical fistula? arises in connexion with the question of their mor-
phology. Since the time of Ascherson the view has been commonly
accepted that these structures arise by persistence of embryonic gill-
clefts, and some of the recent writers 3 on the subject have gone so far
as to apportion the various forms of cervical fistula? among the several
gill-clefts from the first to the fourth, according to the situations of
the external openings, giving diagrams shewing the regions occupied by
each. As Kostanecki and Mielecki point out, this apportionment is
quite arbitrary; for in the development of the neck the external in-
vaginations for all the clefts behind the hyoid arch become included in
the sinus cervicalis of Rabl (sinus pra?cervicalis of His), which is
eventually closed by the growth of the opercular process from the
hyoid arch. The external opening of a cervical fistula may thus
represent a part of the sinus cervicalis still left open, but it cannot on
the ground of its position be referred to any gill-cleft in particular.
►Such reference could only be properly made on the ground of the
position of the internal opening and the course of the duct in relation
to structures whose relation to the visceral clefts is known. More-
over owing to the way in wrhich the 3rd and 4th clefts are shifted
inwards by the formation of the sinus cervicalis, Kostanecki and
.Mielecki consider that they are practically excluded. The same
authors after an analysis of the cases in which the position of the
internal opening has been properly ascertained, come to the conclusion
that in all these it falls within the region of the 2nd visceral sac

1 Neuhofer, M., Ueb. d. angeb. Hatefistel, Inaug. Diss., Munich, 1847.

2 Seidel, J., Defist. colli cungen., Inaug. Diss., Breslau, 1863.

3 Sutton, J.Bland, Lancet, 1888, p. 308; Cusset, Et ude sur Vappareil branchial,
&c, Paris, 1887.

chap, vii.] CERVICAL AURICLES. 177

(hyo-branchial). Besides they point out that the evidence in the few
cases in which the course of the duct has been traced, shewed that it
passed between the external and internal carotids. In their judgment,
therefore, cervical listuhe are all to be referred to the second (hyo-bran-
chial) cleft.

Next it is to be remembered that according to many observers
(especially His) there is at no period a complete connexion between the
outer gill-clefts and the evagination from the pharynx or branchial
sacs, but the membrane separating these chambers is stated by them
never to be broken down. If this account is accepted, it is, as
Kostanecki and Mielecki have said, necessary to suppose that in the
case of any complete cervical fistula a communication between the
exterior and the pharynx has arisen by some abnormal occurrence.
This is illustrated by reference to the normal condition of the first or
hyo-mandibular cleft. Here the auditory meatus represents an external
incomplete fistula, and the Eustachian tube an internal incomplete
fistula, the two being separated by the tympanic membrane. In a
single case given by Virchow1 a complete passage existed congenitally
in this position, together with great abnormality in position and forin
of the external ear.

From the evidence it may thus on the whole be concluded that
incomplete external fistula? result from imperfect closure of the sinus
cervicalis, and that incomplete internal fistula? may arise by persistence
of one of the branchial sacs, but it is doubtful whether many cases of
the latter properly belong to the category of branchial fistula? at all.

Supernumerary A iwicles.

144. Abnormal appendages attached to the neck have been described by
several observers, and by those who have discussed the subject of
cervical fistula? some account of these appendages is generally given.
In the neighbourhood of the external ears, especially near the anti-
tragus, such structures having the form of small warts or flaps of skin
are not very uncommon. Their presence is generally associated with
deformity of the external ear, and often with what are known as
"aural fistula?2." In the region of the neck, supernumerary auricles

1 Virchow, Arch. path. Anat. u. Phys.. 1865, xxxn.

2 Aural fistulae are spoken of by many writers as being of the same nature as
cervical or branchial fistulae. Tbey are blind ducts or pits, opening on some part
of the external ear and are nearly always associated with other abnormalities either
in the form of the ear or defective hearing, <fcc. (Schmitz, De fist, colli congen.,
Inaug. Diss., Halle, 1873 [not seen, W. B.]; Urbaxtschitsch, MonaUch. f. Ohrenh.,
1877, transl. Edin. Med. Jour., xxiii. 1878, p. 690.) They may be either unilateral
or on both sides of the body. Sir James Paget (Trans. Med. Ghir. Soc, lxi., p. 41)
described the occurrence of such fistulae in the ears of several members of a family,
many of whom were affected with deafness. The supposed connexion of ti
fistulae with cervical fistulae was in this case suggested by the fact that several cases
of actual cervical fistula occurred in the same family, several of its members having
both cervical and aural fistulae. From the evidence of the not infrequent association
of the two kinds of malformation most writers (Paget, Urbaxtschitsch. &o.) con-
sider that the aural fistulae must be bianchial in origin and may be taken to
represent the first (hyo-mandibular) cleft.

Kostanecki and Mielecki [1. c), following His, point out that Bince in
no case has an aural fistula ever been known to communicate with the auditory
meatus or tympanic cavity, this belief is unsupported; and in addition, that from
the mode of development of the external ear from a number of tubercles, it is

B. 12

178

M ERISTIC VARIATION.

[part I.

are much rarer, but in several instances they have attained a considerable
development. Of this class of variation the following well-known case
is one of the most remarkable.

145. A healthy female infant was brought to Guy's Hospital in 1851 on account of
two projecting growths about the middle of the lateral cervical regions. The
growths were not removed until February 1858, when they were found to have
increased slightly. Tiny were situated over about the centre of the sterno-cleido-
mastoid muscles. To the touch they resembled the tissue of the lobe of the auricle,
and they contained within them a firm resisting nucleus like the cartilage of the
same organ. They were also covered with peculiarly delicate, soft, downy hairs,
like the lobe of the ear. They were excised without difficulty. Each was supplied
with a small artery. They appeared to be intimately associated with the fibres of
the platysma myoides, not dipping deeper than this structure, and to be entirely
cutaneous appendages. (Fig. 28.)

Fig. 28. Child having a well-developed supernumerary auricle on each side of
the neck (from Berkett).

A vertical section was made in the long axis of each growth; and the tissues of
the lobe and of the fibro-cartilage of the auricle were clearly distinguished. The
shape of the fibro-cartilage resembled more or less closely in parts, the outline of
the proper auricle, and its tissues were the same. Jjirkett, J., Trans. Path. Soc.
Loud., ix., 1858, p. 448, fig.1.

sufficient to suppose that aural fistula? arise by the imperfect union of these tubercles.
The fact, however, that these various defects in development of the branchial
apparatus and its derivatives are frequently associated together is well established.
As indicating the frequency of association with disease of the ear, Urbantschitsch
mentions that in 2000 aural cases, 12 instances of aural fistula? were seen. The
same author gives a remarkable case of the occurrence of aural fistula on the right
side only in many members of the same family with other important particulars (/. c).
1 In Lancet, 1858, n. p. 309 (quoting Harvey), and in a paper by Virchow
(quoting Wilde), Arch. path. Anat. Phys.t 1804, xxx. p. 225, reference is made to a
case of Cassebohm, Tract, sextus, de aure momtri hum., Norimb., 1084, pp. 30
et scqq., describing a child with "four ears." On referring to the original however
it appears that this was merely a double monster, having two incomplete heads,
and thus bears no analogy with the present examples.

chap, vii.] CERVICAL AURICLES. 179

Several cases analogous to the above, though differing in the extent
of the development, are on record '. Kostanecki and MlELECKl (I. c),
who give references to the literature of the subject, consider together
with Virciiow and others, that there is no doubt that these super-
numerary auricles may properly be regarded as "heterotopic" partial
repetitions of the external ears. According to a view which has been
held by the majority of writers- on the subject, and which is in part
alternative to that given above, it is suggested that the cartilages
contained in these appendages are in reality parts of one or other of the
usually undeveloped branchial arches behind the hyoid. As against
this suggestion it is to be remembered that in the subsequent develop-
ment of the neck these arches are pushed in far from the surface, whereas
the cartilages in question are always superficial. The usual histology
of these bodies is in favour of the view that they are repetitions of the
ear-cartilages, but on the other hand a specimen of cervical auricle
in Mus. Coll. Surg. (No. 373, c) contains not only cartilage but also
a small bone of convplex form. But whether or not any part of such
cervical auricles truly represents any part of the gill-bars, it is clear
that these external projections having the structure of the ear, con-
sidered from the point of view of Variation must be regarded as partial
repetitions of the ears, and there is a considerable probability that they
stand to the sinus cervicalis in a relation similar to that which the
normal external ear bears to the hyo-mandibular cleft, being according
to the terminology here proposed, examples of repetition by forward
Homceosis.

In this connexion the question of correlation between supernume-
rary auricles of the neck and cervical fistuhe is especially important.
If it is true that such auricles are repetitions of the ears, it might, on
the analogy of other cases of repetition, be expected that they would
usually be found bounding the external openings of tistuhe. As a
matter of fact they have several times been found in such a position, but
the connexion between these two variations is by no means a close one,
for cervical fistula? are not as a rule accompanied by cervical auricles,
nor are cervical auricles generally associated with cervical fistula', such
collocation being mi the whole exceptional. It should also be men-
tioned that in a few cases small cartilaginous or bony structures have
been found imbedded in the neighbourhood of cervical fistula1, but that
similar structures have also occurred independently of any fistula".

In many domestic animals both cervical fistula' and auricles art-
well known and have been described by Heusinger3 from whom the
following account is chiefly taken.
146. Pig- Cervical auricles are not uncommon and have been referred

1 A figure is given by Sutton, J. B., in III. Med. Xnr.<, 1880 (repeated in
"Evolution and Disease," by the same author 1890, p. 83), representing a large
supernumerary auricle on the right side of the neck of a girl. The structure
is represented as helicoid in form, closely resembling the normal ear. It i<
unfortunate that no description of this specimen is given: in the absence of such
•description this quite unprecedented case cannot be accepted without reserve.

2 Dermoids of many kinds occurring in the cervical region of Man and other
animals are by many writers considered to arise by modification of tissues occluded
from the walls of the branchial clefts.

3 Heusinger, Deut. Arch. f. Thiermed., 1876, n.

i — — *j

180 MERISTK VARIATION. [part I.

to as distinguishing particular local breeds. They are generally paired
structures. The following case is exceptional in the fact that the
auricle was present on the left only, and that it was associated with an
opening possibly of a cervical fistula. A pig having a single appendage
about 7 t-ni. long attached under the lower jaw on the left, is described
by Eudes-Deslono(H ami's !. It contained a stalk of cartilage stated
to have resembled the cartilage of the ear. To this on either side was
attached a small muscle. Unfortunately the appendage had been cut
off close to the skin. A small opening (pertuis) was present on the
skin near the appendage, and from this opening a small brush or tuft of
bristles protruded.

Fistula? in the neck of swine are well known as giving rise to
a tlisease called weisse Borste in Germany (Fr. la Soie or poil pique)
from the fact that certain white bristles are found at the opening of the
duct. In the popular fancy it is supposed that the bristles themselves
In. re the perforation, but according to Zundel" they are congenital and
often bilateral. Heusinger agrees with Ziindel in regarding such open-
ings as branchial fistula?.

147. Sheep and Goats. Cervical fistula unknown, but appendages on the neck
' common. The Bheep of the "Wilster marshes are described3 as having the neck bare
of wool, and an appearance as of a fur-collar. Above the collar and below the
pharynx they have a pair of appendages about the size of an acorn. Such ap-
pendages are said to be not uncommon in Merinos4. Among the Kalmuck and
Kirghiz sheep and goats such auricles are said by Pallas5 to be common. In many
foreign races of goats these auricles seem to be a constant character. In position
they may vary from the angle of the jaw to the middle of the neck. The length is
usually about 3 in. but they are recorded as reaching 15 cm. Figures of goats
having such auricles are given by Sutton6. The anatomy of one of these bodies is
described by Goubaux7, and it is mentioned that a plate of cartilage was found in the
interior. A similar cartilage was found by Stewart8 together with striped muscular
fibre. Goubaux gives a case of two she-goats on a farm, one having cervical
appendages, the other having none. Each gave birth to a pair of kids at the same
time. Each pair was a male and female, and in the one the male only had the
appendages and in the other the female only. The characters of the father of these
kids were not known.

Ox. Neither cervical fistula} nor auricles known.

]4tsj Horse. Cervical auricles unknown. Fistuhe (in the position considered by
Heusinger to indicate the first branchial cleft) are common and are recognized by
their action in soiling the hair near the external opening.

Recapitulation. The evidence as a whole goes to shew that
structures, sometimes of large size, having several essential features
of the external ear, that may in fact be fairly spoken of as repeti-
tions of the ear. may by Homoeotic Variation appear on the neck of
Man and other animals : further, that these repetitions have been
known to occur at the openings of cervical fistulas, suggesting a
comparison with the relation of the external ear to the hyo-mandi-
bular cleft, but that such a relation to cervical fistulae is exceptional.

1 .1/////. Soc. Linn, de Norm., 1842, vn. p. 41, PL iv. fig. 3.
- Dent. Arch.f. Thierm., i. 1875, p. 175.

3 Viborg, Samtl. Vet.-Afhandl., i. p. 14S [Heusinger].

4 Schmalz, Thierveredlungskunde, p. 223 [Heusinger].

5 Spicileg. Z<><>1.. xi. p. 172 (two figures).

6 Sutton, J. 13., Evolution and Disease, pp. 84 and 85.

7 Goubaux, Bee. de Med. Veter., Ser. 3, ix. p. 335.

8 Figured by Sutton, I.e., p. 87.

CHAPTER VIII
linear series — continued. MAMMAE.

Some of the phenomena of Meristic Variation are well seen in
the case of mammae1, and especially in the modes by which increase
in the number of these organs takes place.

The facts regarding these variations in Man have so often been
collected that it is scarcely necessary to detail them again. For
our present purposes it will be sufficient to give a recapitulation
of the chief observations in so far as they illustrate the pheno-
mena of Variation.

The most important collections of the evidence on this subject
are those of Puech2, Leichtexstern3, and Williams4, from whose
papers references to all cases recorded up to 1890 maybe obtained.
Besides these, Bruce 5 has given a valuable account of a consider-
able number of new cases together with measurements and statis-
tical particulars. These accounts contain almost all that is known
on the subject but additional reference will be made to original
authorities in a few special cases.

In Man supernumerary mammae or nipples nearly always occur
on the front of the trunk, being usually placed at points on two
imaginary lines drawn from the normal nipples, converging in the
direction of the pubes. These lines may thus be spoken of as the
:t Mammary lines." It is with reference to supernumerary ma mm*
occurring on these lines that the subject of mammary variations is
chiefly important to the study of Meristic Variation. In addition
to these, however, there are a few well authenticated examples .if
mammae placed in parts of the body other than the mammary Lines
and of these some mention must be made hereafter.

1 It will be understood that facts as to variations consisting in absence of
mammae or nipples and other such changes do not come within the scope of this
volume, but belong rather to the province of Substantive Variation.

2 Puech, Lea Mamelles et leurs anomalies, Paris, 187<>.

3 Leichtensterx, Virch. Arch.f.patk. Anat. u. Pin/*., 1878, i.xxin. p. 222. This
collection was apparently made independently from that of Puech.

4 Williams, W. Roger, Jour. Anat. Phys., 1891, xxv. p. 22-").

5 Bhuce, J. Mitchell, Jour. Anat. Plnja., lsTK, xin. p. 425.

182 MERIST1C VARIATION. [part i.

In the great majority of cases (over 90 per cent., Leichten-
STERN l) of mammae placed on the mammary lines, the supernumer-
ary structures are below the normal ones, being then as a rule in-
ternal to them, while those found above the normal mammae are
less common and are external to the normal mammae. The di-
stance separating the normal from the supernumerary mammae
(lifters greatly in different cases, and most conditions have been
- 11 intermediate between a stage in which the nipple is bifid, and
that in which completely separate supernumerary mammae are pre-
sented. It is of consequence to observe that there appears to be
no case in which a supernumerary mamma is so large as the nor-
mal mamma of the same individual.

The degree to which supernumerary structures of this nature
are developed is very various. They may be fully formed mammae
with nipples, in the female capable of function ; while in other
cases, on the contrary, they may either consist of nipples only,
having no distinguished glandular tissue of mammary character in
connexion with them, or they may be tumours of mammary cha-
racter without nipples or even definite ducts. Between these
>Mveral conditions there is no sharp distinction. It appears there-
fore that there are two rudimentary or imperfect conditions possi-
ble : either supernumerary nipples without recognizable mammary
glands, shading off into small warty elevations of uncertain charac-
ter, and on the other hand redundant portions of mammary gland
without nipples. The latter may be partially connected writh the
normal mammae or quite separate from them. All these states of
imperfection are much more common than the complete super-
numerary mammae.

Fully formed supernumerary mammae have been found above
the normal mammae and also below them, the latter being the
more frequent position. For those found on the mammary lines
the axilla is the highest position and the upper part of the abdo-
minal wall the lowest. Of the rudimentary forms, the mammary
tumours without nipples occur usually if not always above and ex-
ternal to the normal mammae, being generally in or near the axilla.
The supernumerary nipples however are in the great majority of
cases below and internal to the normal ones.

Small supernumerary nipples are quite common in Man, but
the statistics of different observers £ive various results. Bruce
found in 2311 females 14 cases ('605 per cent.), and in 1645 males
47 cases (2"857 per cent.). These persons were patients at the
Brompton Hospital for Consumption and were not specially ex-
amined with a view to this inquiry. Among 315 such persons
examined for the purposes of these statistics, 24 cases were seen
(7'6 per cent.), 1 0 being male and 5 female. In 8 cases two extra
nipples were present, and one doubtful case of three extra nipples

1 Not including mammary tumours without nipples in the axilke.

CHAP. VIII.]

MAMMAE.

183

was seen. Bruce regards 7*6 as for various reasons rather too hio-h

o o

a proportion. In a recent paper Bardelebex however states that
among 2736 recruits examined with regard to supernumerary nip-
ples, 637 cases (23'3 per cent.) were seen, 219 being on right side
248 on left side, and 170 on both sides. The discrepancy between
these statistics no doubt arises through want of agreement as to
the inclusion of cases in which the extra nipples are very rudimen-
tary.

It seems to be clearly shewn that the abnormality is commoner
in men than in women, and there is some evidence that it is more
frequent on the left side than on the right (Bruce, Leichtex-
sterx and Bardelebex). It is also well established that super-
numerary nipples are much more commonly present as single than
as paired structures, and that when paired they are by no means
always at the same level on the two sides. Cases of the presence
of supernumerary mamma? as paired structures symmetrically
placed are nevertheless sufficiently numerous. Organs of this na-
ture may also occur simultaneously on the same side of the bod}*
at different levels. For example in one of Leichtexsterx's cases,
a small secreting supernumerary mamma with a nipple was pre-
sent in the left axilla, while there was also another supernumerary
nipple on the lower border of the left breast. The greatest num-
ber of supernumerary nipples occurred in a case described by Neu-
GEBAUER1, represented in Fig. 29. In this patient there were on
each side three supernumerary nipples above the normal ones, and

Fig. 20. Diagram of a case of four pairs of supernumerary nipples in human
female. The normal breasts raised to shew the lowest pair. (After Nedgebaueb.)

1 Neugebaueb, F. L., Gentralb.f. Gyndk., 1886, p. 729.

184 MERISTIO VARIATION. [part i.

«»ne on each side below them. The latter were concealed by the
pendent breasts. When the child was being snckled milk oozed
from each of the uppermost or axillary nipples, but from the
remaining six supernumerary nipples milk could only be extracted
l>v pressure. The flowing of milk from supernumerary nipples
when the child is at the normal breasts, has often been observed.

A few references to cases exhibiting the several features above
mentioned may be of use.

149. Bifid nipple, the same on each breast [plane of division not
specified]. Duval, 1>" Mamelon et de son aureole, Paris 1861,

P-90.

150. Two nipples on the same areola, bilaterally symmetrical. The

two nipples stood in the mammary line defined above. Tiedemann,
Ztsck.f Physiol, v.. L833, p. 110, Taf. i. fig. 3.

151. Cases are given by Charcot and le Gendre, Gaz. vied, de
Paris, 1859, p. 773, in which an extra nipple was placed external
to the normal one on the same breast. In one of these the extra
nipple had no areola. Leichtenstern (p. 253) in quoting these
cases, speaks of them as instances of supernumerary nipples on
the same level as the normal ones, but this is not expressly stated
in the original account, which does not, as I think, exclude the
possibility that the supernumerary nipples were above and external
to the normal ones. Two functional nipples with separate areolae
on the left breast, which nevertheless was not larger than that of
the light side, ibid. The same authors mention another case in
which such a second nipple had no areola ; the mother of patient
stated to have been the same. See also SlNETY, Gaz. wed. de
Paris, 1887. p. 317 (full description and measurements). In this
ease the supernumerary nipple was placed below7 the normal one.

152. A case in which three nipples were placed on each breast is given
by PAULLINUS, Miscell. Curios., &c, 1687, Decur. ii. Ann. v.
Append, p. 40. The case is given on the authority of Prackel
and the three nipples are said to have been arranged in an equi-
lateral triangle, the normal being above at the apex, and the two
others at the same level below. The description and the figure
accompanying it do not however justify complete confidence in
this observation, and indeed the contributions of Paullinus to the
Miscellanea Curiosa contain so much of the marvellous that they
should not be accepted without hesitation. The same may be
said of the case of five nipples each having an areola quoted by
Percy and Laurent, Diet. Sci. med., xxxiv. p. 517, .9. v. " Multi-
mamme." The authority for this case is a letter of Hannseus to
Borrichius, dated 1675. I have not found any observation of this
class of abnormality later than the seventeenth century, but it is
of course quite possible that cases may occur in which the nipples
are distributed on the breast otherwise than along the mammary
lines.

CHAP. VIII.]

MAMMAE.

185

153. Supernumerary mamma with nipple in axilla, Leichtenstern,
p. 245, and others.

154. Supernumerary mamma above and external to the normal ones.
Numerous cases; see especially case of two bilaterally symmetrical
mammae in this position, Shannon, Dubl. Med. Jour., 1848, v. p.
26Q,Jig. [figure repeated by Ahlfeld, Williams &c.]; also similar
case, Quinquaud, Rev. photogr. des hop., 1870, p. 10.

155. Supernumerary mammae below and internal to normal ones:
numerous cases, see Leichtenstern, &c. In nearly all these the

Fig. 30. Supernumerary nipples and mammae of different sizes in human
female. (After Bruce.)

supernumerary organs are close to the normal mamma'. A few
examples of such structures on the upper part of the abdominal
wall are known, e.g., Tarnier in his edition of Cazeaux, Traite de
Vart des Accouchements, 1870, ed. 8, p. 86. In the male several
such cases are recorded, e.g., Bruce, J. Anat. Phys., XIII. 1879, p.
446, PL Examples of this kind in the female are shewn in Fig.
30 (after Bruce) and in the male in Fig. 31 (after Leichtenstern ).

156. Mammary tumours in the axilla are described by Champneys,
Med. Chir. Trans., 1886, lxix. p. 419, as of common occurrence in
lying-in women. These structures are of various sizes and without
any nipple, pore, or duct. The secretion was obtained by squeez-
ing the lump and oozed through the skin at the situations of the
sebaceous follicles. In this manner both colostrum and milk were
obtained, following each ether as in the normal mammae. Similar
observations in single cases have been made by many writers.

157. Redundant mammary tissue of this kind connected with, and
thus forming an axillary extension of the normal mammae, CAME-
RON, Jour, Anat. Phys., 1879, XIII. p. 149; also Notta, Arch, de
Tocologie, 1882, p. 108.

186

MERISTIC VARIATION".

[part I.

*1 K

158. Two pairs of supernumerary mamma- below the normal ones,
DE MORTILLET, Bull. Soc. d'Anthrop., L883, Ser. 3, vi. p. 458. An

Fig. 31. Supernumerary mammae in the male, symmetrical and asymmetrical.
(After Leichtenstern.)

important case of a man having two pairs of supernumerary
mammae on the mammary lines. There was a gradual diminution
in size from the highest to the lowest, the latter being a little
above the level of the umbilicus. Each pair was at the same level.
159. Four pairs of supernumerary nipples (ten in all) are recorded
only in Neugebaxter's patient, already mentioned. Three of the
supernumerary pairs were above the normal ones, and the other
pair below them. As seen in Fig. 29 the nipples of each pair did
not stand in the case of each pair at precisely the same levels, and
between those of the lowest pair there was a considerable differ-
ence of level, that on the left side being at some, distance below
the normal breast, while that on the right side was on its lower
border.

In a few cases the supernumerary nipple is described as having
been perpendicularly below the normal one, and it is likely that
such cases must be looked on as exceptions to the general rule
that the mammary lines converge posteriorly; but it is not impos-
sible that even in some of them the supernumerary nipple might
have been found to be rather nearer the middle line if this point
had been specially inquired into.

The foregoing examples are given as selected illustrations of
the several facts, and for full lists of cases the reader is referred to
the works already mentioned.

ICO. Of supernumerary mammae placed in parts of the body other than
the mammary line some mention must be made, though those of them

chap, viii.] MAMMAE. 187

tliat are authentic have no close bearing on the subject of Meristic
Variation. There are firstly two often quoted cases1 in the Miscellanea
Curiosa in which mammae are said to have been present on the back,
but as has already been remarked, many of the stories told in this
collection are clearly fabulous, and this is especially true of the contri-
butions of Paullinus. Both these records are given at second hand and
the first case (Paullinus) is said to have been seen in 1564, more than a
hundred years before the date of the account. Helbig's accounts of things
seen by himself are generally trustworthy, but in this case lie is only
repeating what wTas told to him by a Polish noble about a woman seen
in Celebes. There are no modern cases on record. There is however
indisputable evidence of the presence of a mammary gland on the
thigh (especially Robert's case ; for references to several accounts
of this see Leichtenstern, p. 255); on the cheek, Bartii, Arch. f.
path. Anat. u. Phys., 188, p. 569; on the acromion, Klob, Ztsch. f.
K. K. Ges. d. Aerzte in Wien, 1858, p. 815; in the labium majus,
Hartung, Ueb.einen Fall von Mamma Accessoria, Inaug. Diss., Erlangen,
1875. In the two last cases the mammary nature of the gland was
proved by microscopic examination. In Earth's case of a mamma on
the cheek the microscopical investigation did not give a certain result
(q. v.).

As Leichtenstern shewed, the case of inguinal mamma, mentioned
by Darwin and others, really related to Robert's case of a femoral
mamma. In 1885, however, Blaxchard (Bull. Soc. d'Anthrop., 1885,
p. 230) stated that Testut had lately seen such a case and was about
to publish an account of it, but this has not yet appeared (1892).

Most writers on the subject have accepted cases of supernumerary
mamma placed anteriorly in the middle line. These are given by Percv
and Laurent, Diet. Sci. med., xxxiv., 1819, on the authority of several
different persons. One case was seen by themselves (p. 526), and in
it the third mamma stood below and between the other, forming a
triangle with them. In another case given on the authority of Goi;i:i:
there are said to have been a pair of extra mammae below the normal
ones, and a fifth between the supernumeraries. In view of the fact
that many paired organs may by Variation occur compounded in the
middle line, there is nothing incredible in these accounts, nevertheless
there is, so far as I know, no recent observation of such an occur-
rence in the case of mammse, and with the one exception (which is
very briefly described), the accounts given are at second hand". It is
moreover not clear that the words used llai(-tlr#*nHit et an milieu des
deux autres" do not mean simply below and between the other two.
The case contributed by Gorre is nevertheless given in great detail
and cannot lightly be set aside.

Before speaking of the bearing of these facts on morphological
conceptions it is necessary to refer to some of the phenomena of

1 Paullinus, Miscell. Curios., &c., Dec. ii., Ann. iv. 1686, p. 203, Appendix, giving
a case said to have been seen in 1564; also Otto Helbig, ibid., Dec. i., Ann. ix. and
x., pubd. 1693, p. 45(j.

2 Williams (p. 235) quotes Baktels, Arch. f. Anat, 1872, p. 306, as alluding to

such a case, but I do not think that the passage is meant to convey this meaning.

188

MERISTIC VARIATION.

[part I.

mammary Variation in other mammals. In connexion with the
case of Man it may be mentioned that supernumerary mamma
below and internal to the normal ones has been seen in Macacus
and in Cercopithecus patas, Sutton. J. B., Intern. Jour, of Med.
Sci., 1889, XCVII. pp. 2o2 and 253; in the Orang-utan, Owen,
Con/p. A nut., iii. p. 780. In many mammals the number of the
mammae is very inconstant even within the limits of species and
from the facts seen in such cases deductions may be drawn which
arc at once instructive as to the nature of mammarv Variation
and have an application to the morphology of Meristic Series in
general, of these I shall give examples taken from three species.

'161. The first is that of the cow's udder. Normally the cow has
four teats of about equal size. Not unfrequently there are six
teats, of which four are large and may be said in the usual parlance
t<» be the " normal " ones, and two are small and placed posteriorly
to the others. A case of this kind is shewn in Fig. 32, II. Commonly
these extra teats give no milk, but in many cases they have been
known to do so. Their size and position vary greatly; sometimes
they are placed near the other teats as shewn in the figure, but I
have seen them very high up, almost in the fold between the
udder and the thighs.

Very frequently, however, there is only one extra teat making
five in all, such an extra teat being so far as I know, always on

Fig. 32. Supernumerary teats in two heifers. I. The third teat is completely
separate on the left side, but on the right side is united with the second. (The
cleft between the two is incorrectly represented as a sharp line ; there was no such
sharp line of demarcation; the skin being very slightly depressed in this place.)
II. Teats of the third pair both completely separate.

CHAP. VIII.]

MAMMAE.

189

*162. one side of the udder. The sketch given in Fig. 32, I. was taken
from a heifer having an arrangement intermediate between the
condition with four teats and that with six. As the figure shews,
on the left side there were three complete teats but on the right
side the third teat was incompletely separated from the second.
This third teat was joined to the second for its whole length but
had a separate pore. The animal which belonged to the St John's
College Dairy Farm was unfortunately sold before the first calf
was born, so 1 had no opportunity of seeing whether milk was
given by both these teats. The significance of such a case will
afterwards appear.

In many mammals, such as the pig, rabbits, cats and dogs,
the mammae are distributed in two mammary lines along the
ventral surface. The number of the mamma? in such cases is noto-
riously variable, and in some respects this variation is interesting
and has a bearing on questions of the nature of Meristic Repetition.
If a number of such animals be examined it will be found that as
a rule there are the same number of glands on the two sides, and
that they are arranged in pairs, those of each pair standing at the
same level or nearly so. Nevertheless departures from this ar-
rangement are very frequent. Individuals are in the first place
commonlv found with a different number of mammae on the two
sides, and in such cases it is interesting to observe that together
wTith the difference in the number of mammas on the two sides

V

V

Fig. 33. Diagram of nipples in a male Bull-dog. On right side, four ; on left,
five ; the two anterior and two posterior being almost at the same levels.
umb. umbilicus. The dotted line shews the outline of the thorax.

190 MERISTIC VARIATION. [part i.

there is generally if aot always a disturbance in the paired arrange-
1G3. ment. A simple case of t his kind occurring in the dog is represented
in Fig. 33. The animal is a male bulldog lately in my possession.
On the right side there arc four nipples, while on the left there
are five. The most anterior on each side stand almost at the same
level on the thorax. The second on each side are almost at the
same distance below them, that on the left side being J in. higher.
Similarly the most posterior nipples stand on each side at almost
exactly the same level od the sheath of the penis, the total length
from the first to the last nipple on each side being practically the
same. On the left however there are two nipples placed between
the second and the last, but on the right there is only one. This
one nipple stands at a level not far from the middle between the
old and 4th of the other side, making as it were a complement to
or balance with them.
164. Thirty-five young pigs examined with regard to these questions
gave the following results. They belonged to five litters (30 pure-
bred Tarn worths ; 5 cross-bred, out of Berkshire sow, sire unknown).
These pigs were all quite young, about a fortnight old, and conse-
quently there was no displacement due to functional development
of the glands.

M.AMHLM.

Right. Left. Pigs.

A. 6 — 0 regular! v arranged in pairs 3

B. 7 — 7 ditto 10

C. 7 — 7 ditto 5th rudimentary 1

D. 8 — (S ditto 4th rudimentary 3

E. 7 — 8 all paired exc. 1. 4th rudimentary 2

F. 7 — 8 1. 4th rudimentary, 1. 3rd and 5th displaced... 1

I 1 . 7 — 8 rt. 2nd balances 1. 2nd and 3rd 1

H. 8 — 71. 2nd balances rt. 2nd and 3rd 1

I. 8 - — 7 1. 3rd balances rt. 3rd and 4th 1

K. 6-7 rt. 1st balances 1. 1st and 2nd 1

L. 6—7 l.-2nd rudimentary 1. 1st and 3rd displaced... 1

M. 6 — 7 all paired exc. 1. 4th rudimentary 1

X. 7 — 7 altogether irregular 4

O. 6 - - 6 ditto 2

P. 7 — 6 ditto 1

Q. 7 — 8 ditto 1

R. 8 — 7 ditto 1

Total 35

The animals in groups D and E, except one of the latter, be-
longed to the same litter. In them a small rudimentary nipple
stood between the 3rd and 5th, but the latter were not spaced out
for it, being no further apart than any of the others. The measure-

chap, viil] MA1DLE : COMMENT. 191

ments of the distances between the nipples on one side in one of
these cases were, in inches, 1^, 1, T%, ^, ji, ±£ , j* , the rudimentary
nipple standing ^ in. from either of its neighbours. In the I)

O i o

o o

O I

Ol Ol

1 o

0 2 j 0
O _> 0 02 .2

O O O 3

O 2 0

■4 O ° ", 30 04 0-5

°4 0 3

3 O 4 0 O 5 olO O*

O O .5 O °

o 4

0 0 05 O O

, ~ O O

O O 5 O 06 OO O O

7 o o 8 6 o o 7 7 a o 8 6 o o 7 6 o o 7

E F G K L

Fig. 34. Diagrams of nipples in very young pigs. Letters refer to groups in
No. 164.

group this was found on both sides, but in the E group on one
side only, as in the figure (Fig. 34).

Comment on foregoing evidence.

On looking at a series of cases like those roughly illustrated in
the diagrams, one is tempted to inquire as to the factors which
determine the positions of these mammae and nipples. Though
such an inquiry must lead to small definite results it may not be
unprofitable to point out some deductions which may be made
from the facts. I take this opportunity as a good one for illus-
trating the position here adopted with respect to the theory of
Reversion, and for discussing certain features of the phenomena of
Division.

The mammary glands form an example of a class of Meristic
organs which are distributed in series along a body already seg-
mented, but whose positions have no obvious coincidence with the
fundamental segmentation. In the case of the pig, for instance, it
would doubtless be found that the mamma; bear more or less
definite relations to particular vertebrae, but they are not limited
to such positions as the ribs or spinal nerves must be. The seg-
mentation of the mammae is thus a segmentation, or serial arrange-
ment, superadded upon that of the vertebra1. The question to be
considered is. what determines the points at which mammae are to
be formed ?

In the paper to which reference has been made, Williams has
contended for the view that each somite bore originally a pair of
mammae; and we may remark that if this were so the problem of
the segmentation of the mammae would be the same as that of the

192 MERISTIC VARIATION, [part i.

general segmentation of the trunk. The same author then argues
that the appearance of supernumerary nipples or mammae along
the mammarv lines is a reversion to an ancestral condition, and a
figure is given, shewing the places at which mamma? are on this
view believed to have been placed, definite ordinal numbers being-
assigned to each. Against this suggestion may be urged those ob-
jections to appeals t<» the hypothesis of reversion which were men-
tioned in the Introduction (Section XII.), but in addition to these
there are a number of objections applying specially in the case of
mammary Variation. The view that supernumerary mammae are
reversions rests on the frequency and definiteness with which they
occupy certain positions. But though they do occur more often
in some positions than in others they are in no sense limited to
these positions, for they may stand anywhere, at least upon the
mammary lines. To justify the view that the positions of super-
numerary mammae are definite it is necessary to exclude the cases
of bifid nipple, of multiple nipples on the same breast, and of axil-
lary extensions of the mammae, all which phenomena would then
be looked on as belonging to a class different from that of actual
supernumerary mammae. In the argument referred to, this course
is actually adopted. The acceptance of such a view leads to great
difficulty. For example, in Neugebauer's case (see Fig. 29),
Williams considers that the posterior nipples of the two sides be-
long to different pairs, and have consequently different homologies,
because they stand at different levels.

Such distinctions are, I believe, unreal. It is surely impossible
to suppose that the Repetition seen in the udders of the two cows
in Fig. 32 is a phenomenon different in the two cases. In the one
there are two extra teats in symmetrical positions, equally spaced
out from the second teats ; in the other there is a third teat on
one side and a double second or posterior teat on the other. Surely
it is clear that the double condition of this teat represents an im-
perfect phase of a process perfected on the other side. If further
proof were needed it may be found in the fact already mentioned,
that the mammae of the pig and other such animals, may be the
same in number even on the two sides, but nevertheless stand
quite irregularly and without any visible arrangement into pairs.

The existence of these cases in which no order of form or regul-
arity can be traced may seem at first sight to be an insuperable
objection to any attempt at the detection of principles in the ar-
rangement of the mammae. There is however the fact that many,
and indeed in must forms the majority of individuals do shew an
orderly and paired arrangement, and the further fact that of those
cases which depart from this, a certain number present appear-
ances which suggest that this departure has come about in a regular
way. Though the irregular cases remain, something would be
gained if we could comprehend any of the elements on which the
regularity depends. The case of regularity and symmetry, in a

chap, viil] MAMM.£ : COMMENT. 193

sense, includes the cases of irregularity. The difficulty is to under-
stand the causes of regularity and of symmetry ; but if we could be
sure of these it would not be hard to conceive disturbances result-
ing in irregularity.

In the pigs are found, first, cases of six on both sides in pairs,
and also of seven on both sides in pairs ; besides these there were
cases of 6 — 7 and of 7 — 8. Of these there were some in which two
on one side stood in positions which geometrically balanced that
of one of the other side, the others being arranged in pairs. In
such cases the appearances suggest that there has been a division
of one mamma to form two, and that the two have then separated
or travelled apart. The division of organs into two is of course a
common occurrence, and may naturally be supposed to be a pheno-
menon of the same nature as the division of single cells. The case
of mamma? is perhaps instructive inasmuch as it bears witness to
the fact that such division must take place at a remotely early
period in development. For while in cases to be given hereafter
of division, for example, between teeth, it may be supposed that
the travelling apart of the two resulting teeth is mechanical, in the
sense that the two growing teeth may simply push apart from each
other just as two cartilage- cells, &c, may separate by the concen-
tric deposition of material, the separation cannot be supposed to
occur in the mamma? by these late changes, but the process of
mechanical separation, though the same in kind as that in the case
of teeth, must be conceived as beginning early in the history of
segmentation.

At this point a circumstance, very often to be seen in other
cases, should be mentioned. When an organ, single on one side,
corresponds geometrically with two organs on the other side, each
of the latter is frequently of the same size and developed to a like
extent as the single one of the other side. This of course would be
expected on the hypothesis that the division of organs is a pheno-
menon similar to the division of cells, that is to say, not merely
a division, but a reproduction.

But the supposition of division of single members of the series
is not sufficient to account for all the facts of Variation seen. We
have to consider not only the case in which one organ of one side
balances two of the other. We have to deal also with the cases of
six on each side and seven on each side all corresponding in pairs.
In these there is no indication that there has been a division of a
single member on each side. The spacing is regular in each case
and there is no obvious crowding at any part of the series. Even
if therefore in the former case there is a suggestion that the genus
of single mamma? have divided into two at a period of develop-
ment after the series of mamma? was constituted as a series, there
is no such suggestion in the present case. We must, I think, in
the latter suppose that the existences of all the mamma?, whether

b. 13

194 MERISTIC VARIATION. [part I.

six or seven, are determined together. How or at what stage such
determination is made, there is no direct evidence to shew.

The various arrangements seen suggest then that the relative
positions occupied by the mammae depend partly on the number
that are present, and that the position of each mamma is to some
extent dependent on the position of other mamma?, especially of its
neighbours. In this connexion the cases F and L are interesting-
ones (Fig. 34). In L for example, the 1st on the left is at a higher
level than the 1st on the right. It is succeeded by a rudimentary
2nd having none on the same level on the other side. The left
3rd is behind the right 2nd, but posterior to this point the nipples
are approximately paired. These appearances suggest that the dis-
placement of the 1st and 3rd on the left are in some way connected
with the presence of the rudimentary left 2nd. Similarly in F the
left 3rd and 5th are spaced out for the rudimentary 4th. From its
position and small size it might fairly be supposed that this is a
" supernumerary " organ, for at all events it is visibly different from
the others : but in the case of seven on each side in pairs, no one
mamma rather than another can be pointed out as obviously
supernumerary when compared with a similar series of six. It
seems therefore that of the factors determining the relative posi-
tions of the mamma? along the mammary lines, the number of the
mamma? is one, and that the positions of the mamma? are in some
way and to a limited extent correlated with each other. That there
are other factors at work, also, is sufficiently shown by the exist-
ence of cases of apparently utter irregularity.

In seeking to go beyond this and inquire as to the way in
which this correlation is brought about there is, in the present
state of knowledge of the mechanics of Division, not much to be
gained. Reference may be made to recent observations published
in abstract by O. Schultze1. According to him there is in young-
embryos of several mammals (Pig 1*5 cm. long; Rabbit 13 — 14
days, &c.) a ridge running along the dor so-lateral aspect on each
side and at points upon this the mamma? and nipples are even-
tually formed. (The formation of the true nipples is preceded by
the raising of. the epidermis into small elevations, "primitive
teats," which afterwards disappear.) The two mammary lines are
by subsequent changes and growth of the body brought into the
ventro-lateral position. The question of the position of the mamma?
therefore resolves itself into this : what determines the positions
at which mammary centres, to borrow the word used in the case
of bone, are to be formed on the mammary lines ? In a subse-
quent place I shall contend that the facts given are only intelli-
gible on the view that the forces determining the points of growth
of mamma? are compounded into one system of forces. But to the
question what are these forces there is no answer.

1 0. Schultze, Anat. Anz., 1892, vn. p. 265, since published in full {Verh. d.
phys.-med. Gee. zu WUrzburg, xxyi. 1893, p. 171, Pis.).

CHAPTER IX.

linear series — continued.

Teeth.

From the consideration of numerical Variation in mammae we
may proceed to an examination of like phenomena in the case of
the teeth of vertebrates. The modes of Variation in these organs
are, as might be expected, in many ways similar, but several cir-
cumstances combine to make the Variations of teeth more com-
plicated than those of mammae.

Teeth arise developmentally by special differentiation at points
along the jaws, much as the mammae arise by differentiation at
points along the mammary lines ; and as in the case of mammas,
so in the case of teeth, we are concerned first with changes in the
number of points at which such differentiation takes place, and
next with the general changes or accommodations which occur in
the series in association with numerical changes. As in mammas,
so also in teeth, numerical Variation may occur sometimes by the
division of a single member of the series into two, and sometimes
by a reconstitution of at least a considerable part of the series.

Between the case of mammas and that of teeth, there is how-
ever an important point of distinction. The series of mamma? is
practically an undifferentiated series. There is between mammae
standing in one mammary line no obvious qualitative differentia-
tion. Though not all identical in structure, the differences between
them are of size and of quantity, not of form or quality. If
such qualitative difference is present it must be trifling. In con-
sidering Variation in mammae we have thus to deal only with
changes in number, and with the geometrical and perhaps mecha-
nical question of the relative positions of the mammae. The teeth
of most Vertebrates, however, are differentiated to form a series of
organs of differing forms and functions, and the study of Variation
in teeth may thus be complicated by the occurrence of qualitative
changes in addition to simply numerical ones. In teeth, in fact,
there are not only Meristic variations, but Substantive variations

13—2

196 MERISTIC VARIATION. [part i.

also ; and thus, as in the case of vertebrae, for instance, in any
given example of a numerical change qualitative changes must be
looked for too.

As a preliminary to the consideration of evidence relating to
the Variation of teeth it may be useful to call attention to certain
peculiarities of teeth considered as a Meristic Series. In the
Introduction, Section V, it was pointed out that in order to get
any conception of the Evolution of parts repeated in an animal,
the fact of this Repetition must be recognized, and it must be
always remembered that we are seeking for the mode in which not
one part but a series of similar parts has been produced. The
simplest case to which this principle applies is that of organs
paired about the middle line, and in the steps by which such parts
have taken on a given form it is clear that similar variations must
have occurred on the two sides. In the absence of evidence it
might be supposed either that such variations had occurred little
by little on the two sides independently, or on the other hand, that
Variation had come in symmetrically and simultaneously on the
two sides. Upon the answer given to this question the success of
all attempts to form a just estimate of the magnitude of the
integral steps of Variation depends. In many examples already
given it has now been shewn that though in the case of paired organs
Variation may be asymmetrical, yet it is not rarely symmetrical,
and in part the question has thus been answered.

In the evidence that remains many more cases of such sym-
metrical variations will be described, and it may be taken as
established that when the organs stand in bilateral symmetry, that
is to say, as images on either side of a middle line, their Varia-
tion may be similar and symmetrical.

The teeth present this problem of the Variation of parts stand-
ing as images, in an unusual and peculiar wTay. For in the case of
teeth we have to consider not only the steps by which the right
and left sides of each jaw have maintained their similarity and
symmetry, but in addition the further question as to the relation
of the teeth in the upper jaw to those in the lower jaw. There
are many animals in which there is very great difference between
the upper and lower rows of teeth, and it must of course be
remembered that perhaps in no animal are the teeth in the upper
jaw an exact copy of those in the lower, but nevertheless there is
often a substantial similarity between them, and in such cases we
have to consider the bond or kinship between the upper and
lower teeth whereby they have become similar or remained so.
For it may be stated at once that there is some evidence that the
teeth in the upper and lower jaws may vary similarly and simul-
taneously, though such cases are decidedly rare, especially in
numerical Variation, and are much less common than symmetrical
Variation on the two sides of the same jaw.

chap. IX.] TEETH I PRELIMINARY. 197

In speaking of the relation of the series of the upper jaw to
that of the lower jaw as one of images., it must be remembered
that the expression is only very loosely applicable. In particular
it should be noticed that though in so far as the lower teeth are a
copy of the upper ones the resemblance is one of images, yet the
teeth which resemble each other do not usually stand opposite to
each other in the bite, but members of the upper series alternate
with those of the lower. The incisors, as a rule, however, and the
back teeth of a certain number of forms do bite opposite each
other, and in them the relation of images is fairly close.

The importance of the recognition of the relation of images as
subsisting between the teeth of the upper and lower jaws will be
seen when this case is compared with that of the two sides of the
body. For ordinary bilateral symmetry is, as has already been
suggested, an expression of the original equality and similarity of
the two halves into which the ovum was divided by the first
cleavage-plane, or by one of the cleavages shortly succeeding upon
this. The fact that the two halves of the body are images of each
other is thus both an evidence and a consequence of the fact that
the forces dividing the ovum into two similar halves are equal and
opposite to each other. The bilateral symmetry of Variation is
thus only a special case of this principle.

In view of the fact that the teeth in the upper and lower jaws
may vary simultaneously and similarly, just as the two halves of the
body may do, it seems likely that the division of the tissues to form
the mouth-slit must be a process in this respect comparable with
a cleavage along the future middle line of the body. It is difficult,
however, to realize the actual occurrence of such a process of
division in the case of the slit forming the original stomodoeum,
and this difficulty is increased by the recent observations of
Sedgwick1 to the effect that in the Elasmobranchs examined by
him the mouth-slit first appears as a longitudinal row of pores. If
this is so the relation of images must exist in the case of the
mouth, not only in respect of the two sides of the slit, but also in
respect of the anterior and posterior extensions of the slit. But
whatever may be the processes by which the tissues bounding the
mouth of a vertebrate come apart from each other, the result is clearly
in many cases to produce an anterior series of organs in the upper
jaw, related to a posterior series of organs in the lower jaw, much
in the same way that the right side of a jaw is related to the left
of the same jaw. This relation may appear as has been stated,
not only in the normal resemblances between the upper and lower
teeth, but also in the fact that similar and simultaneous Variation
is possible to them.

In another respect the Repetition of teeth may differ from that
of other Linear Series already considered. In many animals, the

1 Sedgwick, A., Quart. Jour. Micr. Sci., 1892, p. 570.

198 MEMSTIC VARIATION. [part i.

Pike, the Alligator, or the Toothed Whales, for example, the teeth
stand in a regular and usually continuous series, differing from
each other chiefly in size, ranging from small teeth in front,
through large teeth, and often down to small teeth again at the
back of the jaw. Such a 'homodont' series as a rule passes through
only one maximum. Most mammals, however, are 'heterodont,'
that is to say, the teeth can be distinguished into at least two
groups, the incisors and canines on the one hand, and the pre-
molars and molars on the other ; and in a large number of animals
having this arrangement the anterior members of the series of
premolars and molars are small, increasing regularly in size from
before backwards, reaching a maximum usually in some tooth
anterior to the last. Though instances will be given of Variation,
and especially of reduplication, occurring in most of the teeth,
even in those which stand well in the middle of the series of back-
teeth, such as the upper carnassials of the Cat, or the fourth pre-
molars of the Seal, yet on the whole Variation in heterodont forms
is more common at the anterior and posterior ends of the series of
back-teeth. In view of this fact it is of some importance to
recognize that the small members at the beginning of the pre-
molar series are as regards their relatively small size, in the con-
dition of terminal members of series, and exhibit the variability of
terminal members almost as much as the last molars.

With these remarks by way of preface, evidence as to the
numerical Variation of teeth in certain groups will be given in full.
This account will for the most part be confined to a brief description
of the conditions presented by the specimens. In the next chapter
the principles which may be perceived to underlie these facts and
the general conclusions to which they appear to lead will be
separately discussed.

The evidence here given relates to certain selected groups1 of
Mammals, and chiefly to the Primates (excepting Lemuroidea), Car-
nivora (CanidaB, Felidse, Viverridse, Mustelidse and Pinnipedise), and
Marsupialia (Phalangerida?, Dasyurida^, Didelphyidas, part of Macro-
podidae, &c).

The facts to be given relate chiefly to increase in number
of teeth. In the case of terminal members of series, such as the
most anterior premolar or the last molar, some reliable facts as to
cases of absence were found, but for the most part the evidence as
to the absence of teeth is ambiguous and each case requires
separate treatment.

The evidence is in this chapter arranged according to the

1 Evidence as to the dental variations of Man is not here introduced. Con-
siderable collections of such facts have been made by Magitot {Anom. du syst.
dent.), Brscn (Dent. Monats. f. Zahnh. 188fi, iv.), and others, and illustrative
specimens are to be found in most museums. I do not know that among these
human variations are included phenomena different in kind from those seen in
other groups, except perhaps certain cases ot teeth united together, a condition
rarely if ever recorded in other animals.

chap, ix.] TEETH ! PRELIMINARY. 199

zoological position of the groups concerned. In several cases
variations of similar nature were seen in different groups ; cases of
this kind will be brought into association in the next chapter.

As regards nomenclature I have in the main followed the
common English system, numbering both the premolars and
molars from in front backwards. In one respect I have departed
from the practice now much followed. It has seemed on the whole
better that the premolar which in any given jaw stands first,
should be called p1, even though in certain cases there may be
reasons for doubting whether it is the true homologue of the p1 of
other cases1. Theoretical views of this kind can only at best be
used as a substitute for the obvious nomenclature in a few re-
stricted cases, such as that of the Cat, in which by the application
of the methods of reasoning ordinarily adopted in Comparative
Anatomy the first upper premolar would be looked on as the
equivalent of p2 in the Dog. There are, however, few who would
feel confident in extending this reasoning to many other cases,
that of Man, for instance, and I believe it is on the whole simpler
to number the teeth according to their visible and actual relations.
As I have already attempted to shew in another place2, in the light
of the facts of Variation, it is to be doubted whether in their varia-
tions teeth do follow those strict rules of individual homology by
which naturalists have sought to relate the arrangements in dif-
ferent types with each other.

The material examined has consisted chiefly of specimens in
the British Museum and the Museums of the College of Surgeons,
Leyden, Oxford and Cambridge, the Paris Museum of Natural
History, and some smaller collections. I have to thank the
authorities of these several museums for the great kindness I
have received from them; and in particular I must express my
indebtedness to Mr Oldfield Thomas, of the British Museum, for
the constant help and advice which he has given me, both as
regards the subject of teeth generally and especially in examining
the specimens in the British Museum3.

PRIMATES.

S0111D.E. The Anthropoid Apes (Orang, Chimpanzee, and
Gorilla).

*165. The teeth of the three large Anthropoids arc perhaps more
variable, both in number and position, than those of any other

1 In cases where confusion might arise any change from common nomenclature
is notified in the text.

2 Proc. Zool. Soc, 1892, p. 102.

:i In the following descriptions B.M. stands for British Museum; C.S.M. lor
Museum of the Boyal College of Surgeons; CM., O.M., U.C.M., Leyd. M., P.M.,
for the Cambridge, Oxford, University College London, Leyden and Paris Museums
respectively.

200 MERISTIC VARIATION. [part i.

group of mammals of which I have been able to examine a con-
siderable number. In different collections 142 normal adult skulls
were seen and 12 cases of extra teeth. Of these one was a case
of extra incisor (Gorilla, No. 186), one of anomalous teeth (Gorilla,
No. 187), and the remainder molars. Thus far therefore there are
nearly 8 per cent, cases of extra teeth. This figure is remarkable
in comparison with the rarity of such cases in Hylobates (51 skulls
seen, all normal), and the like rarity in other Old World monkeys
(42-S normals and 2 cases of extra teeth).

Simia satyrus (Orang-utan).

Normal adult skulls seen, 52.

Supern itinerary molars.
166. Adult male haying additional posterior molar (m4) behind and
in series with the normal teeth, on both sides in upper jaws and on
left side in lower jaw. In each case the in4 is rather smaller than
??i3, but all are well formed, having each four cusps and the normal
complement of fangs, viz., one in front and one behind in the
lower jaw, and two on outer and one on inner side in upper jaw.
On right side of lower jaw there is no trace of additional molar,
though there is almost as much room for it as on the left side.
C. M., 1160, D, described by Humphry, G. M., Jour. Anat. Phys.,
1874, p. 140, Plate.

16/. Female (Borneo) having six cheek-teeth in each upper jaw and in
right lower jaw [doubtless a case like the foregoing] mentioned by
Peters, W., Sitzungsb. naturf. Fr. Berlin, 1872, p. 76.

1G8. Specimen with large alveolus on each side for w\ L. M., 24.

169. Specimen (Borneo) having m4 in right lower jaw, behind and in
series with the normal teeth. The tooth is of rather small size, but is
regular in position and form. B. M., 3, m.

170. Specimen having a right ^ more than half the size of m:i- U. C. M.,
E, 253.

171. Specimen having supernumerary molar on each side in lower jaw.
Mayer, Arch. f. Nature/., 1849, 1. xv. p. 356.

172. Similar case. Fitzinger, Sitzungsb. math. — nat. CI. Ak. Wien,
1853, i. p. 436.

Similar case. Bruhl, Zar Kenntniss des Orangkopfes, Wien, 1856.
[] refers to the case described by Fitzinger.]

Molar absent.

173. Specimen "remarkable for absence of the upper right third
molar and for absence of nasal bones, which are greatly reduced
in some other specimens." C. S. M., 44. See Catalogue Mus. Coll.
Surg. 1884. The other teeth are all normal and fully formed.

Variations in position of teeth. Though not directly pertaining
to the subject here considered, the following examples of consider-

chap, ix.] TEETH : ORAXG. 201

able departure from the normal arrangement may be perhaps
usefully introduced in illustration of the peculiar variability of
the dentition of the group.
*174. A skull from Borneo in the Oxford University Museum (num-
bered 2043 a) has the following extraordinary arrangement. All
the teeth are normal and in place except the second premolar of
each side in the upper jaw. On both sides there is a large
diastema between p1 and «^. The diastema on the left side is of
about the same size as the normal second premolar, but that on
the right side is considerably too small for a normal tooth. The
singularity of this specimen lies in the fact that the missing
tooth of the right side is present in the skull, but instead of being
in its proper place it stands up from the roof of the mouth within
the arcade immediately in front of the right canine and almost
exactly on the level of the second incisor, being in the premaxilla,
at some distance in front of the maxillary suture.

That this tooth is actually the second premolar which has by
some means been shifted into this position there can be no doubt
whatever. It has the exact form of the normal second premolar,
and is of full size. It stands nearly vertically but is a little
inclined towards the outside. The canine is by the growth of
this tooth slightly separated from the second incisor, and the first
premolar is consequently pushed also somewhat further back.
Hence it happens that the diastema for the second premolar on
the right side is not of full size. This should be understood, as
it might otherwise be imagined that the contraction was due to a
complementary increase in the size of the other teeth, of which
there is no evidence.

On the left side of the palate there was a very slight ele-
vation at a point homologous and symmetrical with that at
which the second premolar of the right side was placed. As it
seemed possible that the missing tooth of the left side might
be concealed beneath this elevation, a small piece of bone was
here cut away, with the result that a tooth of about the same
size and formation as f; was found imbedded in the bone. In
this case therefore the second premolar of the right side and of
the left side have travelled away from their proper positions and
taken up new and symmetrical positions in the palate, anterior
to the canines. The facts of this case go to shew that the germ
of a tooth contains within itself all the elements necessary to
its development into its own true form, provided of course that
nutrition is unrestricted. This might no doubt be reasonably
expected ; but since the forms of organs and of teeth in particular
are by some attributed to the mechanical effects of growth under
mutual pressure, it may be well to call special attention to this
case, which goes far to disprove such a view.

175. Specimen having the teeth of the two sides in the lower jaw in
extraordinarily asymmetrical disposition. The bone of the jaw does

170.

177

202

MERISTIC VARIATION.

[part I.

not seem to have been broken, but there appears to have been disease
of the articulations of the mandibles. B. M., S6, 12, 20, 10.

Specimen in which "position of the left upper canine is abnormal.
It is displaced backwards and lies to the outer side of the first premolar,
which it has pushed towards the middle line." C. S. M., 41 (see
Catalogue).

Case in which upper right canine occupies a position within and on
a level with the first premolar, which is pushed outwards. C. S. M.,
40, A.

Troglodytes niger, calvus, &c. (Chimpanzee).

Normal adult skulls seen. 35.

Supernumerary molars.

*178. Specimen having on right side in upper jaw a very small
square tooth behind m*, in the arcade (Fig. 35) ; and in the left upper

1

ms

m 3 V *,

m

m.z

Fig. 35. Posterior right upper molars of Chimpanzee.

I. The case No. 178 {Coll. Surg. Mus., No. 1).

II. A normal Chimpanzee of approximately the same size.

jaw an empty alveolus in the similar place, shewing clearly that
a similar tooth has been present : lower jaw normal. C. S. M., 1.

179. Specimen in which teeth all gone, but alveoli exist behind
those of the normal teeth on both sides in upper jaw, and there
is little doubt that there was here a fourth molar on each side.
C. S. M., 9.

180. Specimen in which teeth all gone, but alveoli shew clearly that
there was a fourth upper molar on right side ; evidence on left
side inconclusive : lower jaw gone. C. S. M., 12.

181. Specimen of T. calvus having an extra mS in lower jaw on
right side. This tooth is about one quarter of the size of mz,
resembling that in case No. 178. This specimen is in the private
collection of Prof. Milne Edwards, who wras so kind as to shew
it to me.

Gorilla savagei (Gorilla).
Normal adult skulls seen, 55.

CHAP. IX.]

TEETH I GORILLA.

203

Supernumerary molars.

*182. Specimen having mi behind and in series with the others
on both sides in lower jaw and on right side in upper jaw. On
left side both teeth are square and somewhat worn, but the
right m* is a curious conical tooth. Gallery of P. M., A, 505,
described by Gervais, P., Journ. de ZooL, in. p. 164. PL

183. Two cases of four molars in each upper jaw. Magitot, Anom. du
syst. dent., p. 100, PL v. tig. 8. [Of these one is in collection of Dr
Auzoux; the other is No. 121 in P. M., but as I did not see it when
examining the collection it is not reckoned in the statistics given
above.]

Similar case, Hensel, Morph. Jahrb., v. p. 543.

184. Specimen having supernumerary molar which had not quite pierced
bone [no statement as to position]. Wyman, Jeffries, Proc. Boston
]ST. H. S\, v. p. 160.

185. Specimen having extra molar in crypt on each side in upper jaw
behind m3. L. M., 3.

Super n umerary incisor.

Fully adult male from Congo having an extra incisor in lower
, There are thus five incisors in lower jaw (Fig. 36), of which

*

186.

jaw

Fig. 36. Lower incisors and canines of Gorilla No. 186. .r, y and z are three
central incisors. The upper figure shews the tooth y as seen from the side.
(Specimen in Coll. Surg. Mus., 21, A.)

one, presumably the supernumerary, stands almost exactly in the
middle line. This tooth is turned half round, so that the plane
of its chisel stands obliquely. The teeth are all well formed
and none belong to the milk-dentition, for the milk-teeth are
much smaller and of different form. I did not succeed in
satisfying myself that the central tooth is certainly the super-
numerary. The second incisors are in place on each side and
are quite distinct, and the right first incisor is similarly normal.

204 MERISTIC VARIATION. [part i.

But whether the oblique tooth, or the tooth between it and
the right il, should be rather considered supernumerary cannot
be declared with certainty. Probably this is one of the cases, of
which more will be said hereafter, in which both teeth replace the
normally single i1. C. S. M. 21, A.

^37 Anomalous extra teeth. A lower jaw in the Museum of the Odontological

Society "having two supernumerary teeth embedded in the hone beneath the coro-
noid process and sigmoid notch. Originally only a small nodule of enamel was
visible on the inner surface of the right ascending ramus, just external to the upper
extremity of the inferior dental canal. On cutting away the bone this nodule was
found to be a portion of a supernumerary tooth having a conical crown and a
single tapering root. Lying above it, another supernumerary tooth was discovered,
of which there had previously been no sign whatever. This was likewise exposed
by removing the superjacent bone, and found to be a larger tooth with a conical
crown and three long narrow roots. The teeth were lying parallel to each other,
with their crowns pointing upwards and backwards, so that they could hardly under
any circumstances have been erupted in the alveolar arch." Trans. Odont. Soc,
1887, xix. p. 206, fig.

Specimen having fragment of a tooth imbedded in bone between left lower canine
and p1; perhaps a fragment of a milk-tooth P.M., A, 506.

[Two specimens in the stores of the P.M. shew great irregularities in the
arrangement of the teeth; but in both cases so many teeth had been lost during
life that a satisfactory description of the abnormalities cannot now be given.]

Hylobates (Gibbons).

Normal specimens seen, 51. No abnormal case known to me.

Old World Monkeys other than Anthropoid Apes.

188. Of the genera Semnopithecus, Colobus, Nasalis, Cercojnthecus,
Cercocebus, Macacus and Cynocephalus ; 419 normal specimens
examined. Only two had definite supernumerary teeth, but in one
other case it was possible that extra molars had been present.

Supernumerary molars.

189. Cynocephalus porcarius, having large extra molar behind
and in series in each upper jaw. The two teeth are of the same
pattern precisely. In lower jaw there is on each side a large
space behind m3, but there is no tooth in it. O. M., 2011, b.

190. Macacus rhesus, old male, having a fourth molar in place in
right lower jaw. The tooth does not stand up fully from the
bone. On the same side in the upper jaw there is also a fourth
molar, but was entirely enclosed in bone and was only found by
cutting away the side of the maxilla by way of exploration. B. M.,
30, c.

191. Macacus radiatus, having small and fairly definite depression behind m} in
each jaw. These depressions seem to be perhaps the alveoli of teeth but it cannot
be positively stated that extra molars have been present. C.S.M., 145.

192. Abnormal arrangement. Only one case of considerable irregularity of arrange-
' ment seen, viz., Cercopithecus lalandii (C. S. M. 113), case in which lower canines

are recurved and pass behind the upper ones. See Cat. JIus. Coll. Surg.

chap, ix.] TEETH : ATELES. 205

New World Monkeys.

*193. In the species of Cebida? and especially in Ateles supernumerary
teeth arc rather common, eight cases being found in 284< skulls,
or nearly 3 per cent, (in addition to cases recorded by others). Of
American monkeys belonging to other genera 92 skulls were seen,
all being normal. Some cases of absence of the third molar were
seen in Ateles, which are interesting in connexion with the fact that
there are normally only two molars in Hapalidse.

Cebid.e : normal formula i J, c\, p f , m§.

Chrysothrix, normal adults, 5.

Cebus, normal adults belonging to about ten species, 66.

Supernumerary molars.

194. Cebus robustus : supernumerary molar in each upper jaw
giving p f , m 4; de Blainville, Laurent's Annal. d'Anat. etPhys.,
1837, i. p. 300°, PL viii. fig. 6.

19o. c variegatus : small tubercular molar in right lower jaw
behind m?. The extra tooth is cylindrical and peg-like, having
about Jth the diameter m?. Leycl. Mus. 8, Cat. 11.

Ateles : normal adult skulls, belonging to several species, 60.

Supern umerary molars.

*196. A. pentadactylus : extra molar in series behind md in both
upper and lower jaws on right side, in each case a small round
tooth. P. M., A, 1505. This specimen described by de Blainville
Laurent's Ann. d'Anat, et Phys., 1837, I. p. 300, PL VIII. rig. 5:
mentioned also by Geoffroy St Hilaire, Anom. d'Organ., i.
p. 660.

197. A. vellerosus : extra molar on left side in lower jaw behind
m3, as a fully-formed and well-shaped tooth, but not so large as m<.
B. M., 89. 12. 7. 1.

198. Ateles sp. : extra molar on left side in lower jaw. Magitot,
Anom. du syst. dent, p. 101, No. 6.

Supernumerary premolars.

*199. Brachyteles hemidactylus [a genus doubtfully distinct from
Ateles] : specimen from S. America having 1. upper series and all
lower series normal. In place of right upper pl are two teeth
(Fig. 37). These two teeth are similar to each other and for
want of space they bulge a little out of the arcade. Each is in
size and shape very like normal £\ having a sharp cusp and a flat
internal part to the crown. Both teeth are slightly rotated in
opposite directions, so that the cusp of the anterior is antero-

206

MERISTIC VARIATION.

[part I.

lateral instead of lateral, while the cusp of the posterior is postero-

Fig. 37. Surface view of upper jaw of Brackyteles hemidactylus, described in
No. 199. From skull in Brit. Mux., 42, a.

lateral. These two teeth stand thus in somewhat complementary
positions. B. M., 42, a.

*200. Ateles marginatus : wild specimen from river Cupai, has

4—4 3—3

P

O O '

O — O

m

3—3'

■m? m3

Fig. 38. Surface view of upper teeth of Ateles marginatum, specimen described
in No. 200, and side view of both jaws together. The specimen is in Brit. 3Ius.,
1214, b.

chap, ix.] TEETH : ATELES. 207

that is to say, an extra premolar on each side in the upper jaw, the
lower jaw being normal. The four upper premolars are perfectly
formed, large teeth, in regular series on both sides. As a conse-
quence the lower canines bite on and partly behind the upper
canines. There was nothing to suggest that any one of these
teeth was supernumerary, rather than another (Fig. 38). B. M..
1.214, b.

Supernumerary incisor.

201. Ateles ater : specimen from Peruvian Amazon : in right
upper jaw there is a large alveolus for i2, which is gone, while a
third incisor stands between this and the canine. This third
incisor bites on lower canine, and lower p1 of the same side bites
in front of the upper canine. B. M., 1108, d.

202. Ateles paniscus : extra incisor in upper jaw. Rudolphi,
Anat.-phys. Abh., 1802, p. 145.

Absence of molars (cp. No. 209). Inasmuch as^f, m% is the
normal formula for the Hapalidae, the following cases of absence of
m3 in Ateles are interesting. There was in no case any doubt that
the skulls were fully adult, and there was no suggestion that the
absent tooth had been lost.
*203. Ateles marginatus : specimen from the Zoological Society's
menagerie, bones rough and unhealthy-looking, but skull well
formed and certainly not very young, has no m3 in either jaw, giving

3 3 2 2

the formula p — 0 , m~ — -, as in Hapalidse. There is no space

in the jaw behind m2, and in the upper jaw the bone ends there
almost abruptly.

204. A. melanochir : Caraccas specimen, having no posterior m2
on either side in upper jaw. The lower series normal, but the
jaws are somewhat asymmetrical, so that the lower posterior right
m3 is behind the level of its fellow of the other side. B. M., 4s.
10. 26. 3.

205. A. variegatus : wild specimen, having lower m3 absent on
both sides. Left *f is also absent, but has been almost certainly
present. CM., 1098, B.

Mycetes : of various species, adult normals, 81.

Supernumerary molar.

206. M. niger : supernumerary molar in the right upper jaw. The
arrangement is peculiar. So far as m- the teeth are normal.
Behind and in series with m2 there is a large tooth, a good deal
larger than the normal m3, and having rather the form of m* than
of m3. Its form is, however, not precisely that of m2, for the
middle or fifth cusp is rather anterior to the centre of the tooth.

208

M ERISTIC VARIATION

[rART I.

instead of being posterior to it as usual. Outside this tooth is
another, standing out of the arcade, having the size and almost the
form of normal m*. B. M., 749, c. (Fig. 39).

This case may be an example of one of two principles which
will be in the next chapter pointed out as operating in the case

Fig. 39. Mycetes niger, No. 20(i ; right upper molars. Brit. Mus., 7-49, c.

of dental Variation. Eitlier m2 may have divided into two, both
standing in series, and the normal ms may have been pushed out
of the arcade in connexion with this reduplication ; or the tooth
standing outside may represent an addition to the normal series,
and in that case the tooth standing as mz in the series may be a
representation of mz, raised to the normally higher condition of m2
in correlation with the presence of an extra tooth in the series, in
the way shewn to occur in other cases (see Chapter x., Section 7).
Between these alternative possibilities I cannot decide.

Super n u merary premolar.

207. Mycetes niger : between and internal to p}_ and $P on left side there is a
premolar. This is probably a supernumerary one, but the jaw is so much diseased
that the relations are not distinct. B. M., 749, d.

208. Callithrix, normal adults, 22. (In B.M., 51, b on both sides rn? is separated
by a narrow diastema from m?. The appearances suggest that possibly a small
rudimentary tooth may have stood between them, but this is quite uncertain).

Nyctipithecus : 1 1 normals.

209. Pithecia : 1 1 normals.

Specimen having no right m*^, and apparently this tooth was not
about to be formed, for the dentition is otherwise complete. C. M.,
1094, a. (Cp. Xo. 202.)

Lagothrix, 6, Chiropotes, 1, Ouakaria, 3 normals respectively.

Hapalid.e. In this group m3 is normally absent ; and no
specimen having this tooth or any other dental abnormality was seen.
Of adult normal skulls 33 were seen, belonging to various species.

chap, ix.] TEETH : CAXID^E. 209

CARNIVORA.

Canid.e.

The evidence of the Variation of teeth in Canidae is divided
into three groups according as it concerns (1) incisors, (2) pre-
molars, (3) molars. No case specially relating to the canines
is known. In each of these groups the cases relating to (A)
ivild Canidae are taken first, and those relating to (B) domestic
Dogs afterwards.

Of wild specimens of the genus Canis (including the Fox)
289 skulls were seen, and amongst them were 11 cases of super-
numerary teeth, about 3*5 per cent, (besides many recorded cases).
Of 216 domestic Dogs (including Pariahs, Esquimaux, &c.) 10
had supernumerary teeth, or 7 "4 per cent, (besides many re-
corded cases). I have not included skulls of edentulous breeds,
in which the original condition of the teeth cannot be told with
certainty.

Statistics of the occurrence of supernumerary teeth are given
by Hexsel, Morph. Jahrb., 1879. Among 345 domestic Dogs
in his collection there are 28 cases of one or more extra molars,
12 cases of extra premolar, and 5 cases of extra incisor. [If
therefore no two of these cases refer to the same skull, there were
in all 45 cases of extra teeth in 345 skulls, or 13 per cent. It
is not stated that the collection was not strictly promiscuous,
but it may be anticipated that this figure is rather high.] An
analysis of Hensel's cases will be given in the sections relating
to the particular teeth.

The usual dentition of the genus Canis is if, c\, p\, m%.
The Wild Dog of Sumatra, Java and India, C. javanicus and
C. primcevus (by some considered as one species) have in':7 ami
have been set apart as a genus under the name Cuon (HODGSON,
Calcutta Jour. N. H., 1842, ii. p. 205). The genus Icticijon differs
in having normally ??ij. The genus Otocyon on the contrary has
usually ??if.

Of the variations to be described in Canis the most notable are
(1) cases of i4—^ ; (2) cases of extra premolar, common in upper, very
rare in lower jaws ; (3) cases of ^3 or m*, and one case of in J giving
the formula characteristic of Otocyon. In several instances a con-
siderable increase in the size of ȣ or m* is found associated with
the presence of ™?_ or m* respectively. An interesting group of
cases of extra molars was found in 0. cancrivorus, in which this
abnormality seems to be common.

The frequent absence of p1 in the Esquimaux dogs is worth
notice. Absence of m? is common in Dogs, but absence of «^ is
rare.

In Otocyon one case of m± is recorded, and in let icy on one
example has m\ instead of m\.

b. 14

210 MERISTIC VARIATION. [part I.

I. Variation in Incisors and Canines.

A. Wild Caxid^e.

No case of extra incisor known to me.
Two cases of absent incisor, viz.

210. [Canis] Vulpes pennsylvanica, Brit. Columbia, having
' \ o ' aPParently il has nut been present on either side. B. M.,

1402, b.

211. Canis vulpes: only 5 incisors in lower jaw, with no trace
of alveolus for the sixth. Schaff, E., Zool, Gart, 1887, xxviil
p. 270.

B. Dogs.

212. Dog (resembling Bloodhound) : four incisors on each side in
upper jaw. The externals, i3, normal, but no evidence as to which
of the other teeth supernumerary. Leyclen Mus.

213. Thibetan Mastiff, Nepal: sockets for four teeth on each side in
pmx. Teeth all gone. Alveoli of two sides nearly symmetrical. In
absence of the teeth it cannot be positively stated that this is not a case
of persistent milk-teeth, but this seemed unlikely. B. M., 166, g.

214. Mastiff: four teeth on each side in front of canines; from form of
teeth probably case of persistent milk-canines. Lower jaw gone. O. M.,
1749.

215. Dog : on right, sockets for three teeth in addition to ?3 which is in
place. These three sockets all smaller than the normal ones, and socket
for upper right canine also slightly reduced in size. Odont. Soc. Mus.

216. Dog : small skull in my possession, has in place of right & two
alveoli, both at the same level, divided by a thin bony septum, the one
internal to the other: left &_ is in place and normal: lower jaw gone.

217. Among 345 Dogs' skulls four had extra upper incisor on one
side, and one skull had perfectly formed fourth upper incisor
on both sides. This tooth smaller than third incisor. Hensel,
I. c, p. 534. Several cases of 7 or 8 incisors in upper jaw, teeth
being usually asymmetrical. Nehring, Sitzb. not. Fr. BerL, 1882,
p. 67.

218 In lower jaw such cases much rarer. Supernum. lower in-
cisor on one side, one case [? in 650 skulls], Nehring, ibid. ; also
a Dog (cJiien chinois-japonais), 4 incisors in each lower jaw.
Magitot, An. syst. dent, p. 81.

Case of divided incisor.

219. Bulldog : right i~ with very wide crown; main cusp partially
bifid, as if intermediate between single and double condition.
Morph. Lab. Cambridge.

Similar case kindly sent to me by Prof. G. B. Howes.

chap, ix.] TEETH: CANIDyE. 211

3 — 3

220. Absence of incisor is very rare in Dog. One case of i- — given by

Hexsel, I. c. p. 534. (Hensel observes that this gives the formula for
incisors of Enhydris [Latax]; he also calls attention to fig. of Enhydris
with three lower incisors in Owen, Odontogr., PI. 128, fig. 12, but as
this is not mentioned as an anomaly in text, it is very doubtful.)

221. Dog having the upper canine imperfectly divided into two on
each side as shewn in Fig. 39. The plane of division was at right

Fig. 39. Eight and left profiles of Dog having the canines partially divided.

angles to the line of the alveolus so that the two parts of each
canine stood in the plane of the series of teeth. The division was
more complete on the right side than on the left. The lower
canines were normal. This specimen was kindly sent to me by
Mr J. Harrison.

II. Variation in Premolars.

Several distinct variations were found in the premolars of
Canidse. A number of cases shew five upper premolars instead
of four, and the question then arises whether the extra tooth is
due to the division of a single tooth, or to reconstitution of the
series1. The occurrence of a fifth premolar in the lower jaw is
much rarer, only three or four cases (Wolf (2) and Greyhound (? 2))
being known to me. The following other forms of Variation oc-
curred. In C. mesomelas, No. 228, an extra tooth stood internal
to fP, and was perhaps a duplicate of this tooth. One case of
bifid p^ was seen, and two cases in which p2 had apparently
divided to form two single-rooted teeth (0. viverrinus, No. 227
and a Sledge-dog, No. 237). A few examples of absence of p1
deserve notice. Lastly, though really an example of Substantive
Variation, I have included a curious case of possibly Homceotic
variation of p^ into the partial likeness of the carnassial (No. 245).

1 On this point see Chapter x. Sections 3 and 5.

14—2

212

MERISTIC VARIATION.

[part I.

Increase in number of Premolars.

A. Wild Canid^e.

222. C. dingo : specimen having two closely similar teeth between p*
and the canine in each upper jaw1. Both the teeth had the form and
size of a premolar. This not a case of persistent milk-tooth, Nehring,
A., Sitzb. naturf. Fr. Berlin, 1882, p. 66.

C. dingo : on right side p] is in place, and there is an alveolus for
second tooth of about same size. On left side P1 is rather small. L. M.

C. lateralis, Gaboon. On 1. side p^ is single, but on rt. side
there are two almost identical teeth between P^ and the canine :
of these the most anterior is level with, but slightly smaller than,
left £. (Fig. 40) B. M., 1689, a, (See Mivart, P. Z. 3., 1890,
p. 377.)

223.

224.

225.

226.

227.

228.

229,

Fig. 40. Cants lateralis, No. 224. View of canines and front premolars of the
upper jaw. pl of the left side is in symmetry with two teeth on the right side.

C. vulpes : in 142 skulls, one case of two teeth between pz and
canine (sc. five premolars) in left upper jaw. Hensel, I. c, p. 548.

In C. vulpes the root of p1 is not rarely partly divided into two by
a groove of variable depth. The division is sometimes nearly com-
plete, as in C. S. M., 651.

C. mesomelas : two teeth between p2 and canine in left lower
jaw, anterior the larger. Doxitz, Sitzb. naturf. Fr. Berl., 1869, p. 41.

Division of p'2

C. viverrinus : left p? represented by two teeth, each having one
root. Of these the anterior is tubercular, while the posterior is rather
long from before backwards. Anterior premolars normal. L. M.
(Compare Sledge-dog, No. 237.)

Reduplication of p*.

C. mesomelas : inside right upper p3 is a supernumerary tooth
which nearly resembles pA, but is a little smaller; lower jaw normal.
C. S. M., 643. (See Nos. 226 and 247.)

C. lupus: in addition to irregularities in position of teeth, there is a doubtful
appearance as of an alveolus inside left P^ which is displaced outwards. C. S. M., 624.

1 Mivart, I.e., by mistake quotes this case as one of extra teeth above and below.

CHAP. IX.]

TEETH : CANID^E.

213

Partially bifid premolar.

230. ^* vulPes • right v\ has three roots and a partially double crown
with two cusps (Fig. 41). The whole crown is pyramidal, the labial
face being parallel to the arcade and the three roots stand each at one
angle of the base : left pj normal; lower jaw missing. B. M., 175, o.

Jh

Iji

l[

Fig. 41. Teeth of Fox (C. vulpes) described in No. 230. The separate view-
shews the right first premolar removed, seen from the labial side.

Extra premolar in lower jaw.

231. C. lupus : two teeth between p2 and canine in lower jaw on right
side, one case: and the same on left side also, one case. These two
occurred in 27 Wolf skulls seen by Hexsel, Morph. Jahrb., 1879, v.
p. 548.

B. Domestic Dogs.

*232. Dog : between F2 and canine on rt. side there are two teeth,
each shaped like a normal £\ the anterior being somewhat the
larger. This seen in two cases, figured in Fig. 42, II. and III.

right

m

Fig. 42. Profiles of canines and anterior premolars in three dogs having two
teeth on one side in symmetry with one tooth on the other.

I. C. S. M., 570. II. and III. Skulls in Cambridge Univ. Morph. Lab.

Lower jaws absent. The property of the Zool. Lab., Cambridge
(cp. G. lateralis, No. 224).
233. Spaniel : similar case, left side, Fig. 42, I. C. S. M,, 570.

214 MERISTIC VARIATION. [part i.

5 5

234. Dog : large skull, having^ =--, all the normal teeth being

o — o

in place, of proper form and size, standing evenly without crowding.
O. M, 1780.

235. Dogs. In 3 t5 skulls were 1 1 cases of supernumerary premolar in
the upper jaw. viz.

on both sides, 1 case,
on right side, 7 cases,
on left side, 3 cases.

These were all cases described by Hensel as instances of the presence
of "pb" of his notation, i.e. a tooth between p] and canine. Hensel,
Morph. Jahrb.f 1879, v. p. 546. Out of 650 skulls, including Hensel's
."U">, 18 had two anterior premolars as described, on both sides in upjDer
jaw. Nehring, Sitzb. naturf. Fr. BerL, 1882, p. 6Q.

English Spaniel: outside and anterior to right & is a worn stump, probably of
an extra tooth (?). B. M., KJG, j.

236. Deerhound : tiro alveoli where p~i should be; probably two distinct teeth stood
here, but it is possible that the two alveoli were for distinct roots of a single tooth.
C. M., 991, B.

Division of rp~.

237. Sledge-dog, Greenland : all teeth normal except left upper
p2. This tooth normally of course has two roots. Here it is
represented by two distinct teeth, each having one root. The
anterior has a fairly sharp cusp, but the posterior has a rounded
crown. The teeth are in perfectly good condition and do not
look worn. They are separated from each other by a considerable
diastema. It appears clear that instead of the normal p*} two
distinct teeth have been formed. 0. M., 1787 (compare C.
viverrinus, No. 227).

Absence of Premolars.

A. Wild Canid.e.

236. C corsac : fi absent on both sides without trace. Giebel,
Jirouits Kl. u. Orel., Mamm. p. 196, Xote.

239. c. occidentalis : p absent on both sides. C. S. M., 629.

240. C. vulpes : in 142 skulls :

P^ absent from both sides 1 case,
do. „ „ left „ 1 „
do. „ ,, right „ 1 ,,
p1 » „ both „ 1 „

do. „ „ left „ 2 „

do. „ ,, right „ 2 „

Hensel, Morph. Jahrb., 1879, p. 548. A doubtful case of absence of
left p. B. M., 175, c.

chap, ix.] TEETH : CANID.E. 215

241. C. (Nyctereutes) procyonoides : p^ absent on both sides with-
out trace in B. Ms, 186, e; and absent on right side in B. M., 186, d.
On the contrary B. M. 186 a and b and C. S. M., 672, are normal.

The following cases of absent premolars were doubtful : C. dingo : right v^ and
left J^. C. S. M. C. antarcticus: pl above and below on left side. C. S. M., 635.

B. Domestic Dogs.

242. From the nature of the case it is not often possible to say with con-
fidence that p1 has not been present in a given skull, but from the
material examined this variation appears to be rather rare. In 216
skulls, excepting those of Esquimaux dogs, I only saw two clear cases
in which the bones were smooth, without trace of alveolus, viz.
"Danish" Dog: p~i absent on both sides, O. M., 1786. Terrier:
p} absent on both sides. C. S. M., 579. Many others doubtful.

According to Hensel, however, absence of pl is common, and he
states that in 345 skulls the following occurred :

1^ absent on both sides 5 cases,

do. ,, ,, one 4 ,,

pi ,, ,, both frequently,

do. ,, ,, one 9 cases,

p1 absent on both sides and F1 on one side, 1 case.

Jforph. Ja/trb., 1879, p. 546. [This is of course a far higher frequency
than was found by me, but perhaps discrepancy arises from difference
in reckoning the evidence of absence.]

Two doubtful cases of absence of p were seen in Dogs.

*243. Esquimaux Dogs: absence of pl quite common, the following
skulls being all of the breed that I have seen.

Normals, withp~, only two specimens. Specimens with nop1, above
or below, the canines in such cases standing close to p1, three cases,
viz. B. M., 58. 5. 4. 96; B. M., 166, a; C. S. M., 542. £ absent on left
side and pi on both sides, C. M., 1000, c. pi absent both sides and pi
absent on left side, L. M. p^ and pi both absent from right side; left
normal, O. M., 1789. p~l absent on left side, B. M., 166, r, 3. p~l
absent on right side, B. M., 166, t, 2.

The partial establishment of a character of this kind in a
breed, which, if selected at all, has been selected for very different
qualities, is rather interesting. It need scarcely be remarked
that the partial loss of this tooth cannot in the Esquimaux dog
have occurred in connexion with an enfeebled habit of life, as
might perhaps be supposed by some in the case of the edentulous
lap-dogs.

As will be shewn in the next section, absence of the front
premolars is a common character in the dogs of the ancient Incas,
but in them the posterior molars are also frequently absent.
There is no special reason for supposing that the Esquimaux
dogs came originally from America, but it may be worth recalling
as a suggestion, that according to anthropologists the relations

•2 1 6 MERISTIC VARIATION. [part i.

of the Esquimaux are rather with American tribes than with
Europeans. If this were established, it would be not unlikely
thai the Esquimaux dogs might be descended from dogs domesti-
cated in America before the coming of Europeans, and so far belong
rathe]- with the Inca dogs than with ours1.

*244. Inca Dogs. The domestic dogs from the Inca interments, be-
longing to a period before the coming of the Spaniards, have been
investigated by Xehrinr. Of nine skulls not one had the full number
of teeth and there was no case of supernumerary teeth. Sometimes
the anterior premolar was absent, sometimes a posterior molar, and in
soiih' cases both. The formulas were as follows:

4—4
';4-3'

m

2-

-2 .

0

— o

4 — 4
^3-3'

7)1

2-

3-

_9

— 1 case.

4—4
';3-3'

m

2-
3-

_9

— ~1 3 cases

— o

4 — 4
*3-3'

m

9

—

9

-J

-1 ,

— - 1 case.

-2

4 — 3

7)1

2-

2-

-2 -

— - 1 case.

-2

3 — 3
^3—3'

7)1

9_

3-

_9

— 2 cases

— o

The dogs were all of moderate size, and none shewed any defects
in the form of teeth, which were all strong and sound. Nehring, A.,
A'osntos, 1884, xv. p. 94.

Variation (J Homceotic) in form of third Premolar.

245. Dog : large breed. In the upper jaw on both sides the third
premolar, instead of having only two roots, has a third internal root,
thus somewhat resembling the carnassial. The crown of the tooth
very slightly changed. This is not a case of persistent milk-tooth, which
though a three- rooted tooth, is very different. C. S. M., 558.

III. Variation in Molars.

Supernumerary molars are not rare in Canidae. In all cases
seen by me these teeth are single-rooted, round-crowned, rather
tubercular teeth, placed behind m? or m? as the case may be.
HENSEL1 has observed that if m± occurs, then m? which is normally
single-rooted, not infrequently has a double root, though the same
variation may occur when there is no m4 present. Conversely,
when ///'• is absent, not a rare variation, then rn? is often of a

1 Bartlett, arguing chiefly from habits, considers the Esquimaux dogs to be
domesticated wolves, and says that they often breed with the wolf. P. Z. S.,
1890, p. 47.

- Hexsel, Morph. Jahrb., 1879, v. p. 539.

chap, ix.] TEETH : CANIDyE. 217

size below the normal, having a single root and a crown slightly-
developed, like that of m*. This reduced condition of ~m* may
also occur in cases in which mTi is not absent. These observations
of Hensel's, which are of great consequence to an appreciation
of the nature of Repetition, I can fully attest, and similar cases
of Variation in adjacent teeth associated with the presence of a
supernumerary were seen in other animals also.

A. Wild Canid.e.
Supernumerary Molars.

246. CJ. lupus: 26 normals seen. Specimen from Courland having
supernumerary m? on left. In this specimen m? is rather ab-
normally large on both sides, and the lower third molar, on the
left side, viz. that on which the upper jaw has an extra tooth, is
larger than right m?} but it is not larger than usual. C. M.,
976, M.

Hexsel, I. c, p. 548, saw 27 skulls, none having extra molar, but
one specimen known to him had a right m?.

247. C. mesomelas J (a Jackal): small, bitubercular left w^. Doxitz,
Sitzb. naturf. Ft. Berlin, 1872, p. 54. (See Nos. 226 and 228.)

The S. American Canidce {Lycalopex group) are remarkable
for the frequency with which they possess extra molars, as the
following cases (C. azarcv, vetulus, magellanicus and cancrivorus)
testify. Flower and Lydekker1 speak of the occasional presence
of ™? in G. cancrivorus, but the evidence taken together seems
rather to shew that there is a general variability at the end of
the molar series in both jaws in these species ; for not only is
*J}? found, but in some cases m* also, while in one instance there
was an 'odontome,' or rather a complex of 4 small teeth attached
to m3.

248. O- vetulus, Brazil : specimen having an extra molar in right
lower jaw (Fig. 44, 1.). The posterior part of ^ is slightly pushed
outwards and a very small extra tooth stands behind and partly
internal to it. Right m3 is slightly larger than left nfi and differs
from it also a little in pattern. The extra tooth has one large
and about three smaller blunt cusps on its crown, and might be
described as a small representation of the larger m* seen in other
cases. B. M., 84. 2. 21. 1 (mentioned by Mivart2, Monogr. Canidce).

*249. Canis azarae : Brazilian specimen having a large super-
numerary molar (w3) in each upper jaw placed in series with the
others. In this specimen the great enlargement of ȣ is very

1 Mammals, Living and Extinct, 1891, p. 540.

2 In the same place Mivart mentions a case of m? in " C. cancrivorus" but I have
not seen it. Perhaps this reference is to van der Hoeven's case (No. 249) which was
by Burmeister named C. cancrivorus (see Huxley, P. Z. S., 1880, p. 268).

218

MERISTIC VARIATION.

[part I.

noticeable on both sides, and this tooth is present as a large tooth
with apparently three roots. In the lower jaw there is no extra
booth, but the molars are considerably larger than those of a

2.30.
*251.

2") 2

Fig. 43. ( 'anis </: ira. I. and II. Right upper and lower jaws of the specimen
described in No. 248, shewing the extra upper molar and the correlated enlarge-
ment of "I2 and ,//■'. III. and IV. are taken from a normal specimen of slightly
Larger size. C, carnassial teeth.

This figure was kindly drawn for me by Mr J. J. Lister.

normal spreimen (Fig. 43). In the figure, side by side with the
teeth of the abnormal form, are shewn the teeth of a normal skull
which was slightly larger than the abnormal one, for comparison.
Leyden Mns. '

C. magellanicus : specimen having m* on both sides. B. M., 46.
11. 3. 0 (mentioned by Huxley, I. c).

C. cancrivorus. The only skulls of this species seen by me are
those in B. M. Of these one skull with lower jaw, one skull without
lower jaw. and one lower jaw without skull, have numerically the
normal dentition of Canis, but of these, one has right m73 much larger
than corresponding left tooth. The following were abnormal: small
tubercular m* on both sides, upper series normal, B. M., 1033, b, and
also B. M., 1033, c, (Fig. 44, II.) mentioned by Huxley, I. c.

Specimen having upper series and left lower series normal. On
inner side of right mz and as it were growing out from this tooth is a

1 This is no doubt the skull described by van der Hoeven. Verh. k. Ah. Wet.,
Amst., iii. 1856, PL See Huxlky, P. Z. S., 1880, p. 208.

CHAP. IX.]

TEETH : CAXID.E.

219

large 'odontome' composed of four small tubercular teeth. Each of
these has a distinct crown and neck, but apparently the necks join with

R

ia

n

Fig. 44. Posterior lower molars of S. American Foxes. I. C. vetulus No. 249.
II. G. cancrivorus No. 251. III. C. cancrivorus No. 252. In each case the right
and left sides are shewn. R, right. L, left.

each other and with the neck of m3, which is displaced (Fig. 44, III.).

B. M.5 1033, a. (mentioned by Huxley, P. Z. S., 1880, p. 268;
figured by Mivabt, P. Z. S., 1890, p. 377).

In answer to an inquiry, Prof. Nkhrixg informs me that he has three skulls of

C. cancrivorus Desm. ( = G. braziliensis Lund.) from the province of S. Paolo, Brazil,
which are normal, except that in one pi has never replaced a*, which is in place ;
and that another Venezuelan skull of this species is also normal. [Whether
the B. M. specimens are really of the same species as these I do not know.]

60i5. T/he rarity of supernumerary molars in G. vulpes, the common
Fox, is remarkable in contrast with the foregoing evidence. In
142 cases (to which I can add 37), Hensel, Morph. Jahrh.\ 1879,
found no single case.

Absence of Molars.

254. mr is very rarely absent in Canidae, and among the wild forms no
case seen in 289 skulls (except a doubtful case in 0. occidentalism right

220 M ERISTIC VARIATION'. [part i.

side, C. S. M., 628). ,7r; was observed to be absent in the following : C.
lag-opus, from Kamtschatka, absent on both sides in two cases
received in same consignment with 4 normal skulls. B. J/., 88. 2. 20.
9 and 10; another case from Norway. Leyd. Mus. C. zerda : on left
side. C. S. M., 671. C. vulpes : ditto, 2 cases. B. M., 177, a and
175, b. C. viverrinus : on right side. Leyd. Mus. C. procyonoi-
des : ditto. Leyd. Mus. Hensel, /. c, gives the following : C. vulpes:
142 skulls; ,„■'■ absent on both sides, 5 cases; on left side, 3 cases. C.
lupus : iit» absent on left side, 2 cases; on right side, 1 case.

ICTICYON AND OtOCYON.

* It is remarkable that in each of the two genera Icticyon and

Otocyon, which are especially distinguished from Canis by the
possession of unusual dental formulae, numerical Variation in the
th has been recorded, though the number of skulls of these
forms in Museums is very small. The two forms, besides, differ
from Canis in opposite ways, the one having a tooth less in each
jaw while the other has in each jaw a tooth more, so that the
presence of extra teeth in the two species is all the more im-
portant.

255. Icticyon venaticus : according to the authorities has p±, m\,
viz. a molar less than the Dog in each jaw. The following skulls are
all that I have seen. The carnassials did not vary appreciably in the
three skulls. Each skull differs from the others, as follows.

j>\ , m\, B. M., 185, a.

/<{, m~ i, B. M., 185, b.

yj, rnf, C. S. M., 533. (See Flower, P. Z. S., 1880, p. 71.)

25G. Otocyon megalotis [ = lalcmdii and coffer]: the usual formula

is />;}, m:j, that is, one molar more than the Dog in each jaw. It occurs

in 4 skulls at B. M. and in 2 at C. S. M. One specimen has in adcli-

4 — 4
tion an extra molar of good size in each upper jaw, giving on — — j.

4 — 4

In this case m? is enlarged also on both sides. C. S. M., 675 (see Cat,

Mus. Coll. Surg., Arc). Three specimens having mf mentioned by

Doxitz, Sit-.h. naturf. Fr. Berlin, 1872, p. 54.

B. Domestic Dogs.

Super n itinerary Mola rs.

257. Dogs. In 345 skulls the following 28 cases occurred, chiefly in
large breed- :

"^ on both sides and v? on one side, 1 case.

"^ on both sides 2 cases.

mP on one side 9 cases.

'»:: and ]n* on one side only 2 cases.

m* on both sides 6 cases.

m4 on one side only 8 cases.

Hensel, Morpk. Jahrb., 1879, v. p. 538.

CHAP. IX.]

TEETH I CANID.E.

221

In addition to these,

wi3 and m* absent on both sides, 1 case.

This was the only case in 860 skulls of Canis, of which about 650
were Dogs. The formula in it is thus that of Otocyon or the fossil
Amphicyon. Nehring, Sitzb. naturf. Fr. Berlin, 1882, p. 66.

In 216 skulls seen by me there were 8 cases of extra molars, viz. : —

258. Sheep dog : left m3. C. S. M., 587; Bulldog : left m3. B. M.,
166 s; Dog from New Zealand, having left m\ left m* being larger
than right m». C. M., 1000; Bhotea Mastiff: m+ on right B. M., 166,
f.; Pointer: lefty. C. M., 1000, A; Dog: right Ji? Carnb. Morph.
Lab.; Pariah : m4 has been present on both sides, also a small stump
below ^ and p2, possibly part of a milk-tooth. B. M., 166, <l.

259. Mastiff: supernumerary m4 on right. The right m? materially
larger than left ^ (Fig. 45). C. S. M., 555.

right

left
reversed

200.

261.

Fig. 45. Posterior molars of lower jaw of Mastiff No. 259, having an extra m4
on the right side. Right m? is materially larger than left ^i.

Dog, large size, supernumerary m* on right side. On both sides
m? is two-rooted1 and of large size. Leycl. Mas., 258.

Windle and Humphreys, P. Z. S.} 1890, p. 27, give an account of
extra molars in the Dog, speaking of upper jaws only, and some of the
foregoing are mentioned by them. As they do not specify the collec-
tion in which each is found the identity of the cases is not easy to tell.
The following cases given by them are, I believe, all in addition to
those already specifiecl : — Bulldog, Lurcher, Pointer and Terrier,
m? on both sides. Bulldog w3 on left side; Esquimaux, Pug,
Spaniel, West Indian Dog, »f on right side.

Coach-dog : ?/74 on both sides, Magitot, Anom. Syst. dent., p. 103.

Absence of Molars.

262. Dog: in 345 skulls the following seen : ?«'- and ^ absent on both sides, 2 cases;
^2 and ^a absent on both sides, 1 case ; ^ absent on both sides, 25 cases ; ^ absent
on one side, 9 cases. Hensel, /. c.

In 216 seen by me the following occurred: ^3 absent on both sides, 7 cases;
C. M., 993 and 978; C. S. M. {Store), 65 and 67; two skulls marked " Skye Terrier/'

1 It generally has a simple, conical root, but not rarely it has an imperfectly
divided root, e.g. Newfoundland dog, O. M., 1778.

222 MERISTIC VARIATION. [part i.

probably both of the same strain, C. M. 991, F and G; and Fox Terrier, C. M.,
991, K; ^ absent on left side, 2 cases. Irish Wolf-dog, B. M. 82. 11. 11. 1; Fox
Terrier, C. S. M., 580, A ; llti absent on right side, 1 case, Bloodhound, B. M., 166, t.
besides a few doubtful cases.

Inca dogs : for evidence as to absence of molars, see No. 244.

FELIDAE.

The following evidence relates to the genera Veils and Cyn-
cdurus. The usual formula is /§, c\, />§, ni\. Of wild species,
27 8 adult skulls having no extra teeth were seen, and 8 cases
of extra teeth (nearly 3 per cent.): of domestic Cats, 35 adults
without, and 3 cases with extra teeth (so far, about 9 per cent.).
Aj3 in Canidte so in Felidae, there is a remarkable group of cases
of variation in the anterior premolars. In the normal a small
anterior premolar stands in the upper jaw, and commonly it is
oiK'-rooted, sometimes two-rooted (cases given); but there is no
small anterior premolar in the lower jaw.

Cases of variation consisting in the presence of two small
premolars above are common1, just as there are often two small
anterior premolars in the Dog. There are besides a few cases
of the presence of a small anterior premolar in the loiver jaw,
but they are rather rare, and curiously enough there seems to
be no case of the coincidence of these two variations in the same
skull.

As already stated, in describing cases, the small anterior pre-
molar in the upper jaw will be here spoken of as p^, though no
suggestion that it is the homologue of the Dog's p^_ is meant.

In a few species p^_ is most commonly absent (cases given).
There are some curious cases of duplicates of large premolars (Cat)
and one of duplicate canine (Tiger), also a few of supernumerary
molar. Though so small, and biting on no tooth of the lower
jaw, n& is nearly always in place even in old skulls (Hexsel).

Variation in Incisors.

No quite satisfactory case of numerical variation in incisors of Felidae known to
me. The following should however be mentioned.
203. F- lynx : two extra teeth in premaxillai. Bight incisors normal; sockets for left
incisors normal. Outside left f and close to canine is an extra tooth of good size,
and in same place on right is a socket for a similar tooth. Since they are in pre-
maxillffi these teeth are probably not persistent milk-canines. Lower canines bite in
front of the extra teeth. B. M., 1156, a.

Incisors absent.

9(34_ F. pardalis: il and fl absent on left side. As regards the lower jaw the tooth
may have been present, and been lost, but left £ has probably never been present.
It is especially notable that left f is larger than right f, but there is no indication
that £ is compounded with it. B. M., 1068, a.

F. chate [?= pardalis]: doubtful if i1 has been present on either side. B. M.,
55. 12. 26. 178.
2Qr>. Cynaelurus jubatus : no trace of right P ; same skull has no p^\ lower jaw
' normal. B. M., 135,/.

1 For discussion of such cases see Chapter x. Section 5.

CHAP. IX.]

TEETH I FELID^E.

223

Anterior Premolars {supernumerary).

Upper Jaw.

266. F. pardus : right P^ single and normal; on 1. side two such teeth,
both standing at level anterior to right P1 . The anterior is of same size
as right p^, the posterior is rather smaller. B. M., 87. 4. 25. 1.

267. F. eyra : two small anterior premolars in left upper jaw, Baird, U. S. and Mex.
Bound. Swrv., Pt. 2, PI. xni. figs. 2, a and 2, c [anomaly not mentioned in text].

*268. F. catus, Athens. Two small anterior premolars in upper
jaw both sides (Fig. 40, I.), small and standing close together.
On rt. anterior the larger, on 1. posterior the larger. B. M., 47.
7. 22; 2.

*

269.

270.

271.
272.

Fig. 46. Left-hand figure : upper jaw of F. catus, No. 268. Eight-hand figure :
upper jaw of F. inconspicua, No. 269.

F. inconspicua (= torquata). Rajpootana. Two small an-
terior premolars in upper jaw both sides ; both small, diastema
between them. Posterior is nearly in contact with "jt)3", while
anterior is only a little behind canine (Fig. 46, II.). B. M., 85.
8. 1. 26. (Another specimen has p^_ as large single-fanged
tooth.)

F. domestica (out of 38 skulls) : internal to and rather behind left p} is an
almost identical copy of it, though rather smaller. Not a milk-tooth. C. S. M., 414.

Out of 252 skulls two anterior premolars on Ijoth sides, 4 cases ; on right, 2 cases;
on left, 1 case [none specially described]. Hensel, Morph. Jahrb., 1879, v. p. 553.

F. caligata, Socotra : outside right p}t a small extra tooth. In this specimen )j}
on each side has two roots. B. M., 857, b.

Doubtful cases of extra upper anterior premolar, F. pardus, C. S. M. 365 ; F. leo,
C. S. M. 308.

Lower Jaw.

273. F. concolor : a supernumerary anterior premolar on both sides
present, Berl. Anal. Mus., 3678. Hensel, ibid. F. catus or mani-
culata : ditto. Frank/. Mils., Hensel, ibid. F. catus : ditto, on
left side, closely resembling^1. Two cases, B. M., 1143 and 1143, a.

274. F. domestica : (in 252 skulls) a supernumerary premolar on both
sides, just in front of and nearly same size as the usual "P2," one case ;
on left, as a very small tooth midway between canine and "p*" one
case; on right, rather larger than in foregoing and nearer to "//-',"
one case. Hensel, ibid.

275. F. tetraodon: alveolus for small anterior premolar in right lower
jaw; but as this fossil form very rare, uncertain whether normally

224 MERISTIC VARIATION. [part i.

present in the species, de Blainville, Osteogr., Atlas, PI. xvi. Feles
fossiles.

Variations- in size of P^.

27(3. r. pardus : j£ sometimes two-rooted, as C. S. M., 360 (African); more often
one-rooted, as C. S. M., 304, Arc: many gradations between these. In B. M., 115, q
right i± extraordinarily large, left normal. Minute alveolus external and posterior
to each of these ; on left side a small worn stump ['? of milk-tooth] in this alveolus.

277 r. domestica : />} two-rooted C. S. M. 40'J and B. M., 127, q ; on right side two-

' rooted B. M. 127, 8. F. catus C. S. M. 401 and F. minuta (Borneo) B. M., 122,/,
P1 partially two-rooted. F. caligata, see above, No. 272. F. chaus: left p} very
small, right p] fair size. B. M. 131, e. F. jaguarondi, ditto, B. M.

Absence of p1 .

In the following cases it appeared that p^ had not been

present.

278. F. catus. both sides, a cave-skull, Hexsel, I. c. ; left side only, Caucasus, B. M.
1113, m ; F. tigris, Hexsel, F. onca, both sides, B. M. 117, c ; F. xnanul, ditto,

B. M. 1863, a; F. nebulosa, ditto, two cases [? normal for species] B. M.; F. rubi-
ginosa. Malacca, ditto, B. M., 1856, a; F. chaus: both sides in domesticated
specimen from India, B. M. ; and in B. M. 58. 5. 4. 69, similar specimen, this tooth is
small on left, absent on right; F. brachyurus, absent both sides, B. M. ; F.
cbinensis, right absent, B. M., 70. 2. 18. 25; F. javanensis, left absent, B. M. 1641, a
(but in B. M. 1309, b, p} is particularly large). F. domestica : in 252 skulls v^
nl Kent both sides 6 times, and one side, once (in 2 cases anterior deciduous tooth
remained on both sides in upper jaws of adults) Hexsel, /. c. p. 552; in 38 skulls
seen by me, n} absent both sides, 2 cases ; right side in one case (Manx, C. S. M.,
428, a).

In the following species the absence of vl was so frequent as to call
for special notice.

279. Cynaelurus jubatus : of 8 skulls 3 (2 African) were like Cat,
having 2^ both sides; p1 absent both sides, 3 cases, B. M., 135,/.
and 0. S. M. — ; left p^ absent, right very small, C. S. M., 441; right
;/ absent []]. B. M., 135, c.

280. F. caracal : out of 8 skulls only 4 had any indication that i^1
might have been present, and in these it was doubtful.

281. Lynx : of Lynxes of possibly different species, 17 skulls have no .P1,
a skull marked "Lynx borealis" B. M., 1230, a has a small, worn stump
as p1 on each side.

2S2. F- pajeros ( =pampana)i Chili: 2 skulls only known to Hensel,
I c, both without^. This tooth absent in B. M. 126 and 126, c; but
in one specimen seen, right p^ absent but left p} of good size.

Partial division (?) of lower premolar.

Two cases relate to this subject. The first lower premolar
of Felidse is a two-rooted tooth of well-known form. In the first
of the following cases it bore an extra talon and root ; in the
second there wras a small extra root on the internal face. (Cp.

C. vulpes, No. 230.)

283. F. tigris : anterior right lower premolar has a thin supernumerary
root on internal side of the tooth at the level between the two normal
roots. This tooth in form resembled a milk-carnassial to some extent,
but it was certainly not one of the normal milk-teeth. C. S. M., 333.

CHAP. IX.]

TEETH : FELID^E.

225

*284. F. fontanieri (see No. 290): anterior premolar of right lower jaw
has additional talon on internal and anterior surface (Fig. 47). This

B

C

Fig. 47. Veils fontanieri, No. 284.
A. The normal anterior premolar of the left lower jaw. B. The corresponding
tooth of the right side from above. C. The same from the lingual side.

portion has a separate root, and stands somewhat apart from rest of
crown, looking like a partially separated tooth. B. M., 90. 7. 8. 1.

Duplicate Teeth.

285. F- tigris: on right side, two canines in the same socket, both of
large size, the anterior being the smaller; neither is a milk-tooth.
Mus. Odont. Soc.

28C. F. domestica : having a large supernumerary tooth in each
upper jaw. The extra tooth was in each case a small but accurate
copy of the carnassial tooth (Fig. 48) of its own side. In each

Fig. 48. The teeth in upper jaw of Cat, No. 286.

case the extra tooth stood internally to the carnassial tooth, ex-
tending from the level of the middle of the carnassial tooth to
the level of the middle of the molar. B. M., 83. 3. 10. 1.
287. Specimen having a tooth in the upper jaw closely resembling the
second premolar ("ju3" auctt.) internal to and between it and the
carnassial. The internal tooth is slightly smaller than the second pre-
molar1 (Fig. 49). C. S. M., 414.

1 In this case, it is not possible to say strictly that either of the two teeth " is "
the normal second premolar, rather than the other.

B. 15

226

MERISTIC VARIATION.

[part I.

288. Specimen having a small tooth internal to the middle of the lower
[?side] carnassial (»?): the extra tooth was here divided into two cusps
so that it was a copy of the carnassial.

Iensel, I. c.

rK/

^ ~&

Fig. -49. Plan of teeth in upper jaw of Cat, No. 287. The two teeth marked
with crosses are separately shewn, that on the right being the external.

289. Specimen having a tooth like the last, but not so distinctly divided
into two cusps, internal to posterior end of lower carnassial [?side].
ibid.

Supernumerary Mo lars.

Cases like the last cannot be clearly separated from cases of
true extra molars in series, such as the following.

It is remarkable that no case of supernumerary upper molar in
series seems to be known in Felidas. In the Tiger and other
species the upper molar is sometimes single- and sometimes
double-rooted.
'290. F. fontanieri : a species nearly allied to the Leopard (F.
jxirdus), inhabiting the Kiu-Kiang, a geographically isolated region
of X. China. Only two skulls are known, and each of them pre-
sents an abnormality in dentition (see No. 284). Skull having
supernumerary tubercular tooth in series (nfi) behind the left
lower molar (ml). B. M., 1490, a.

291. r- pardalis: "^2 on left side. Hensel, Morph. Jahrb., 1879, v, p. 541.
F. tigrina : tubercular ^2 on left side. Schlegel, P. Z. S., 1866, p. 419. r. lynx :
ditto [? side}. Magitot, A nom. syst. dent., p. 103. F. domestica : "supernumerary
permanent molar in lower jaw" [no particulars]. Wtman, J., Proc. Boston N. H. S.,
V, p. 160. F. pardus : doubtful indication that a left m2 has been present. C. M.,
933, F.

Absent Molar.

F. leo : ml absent on both sides, and there is no space for it behind the upper
carnassials. B. M., 3043. The only case seen in all Felidas examined. F. domes-
tica : "^ absent [? both sides]. Hensel, /. c, p. 541.

chap, ix.] TEETH : VIVEKRID^E. 227

VIVERRIDJE.

Of the Viverrida?, Herpestes and Crossarchus are the only
genera represented in collections in quantity sufficient to repay
study of their dental variations. In the teeth of these two genera,
however, variation is considerable and appears in some interesting
forms.

In Herpestes there is first some evidence of variability in the
number of the incisors, including one case of extra incisor. Next
the facts respecting the presence or absence of the anterior pre-
molar are of some consequence, both as illustrating the general
variability and modes of Variation of this tooth, and also be-
cause the normal presence or normal absence of the anterior pre-
molar is one of the characteristics of different species, which shew
a progression in this respect. There is one case which should
probably be looked on as an example of duplicate anterior pre-
molar.

There are besides two cases of duplicates of large premolars,
but of true supernumerary molars in series only one case was
seen. Another specimen shewed what is perhaps partial division
of a molar. Of 130 skulls, five had supernumerary teeth, not
including cases of unusual presence of anterior premolar.

Incisors.

The following cases shewed departure from the normal i

1

292. Herpestes gracilis : an extra incisor in lower jaw. ^ and P in
place and clearly recognizable on both sides, but between the two
second incisors are three small teeth, all of about the same size and
shape. Neither of these is a milk-tooth, for the milk-teeth are dis-
tinctly different both in size and form. There was no evidence to shew
which tooth was the supernumerary one. B. M., 826, a.

*293. H. nipalensis J" : only four incisors in lower jaws. This is a re-
markably clean and sound skull. The four incisors stand close together,
filling up the whole space between the two lower canines. There is no
reasonable doubt that only four lower incisors have been present. It
is difficult to see that any of the four incisors exactly corresponds with ■
any of the normal teeth; for while the two lateral teeth are of about
the same size as normal p, they have a different position, arising from
the outer sides of the jaw, slightly in front of the roots of the canines,
whereas normal P arises internal to the other incisors. To what extent
the alteration in position is correlated with the change in number
cannot be affirmed. B. M. 146, m.

*294. H. persicus : only four incisors in lower jaw. Judging from
general appearances it seemed that Tl was missing from both sides. The
teeth stand in a close series between the canines, which are nearer
together than in normal specimens. The consequence of this to the
arrangement of the bite is curious. The left lower canine bites in its
normal place, between the upper canine and &; but the right lower
canine bites in front of the upper ^, which is displaced backwards

15—2

228 MERISTIC VARIATION. [part i.

towards the right upper canine. The whole anterior part of the lower
jaw is thus twisted a little towards the left side.

Besides these two definite cases of absence of incisors, in the following instances
there was a presumption that the absence was due to variation, but a definite state-
ment cannot be made.

H. smithii: only four incisors in lower jaw. B. M., 1435, a. H. gracilis:
doubtful casu of absence of p on both sides. B. M., 789, b. H. nyula : doubtful if
right £ has been present. B. M.

Anterior Premolars.

In the great majority of both Asiatic and African species of Her-
pestes the anterior premolar (;/) is normally present in both jaws, and
in these species 6 cases of absent ^ were seen. When present it
is a tootli of small but still considerable size. It appeared from
the specimens that pi in the species H. gracilis (Africa generally),
and both l^_ and y in H. galera (E. Africa) are commonly absent. As
in other cases of absence of teeth the question arises whether the
absence is due to age or accident, or on the other hand to original
deficiency. This question cannot be definitely answered, but some
considerations touching it should be mentioned.

First, as has been said, the tooth when present is of moderate size:
though small, it is quite large enough to be functional, and is in no
sense rudimentary. In his synopsis of the genera, Thomas1 says of
Herpestes, " Premolars ± (if only 3 in either jaw, a diastema always
present)." There is however no reason for supposing that the presence
or absence of pl is determined by chance. From the fact that a tooth
is small, it by no means follows that it is often lost. To any one
handling large numbers of skulls, instances of the contrary must be
familiar. .A case in the Otters well illustrates this point. In Lutra
vulgaris upper pl is a small tooth, and from its singular position internal
to the canine, it might be supposed that the development of the canine
might easily push it out; yet in 41 skulls of Lutra vulgaris, only
1 case of absence of P^ was seen. Of L. cinerea on the contrary six
skulls are without p] ; but as in two young skulls it is present on
both sides, there is thus a strong presumption that in this species the
tooth is lost with maturity. The frequent absence in the one species
and the constant presence in the others points to a difference in
organization between them. When p1 is missing in a skull, though we
are not entitled to infer that it has not been present, still the fact of
its presence in one case and of its absence in another is on the face of
it an indication that between the two there is a difference or Variation,
but whether the Variation lay in the number of teeth originally
formed or in the mode in which they were affected by subsequent growth
is uncertain. In the specimens to be described the absence of pl in
certain individuals or species is no less definite than its presence in the
others, and that which is a variation in one species will be seen to be
the rule in others.

As regards the presence of px the specimens thus make a progressive
series. Most species having^, but p± as a variation; H. gracilis (and

pulverulentus) having p± normally, but pj as a variation and p

o — o

1 Thomas, 0., on the African Mungooses, P. Z. S., 1882, p. 62.

chap, ix.] TEETH I HERPESTES. 229

also as a variation ; and lastly //. galera having p^ normally but shew-

3 4 4 4

ing a case of p-~- and another of p- ~ . Lastly, all specimens of

Crossarchus seen had p^.

Of species commonly having p±, 91 such skulls and the following cases of absence
of jJl were seen :
*295. H- ichneumon, 9 normals: ^i absent both sides. B. M. ; on left, C. M.,
965, D. H. griseus, 21 normals : pi absent on right, two cases. B. M.,
145, k and m. H. smithii. 6 normals: pi absent both sides. B. M., 979, b; on
left side, B. M. 84. 6. 3. 13.

296. H. gracilis on the contrary shewed j^i m 8 specimens, p1 present both sides
once, B. M., 789, a ; left pi absent once. B. M., 789, b.

H. pulverulentus : p± in 2 specimens.

297. H. galera : pf in 7 skulls, one being quite young: p1 is present in all four places,
in one young skull making pf, B. M., 148, d; pi and p} both present and well
developed on right side in old skull. On the left there is ample room for them. B.
M., 79, a, P} present on both sides and alveolus for pi on right. B. M., 148, I.

Crossarchus : 13 skulls assigned to 4 species, all had pf •

Case of two Anterior Premolars.

298. H. microcephalus : on right side two teeth like p^, crowded
together, others normal. Leyd. M. Compare JRhinogale melleri (an

5 Q

African Mungoose) of which only known skull (in B. M.) has p j -.

The appearance here is that a tooth unlike and rather larger than p^
stands in front of it on each side (see Thomas, I.e., pp. 62 and 84).

Supernumerary Large Premolars.

Taken together the two following cases are important as illustrating
the difficulty of drawing any sharp distinction between cases of dupli-
cates of particular teeth and cases of extra teeth in series. They
should be read in connexion with the cases of F. domestica (No. 286),
Helictis orientalis (No. 312), Vison liorsfieldii (No. 311), Ommatophoca
7'ossii (No. 320), Plioca grcenlandica (No. 324), &c.
*299. Herpestes gracilis: supernumerary tooth in right lower jaw
(Fig. 50). On comparing the teeth of this specimen with those of

Fig. 50. Bight lower jaw of Herpestes gracilis, No. 299. View from labial side ;
ground-plan of the jaw ; separate view of the tooth + . C, the canine.

other Herpestes in which jp is present it is quite certain that no tooth
in the abnormal jaw corresponds with p. The foremost of its pre-
molars on both sides clearly has the form of $K The next teeth have
the correct form of p*. In the left lower jaw the next tooth is p; but

230

MERISTIC VARIATION.

[part I.

on the right side immediately in succession to j? but slightly within
the arcade is another tooth (marked + in the figure), which is very nearly
a copy of p*, though a little smaller. On the outside of the jaw and
behind this tooth is a normal p. From its singular position outside
the series, this tooth might easily be taken for a supernumerary one
though its form clearly shews it to be a natural p* displaced, while two
teeth having the form of p* stand in succession. B. M., 63. 7. 7. 18.
(mentioned 'by Thomas, P. Z. S., 1882, p. 62).
300. H. ichneumon (Andalusia): in one of the upper jaws between
and internal to l^ and i^3 is a 3-rooted tooth (not a milk-tooth) which
in size and shape is about intermediate between P^ and p\ Leyd. M.

Molars.

The only cases of noticeable variation in molars were both in
the same species, Crossarchus zebra. Of this species six skulls were
seen, four normal, and also the two following, the first being a case
of extra molar on each side, the next a case of increase in size and
complex variation in w2, on the left side suggesting a partial divi-
sion of this tooth.
f301. Crossarchus zebra : small but well-formed additional molar
in upper jaw on each side, making pf, m\. (Fig. 51, III.) Teeth
unfortunately all much worn, so that it is not possible to determine
whether any of the molars differ from their normal forms in corre-
lation with the existence of these extra teeth ; but as far as size is
concerned, there was no sign of such change, ^ and ȣ being of
the usual size. B. M., 73. 2. 24. 18 mentioned by Thomas, P. Z.
S., 1882, pp. 61 and 89.

Fig. 51. Crossarchus zebra. I. Posterior upper molars of No.
II. A normal specimen, right upper jaw.
III. Upper jaw of No. 301.

302.

chap, ix.] TEETH : MUSTELINE. 231

302. C. zebra: all teeth normal except second molars in the upper
jaws on each side, which depart from the normal in the following
manner. Right ^ has a small extra cusp (Fig. 51, I.) on its outer
side, making four instead of three as usual (cp. figure of normal,
Fig. 51, II.). The left ™? is very extraordinary. It is rather less
than twice the size of its fellow of the other side (Fig. 51, 1.). The
crown is of an irregularly elliptical form, the long axis being oblique.
The posterior and anterior faces are marked by a shallow groove,
giving an appearance of imperfect division into two teeth. The total
number of cusps is greater than twice that borne by the other, but
from the irregularity of the surface it is not possible to speak more
precisely. For fear of injury the tooth was not extracted, so that
the number of roots cannot be specified. B. M., 82. 5. 26. 1.

303. H. ichneumon (Egypt), having no right m2- Leyd. Mus.

MUSTELIDiE1.

The evidence of dental Variation in this family is at present too
small in amount to be of much value. It is chiefly interesting in so
far as it relates to cases of the occurrence in one genus or sub-family,
of a formula characteristic of another. Variations of this class, con-
sisting in the presence of or absence of the anterior premolar or last
molar, are in some of the forms very common. As will be suggested
in the next chapter, some of these, for example, the variations in p1 in
the Badger, have a certain importance as giving some measure of the
magnitude which a tooth may have when the species is, as it were,
oscillating between the possession and loss of the tooth in question.

Amongst Mustelidse there were two cases of supernumerary large
premolars, probably reduplicatory.

A nterior Premo lars.

Mustela (Martens), normally p±, m%. Seen in adult skulls of various species
[M . peunanti, mattes, foina, zibellina, Jlavigula, americana), 62: also the following:
3Q4 M. foina <? : pi absent both sides. B. M., 1229, k. M. zibellina: pl absent
both sides from both jaws [perhaps lost], B. M., 58. 5. 8. 189. M. flavigula.
Madras, p1 clearly absent from both jaws, B. M., 79. 11. 21. 621. M. martes ?
the same. C. S. M., 681. Ufl. melanopus: p1 absent, probably lost, B. M., 42. 1.
19. 100.

Futorius (Weasels, Stoats, Ferrets and Polecats), normally p% , mh. Seen in

adult skulls of various species (P. vulgaris, erminea, brasiliensis = xanthogenysf

fcetidus = eversmanni = sarmaticus, lutreola, nudipes, &c), 105: also the following:

305. p- erm*nea: 1. ^ absent, B. M., 43. 5. 27. 11. On the other hand, P. foetidus,

' B. M., 192 s, has rt. ^ as a two-rooted tooth, standing in a plane at right angles to

the arcade.

Gulo : p^, mh 5 specimens.

1 Totals of normal skulls refer to Brit. Mus. and Cambridge Mus. only.

232 MERISTIC VARIATION [part I.

Galictis : ;>:], mk. Normal adults (G. barbara 8, vittata 4, alla-
mo it'll 2), 14 specimens.
*306. Gr. barbara, having minute extra anterior premolar (making 4) in
each lower jaw. B. M., 839, f.

In 28 skulls Hensel found the following variations in premolars,
the molars being always ?/*.!•

p - — , viz. the normal, 12 cases
o — o

3—3 „

'■■1=2 6 »

3—3 ,

';3-2 3

53

3—3
* 2-3

9

-1 5)

2 3 3 2 4 4 2 2 3 4

;i]s° J' J^2,P 3~r3' P 2--rP 2~~3'7' 3^3 ea°h ™ °ne CaSG'
Taken together therefore there were 12 normals with j>%, 16 cases of
greater or less reduction, and 2 cases of increase. Hensel1, Saugethiere
Sud-Brasiliens, p. 83.

307. G- vittata: p1 may be absent, especially from upper jaw. Bukmeister, Reise
durch d. La Plaata-Staten, Halle, 1861, n. p. 409 [this variation not seen by
Hensel].

Poccilogale: p|, m{. 3 specimens.
Mephitis : p!}, mh. 9 specimens.

308. Conepatus: p$, m$. 12 specimens. Conepatus is the S. American representa-
tive of Mephitis, and normally differs from it in having one premolar less in upper
jaw. This tooth is sometimes present as a minute tooth making p% . Sometimes
on the contrary there is a premolar less in the lower jaw, giving p\. Coues,
Fur-bearing Animals of N. Amer., p. 192 and Note.

In addition to the 12 normals mentioned two cases of pf were seen, viz.
C. mapurito, B. M., 88. 11. 25. 8, and C. chilensis, B. M. 829, a. In the former
the anterior premolar is of good size, but in the latter it is very rudimentary.
Another case mentioned by Baibd, Mamm. of N. Amer., p. 192.

Mydaus : pf, ml. 4 specimens.

*309. Meles : commonly pj-, m\. In M. taxus, the common Badger,
p} is frequently absent from one or more places. Of 36 skulls only 16
had p* in all jaws, 7 have it in each lower jaw and 2 had no such tooth
in either jaw. In remaining cases it was sometimes absent on right,
sometimes on left, sometimes from above and sometimes from below.
Some of these cases may be due to senile changes but this was certainly
not so in all. Absence from lower jaw seems the most common.
Hensel, Morph. Jahrb., 1879, v. p. 550.

Of genus Meles the following were seen by myself. + means pre-
sence, — absence of pl.

1 The numbers given by Hensel are the totals of p + m, but he states that
the variation always concerned the small anterior premolars next the canines.

CHAP. IX.]

TEETH : MUSTELID^E.

233

Upper jaw

Lower jaw

ji.

i

Cases

right

left

r"

right

left

Meles ta.riis

+

+

+

+

3

)> )j

-

-

+

j-

16

>5 »1

-

-

?

?

1

») 11

—

—

—

—

1

)) )J

+

-

4-

+

3

il/. ana kirn )

+

+

+

1

25

2

Japan )

M. chinensis

3

Taxidea : p% , mj. 7 specimens.
IVIellivora : p% , m^-. 7 specimens.
Helictis: p±, m\. 6 specimens.
Ictonyx ( = Zorilla) : p%, m\. 14 specimens.

310. Lutra. The Otters for the most part have p±, mh. The anterior
premolar of the upper jaw is a small tooth standing internal to the
canine, but in the common Otter its presence is most constant. In the
Oriental L. cinerea, and the Neo-tropical L.feUna on the contrary this
tooth appears to be more frequently absent than present. The follow-
ing table gives the results of examination of a series of skulls.

+ signifies presence, — absence of p\

Lutra vulgaris

11 11

,, macrodus

11 11

,, cinerea

'» >j

,, Sumatra na

,, capensis

ii ii

,, maculicollis

,, felina

ii ii

>) )>

,, sp. (S. America)

»j ii

ii ii

right

left

Cases

+

+

40

—

+

1

+

+

11

—

2 (1 old ; 1 young)

+

+

2 (young)

—

—

6

+

+

4

+

+

1

—

—

1

+

+

1

+

+

3

—

—

3

+

—

2

+

+

14

—

—

1

+

~

1

In L. cinerea ( = leptonyx) the absence of l^_ is associated with a
more forward position of p^, of which the anterior border is then level
with the posterior border of the canines1.

1 See Flower and Lydekker, Mammals, Living and Extinct, p. 568, Fig. 261.

234

MEBISTIC VARIATION.

[part I.

Large Premolars.

311. Putorius (labelled " Vison Horsfieldii"): at the place in which
the right lower posterior premolar ("j74") should stand there are two
such teeth at the same level. They are almost identical, but the inner

-A

Fig. 52. Putorius, No. 311, right lower jaw, ground-plan of teeth and profile
views of two teeth at the same level. Upper figure is the internal tooth.

(upper in figure) is slightly the smaller (Fig. 52). B. M., 823, a.
312. Helictis orientalis, Java: having supernumerary two-rooted
tooth internal to and between p2 and f£. This extra tooth is almost a
copy of if (Fig. 53). B. M., 824, a.

Fio. 53. Helictis orientalis, No. 312. Surface view of upper jaw and a
representation of the right upper teeth as seen from inside.

Molars.

313. Putorius: Hensel, Morph. Jahrb., v. 1879, p. 540, states that he
has several skulls of Fcetorius putorius with an extra upper molar on
one side in a rudimentary condition. Giebel, Bronn's Kl. u. Ord., p.
18G, Taf. xv. figs. 1, 2 and 3, figures a specimen of "Putorius typus"
having a fairly well developed extra upper molar on each side making
m# instead of m\. Probably both these accounts refer to P. fcetidus.

314. Lutra platensis: supernumerary molar on one side of upper jaw.
Such a tooth normally present on both sides in L. valetoni, a fossil
form. Von Heuglin, Nov. Act. Leop. Car. Cces., xxix. p. 20. Lutra

*

chap, ix.] TEETH : PINNIPEDIA. 235

sp., S. America, B. M., 85. 11. 23. 1, has small alveolus behind?^ on each

side.
315. Mellivora (= Ratelus): similar case. Vox Heuglix, ibid.
31(3. Meles taxus has normally m\. Skull from Quarternary diluvium

of Westeregeln has small alveolus behind right w^ and left m7-. Another

fossil skull has m§. Nehring, Arch. f. Anthrop. x. p. 20. [1 Small

alveolus behind left m* in B. M., 211, L]

31/. Lutra: case of absence of ^a; Mustela : ^ may be absent. Hensel, I. c.

PINNIPEDIA.

With reference to dental Variation in Otariidae and Phocidse
there is a considerable quantity of evidence. Id some of the species
the frequency of abnormalities is remarkably great. Among the
most interesting examples are two cases of reduction in the number
of incisors, both occurring in Phoca barbata. These cases are
especially important in connexion with the fact that the Seals are
exceptional among Carnivores in having a number of incisors other
than §, and that among the different sub-families of Seals there is
diversity in this respect.

Taken together, the cases of Variation in the premolars and
molars of Seals illustrate nearly all the principles observed in the
numerical Variation of teeth. In both premolars and molars there
are examples of the replacement of one tooth by two, and in some
of these the resulting teeth stand in series while in others they
do not. Besides these there are numerous instances of extra pre-
molars and molars belonging to various categories.

As regards the frequency of extra teeth in Seals it may be
mentioned that of Phocidae 139 normals were seen, and 11 cases of
supernumerary teeth ; of Otariida? 121 normals and 5 cases of super-
numerary teeth.

From the simplicity of the normal dentition and from the
diversity of the variations presented, the evidence as to the teeth
of Seals may conveniently be studied by those who are interested
in the phenomena of Variation without special knowledge of the
subject of mammalian dentition.

Incisors.

It will be remembered that of Phocidae the sub-family Phocinae
(like Otariidae) has normally if, while the Monachinae have if and
the Cystophorinas i \. Of Phocinae of various genera and species
105 skulls having if were seen, and in addition the two following.

318. Phoca barbata. Greenland: skull having i\ on both sides
(Fig. 54). This skull is a particularly good one and is neither very
old nor very young. The teeth stand regularly together and there
is no lacuna between them. There is no reasonable doubt that
an incisor is absent from each side of each jaw. The shape of the

236 MERISTIC VARIATION. [part i.

premaxillae is different from that seen in other specimens of Phoca,
and, doubtless in correlation with the absence of the two upper

Fig. 54. Incisors and canines of Phoca barbata, No. 318.

incisors, the width of the premaxillae is considerably less than in
specimens having the normal dentition. B. M., 90. 8. 1. 6.
319. P« barbata: in left upper jaw are three normal incisors; but
on the right side the incisors have been lost. The alveoli, however,
shew plainly that only two incisors had been present. Of these
the outer one in size agrees with P, being a large alveolus equal to
that of i"3 of the other side, but the second alveolus, occupying the
place of il and i2, is also a large alveolus, scarcely smaller than that
for R It appears therefore that in this specimen a single large
tooth stood in place of i1 and %K A lower jaw placed with this skull
was normal, but it was not certain that it belonged to the skull.
O.M., 1724.

Premolars and Molars.

Normal arrangement. In Phocidae there are normally five
teeth behind the canines in each jaw, and according to the received
accounts, of these teeth 4 are premolars and one is a molar, giving
p f> m p Tne Otariidae on the other hand have generally p |, m f ,
but both the two upper molars stand at a level behind that
of the lower molar, so that the posterior molar, w*2 is placed so
far back that it meets no tooth in the lower jaw. Some of the
Otariidae, however, as 0. californiana, do not possess such a pos-
terior tooth, and have only m {. 0. stelleri is peculiar in the fact
that it also has only one upper molar, but this tooth is separated
by a large diastema from p4, and stands in the position character-
istic m2 of the other Otariidae. Hence it may be supposed that ^
is really absent while »&2 is present.

Amongst the cases will be found some of the presence in Pho-
cidas, especially Halichoerus, of an extra molar placed in the usual
position of ȣ in the Otariidae. But lest any one should think it
manifest that this is an example of Reversion to the Otarian con-
dition, attention is called to cases of such an extra molar in the
Otariidse also. Similarly there are instances of absent molar in
those Otariidae which have m f , leaving m -j- ; and of these cases one
occurs in such a way as to leave the peculiar diastema between

CHAP. IX.]

TEETH : PINNIPEDIA.

237

*

P^ and the molar, referred to above as characteristic of 0. stelleri
(see No. 342).

The cases are grouped in an arbitrary collocation, according as
it seemed desirable that particular variations should be studied
together. In the sections dealing with premolars, Phocidae are
not separated from Otariida1.

First Premolar.

320. Ommatophoca rossii, an Antarctic Seal. Of this form only
two skulls are known, both in the British Museum. One of these
(B. M., 324, b.) has the arrangement usually found in Phocidae,
namely, five teeth behind the canines in each jaw, giving the
formula

.2—2 1 — 1 5—5

*2ZT2'flI— I>^ + m5=5

(on the analogy of other Seals p|, m\). The other specimen is
exceedingly remarkable (Fig. 55). In it the incisors and canines

Fig. 55. Ommatophoca rossii, No. 320, teeth of the upper jaw.

are as in the first specimen, but the first tooth behind the canines
on both sides in the lower jaw and on the right side in the upper
jaw, has a very peculiar form, having a deep groove passing over
the whole length of the tooth, on its outer and inner sides. These
grooves extend from the tip of the root along both sides of the
crown, and thus imperfectly divide each tooth into an anterior and

238 MEBISTIC VARIATION. [part i.

a posterior half. The cusp of each tooth is also divided by the
grooves so as to form two small cusps. Each of these teeth is
therefore an imperfectly double structure, and may be described as
being just half-way between a single tooth and two teeth. These
teeth are shewn in Fig. 56.

Fig. 56. Ommatophoca rossii, No. 320. The anterior premolars of upper and
lower jaws from the side. (The left lower and right upper teeth were not
extracted.)

On the left side in the upper jaw, as the vis-a-vis to one of
these double teeth, there are actually two complete teeth, of very
similar but not identical form, as shewn in Fig. 56. Each stands
in a distinct alveolus, the two being separated by a bridge of bone.
The dental formula of this skull, taken as it stands, is therefore

p' i' mn T> f°r snlce the bigeminous teeth are not com-
pletely divided, they must be reckoned as single teeth.

321. Cystophora cristata : internal to and slightly in front of p1 on
each side in the upper jaws is an extra tooth. These extra teeth are
alike in form but are rather smaller than jp\ C. M., 895.

322. Cystophora cristata (label, Phoca cristata): internal to right
upper p^ is an alveolus for a small one-rooted tooth. In the corre-
sponding situation in the left lower jaw there is such an extra tooth in
place. Leyd. M.

323. Zalophus lobatus ( = Otaria lobata): left 2^ smaller than right
j^, and between the canine and the left F1 there is a supernumerary
tooth, smaller than left P1. (The same skull has another extra tooth
outside and between F* and i^, see below No. 333.) Leyd. M.

[P. vituUna: alveolus for left #] much larger than that for rt. vl\ the latter
tooth is in place, hut left & is missing. C. M., 902.]

Large Premolars.

324. P« groenlandica : in the position in which left upper p*> should
stand there are two whole and complete teeth, each as large as normal
p^. Fig. 57). The two stand perfectly in series, and owing to the wide

CHAP. IX.]

TEETH : PINNIPEDIA.

239

gaps normally existing between the teeth in this species there is no
crowding. Between these two teeth there are slight differences of

325,

Fig. 57. Phoca groenlandtca, No. 324. Left and right profiles.
This figure was kindly drawn for me by Mr J. J. Lister.

form, and the posterior is rather the larger. On both sides w^ is in
place and at the same level. Both the two teeth in place of p^ bite be-
tween p* and ™} of the lower jaw. On the right side F* is normal and m^
is also normal but P^ is a very large and thick tooth, and its main cusp
is cloven, giving it the appearance of imperfect division into two. In
this case therefore p^ on the one side may be supposed to have divided
into two perfect and nearly similar teeth, while on the right side this
division is begun but not completed. Leyd. M.

Otaria ursina £ : supernumerary premolar in left upper jaw.
This is a curious case. The right upper and both lower jaws are
normal. On comparing the left upper series of 7 teeth with the right
series which has 6 normal teeth, it is seen firstly that the two molars
of each side are alike in form and stand at their proper levels (Fig. 58).

Fig. 58. Otaria ursina, No. 325, seen from left side. 1, 2, 3, 4, first to fourth
lower premolars ; 5, lower molar.

Next, the two posterior premolars of each side (f* and F4) agree so
nearly that there is no reasonable doubt that they are not concerned
in the variation. Anterior to this there is difficulty, for whereas pl
and p2 are normal and in place on the right side, there are three teeth
on the left side to balance them. These three teeth moreover are so
nearly alike that it is impossible to say that either of them is

240

MEMSTIC VARIATION.

[part I.

*

definitely the extra tooth. The first premolars of each side are almost
exactly alike, and the second and third of the left side are each very
like the second on the right side (p2), so that it might be said that p2
was represented by two teeth on the left side; and as seen in Fig. 58
the second and third on the left side bite between f- and p of the lower
jaw, as the normal p2 would do. This is however accomplished by the
backward displacement of p*. Probably therefore this should be looked
on as a case of division of P^, but there is no proof that the three first
premolars of the left side are not collectively equivalent to the first
two of the right side. C. M., 911, f.

326. P. grcenlandica : the second upper right premolar is represented
by two teeth, each of which has two roots; the two teeth stand at the
same level in the arcade, the inner one being rather smaller. On the
left side the second upper premolar is incompletely double, the crown
being partially divided by an oblique constriction into an anterior and
internal portion and a larger posterior and external part. The former
has one root and the latter two. P. M., A, 2897.

327. Otaria jubata : left upper p3 a bigeminous tooth something like
the anterior premolars of Ommatophoca (No. 320). In this animal all
the premolars and molars are one-rooted and have single conical
crowns. The abnormal tooth is formed as it were of two such simple
teeth imperfectly divided from each other through their whole length,
the plane of division being transverse to the jaw. The teeth of the two
sides are not alike and in particular the posterior lower m} is much
smaller than the right. The skull has been much mended and the
position of some of the teeth is not very certain, but the above-
mentioned facts are correct. C S. M., 975.

oZo. Otaria cinerea : supernumerary tooth in upper jaw on both sides.
The extra tooth in each case stands within the arcade, internal to the

Fig. 59. Otaria cinerea, No. 328. A diagram of the positions of the upper
teeth, and profiles of the teeth standing internal to each m*.

5th tooth behind the canine (sc. »^), which is pushed outwards by it.
The extra tooth of the left side (Fig. 59) is a little larger and at a level
rather anterior to that of the left extra tooth. C. M., 911 **.

CHAP. IX.]

TEETH .* PINNIPEDIA.

241

*329. P. vitulina : having a supernumerary tooth in each jaw on the
right side. This is a somewhat remarkable case. In both jaws the
extra tooth does not stand in series with the others but is placed
within the arcade (Fig. 59, + + ). That of the upper jaw is a curved
tooth with one large median cusp and a small cusp anterior to and
posterior to it, having somewhat the form of p* of the lower jaw. This
tooth stands within the arcade at a level between that of l^ and F5 which
are pushed outward by it. The extra tooth of the lower jaw in shape
closely resembles that of the upper jaw, but is slightly larger, having
very much the size and shape of the lower right jp. In position this
extra tooth does not stand between p2 and p3 like the upper supernum-
erary, but is placed ivithin the arcade and p and p* which are some-
what separated by it. C. M., 903. [Judged by the ordinary rules of
dental homology, the two extra teeth are not homologous, for the
upper one is between p2 and p-\ while the lower one is between p and
p4. But when the jaws are put together it appears that the two extra
teeth are opposite to each other almost exactly, the large cusp of the
lower one being in the bite scarcely at all posterior to the large cusp of
the upper. The tooth of the lower jaw is thus almost exactly the
image or reflexion of the tooth in the upper jaw.]

Fig. 60. Phoca vitulina, No. 329 ; view of upper teeth from the surface, and
an imaginary profile of the upper and lower teeth of the right side seen from
within.

330. Otaria ursina : this skull in bad condition. The Catalogue
(1884) states that between F2 and l^ on both sides and between P^ and nfl
on both sides there was a small supernumerary tooth, in all, four extra
teeth in the upper jaw. The anterior supernumeraries are in place and
one rather smaller than v\ The posterior supernumeraries are lost, but
from the alveoli they must have been of fair size, though not so large

B. 16

242 MERISTIC VARIATION. [Px^rt i.

as lA In each case the extra tooth is placed a little within the arcade
though the adjacent teeth are also spaced out for it. This skull has
been a good deal mended. C. S. M., 990.

331. Phoca grocnlandica : in right upper jaw p^ is smaller than the corresponding
tooth of the left side, though it is two-rooted as usual. Between it and pI there is
a small, peg-like, supernumerary tooth. Both p^ and the extra tooth bite between
pi and m1 of the lower jaw. Leyd. M.

332. P. grocnlandica: supernumerary tooth with two roots placed internally to and
between left & and m\ The last molars stand at the same level on the two sides.
B. M.,328, i.

333. Zalophus lobatus: in right upper jaw a supernumerary tooth placed on the
outside of the arcade on a level with the interspace between p* and p4. This tooth
resembles p4 or m1. On the left sidep1 is smaller than on right side and a supernu-
merary tooth which is still smaller stands between p^ and the canine. Leyd. M.
[given above, No. 323].

334. P. vitulina: in right lower jaw a supernumerary tooth inside the arcade,
between pi and pi. In size and form it agrees very nearly with the first premolar
of the right lower jaw: other teeth normal. C. M., 903, F.

335. 3P. vitulina: in front of p* on left side the teeth are all lost but there has been
some irregularity, probably a supernumerary tooth level with pi : also behind right
nfl there is a small tubercular nodule of bone which may perhaps cover a supernu-
merary molar. C. S. 31., 1064.

Molars.

336. P. vitulina : on left side there is a small supernumerary molar
placed behind »^. This tooth stands in the line of the arcade (Fig. 61)

Fig. 61. Phoca vitulina No. 336, a profile of the left teeth in the bite as seen
from within.

but is turned so that its greatest width is set transversely to the jaw.
In the lower jaw of the same side there is a supernumerary tooth placed
internally to ml. This tooth has two roots and three cusps, and is
therefore not a copy of m1, which has 4 — 5 cusps. C. S. M., 1067.

'337. Halichoerus grypus : of 47 skulls seen, 12 have one or more
supernumerary molars. One case of p% , m§. Nehring, Sitzb.
naturf. Fr. Berlin, 1883, p. 110.

2 2

Of 34 skulls in Greifswald Museum there were 3 cases of m ^ ,

and five cases of m\ on one side only. Ibid., 1882, p. 123.

Of 11 skulls seen by myself two individuals (C. M.) have an
extra molar on left side. In these cases the extra teeth are
placed at a considerable distance behind ȣ as they are in Otaria.
[In addition to these Gray figures a skull with m\ but without
allusion to this fact in the text. Hand-list of Seals in B. M.,
1874, PL vil]

chap, ix.] TEETH : UNGULATA. 243

A skull having left ml two-rooted, right ml being much less so.
C. S. M., 1059.

338. •P- groenlandica : minute supernumerary molar on each side in
upper jaw making m'f . P. M., A. 2898.

339. Zalophus californianus, an Eared Seal not far removed from

0 tar la. but having p + mi instead of ~. The five back teeth are arranged
as a rule in a continuous series, but sometimes there is a small space
between the last molar and the penultimate [cp. 0. stelleri], and occa-
sionally they are all slightly and evenly spaced.

One case of p + m £ on both sides and two cases of p + m£ on one
side only. In these the extra teeth were behind the (normally) last
molar and smaller than it. being without the accessory cusps seen in
that tooth. Allen, J. A., J\\ Amer. Pinnipeds, 1880, pp. 209, 224 and
226.

340. Z. lobatus : one specimen having p + w^f on right and £ on left,
Leyd. M. [in addition to 3 specimens with the normal £].

7 — 7

341. Callorhinus ursinus : normally £> + m£; one case having

o — o

and one case with - -. Allen, I. c, p. 224 (cp. No. 343).

o — o

deduction in numbers of molars.

q 5

342. Arctocephalus australis, normally p + mf : one case of „ — .

General statement made that in cases of absence of a tooth it is the
antepenultimate molar which is missing [not described in a specific
case]. Allen, I. c, p. 224.

343. Callorhinus ursinus, normally £; 2 cases of i. Allen, I. c. (cp.
No. 341).

344. Otaria jubata, normally 4: one specimen having 4- on both sides,
Leyd. M.; one specimen having right 4 left 4. Leyd. M.

Cystophora cristata: only one molar, viz. left ^ present; from the state of
the bones it seemed possible that the others had not been formed, but this is quite
uncertain. C. S. M., 1101. Macrorhinus leoninus: doubtful if the molars had
been present. C. S. M. 1109.

UNGULATA.

As to the occurrence of Variation in the dentition of Ungulates

1 have no statistics, but a certain number of miscellaneous cases
have been collected from different sources. Most of the cases
relate to domestic animals and are given on the authority of
Morot and Goubaux.

Perhaps the most interesting evidence is that regarding the
change of form in the "canines" of the Sheep. These teeth of
course have normally the shape of incisors, but in the cases
described by Morot they had more or less of the character of
canines. This evidence, though belonging properly to the Sub-
stantive class, is introduced here on account of its close relation to
some general aspects of variation in teeth.

1G— 2

244 MERISTIC VARIATION. [part i.

* It is noticeable that there is so far no case of an incisor appear-

ing in the upper jaw of Ruminants.

The evidence is divided into two groups, the first relating to
incisors and canines, the second to premolars and molars.

Incisors and Canines.

345. Elephas africanus g : the left tusk imperfectly doubled. The
root of this tooth was double1, one root being outer and the other inner.
The half of the tusk arising from the outer root twisted round and over
the other half so that at the other end it lay above and internal to it.
The structure of the tusk was essentially double, but the two parts
were more or less blended together in the middle third. The ex-
ternal ends were separate, but broken and somewhat deformed.
Friedlowsky, A., Sitzungsb. d. K. Ak. Wien, 1868, lix. i. p. 333.
Plate.

346. Horse. Supernumerary incisors common. Magitot, Anom. Syst.
dent., p. 104, Plates. Numerous specimens in Museum of Veterinary
School at Alfort.

347. Specimen having 12 upper incisors and 12 lower incisors belonging
to the permanent dentition. Goubaux, Pec. med. vet., 1854, Ser. 4, I. p.
71. Similar observation, Lafosse, Cours Hippiatrique, 1772, p. 32.

348. Extra teeth of more or less irregular form placed behind upper
incisors very common : many specimens in museum at Alfort. Speci-
men having left ^ as a double structure, the two halves not being
separated. (Alfort Mus.) Magitot, /. c, PI. xix. fig. 25.

Absence of incisor in Horse is rare. Goubaux, who has largely studied the subject,
knew no case of absence of any tooth in Horse, /. c.

349. Skeleton of Cart-mare in C. M. has only two incisors on the left side in the
upper jaw. The teeth stand evenly and without break or trace of any other incisor
having been present. There is no sufficient indication to shew which of the incisors
is missing, but the two incisors present agree most nearly with i2 and i3. This
specimen was first pointed out to me by Mr S. F. Harmer. (See also case given by
Kudolphi, Anat.-phys. Abh., 1802, p. 145.)

*350. Mare of common breed, foaled March, 1876, having in the upper jaw no i3 in
either milk or permanent dentition, and in the lower jaw no permanent P. In the
upper jaw there were only 4 milk incisors, which were subsequently replaced by
4 permanent incisors. Animal seen by Morot in Apr. 1880 ; it then had 4 per-
manent incisors in the upper jaw, but no i3. In the lower jaw permanent i1 and i-
were in place, together with i3 of the milk series on each side. As Morot remarks it
is still possible that the other incisors might appear. Dam normal; half-sister
abnormal, given in next case. Morot, Bull. Soc. med. vet., 1885, Ser. 7, n. p. 125.

*351. Mare out of same mother as last case, by another sire, foaled Apr. 1877, had only
4 milk-incisors in upper jaw. Seen by Morot at 3 years old, had then the teeth of
lower jaw normal, viz. permanent i1, and milk i2 and i3 all in place. In upper jaw
were permanent i1 and milk i2 on each side. The right milk /- on the external side
had a light groove parallel to the long axis of the tooth, suggesting that it might be a
double structure, but the groove was very slight and the crown was single. At five
years old this animal had the normal 6 lower incisors, but in the upper jaw left i3
was absent. On the other hand a well-formed supernumerary tooth stood behind
right i3, right i2 being partly rotated. Ibid., p. 127.

1 See also a curious case of "nine tusks " imperfectly described by Chapmax, J.,
Travels in Interior of S. Africa, n. p. 98.

chap, ix.] TEETH : TJNGULATA. 245

352. Ass : ( $ some 20 yrs. old) on right side in upper jaw were two
canines, one in front of the other in the same alveolus. Morot, Rec. med.
vet., 1889, Ser. 6, vn. p. 480. Another somewhat similar case, ibid.

353. Cow : in j}lace of right p, two third incisors placed side by side.
Morot, Bull, et mem. Soc. med. vet., 1886, p. 321.

Goat, 4 — 5 weeks old ; supernumerary lower incisor placed be-
tween the two median incisors which rose above it. This tooth stood
transversely so that its edge lay exactly in the long axis of the head.
Morot, /. c.

354. Sheep : extra incisor on left side. (Alfort Mus.). Goubaux, Rec. med.
vet., 1854, Ser. 4, I. [Several other cases.]

Abnormal form of Canines in Sheep.

355. In the lower jaw of the Sheep there are on each side 4 incisi-
form teeth, arranged in close series without any diastema. Of
these the outermost, known in veterinary works as " corner teeth,"
are considered by zoologists as representing canines.

The corner teeth or canines have been found in a considerable
number of cases actually shaped like canines instead of like the
incisors as usual. These teeth have been found presenting this
modification in several degrees, but in order to gain a fair view of
the matter it is necessary to read the evidence in its entirety.

The facts given were founded on 18 animals, 15 ewes and 3
males [whether rams or wethers not stated]. In these 18 cases
there were 28 individual teeth of abnormal form. Of these 14
were conical with a point either sharp or rounded ; 7 were conical
with a bifid point ; 5 were cuneiform ; 1 was cylindrical with a
surface shaped like an ass' hoof; 1 was pyramidal.

In 8 specimens the abnormality was unilateral and in 10 it
was bilateral, but in the latter the corner teeth of the two sides
were frequently of differing forms [details given]. Morot, Bull.
Soc. med. vet., 1887, p. 166.

Pig". No case of Variation in incisors met with.
[This is perhaps singular in connexion with the fact that the
Peccaries (Dicotyles) have i -§.]

356. Dicotyles torquatus (normally £§) : two specimens having

3 2

i-= ; in one of them i* of the side having the extra tooth is deformed.

o — o

Another young skull of Dicotyles also had 3 incisors on left side.

Hensel, Sdugetldere Sild-Brasiliens, p. 94.

Molars.

357. Horse: supernumerary molars exceedingly rare; case of such a tooth in left
upper jaw, behind and in series with the others. Goubaux, Rec. med. vSt.} 1854,
Ser. 4, i. p. 71, same case, figured by Magitot, /. c, PI. v. fig. 9.

*

246 MERISTIC VARIATION. [part i.

*358. Ass : thoroughbred Spanish she-ass, in the Museum of the Royal
College of Surgeons, has a large supernumerary molar on each side in
series in the upper jaw, and a similar tooth in the left lower jaw. The
same skull has the first premolar also present on each side in the upper
jaw, as is not unfrequently the case in Equidse. All four canines are
present as minute teeth. The dental formula for this skull is therefore

,3_3 l_i 4_4 4 — 1 tK
^3=3Cr=Ti^3=3m4^3=45'

359. Auchenia lama : specimen having a suj>ernumerary (fourth)
molar in the lower jaw [? on both sides]. This tooth was fully formed
and resembled the normal last molar. In the upper jawT was a small
alveolus behind ?/i3, for another tooth which was not present in the
specimen. Rutimeyer, L., Vers, einer nattirl. Geschichte des Binder,
Zurich, I. p. 55, Note.

360. Cervus axis $ : specimen having a supernumerary grinder placed
on the inside of the normal series on the left side of the upper jaw.
In the lower jaw of the same specimen the following supernumerary
teeth : (1) a small, compressed accessory tooth on both sides placed
internally to m? ; and (2) behind the large three-fold sixth molar was a
smaller two-fold tooth which had caused a displacement of the 6th
molar. Donitz, Sitzungsb. d. naturf. Fr., Berlin, 1872, p. 54.

361. Cervus rufus : having supernumerary (4th) premolar on one side
in lower jaw. Hensel, Morph. Jahrb., v. p. 555.

362. Ox : supernumerary upper molar on left side. Magitot, I. <?., p.
106.

Sheep : extra molar in left lower jaw, ibid., p. 105, PI. v. fig. 10.
[? some error ; the figure represents a normal jaw.]

MARSUPIALIA.

The facts given in illustration of Variation in the dentition
of Marsupials relate only to a part of the subject and to selected
forms. Some of the cases to be given are however of exceptional
importance. Evidence is offered in reference to the following
subjects:

(1) Incisors.

(2) Premolars, and the "Intermediate" teeth (in the lower

jaw), of Phalangerida3.

(3) Premolars and Molars of Dasyuridaa and Didelphyidre.

(4) Molars of certain Macropodida?.

(1) Incisors.

The following cases of Variation in incisors are all that were
met with in the Marsupials examined.

Didelphyid/E : incisors normally f, thus differing from the Dasy-
uridpe (i |) with which they have much in common1. Of various

1 Thomas states that the family Didelphyidae "is, on the whole, very closely
allied to the Dasyuridae, from which, were it not for its isolated geographical
position, it would be very doubtfully separable. " Cat. Marsup. Brit. Mas., 1888, p. 315.

CHAP. IX.]

TEETH I MARSUPIALIA.

247

species 90 adult skulls seen having this number of incisors and three
cases of abnormal number of incisors. Of these the first two must not
be reckoned in estimating the percentage of abnormalities in a pro-
miscuous sample, for Mr Thomas, who kindly shewed me these speci-
mens, informs me that they were preserved and brought to the Museum
expressly as abnormalities. The existence of these variations is never-
theless particularly interesting in connexion with the exceptional
number of incisors normal in Didelphys.

363. Didelphys marsupialis : in right upper jaw six incisors ; left
upper jaw and the whole lower jaw missing. B. M., 92. 11. 3. 28.

364. Another specimen has on the right side |- as usual, but on the left
i |-. It appears that i1 and 72 of the two sides correspond, but on the
left side three very similar teeth stand in series behind P. B. M., 92.
11. 3. 29.

365. D. turneri (= crassicaudata), Demerara. A single specimen of

.4 — 4
this species in collection. It has i- 7, but there is no evidence to

4—4'
shew which of the upper incisors were missing

B. M.

*

Dasyurid^e : incisors normally ±; of genera other than Myrme-
cobius, 63 normal skulls seen.

Dasyurus sp., having only two incisors in left lower jaw; right lower jaw
normal, upper jaws missing [doubtful case]. B. M., 250.

Myrmecobius fasciatus: with incisors normal 4 whole skulls,

Right

n

Right

left

Fig. 62. Myrmecobius fasciatus.

I. Right and left profiles of upper jaw of No. 366.

II. Eight and left profiles of the two jaws of No. 367.
(Premaxillary teeth alone shewn.)

248 MERISTIC VARIATION. [part It

5 skulls without lower jaws, and 1 lower jaw without skull ; ab-
normals 2, as follows :
*3G6. A young skull having in the upper jaw on the left side
(Fig. 62, I.) two teeth, both apparently in place of left «?, making

i%~ . B. M, 314, g.

*367. A specimen having four incisors in the right lower jaw, the
left being normal. Perhaps the two hindmost of the four repre-
sent the third lower incisor of the left side in the way suggested
by the dotted lines in the figure (Fig. 62, II.). B. M., 314, b.

Phalaxgerid.e : incisors (neglecting " intermediate " teeth of
lower jaw) normally y ; this seen in 209 skulls of various genera and
species.

368. Phalanger orientalis, Solomon Islands: left i3 as an imperfectly double tooth,
having two sub-cylindrical crowns and only one root (Fig. 63). The two crowns

Fig. 63. Phalanger orientalis. No. 368.

Upper incisors and canines. The separate figure shews the left P extracted.

stand in the same transverse plane, the one being internal to the other and rather
smaller than it. Lower jaw missing. B.M., 1936, c. [Two other skulls from same
locality normal.]

369. P- maculatus, Port Moresby: only two incisors on each side in the upper jaw.
The centrals, £, of each side, are in place; externally to them there is on each side
an alveolus for a tooth, which, judging from the size of the alveolus, was probably f .
Immediately behind these alveoli the canines follow on each side. In this case it
may be said that the missing teeth are & in all probability. Lower jaw normal.
B. M., 79. 3. 5. 8.

370. Specimen having "in each upper jaw two incisors instead of three," [also has
no left p}, see No. 377]. Leyd. Mus., 55. Jentixk, F. A., Notes Leyd. Mas., 1885,
vii. p. 90. Two specimens, Leyd. Mux., 56 and 61 are without & of right upper
jaw, ibid., p. 91. Specimen in which "five of the upper incisors are wanting [only
one "intermediate" tooth in left lower jaw, see No. 377]. Leyd. Mas., 63, ibid., p. 91.

371. Pseudochirus forbesi: of this species only a single skull known; it has no
upper P [and no upper first premolar, see No. 379]. B. M., 1943. Thomas, 0., Cat.
Marsup. Brit. Mas., 1888, p. 183.

(2) Premolars, and the "Intermediate" teeth {in the lower jaw) of

Phalangerid^e.

The evidence here offered relates to the following genera : —
Phalanger, Trichosurus, Pseudochirus, Petauroides, Dactylopsila
and Petaurus. Before speaking of the variations seen, a few
words are needed in explanation of the nomenclature adopted.

chap, ix.] TEETH : PHALANGERIDJE. 249

In these forms there is only one tooth having a milk -pre-
decessor, and in all the genera here referred to this is a distinct
and recognizable tooth, with a chisel-shaped crown. Following
Thomas' system I shall call this tooth p4 throughout. This name
is used as being well understood and convenient, but without
any intention of subscribing to the principles of homology upon
which the system of nomenclature is based.

In front of p4 there is great diversity.

In Thomas' paper1 a careful and well-considered attempt was
made to bring these anterior teeth into a formal scheme of homo-
logies, and though the application of this method to the teeth
of the lower jaw was avowedly tentative, yet at first sight the
results in the case of the upper teeth were fairly satisfactory.
Nevertheless it appears to me that in view of the facts of Variation
about to be related, the system elaborated by Thomas breaks
down; not because there is any other system which can claim
to supersede it, but because the phenomena are not capable of
this kind of treatment. To anyone who will carefully study the
examples given in the following pages, especially those relating
to the genus Phalanger, it will, I think, become evident that it
is not possible to apply any scheme based on the conception that
each tooth has an individual Homology which is consistently
respected in Variation.

The evidence concerns first the premolars of the upper jaw, and
secondly the lower " intermediate " teeth. Inasmuch as in several of
the cases there was Variation in both these groups of teeth, the evidence
relating to them cannot well be separated. As regards the upper
teeth, all the cases of importance occurred in Phalanger and Trichosurus,
and owing to the similarity between the dentitions of these two genera
it is not difficult to emj)loy terms which shall be distinctive, though
the question of the homologies of the teeth go unanswered. In all
the forms concerned there are three upper incisors, and the tooth
immediately succeeding them will be called the canine, though its
position and form diner greatly in the various genera ; for while in
Phalanger and Trichosurus it is a large caniniform tooth placed on the
suture between premaxilla and maxilla, in Pseudochirus, for instance,
it is proportionally smaller and stands in the maxilla at some distance
behind the suture.

Upper jaw. As already stated, the large premolar having a milk-
predecessor will be called p*.

In Trichosurus between the canine and p4 there is usually one
large tooth, in shape and size much like the canine : this tooth will be
called F1 as Thomas proposed. Though when present it is large, it is not
rarely absent altogether (v. infra). In Phalanger there is a similar^1,
though of somewhat smaller size ; but besides X there is usually another
premolar, a small tooth, placed between l^_ and jp\ On Thomas' system
this is FJ and for purposes of description the name will be used here.
In the left upper jaw of the skull shewn in Fig. 65 C, if, if and P^ are

1 Phil. Tram., 1887, clxxviii. and Cat. Marmp. Brit, Mus.

250 MERISTIC VARIATION". [part i.

shewn in the ordinary stcate. Lastly, in Psendochirus behind the canine
there is a very small tooth, presumably p\ and between it and p4 a
tooth of good size, presumably jr.

Lower jaw. In the front of the lower jaw there is on each side one
long incisor. Between it and the tooth corresponding to p4 of the
upper jaw there are several small or "intermediate" teeth, whose
number varies greatly throughout the group. Thomas has made a
provisional attempt to find homologies for these small teeth, but in
view "of the facts of their Variation it seems impossible to attribute
individuality to them and they will therefore be here merely numbered
from before backwards.

Phalanger orientalis. In this species evidence will be
offered to prove the following facts : —

(1) That between p-\ and p^_ there may be two small teeth,
one or both of which may perhaps represent P^_ (Fig. 65).

(2) That between p*_ and the small p3 there may be a
large tooth (Fig. 64, C), like the p3 of Psendochirus.

(3) That p^ may be absent.

(4) That in case of absence of p3 , p1 may be near to p^_
(Fig. 64, A).

(5) That between the canine and p*_ there may be on one
side the usual large pl , but on the other two teeth, evenly spaced,
each of about the proportions of p^ (Fig. 64, B;.

(6) That in the lower jaw the number of intermediate
teeth may vary from none to five, three being the most usual
number.

372. Specimen having left side normal, one small premolar standing be-
tween P^ and F4. In the right upper jaw F1 is normal and stands at the
same level as left F1 ; p4 is also normal in size, form and position (Fig.
64 C). In front of F* however there is a two-rooted tooth (marked y in
the figure) having somewhat the same shape as F4, but about -|rds the
size. This tooth has not the form of the milk-predecessor of F4. A
small peg-like tooth (x in the figure) matching the small premolar
("p3") is also present, but is crowded out of the arcade and stands
internal to the tooth y. The lower jaw has three intermediate teetli
on each side. B. M., 1780, f. The form and position of the tooth y
suggest a comparison with the arrangement in Pseudochirus, in which
"/';:" is in a very similar condition. In Fig. 64, D, a profile of Pseudo-
chirus is shewn, the dotted lines indicating the comparison suggested.
It will thus be seen that if the tooth y corresponds to pz of Psendo-
chirus, the tooth x then has no correspondent.

*373. Specimen (var. breviceps, Solomon Islands) having in right
upper jaw pl and p* but no "ps": in left upper jaw p1 stands at
a level anterior to that of right pl, and a small peg-shaped
tooth, "j/," is present close to and almost touching p4. (Fig.
64, A) Lower jaw, right side, two intermediate teeth, of which
the posterior stands internal to p* ; right side three intermediate
teeth. B. M., 1936,/

CHAP. IX.]

TEETH : PHALANGERID^E.

251

*374. Specimen (var. breviceps $ , Duke of York I.) having in rt.
upper jaw p1 and p4, but no "p8": in left upper jaw there are
two teeth of the size and shape of p1 (Fig. 64, B), one of them

P'[A ..P3 ( of Thomas.)

right
profile

IP P4 ps P c

B

left profile

f'xettt/pi hints
rt. pis file.

B

right pirfihi

Fig. 64. Dentition of Phalanger orientalis.

A. P. orientalis, No. 373, having no right ";r{ " : left pl in front of right p1.

B. P. orientalis, No. 374 : no right "ps"; on left, two teeth both like p1, in
symmetry approximately balancing right p1. Below are the right and left profiles
of the upper jaws of this skull.

C. P. orientalis, No. 372. The left side normal, lettered on Thomas's system.
Bight side described in text. Below is a profile of right side.

D. Pseudochirvs, profile of normal upper teeth from right side enlarged to
compare with C. Teeth lettered on Thomas's system.

being at a level anterior to right p1 and the other posterior to
it (see figures). On neither side is there any tooth having the

252

MERISTIC VARIATION.

[part I.

size and form of "ps." In lower jaw, right side 3 interm. teeth ;
left side no interm. tooth. B. M., 1936,^'.

*375. Specimen having two small premolars on each side between p} and
l£. The two teeth are very small and sharply pointed (Fig. 65). In

III

II

IV

Fig. 65. Teeth of Phalanger orientalis. No. 375.

I. Premolars of left upper jaw, surface and side views.

II. aud III. Eight and left lower jaws as far as p4.
IV. The same in surface view.

(From a drawing kindly sent by Dr Jentink.)

the lower jaw there are on the right side five intermediate teeth be-
tween the incisor and p~4, and on the left side /our such teeth (instead
of three as usual). Leyd. Mus.,104:, Jextixk, F. A., Notes Leyd. Mus.,
1885, vii. p. 90.

*

Statistics of the occurrence o/ small Premolars and lower

"Intermediate" teeth in Phalanger orientalis and

Phalanger maculatus.

376. Phalanger orientalis.

Statistics as to the absence of the small "p;i," and as to the number of the
"intermediate" teeth, may conveniently be given together in tabular form. The
species has a wide distribution and is by Thomas divided into a larger var. typicu*,
and a smaller eastern var. breviceps. In the latter the small p3 is usually absent.
The Leyden specimens are not thus divided by Jentink, and in order to include the
statistics given by him (/. c.) the distinction into two races is not followed in the
table.

When present, "^3" generally stands at an even distance from j;1 and p4, as
in the left side of Fig. 64, C, and not as in the left side of Fig. 64, A. The

CHAP. IX.]

TEETH I PHALANGEEID^E.

253

positions of the intermediate teeth are most various, sometimes they are evenly
spaced out between p1 and p4, but sometimes they are crowded together. The
teeth in corresponding ordinal positions do not always stand at the same levels
on the two sides.

*

Small upper
premolar

No. of
intermediate
teeth in 1. j.

A

Leyden
(Jentink)

Cases.

Other
Museums

Total

(No. 374)

(One of these is No.
372)

(No. 375)

r
right

left

1

right

left

+

+
+
+
+
+
+
+
2

+
+
+
+
+
+
+
+
2

1
3
1
2
3
3
4
1
2
2
3
3
3
4
5

1
0
3
3
3
3
3
2
2
3
2

4
3
4

1
3
2
1
1
2
1
2
44
1
1
1

3

1
1
1
2

2

6

2

1
1
2
5
2
1
1
4
1
2
50
1
1
1

76

377. Phalanger maculatus: in this species the small premolar ("£>3") between upper
p1 and p4 is generally absent, and in the lower jaw there are usually only two
"intermediate" teeth. The following table shews the variations seen in 58 skulls
and 7 lower jaws wanting skulls (including 43 1 Leyden skulls described by
Jentink, I. c).

Small upper

Intermediate

Cases.

premolar

teeth in 1. j.

A

Leyden

Other

Total

r

>

r \

right

left

right I left

(Jentink)

Museums

+ 1 lr. jaw

—

—

1

1

2

1

3

—

—

1

2

2

2

-

—

2

1

2

3

+ 2 lr. jaws

—

—

2

2

27 1

8

35

+ 4 lr. jaws

—

—

3

2

2

2

-

-

3

3

2

2

1 In one of these 1. Pl

+

-

2

3

1

1

absent (see No. 370)

—

+

3

3

1

1

+

+

2

1

1

1

+

+

2

3

1

1

+

+

3

2

2

2

+

+

3

3

2

1

4

+

+

4

3

1

1

58

1 Not including the case, Leyd. Mm., 153 (Jentink, I.e., p. 91), in which the
"small" upper premolar is stated to be absent as an abnormality. As p3 is usually
absent in the species, probably this refers to p1.

254

MEEISTIC VARIATION.

[part I.

The above includes six skulls from Waigiu, the individual peculiarities of
which are given below :

3

3

1

1

+

3

3

1

1

B. M., 61. 12. 11. 18.

+

+

2

3

1

1

+

+

3

2

1

1

+

+

3

3

1

1

B. 21. , 61. 12. 11. 17.

+

+

4

3

1

1

The great variability of these skulls from the island of Waigiu is
very remarkable. The 4 Leyden specimens were described by Jen-
TINK1. In one of these there was besides no left upper 2nd molar,
which was entirely absent without trace, leaving a diastema between
m1 and m3. In connexion with the variations of the dentition of P.
maculatus in Waigiu the following singular circumstance should be
mentioned. In all other localities the male P. maculatus alone is
spotted with white, the female being without spots, but in Waigiu the
females are spotted like the males2. This curious fact was first noticed
by Jextixk (I. c, p. 111).

In the other species of Phalanger no case of special importance met with; but
since in P. ursinus px is normally (4 skulls seen) two-rooted, it may be of interest
to note that such a two-rooted condition of pl was seen on both sides as a variation
in P. ornatus, B. M., 1317, b (2 other specimens having single-rooted px).

*

378. Trichosurus vulpecula ( = Phalangista vulpina). The typical
form of this species is Australian, while the large variety, fuliginosa,
is peculiar to Tasmania. In the typical form no instance of absence of
P^ seen in 17 specimens examined. All possessed this tooth on each
side, and though varying a good deal in size, it was in every case well-
formed and functional, never being in a condition which could be called
rudimentary.

Of the Tasmanian variety fuliginosa, 18 specimens (8 in B. M., 10
in C. M.) were examined.

In 6 F1 was present on both sides.

1 right side only.

1 left.

2 p1 was absent altogether. C. M., 14 k and I.
Nevertheless in every case in which this tooth is present it is a large
tooth of about the size of the canines. In one case P^ is two-rooted on
each side, as (Thomas, Cat. Marsup., p. 186) in the Celebesian Phalan-
ger ursinus. C. M., 14 a, Hobart Town, Tasmania.

Of the "intermediate" teeth in lower jaw one only is usually present, being

1 The small premolar was accidentally described in the paper referred to as
being between the canine and p4, instead of between the anterior premolar and pA.
Jentink, in litt.

2 Compare the converse case of Hepialus humuli (the Ghost Moth), of which,
in all other localities, the males are clear white and the females are light yellow-
brown with spots; but in the Shetland Islands the males are like the females,
though in varying degrees. See Jenner Weir, Entomologist, 1880, p. 251, PI.

CHAP. IX.]

TEETH : DASYURIDJE.

255

close to the large incisor. In two cases (C. M., 15 p and h, pi-ob. both Australian)
there are two intermediate teeth, one near the incisor, the other near fi.

379. Pseudochirus. Of various species 29 skulls shew no numerical variation in
upper series. The number of "intermediate" teeth in lower jaw is very variable,
2 on each side being the most frequent, but 1 and 3 being also common. P. pere-
grinus, Upper Hunter E., B. M., 41, 1182, has 2 intermediate teeth in left lower
jaw, but on the right side one partially double intermediate tooth. (See also No. 371.)

Petaurus : 25 skulls shew no numerical variation in upper series.
In this genus the number of small teeth in the lower jaw is remarkably
constant. In addition to p* there were 3 small teeth on each side in

380. all cases seen except two, viz. — P. breviceps var. papuanus (8
normals): right side normal; left lower jaw has 4 teeth besides^4 (Fi^.
66). B. M.5 77. 7. 18. 19.

Bight

Left

Fig. 66. Petaurus breviceps, No. 380. Lower jaws in profile: on right side
three intermediate teeth, on left side four.

381. Another specimen has, in addition to ~j?,four small teeth in each
lower jaw. There is a small diastema between the 3rd and 4th. B. M.,
42. 5. 26. 1. [no skull].

382. Dactylopsila trivirgata : 3 specimens have upper series normal.
In addition one has an extra tooth in left upper jaw between i^ and
canine. This tooth somewhat resembles but is rather smaller than the
canine, near and slightly internal to which it stands [? reduplicated
canine]. B. M., 1197, d.

(3) Premolars and molars of Dasyuridse and Didelphyidse.

Thylacinus, 19 normals; Sarcophilus, 9 normals, no abnormal
known to me.

Dasyurus, 37 normals (4 species).

383. D. geoffroyi : specimen in which p4 in right lower jaw has its
crown partially divided into two, the plane of division being at right
angles to the jaw. C. M., 39, a.

256

MERISTIC VARIATION.

[part I.

384. D. viverrinus : rigKfc upper m4 slightly larger than the left, which
is normal. C. M., 38, g.

*385. D- maculatus, Tasmania, having a supernumerary molar
in left upper jaw, and on both sides in the lower jaw. The
fourth molar in the upper jaws is increased in size in a remark-
able manner ( Fig. <>7, B and C).

This case requires detailed description. In Fig. 67, A, a
normal right upper jaw is shewn. It belongs to a specimen
considerably larger than the abnormal one, but the latter,
Mr Thomas tells me, is a good deal smaller than the normal
size of the species. In the normal there are two small pre-
molars ( p1 and p9 of Thomas), and behind these, four molars.
The molars increase in size from the first to the third, which is
by far the largest. Behind the third is the fourth molar, which
is much smaller than the others, having the peculiar flattened
form shewn in the Figure 67, A.

Fig. 67. A. Eight upper jaw of normal Dasyurus maculatus (shewn as far as
the canine) for comparison with the variety. (N.B. The latter is considerably
smaller.)

B. Upper jaw of D. maculatus, No. 385.

C. Lower jaw of the same specimen.

On comparing the abnormal skull with a normal one it is
seen that the two premolars and first three molars on each side
are unchanged. Behind the third molar on the right side there
is a single tooth ; but this, instead of being a thin tooth like
normal ™4, is considerably larger and the longitudinal measure-
ment in the line of the jaw is not very much less than the
transverse measurement. In the right upper jaw therefore the
number of the teeth is unchanged.

On the left side, behind the third molar, there is a square
tooth (w*4) of good size, about equal in bulk to half w3, while
behind this again there is another tooth, _^3, which is a thin

CHAP. IX.]

TEETH : DASYURID^E.

257

386,

and small tooth having nearly the form and size of normal w4.
The lower series is alike on both sides, each having an extra
molar behind m"4 (Fig. 67, C). The two extra teeth are well formed,
being as long but not quite so thick as m*. B. M., 41, 12, 2, 3.

In Cat. Marsup. Brit. Mus., 1888, p. 265, note, Thomas refers
to this skull, and describes it as an instance of an additional molar
inserted between m3 and m4 on the left side above and on both
sides below. This view is of course based on the resemblance
that the extra »»? of the left side bears to a normal mt and on
the fact that the left w4 is like no tooth normally present. In
the light however of what has been seen in other cases of super-
numerary molars a simpler view is possible. For in cases in
which a supernumerary molar is developed behind a molar which
is normally a small tooth, the latter is frequently larger than
its normal size. In the present case it appears that on the right
side ™4 has been thus raised from a small tooth to be a tooth
of fair size, while on the left side the change has gone further,
and not only is ««* promoted still more, but a supernumerary
ra5 is developed as well. It is interesting to note that this ft&
is a small tooth, very like normal ^_4, and it thus may be said
to be beginning at the stage which m^ generally reaches. In
the lower jaw wf is added without marked change in ~m± ; for
mF is normally a large tooth and has, as it were, no arrears to
be made up. Mr Thomas, to whom I am indebted for having
first called my attention to this remarkable case, allows me to
say that he is prepared to accept the view here suggested.

Phascologale. In the upper jaw normally 3 premolars, by Thomas
reckoned as p\ p3 and p*. Between the first and second ("p3") there
is sometimes, but not always, a small space, and in the following case a
supernumerary tooth was present in this position.

Phascologale dorsalis, (Fig. 68) having an extra premolar
between the first and second in the left upper jaw : rest normal. B. M.,
1868, b. Thomas, O., Phil. Trans., 1887, p. 447, PL 27, figs. 7 and 8.

In the lower jaw ~jfi is often small and may be absent. As Thomas
has observed, the size of p4 in the upper and lower jaws maintains a

left

ri/fht
reversed

Fig. 68. Phascologale dorsalis, No. 386. Teeth of left upper jaw from canine
to first molar; below, the teeth of the right side reversed (after Thomas).

b. 17

258 MERISTIC VARIATION. [part i.

fairly regular correspondence. Within the limits of one species p* may

387. shew great variation ; for instance, of Phascologale fiavipes 7
specimens were seen ; in 1 jT1 was absent, in 2 it was small, in 2 mode-
rate, and in 2 it was large.

388. Didelphys : 79 specimens normal. One specimen alone, D. lanigera, Colombia,
B. At., 1733, b, was abnormal, having no m4 in either upper or lower jaws.

D. opossum (one specimen, B. M.) had right n* larger than the left.

(4) Molars of certain Macropoclidae.

The following evidence relates to the genera Bettongia, Potorous
and Lagorchestes. In these forms the molars are normally four in each
jaw. As Thomas observes (Cat. Marsup. Brit. Mus., p. 105, note), in
Bettongia cases of fifth molar occur, but on the other hand cases of non-
eruption of m4 occur also. The variations seen in the three genera
were as follows.

4 4

Bettongia penicillata : 8 specimens have m . ; in 7 of them

m4 is small (in B. M., 279, j, ™^ is very minute; but in B. M., 278, m,

the lower m* is large).

*389. 1 specimen °. has m4 in left lower jaw only, this tooth being small.

B. M., 279, a.

*onn i • x. 1.2.3.0.5 — 1.2.3.0.0 _ , .,

*390. 1 specimen has m = — s — = — - — = = — - — =- — . In both upper laws

r 1.2.3.4.5 — 1.2.3.4.0 rr J

there is a small empty crypt behind m3, and on right side behind this

again there is a minute tubercular tooth not represented on the other

side. B. M., 279, b.

4 — 4
B. cuniculus : 2 specimens have m- - .

391. 1 specimen has no left v?. B. M., 982, c.

5 5

*392. 1 specimen has m— — = ; in upper jaws m5 very small in crypts, but

o — o

in lower jaws they are of good size. B. M. 51. 4. 24. 7.

4 4

B. lesueri : 13 specimens have m - (in one of them on4 very

small. B. M., 277, g).

5 5

393. 1 specimen has m , m5 being minute and lying in crypts.

B. M., 41, 1157.

4 4

394. Potorous (Hypsiprymnus): mj- in 5 specimens of P. tri-

dactylus and in 2 of P. platyops. A single specimen of P. gilberti
has no right upper m\ B. M., 282, b.

395. Lagorchestes. In this genus m4 is present and is a large tooth,
not materially smaller than ms. Nevertheless it commonly falls short
of the other teeth and remains partly within the jaw. This was the
case in 10 skulls of L. leporoides and L. conspicillatus. In one skull
of L. leporoides, m4 stood at the same height as the other teeth. I see
no reason to suppose that all the other skulls were young, and it seems
more likely that this imperfect eruption of m4 is characteristic.

chap, ix.] TEETH : RHINOPTERA. 259

Selachii.

Some features characteristic of Meristic Variation are well
seen in the case of the teeth of Sharks and Rays. Of these fishes
there are many having little differentiation between the separate
rows of teeth. In these a distinct identity cannot be attributed
to the several rows, and numerical Variation is quite common.
But besides these there are a few forms whose teeth are differ-
entiated sufficiently to permit a recognition of particular rows
of teeth in different specimens, and to justify the application of
the term "homologous'' to such rows. Nevertheless with such
differentiation Meristic Variation does not cease.

In the following examples it will be seen further that in such
Variation there may be not merely a simple division of single
teeth but rather a recasting of the whole series, or at least of that
part of it which presents the Variation, for the lines of division
in the type may correspond with the centres of teeth in the
variety.

These cases also exemplify the fact that variations of some
kinds are often only to be detected when in some degree im-
perfect ; for if the divisions in No. 396 for instance had taken
place similarly on both sides, it would have been difficult to
recognize that this was a case of Variation.

Rhinoptera jussieui (= javanica) : specimen in which the
number and arrangement of the rows of teeth is different on
the two sides, as shewn in Fig. 69, upper diagram. The dis-
position on the right side of the figure is normal, that on the
left being unlike that of any known form. Specimen in B. M.
described by Smith Woodward, Ann, and Mag. N.H., Ser. 6,
vol. i. 1888, p. 281, fig. As Woodward points out, the rows of
plates on the left side may be conceived as having arisen by
division partly of the plates of the central row and partly from
the lateral row, marked I. But if this be accepted as a repre-
sentation of the relation of the normal to the abnormal, in the
way indicated by the lettering, the plates of the row marked 0 b,
for instance, must be supposed each to belong half to one rank
and half to a lower rank. The same applies to the plates in the
row I b. By whatever cause therefore the points of develop-
ment of the teeth are determined, it is clear that the centres
from which each of the teeth in the rows I b and 0 b was de-
veloped were not merely divided out from centres in the normal
places but have undergone a rearrangement also. With change of
number there is also change of pattern.

The tessellation on the abnormal side is so regular and definite
that had it existed in the same form on both sides the specimen
might readily have become the type of a new species.

There is indeed in the British Museum a unique pair of jaws
in both of which (upper and lower) a very similar tessellation

17—2

260

MERISTIC VARIATION.

[part I.

occurs in a nearly symmetrical way. This specimen is described
as Rhinoptera potyodon, but it is by no means unlikely that it

T Th la Oc Ob
wMlL £ HLUL

Oa

0

M M

jt m

Fig. 69. Upper figure ; Rhinoptera jussieui, No. 396, after Smith Woodwakd,.
from whom the lettering is copied.

Middle figure, Rhinoptera, sp., No. 397.

Lower figure Rhinoptera javanica, No. 398, after Owen.

is actually a Variation derived from the usual formula of Rhino-
ptera. It is figured by Gunther, Study of Fishes, 1880, p. 346.
Fig. 133.

*QQ7

39/. Rhinoptera sp. incert. : teeth as in middle diagram, Fig. 69. On
the left side three rows of small lateral teeth, while on the right side
two of these rows are represented by one row, which in one part of the
series shews an indication of division. C. S. M. {Hunterian Specimen).

CHAP. IX.]

TEETH I SELACHII.

261

398. Rhinoptera javanica : the row of teeth marked I is one side
single, but on the other side is represented by two rows. Fig. 69,
lower diagram. Owen, Odontography, PI. 25, Fig. 2. C. S. M.
(Hunterian specimen).

399. Cestracion philippi : an upper jaw having the teeth disposed as
in the figure (Fig. 70). C. S. M.

Fig. 70. Upper jaw of Cestracion philippi, No. 399.

400,

On comparing the teeth of the two sides it will be seen first that
the rows do not correspond individually, and secondly that they do not
at all readily correspond collectively. Assuming that the rows marked
4 on each side are in correspondence (which is not by any means cer-
tain) several difficulties remain: for right 5th is larger than left 5th,
but left 6th and 7th together are larger than right 6th; right 7th is
about the same size as left 8th, but right 8th is larger than left 9th.
The proportions in the figure were carefully copied from the specimen.

" Cestracion sp." [so labelled, but probably not this genus] :
lower jaw as in Fig. 71. On the right side the second row of large
plates is represented by two rows, properly fitting into each other,
but on the left side the plates of the inner side are completely

262

MERISTIC VARIATION.

[part I.

divided, but the division is gradually lost towards the middle of the
jaw and the external plates are without trace of division. C. S. M.

Fig. 71. The lower jaw of a Selachian, No. 400. The proximal ends shewn
(enlarged). The right is reversed for comparison with the left.

RADUL.E of a Gasteropod.

*

The following example of Meristic Variation in the teeth
of a Molluscan odontophore may be taken in connexion with
the subject of teeth, though the structures are of course wholly
different in nature. For information on this subject I am in-
debted to the Rev. A. H. Cooke.

Generally speaking the number and shapes of the radular
teeth are very characteristic of the different classificatory divi-
sions. There are however certain forms in which a wide range
of Variation is met with ; of these the case of Buccinum undatum is
the most conspicuous.
401. Buccinum undatum. In most specimens the number of
denticles on the central plate is 5 — 7 and on the laterals 3 — 4.

In 27 specimens from Hammerfest and Vardo the teeth were
as follows : —

Lateral plates. Cases.

4 8

4 12

4 2

4 1

4 1

3 & 4 1
3& 4 1

4 & 5 1

Central plate.
5
6
7
6—8
9
6
7
8

from Friele, Jahrb. deut mat. Ges., VI. 1879, p. 257.

CHAP. IX.]

RADUL^E I BUCCINUM.

263

*402. The range of Variation may be still greater than this, the
number of centrals being sometimes as low as 3. Fig. 72 shews
the different conditions found. In it eight varieties are shewn,

M/vWV.

IV

VI

Fig. 72. Variations in odontophore of Buccinum undatum.

I. Three centrals (Labrador). II. Four centrals. III. Five centrals, approxi-
mately symmetrical bilaterally. IV. Five centrals, not symmetrical ; the two
external centrals on one side almost separate, correspond with a bifid denticle on
the other side (Labrador). V. Six complete centrals (Labrador). VI. Seven
centrals (Lynn). VII. Nine almost distinct centrals. VIII. Eight centrals ;
laterals asymmetrical (4 and 5).

I. II. IV. — VI. from photographs made and kindly lent by Mr A. H. Cooke.
III. VII. VIII. after Friele.

I. II. IV. — VI. being taken from Mr Cooke's specimens, III. VII.
and VIII. from Friele's figures.

As thus seen, in these variations considerable symmetry may
be maintained. This symmetry and defmiteness of the varieties
in the cases with 3 and 4 centrals is especially noteworthy, in-
asmuch as these are abnormal forms and have presumably arisen
discontinuously. As also seen in the figure, e.g. IV. and VI.
this symmetry is not universal, and may be imperfect. The
specimen shewn in VIII. is remarkable for the asymmetry of the
lateral plates, which have 4 and 5 denticles respectively.

In connexion with the subject of symmetrical division interest
attaches to cases like that shewn in Fig. 72, IV. in which on the

264 MEBISTIC VARIATION. [part i.

outside of the central plate a pair of almost wholly separate
denticles on one side correspond with a large, imperfectly divided
denticle of the other side. A very similar specimen is figured by
Friele, Norske Nordhavs-Exp., viii. PL v. fig. 16.

The number found in one part of the radula is usually main-
tained throughout the whole series, but this is not always so.
A case in which the number of centrals at the anterior end of
the radula was 6, and at the posterior end 8, is given by Friele,
Norske Nordhavs-Exp., 1882, viii. p. 27, Taf. v. fig. 17.

CHAPTER X.

Linear Series — continued.
Teeth — Recapitulation.

In this chapter I propose to speak of those matters which seem
to have most consequence in the foregoing evidence as to the
Variation of Teeth. Each of the following sections treats of some
one such subject, specifying the cases which chiefly illustrate it.
It will be understood that the sections do not stand in any logical
collocation but are simply arranged consecutively. The treatment
given is of course only provisional and suggestive, being intended
to emphasize those points which may repay investigation.

The subjects which especially call for remark are as follows :

(1) The comparative frequency of dental Variation in differ-

ent animals.

(2) Symmetry in Meristic Variation of Teeth.

(3) Division of Teeth.

(4) Duplicate Teeth.

(5) Presence and absence of Teeth standing at the ends of

series (first premolars, last molars).

(6) The least size of particular Teeth.

(7) Homceotic Variation in terminal Teeth when a new

member is added behind them.

(8) Reconstitution of parts of the Series.

(1) The comparative frequency of dental Variation in different

animals.

The total number of skulls examined for the purpose of this
inquiry was about 3000. From so small a number it is clearly
impossible to make any definite statement as to the relative
frequency of Variation in the different orders, but some indications
of a general character may be legitimately drawn.

First, the statistics very clearly shew that while dental Varia-
tion is rare in some forms, it is comparatively frequent in others,
but there is no indication that this frequency depends on any
condition or quality common to these forms. Setting aside
examples of the coming and going of certain small and variable

266 MERISTIC VARIATION. [part i.

teeth, the animals shewing the greatest frequency of extra teeth
were the domestic Dogs, the Anthropoid Apes and the Phocidse.

Attention is especially called to the fact that the variability of
domestic animals is not markedly in excess of that seen in wild
forms. From the hypothesis that Variation is uncontrolled save
by Selection, there has sprung an expectation, now fast growing
into an axiom, that wild animals are, as such, less variable than
domesticated animals. This expectation is hardly borne out by
the facts. It is true that, so far as the statistics go, supernumerary
teeth were more common in domestic Dogs than in wild Canidse,
and though the number of Cats seen was small, the same is true
in their case also as compared with wild Felidse. But though it is
true that the domestic Dog is more variable in its dentition than
wild Doofs, it is not true that it is much more variable than some
other wild animals, as for instance, the Anthropoid Apes or the
genus Phoca. The doctrine that domestication induces or causes
Variation is one which will not, I think, be maintained in the
light of fuller evidence as to the Variation of wild animals. It
has arisen as the outcome of certain theoretical views and has
received support from the circumstance that so many of our
domesticated animals are variable forms, and that so little heed
has been paid to Variation in wild forms. To obtain any just view
of the matter the case of variable domestic species should be com-
pared with that of a species which is variable though wild. The
great variability of the teeth of the large Anthropoids, appearing
not merely in strictly M eristic and numerical Variation, but also
in frequent abnormalities of position and arrangement, is striking
both when it is compared with the rarity of variations in the teeth
of other Old World Monkeys and the comparative rarity of great
variations even in Man. If the Seals or Anthropoids had been
domesticated animals it is possible that some persons would have
seen in their variability a consequence of domestication.

When the evidence is looked at as a whole it appears that no
generalization of this kind can be made. It suggests rather that
the variability of a form is, so far as can be seen, as much a part
of its specific characters as any other feature of its organization.
Of such frequent Variation in single genera or species some
curious instances are to be found among the facts given.

Of Canis cancrivorus, a S. American Fox, the majority shewed
some abnormality. Of Felis fontanieri, an aberrant Leopard, two
skulls only are known, both showing dental abnormalities. In
Seals only four cases of reduplication of the first premolar were
seen, and of these two were in Cystopliora cristata. The number
of cases of abnormality in the genus Ateles is very large. Of six
specimens of Crossarchus zebra, two shew abnormalities. Of the
very few skulls of Myrmecobius seen, two shew an abnormal num-
ber of incisors. Three cases of Variation were given in Canis
mesomelas, not a very common skull in museums. On the other

chap, x.] TEETH : SYMMETRY. 267

hand the rarity of Variation in the dentition of the Common Fox
(G. vulpes) is noteworthy, especially when compared with the
extraordinary frequency of Variation in the molars of S. American
Foxes. The constant presence of the small anterior premolar in
the upper jaw of Otters (Lutra) of most species, as compared with
the great variability of the similar tooth in the Badgers (Meles)
and in other species of Otters, may also be mentioned.

The evidence given in the last chapter should not, I think, be
taken as indicating the frequency of dental Variation in Mammals
generally. The orders chosen for examination were selected as
being those most likely to supply examples of the different forms
of dental Variation, and it is unlikely that the frequency met with
in them is maintained in many other orders.

(2) Symmetry in Meristic Variation of Teeth.

With respect to bilateral Symmetry an examination of the
evidence shews that dental Variation may be symmetrical on the
two sides, but that much more frequently it is not so. The in-
stances both of bilaterally symmetrical Variation, and of Variation
confined to one side are so many that examples can be easily
found in any part of the evidence.

Besides these there are a few cases in which there is a variation
which is complete on one side, while on the other side the parts
are in a condition which may be regarded as a less complete
representation of the same variation. Such cases are Ommato-
phoca rossii No. 320, Phoca gramlandica No. 324, Dasyurus macu-
latus No. 385, Ganis lupus No. 246, G. vetulus No. 248, &c.

In the remarks preliminary to the evidence of dental Variation,
reference was made to a peculiarity characteristic of the teeth
considered as a Meristic Series of parts. As there indicated, the
teeth are commonly repeated, so as to form a symmetry of images
existing not only between the two halves of one jaw, but also to a
greater or less extent between the upper and lower jaws. It was
then mentioned that cases occur in which there is a similar Varia-
tion occurring simultaneously in the upper and lower jaws of the
same individual. Such similar Variation may consist either in
the presence of supernumerary teeth, or in the division of teeth,
or in the absence of teeth. It should, however, be noticed that
examples of Variation thus complete and perfect in both jaws are
comparatively rare. Speaking generally, it certainly appears from
the evidence that similar Variation, (1) on one side of both jaws,
or (2) on both sides of one jaw and on one side of the other, or
(3) on both sides of both jaws are all rare. Of these three the
following examples may be given : —

Of (1), Macacus rhesus No. 190, Ateles pentadactylus No. 196,
Esquimaux dog No. 243, Phoca vitulina No. 329.

268 MERISTIC VAKIATIOX. [part i.

Of (2), Simla satyrus No. 106, Dasyurus maculatus No. 385,
E. asinus No. 352.

Of (3), Dog Xo. 257, Bettongia cuniculus, No. 392, Ateles margi-
natus No. 203, Phoca barbata No. 318, Ommatophoca rossii No. 320.

Of these, further examples may be seen in the evidence given
regarding the anterior premolars of Galictis barbara, Meles, and
Herpestes.

(3) Division of Teeth.

Among the cases of increase in number of teeth are many in
which by the appearances presented it may be judged that two
teeth in the varying skull represent one tooth in the normal, and
have arisen by the division of a single tooth-germ.

Of such division in an incomplete form several examples have
been given. The plane of division in these cases is usually at
right angles to the line of the jaw, so that if the division were
complete, the two resulting teeth would stand in the line of the
arcade. Incomplete division of this kind is seen in the first
premolar of Ommatophoca rossii No. 320, in the fourth premolar of
Phoca groenlandica No. 324, in the incisors of Dogs No. 219,
in the canine of Dog No. 221, in the lower fourth premolar of
Dasyurus geoffroyi No. 383. The plane of division is not however
always at right angles to the jaw, but may be oblique or perhaps
even parallel to it, though of the latter there is no certain case.
Cases of division in a plane other than that at right angles to the
jaw are seen in C. vulpes No. 230, Phalanger orientalis No. 368,
Phoca groenlandica No. 326 and doubtfully in a few more cases. The
existence of the possibility of division in these other planes is of
some consequence in considering the phenomenon of duplicate teeth
standing together at the same level in relation to that of the
presence of duplicate teeth in series. Beyond this also it may be
anticipated that if ever it shall become possible to distinguish
the forces which bring about the division of the tooth-germ, the
relation of the planes of division to the axis of the Series of Repe-
titions will be found to be a chief element.

(4) Duplicate Teeth.

Teeth standing at or almost at the same level as other teeth
which they nearly resemble may conveniently be spoken of as
duplicate teeth, though it is unlikely that there is a real distinc-
tion of kind between such teeth and those extra teeth which stand
in series. Duplicate teeth were seen in Felis domestica Nos. 286
and 287, Ganis mesomelas No. 228, Herpestes ichneumon No. 300,
[Putorius] Vison horsfieldii No. 311, Helictis orientalis No. 312,
Cystop)iora cristata No. 322, and perhaps in some other cases. That
these cases are not separable on the one hand from examples of
extra teeth in series may be seen from Herpestes gracilis No. 299,
Cystophora cristata No. 321 [compare with No. 322], Brachy teles

chap, x.] TERMINAL TEETH. 269

hemidactylas No. 199 [compare with Ateles rnarginatus No. 200].
PJioca vitulina No. 336 ; and that on the other hand they merge
into cases of supernumerary teeth standing outside or inside the
series, and whose forms do not correspond closely to those of
any tooth in the series, may be seen by comparison with Otaria
iwsina No. 325, Phoca vitulina No, 329, Phalanger orientalis No.
372. Though in some cases the shapes of duplicate teeth make a
near approach to the shapes of normal teeth, yet they are never
exactly the same in both, and teeth whose forms approach so
nearly to those of other teeth in the series as to suggest that they
are duplicates of them and that they may have arisen by multipli-
cation of the same germ, cannot be accurately distinguished from
extra teeth whose forms agree with none in the normal series.

(5) Presence and Absence of Teeth standing at the ends of Series
(first premolars, last molars): the least size of particular Teeth.

Of the cases of numerical Variation in teeth the larger number
concern the presence or absence of teeth standing at the ends of
Series. As was mentioned in introducing the subject of dental
Variation, in many heterodont forms the teeth at the anterior end
of the series of premolars and molars are small teeth, standing to
the teeth behind them as the first terms of a series more or less
regularly progressing in size. Not only in teeth but in the case
of members standing in such a position in other series of organs,
e.g. digits, considerable frequency of Variation is usual.

Variability at the ends of Series is manifested not only in the
frequency of cases of absence of terminal members, but also in the
frequency of cases of presence of an extra member in their neigh-
bourhood. An additional tooth in this region may appear in
several forms. It may be a clear duplicate, standing at the same
level as the first premolar (e.g. Cat, No. 270). On the other hand,
as seen in the Dogs (Nos. 232 and 233) there may be two teeth
standing between the canine and (in the Dog) the second pre-
molar. The various possibilities as to the homologies of the teeth
may then be thus expressed. The posterior of the two small teeth
may correspond with the normal first premolar, and the anterior may
be an extra tooth representing the first premolar of some possible
ancestor having five premolars; or, the first of the two premolars
may be the normal, and the second be intercalated (see No. 224) ;
or, both the two teeth may be the equivalent of the normal first
premolar ; lastly, neither of the two may be the precise equivalent
of any tooth in the form with four premolars, Of these possibili-
ties the first is that commonly supposed (Hexsel and others) to
most nearly represent the truth. But the condition seen in cases
where there is an extra tooth on one side only, as in the Dogs
figured (Fig. 42), strongly suggests that neither of the two teeth
strictly corresponds with the one of the other side. Seeing that in
such cases the single tooth of the one side stands often at the level

270 MERISTIC VARIATION. [part i.

of the diastema on the other, it seems more likely that the one
tooth balances or corresponds to the two of the other side, which
may be supposed to have arisen by division of a single germ. On
the other hand since the two anterior premolars found in such
cases are not always identical in form and size, either the anterior
or the posterior being commonly larger than the other, there is no
strict criterion of duplicity, and it is clearly impossible to draw
any sharp distinction between cases of duplicity of the first pre-
molar and cases in which the two small premolars are related to
each other as first and second. These two conditions must surely
pass insensibly into each other. If the case of the teeth is com-
pared with that of any other Linear series in which the number of
members is indefinite, as for example that of buds on a stem, the
impossibility of such a distinction will appear. A good illustration
of this fact may often be seen in the arrangement of the thorns on
the stems of briars. For large periods of the stem both the angular
and linear succession of the thorns of several sizes may be exceed-
ingly regular ; but it also frequently happens that a thorn occurs
with two points, and on searching, every condition may sometimes
be found between such a double thorn and two thorns occurring
in series, having between them the normal distinctions of form or
size. Very similar phenomena may be seen in the case of the
strong dermal spines of such an animal as the Spiny Shark (Echi-
norhinus spinosus). These structures are of course from an anato-
mical standpoint closely comparable with teeth. In them, spines
obviously double, triple or quadruple, are generally to be seen
scattered among the normal single spines, but between the double
condition and the single condition, it is impossible to make a real
distinction.

The remarks made as to the first premolars apply almost
equally to the last molar. See Phoca vitulina No. 336, Mycetes
niger No. 206, Man, Magitot, Anom. syst. dent, PI. v. figs. 4, 5
and 6, Canis cancrivorus Nos. 251 and 252, Crossarchus zebra
No. 302.

(6) The least size of 'particular Teeth.

What is the least size in which a given tooth can be present in
a species which sometimes has it and sometimes is without it ? In
other words, what is the least possible condition, the lower limit of
the existence of a given tooth ? This is a question which must
suggest itself in an attempt to measure the magnitude or Dis-
continuity of numerical Variation in teeth.

The evidence collected does not actually answer this question
completely for any tooth, but it shews some of the elements upon
which the answer depends.

In the first place it is seen at once that the least size of a
tooth is different for different teeth and for different animals.

chap, x.] LEAST SIZE OF TEETH. 271

Considered in the absence of evidence it might be supposed that
any tooth could be reduced to the smallest limits which are histo-
logically conceivable ; that a few cells might take on the characters
of dental tissue, and that the number of cells thus constituting a
tooth might be indefinitely diminished. Indeed on the hypothesis
that Variation is continuous this would be expected. Now of
course there is no categorical proof that this is not true, and that
teeth may not thus occur in the least conceivable size, but there is
a good deal of evidence against such a view. The facts on the
whole go to shew that teeth arising by Variation in particular
places, at all events when standing in series in the arcade, have a
more or less constant size on thus appearing. Within limits it
seems also to be true that the size in which such a tooth appears
has in many cases a relation to the size of the adjacent teeth and to
the general curves of the series. For example in the Orang, the
series of molars does not diminish in size from before backwards,
and extra molars when present are, so far as I know, commonly of
good size, not wholly disproportionate to the last normal molar.
The same is I believe true in the case of the Ungulates. In the
Dogs however the series of lower molars diminishes rapidly at the
back, and the extra molars added at the posterior end of the series
are of a correspondingly reduced size. As presenting some ex-
ception to this rule may be mentioned two cases in the Chimpanzee,
Nos. 178 and 181 and the case of Cebus robustus No. 194, in each
of which the extra molar is disproportionately small.

The principle here indicated is of loose application, but speaking
generally it is usual for an extra tooth arising at the ends of series
to be of such a size as to continue the curves of the series in a
fairly regular wTay. It would at all events be quite unparalleled for
an extra tooth arising at the end of a successively diminishing
series, as the Dog's lower molars, to be larger than the tooth next
to it, and with the exception of cases of duplicate anterior pre-
molars (see Dogs Nos. 232 and Cat No. 268) I know no such case.
In these besides, the anterior tooth is very slightly larger than its
neighbour, and it should be remembered that the first premolar,
though the terminal member of the series of premolars, is not
actually a terminal tooth.

Examples have been given of animals which seem to be oscil-
lating between the possession and loss of particular teeth, the first
premolar of the Badgers, p1 of some species of Otter, &c. In these
cases we are not yet entitled to assume because in a given skull
the tooth is absent, that it has never been formed in it, though
this is by no means unlikely, but as already pointed out (p. 22<S).
the fact of its presence or absence may still indicate a definite
variation. Attention should be called to the case of Trichosurw
vulpecida, var. fuliginosa No. 378, in which the first premolar is
generally of good size if present, and there can be no doubt that it
has never been present in those skulls from which it is absent.

272 MERISTIC VARIATION. [part i.

Variation of unusual amplitude may be seen also in the molars
of Bettongia Nos. 389, &c, for while on the one hand the last or
fourth molar may be absent, it may on the contrary be large and
may even be succeeded by a fifth molar as an extra tooth. All
these conditions were seen in looking over quite a small number
of specimens.

(7) Homceotic Variation in terminal Teeth token a new member
is added behind them.

Upon the remarks made in the last Section the fact here
noticed naturally follows. We have seen that there is a fairly
constant relation between the size of extra teeth and that of the
teeth next to which they stand, so that the new teeth are as it
were, from the first, of a size and development suitable to their
position. We have now to notice also that the teeth next to which
they stand may also undergo a variation in correlation with the
presence of a new tooth behind them.

It may be stated generally that if the tooth which is the last
of a normal series is relatively a small tooth, as for example m» or
ra^ in the Dog, then in cases of an addition to the series, by which
this terminal tooth becomes the penultimate, it will often (though
not always) be found that this penultimate tooth is larger and
better developed than the corresponding ultimate tooth of a normal
animal of the same size.

Of this phenomenon two striking examples (q.v.) have been
given, Canis azarce No. 249 and Dasyurus maculatus No. 385.
Besides these are several others of a less extreme kind e.g. Otocyon
megalotis No. 256, Mastiff No. 259, Dog No. 260. The same was
also seen in the molars of Bettongia,

This phenomenon, of the enlargement of the terminal member
of a series when it becomes the penultimate, is not by any means
confined to teeth ; for the same is true in the case of ribs, digits,
&c, and it is perhaps a regular property of the Variation of Meristic
Series so graduated that the terminal member is comparatively
small. This fact will be found of great importance in any attempt
to realize the physical process of the formation of Meristic Series,
and it may be remarked that such a fact brings out the truth that
the members of the Series are bound together into one common
whole, that the addition of a member to the series may be cor-
related with a change in the other members so that the general
configuration of the whole series may be preserved. In this case
the new member of the series seems, as it were, to have been
reckoned for in the original constitution of the series.

(8) Reconstitution of parts of the Series.

Lastly there are a few cases, rare no doubt in higher forms but
not very uncommon for example in the Sharks and Rays (see

chap, x.] TEETH : HOMOLOGIES. 273

pp. 259, &c), in which the members of the series seem to have been
so far remodelled that the supposed individuality of the members
is superseded. In the Selachians several such cases were given,
but in Mammals the most manifest examples were seen in the
Phalangers and Ateles marginatus No. 200 (q.v.). In the latter
specimen there were four premolars on each side in the upper jaw,
and there was nothing to indicate that any one of them was super-
numerary rather than any other. In such a case I submit that the
four premolars must be regarded as collectively equivalent to the
three premolars of the normal. The epithelium which normally
gives rise to three tooth-germs has here given rise to four, and I
believe it is as impossible to analyze the four teeth and to apportion
them out among the three teeth as it would be to homologize the
sides of a triangle with the sides of a square of the same peripheral
measurement.

Such a case at once suggests this question : if the four premo-
lars of this varying Ateles cannot be analyzed into correspondence
with the three premolars of the typical Ateles, can the three pre-
molars of this type be made to correspond individually with the
two premolars of Old World Primates ?

In the case of Rhinoptera No. 396, for the reason given in
describing the specimen, there is plainly no correspondence be-
tween the rows of plates of the variety and those of the type, and
the rows are, in fact, not individual, but divisible.

Though cases so remarkable as that of Ateles marginatus are
rare, there are many examples of supernumerary teeth, in the
region of the anterior premolars of the Dog or Cat for instance,
which cannot be clearly removed from this category. As indicated
in the fourth section of this Chapter, it is impossible to distinguish
cases of division of particular teeth from cases of the formation of
a new number of teeth in the series. Finally, on the analogy of
what may be seen in the case of Meristic Series having a wholly
indefinite number of members, it is likely that the attempt thus to
attribute individuality to members of series having normally a
definite number of members should not be made.

b. 18

CHAPTER XL

linear series — continued.

Miscellaneous Examples.

In this chapter are given some miscellaneous examples. Most
of them illustrate the Meristic Variation of parts standing in
bilateral symmetry on either side of a median line.

Here also are included certain cases of Variation concerning
the series of apertures in the shell of Haliotis, though probably
they are of a wholly different nature.

Scales.

Among animals possessing an exoskeleton composed of scales,
the number of the scales or of the rows of scales found in par-
ticular regions is usually more or less definite. So constant are
these numbers in their range of Variation that in both Reptiles
and Fishes either actual numbers or certain ranges of numbers are
made use of for purposes of classification.

Considerable Variation in these numbers is nevertheless well
known, and many instances are given in works dealing with
Reptiles or Fishes. The following cases are given as illustrations
of some of the larger changes which may occur.
403*. Clupea pilchardus (the common Pilchard). Among the
Pilchards brought to the curing factories at Mevagissey, Corn-
wall, specimens have from time to time been found by Mr Mathias
Dunn, the director, having the scales of one side very many more
in number than those of the other side. Two specimens1 shewing
this abnormality were given to me by Mr Dunn in 1889. Owing
to the fact that the fresh Pilchards are shovelled wholesale into
the brine-vats, it is not until the fish are picked over for packing-
after the salting process that any individual peculiarities are

1 These specimens are now in the Museum of the Royal College of Surgeons.
An account of them was published in P. Z. S., 1890, p. 586. Figures of the same
variation were given by Day, F., P. Z. S., 1887, p. 129, PI. xv.

chap. XL] PILCHARD: SCALES. 275

noticed. This was the case with the present specimens, which
were given to me as they came salted from the presses. Never-
theless when received they were in fairly good condition.

The first specimen measured 8 in. to the base of the caudal fin.
The head and opercula were normal on both sides. The number of
scales along the lateral line or the left side is 32 and the number on
the right side is 56 or 57. On the left side the scales have the
size usually seen in Pilchards of this length, and on the right side
for a distance of about an inch behind the operculum the scales
are not much smaller than those of a normal Pilchard, but behind
this point each scale is of about half the normal size.

The second specimen has a very similar length. It differs
from the first in having the reduplication on the left side in-
stead of on the right. Furthermore the scales are normal in
size as far as the level of the anterior end of the dorsal fin, behind
which place they are of about half the normal size. The transi-
tion in this specimen is quite abrupt. The scales had been
somewhat rubbed, and the counting could not be very accurately
made, but the total number along the left lateral line was
approximately 48.

As these abnormal individuals were taken with the shoal there
can be little doubt that they were swimming with it.

In P. Z. S., 1887, p. 129, PI. xv. Day described a specimen, also
obtained from Mr Dunn, exhibiting characters similar to those above
described. The number of scales along the lateral line is given as 32
on the right side and 51 on the left. In the figure no transition from
normal to abnormal scales is shewn, but there is a general appearance
of uniformity.

Mr Day regarded this specimen as a hybrid between the Herring
(C. harengus) and the Pilchard, and before adopting the view that the
case is one of Variation this suggestion must be discussed. This view
was chiefly based on the presence of the small scales on one side, but it
is added that the ridges on the operculum, which are characteristic of
the Pilchard as compared with the Herring, were better marked on
the right side than on the left, though they are stated to have been
very distinct on the left side also. In the specimen described, the
gill-rakers were 61 in the "lower branch of the outer branchial arch"
(viz. the bar consisting of the first hypobranchial and ceratobranchial),
and it is mentioned that this number is intermediate between that
found in a Pilchard (71) and in a Herring (48); but whether this
intermediate number was found on the side shewing the " Herring "
characters, or on the other, or on both, is not stated. These gill-rakers
are also said to have been intermediate in length between those of a
Pilchard and those of a Herring. From these points of structure
Mr Day concludes that the specimen was a hybrid between the Herring
and the Pilchard.

As against the theory that these specimens are hybrids it may be
remarked that no direct evidence is adduced which points to hybrid
parentage. The suggestion is derived from (1) the condition of the

18—2

276 MERISTIC VARIATION. [part I.

scales, (2) the number of the gill-rakers, (3) the alleged difference in
the opercula of the two sides. In view of the first point, viz. that the
number of the scales on one side is intermediate between that of the
Pilchard and that of the Herring, it seemed desirable to know whether
the resemblance extended to the minute structure of the scales or was
restricted to their number only. On comparing microscopically the
scales of the Pilchard and the Herring, I find that those of the
Herring bear concentric lines which are almost always smooth and
without serrations, while those of the Pilchard are marked with lines
which are waved into very characteristic crenelated serrations. On
comparing the scales which are repeated, it was found that they also
shew these characteristic serrations and that in pattern they differ in
nowise from the scales of the Pilchard. This evidence appears to tell
very strongly against the theory that the small scales are derived from
a Herring parent.

The evidence from the gill-rakers seems to be also unreliable. In
a normal Pilchard Mr Day found 71 on the hypo- and cerato-branchials
of the first gill-bar, and in a specimen examined by me 72 were present
and in normal Herrings 48. But in my two specimens shewing the
repeated scales there were present, on the normal sides 79 and 67
respectively, and on the abnormal sides 78 in the one fish and 67 in
the other. In size and shape the gill-rakers were like those of the
Pilchard, being smooth, and unlike those of the Herring, which bear
well-marked teeth.

As it is stated that the serrations characteristic of the operculum
of the Pilchard were very distinct on the abnormal side, it is impossible
to lay much stress on the circumstance that they were less distinct than
those of the other side.

In addition to the considerations given above, there are several
d, priori objections to the hypothesis of the hybrid origin of these
forms ; as, for example, that unilateral division of parental characters
is certainly not a common phenomenon in hybrids, if it occurs at all,
and so on. But since the evidence advanced for the theory of hybrid
parentage is already open to criticism, it is perhaps unnecessary to
discuss these further difficulties.

On the whole, therefore, it seems simpler to look on these
abnormalities as instances of the phenomenon of Meristic Variation1.

In Ophidia the number of scales occurring in different parts
of the body is constant in some genera and species, and variable in
others. Variation in the number of rows of scales on the body
may be specially referred to as an instance of a change in number
occurring at right angles to that just described. The number of
such rows in Tropidonotus, for example, is generally 19, but Mr

404. Boulenger informs me that the Swiss Tropidonotus viperinus
has either 21 or else 23 rows.

405. Tropidonotus natrix is remarkably constant in the posses-
sion of 19 rows of body scales. A specimen taken in Switzerland

1 Compare with an interesting series of cases in Gasterosteus (Stickleback).
Boulenger, G. A., Ann. and Mag. N. H., 1893, S. 6, xi. p. 228, see also Zool.,
1864, p. 9145; Sauvage, Nouv. Arch, du Mus., 1874; Day, Jonrn. Linn. Soc, xm.
1878, p. 110 ; &c.

chap, xi.] SNAKES : SCALES. 277

is described by Studer, Mitth. natur. Ges. Bern, 1869, p. 24, as
having 20 rows. This specimen was unusually dark in colour.
[The presence of an even number of rows is in itself remarkable,
but it is not stated whether this total was reached by duplicity in
the median dorsal row or by inequality on the two sides.]
406. A specimen of Snake from Morocco closely resembled Macropro-
todon mauritanicus Guichenot (= Lycognathus cucullatus Dum.
Bibr.), but differed from it in having 23 rows of body-scales
instead of 19, being 4 rows in excess of the normal number.
Peters, W., Sitzb. Ges. naturf. Fr. Berlin, 1882, p. 27.

For particulars as to the range of variation in these numbers
in different species, see numerous examples given by Botjlenger,
G. A., Fauna of Brit. India : Reptilia and Batrachia, 1890.

Kidneys ; Renal Arteries ; Ureters.

Meristic Variation in these organs is well known and the
principal forms found are described in most text-books of anatomy.
Some information as to these is given below. The examples are
all from the human subject.

407. Kidneys. Male having three kidneys. The left kidney was
normal in shape, position and consistency but was abnormally
large. The right kidney was placed opposite to it and weighed
only half as much as the left. From it a ureter with a small
lumen arose and passed in a normal course so far as the division
of the aorta. At this point its course lay along the surface of the
third kidney. This third kidney lay over the whole right iliac
artery, a portion of the right crural artery for the space of 9 lines,
the right crural vein and the psoas major muscle. It was larger
than the upper right kidney and had the form of an oval with its
ends cut off. The anterior and posterior surfaces were convex. The
anterior surface was grooved for the passage of the ureter men-
tioned above, which received the ureter of the second kidney and
passed normally into the bladder. The man was a sailor and died
of enteritis at the age of 39. Thielmanx, C. H., Midlers Arch,
f. Anat. u. Phys., 1835, p. 511.

408. Renal Arteries. The number of the renal arteries in Man is
liable to great variation. In specimens in which the kidneys are
normal in position the arteries may be (a) diminished or (b)
increased in number. The latter is much more common.

Multiple renal arteries may be threefold, (a) Most commonly
the additional branches spring from the aorta, (b) they may come
from other sources ; or (c) there may be a co-existence of additional
vessels from both sources.

278

MERIST1C VARIATION.

[part I.

Of the first class, there have been described cases of

one,

two,

or

three

r one, "
right aortic | two,

renals -I three i-left aortic renals.
associated with or

, four .

409.

In the commonest form, next to the normal condition of one on
each side, there are two on the right side and one on the left. In the
second commonest condition there are two on the left and one on
the right ; but among the forms with larger numbers, the greatest
number is more frequently seen on the left than on the right side.
In all these cases one vessel arises in the position of the normal
renal ; a second commonly springs from the aorta much lower
down, generally on the level of, or below the inferior mesenteric ;
the third when present, is at a very short distance above the
normal renal, very close to the supra-renal and on the level of the
superior mesenteric. Cases of five on the right are described by
Otto and Meckel, and other multiple forms are recorded by the
older anatomists. Macalister, A., Proc. Roy. Irish Ac, 1883, p.
624.

Three renal arteries on each side, symmetrically placed (Fig.
73). In this case the posterior ends of the kidneys were united

Fig. 73. Case of three renal arteries on each side combined with " horse-shoe
kidney" (Man). (From Guifs Hosp. Rep.).

across the middle line in the condition known as " horse-shoe
kidney" [see evidence as to Bilateral Series]. Guy's Hosp. Rej).,
1883, p. 48, fig.

410. Ureters. Male. Four ureters emerging from the hilum of
each kidney. After proceeding about four inches they became
united, forming a pelvis from which sprang the proper ureter. The
hilum of the kidney was found to be occupied by a quantity of

CHAP. XI.]

EYES I MOLLUSCA.

279

fat and connective tissue, imbedded in which the ureters could be
traced to the infundibula, communicating with the calices and
pyramids : thus there was no pelvis within the hilum, but the
calices united to form infundibula of which these ureters seemed
to be the continuation, and they became united in a pelvis some
distance removed from the kidney. There were other signs of
abnormal urino-genital development and the author believes that
it is almost certain that the abnormality described was congenital
and not a sequel of disease. Richmond, W. S., Jour. Anat. Phys.,
xix. p. 120.
411. Two ureters from one kidney are frequent. For an example,
see Guys Hosp. Rep., 1883, p. 48.

Tentacles and Eyes of Mollusca.

412. Subemarginula : specimen having a supernumerary eye on
each eye-stalk (Fig. 74, II.). Author remarks that supernumerary
eyes are common in forms having eyes borne on tentacles, but are
rare in forms in which the tentacle is reduced as it is in Subemar-
ginula. Fischer, P., Jour, de Conch., S. 2, i. p. 330, PL xi. fig. 4.

413. Patella vulgata : tentacle and eye repeated on left side (Fig.
74, I.). Right side normal. Supernumerary eye and tentacle of

. normal size. Ibid., S. 3, iv. p. 89, PL till. fig. 8.

n

v

in

Fig. 74. Repetitions of eyes and tentacles in Molluscs. (After Fischer and
Moquin-Tandon.)

I. Patella vulgata, No. 413. II. Subemarqinula, No. 412. III. Helix kermo-
vani, No. 416. IV. Clausilia bidens, abnormal, No. 417 ; V. normal of the same.

280 MERISTIC VARIATION. [part I.

414. Triopa clavigera (a Nudibranch): adult of the usual size,
having the lamellar rhinophore of the right side formed of three
branches, of which the two anterior were lamellar, borne on a
common peduncle, and the posterior was simple, of regular shape
and probably representing the normal rhinophore of the right side.
The rhinophore of the left side was normal. Ibid., S. 3, XXVIII. p. 131.

415. Physa acuta: right tentacle bifid, left normal. Moquin-
Taxdox, Hist. not. des Moll. terr. et fluv. de France, I. p. 322, PL
xxxn. fig. 15.

416. Helix kermorvani : a second eye present, close to, but
separate from the normal eye (Fig. 74, III.) on the left tentacle.
Ibid., PL xi. fig. 10.

417_ Clausilia bidens : supernumerary eye on the right tentacle

' as shewn in Fig. 74, IV. Ibid., PL xxm. fig. 24.
41 $ Littorina : supernumerary eye on one tentacle. Pelsexeer,
Ann. Soc. beige de microscojne, XVI., 1891.

In examining large numbers of Pecten of several species, Mr Bkindley
occasionally found one of the eyes imperfectly divided into two, the division
being at right angles to the mantle-edge.

Eyes of Ixsects.1

The following are examples of supernumerary eyes in Insects.
They are mentioned as examples of the development of tissues of
the same nature as those of the normal eye in abnormal situations.
All the cases known to me occur in Coleoptera.

419. Toxotus ( = Pachyta) 4 — maculatus: a normal female. On
the vertex of the margin of the right eye and abutting against it
is a small third eye. This third eye is round-oblong in shape. It
is separated from the large eye only by the outermost margin of
the eye, and though it is more convex than the latter there is
nevertheless a considerable depression between the upper surfaces
of the two eyes. This supernumerary eye is of a brighter colour
than the normal eye, being brownish-yellow, while the latter is of
a pitchy black. It is facetted in the same way as the normal eye
is. Letzxer, K., Jahresb. d. Schles. Gesell.fur vaterl. Cidtur., 1881,
p. 355.

420. Calathus fuscus : having a third eye. On the left side of the
vertex was placed a supernumerary eye. This structure was
smaller and less projecting than the normal eye and was separated
from it by the usual groove. It did not appear to be a part of the
normal eye which had separated from it, for the normal eyes of
the left and right sides were exactly alike. The integument of
the head was slightly wrinkled around the supernumerary eye.
de la Brulerie, P., Ann. de la Soc. Ent. de France, S. 5, v., 1875,
p. 426, note.

421. Vesperus luridus $ : head abnormal and bearing a third

1 For cases of eyes compounded in the middle line (Bees), see evidence as to
Bilateral Series.

chap, xi.] WINGS OF INSECTS. 281

facetted eye. The consistency of the chitinous covering of the
head, its sculpture and hairs, colour, &c. are all normal and of the
usual structure. The left side of the head however is rather less
developed than the right, and the left eye seems to be smaller and
somewhat less convex, but there is no special deformity or altera-
tion in the facetting.

At the left side of the head arises an irregular chitinous loop
of unequal thickness and having' a diameter of about 2*5 mm.
This loop is attached to the substance of the head before and
behind and these two attachments are distant from each other
about 1 mm. The height of this loop from the surface of the head
is about 1 mm. in the highest part. Upon the upper surface of
the loop is a small, irregularly rounded eye. The diameter of this
eye is about 2 5 mm. and its convexity is considerable. It is
facetted, but its facetting is not quite regular and is finer and
slighter than that of the normal eyes. VON Kiesen wetter, Bed.
Ent. Ztschr., 1873, xvn. p. 435, Plate.

[A case is recorded by Reitter (Wiener Ent. Ztg., I v., 1885,
p. 276) of a Rhyttirhinus deformis, having a "complete and fully
formed facetted eye placed on the left side of the thorax." Upon
the request of Dr Sharp, this specimen was most kindly forwarded
by Dr Reitter for our examination, when it was found that upon
the application of a drop of water, the supposed abnormal eye
came off. The eye appeared to be that of a fly, and had no doubt
become accidentally attached to the beetle either in the collecting-
box or before its capture.]

Wings of Insects.

Supernumerary parts having the structure of wings have been
occasionally recorded in Lepidoptera, but their occurrence is ex-
ceedingly rare. In a subsequent chapter detailed evidence will
be given respecting supernumerary legs and other of the jointed
appendages of Insects and it will be shewn that in very man)'
and perhaps all of these cases the supernumerary parts constitute
a Secondary Symmetry within themselves (see p. 90). Extra
wings however are of a different nature altogether, and there is
so far as I am aware no indication that any of their parts are
disposed as a Secondary Symmetry. In other words, an extra
wing if on the left side is a left wing, and if on the right side
a right wing.

In some cases the extra wing is a close copy of a normal struc-
ture, in others it seems to be more or less deformed. No genuine
case of an extra wing present on both sides of the body is known
to me.

From the fact that no specimen of supernumerary wing has
ever been properly dissected, it is not possible to make any
confident statement as to the attachments or morphology of
such parts. (See also No. 78.)

282 MERISTIC VARIATION. [part i.

The cases of S. carpini, No. 422, and of Bombyx quercus, No.
429, nevertheless suggest that Variation in number of wings is of
the same nature as that seen in teeth, digits, or other parts
standing in a Meristic Series. In the specimen of S. carpini
it is especially noticeable that on the side having three wings,
both the wings formed as secondaries were smaller than the
secondary of the normal side ; but in other cases, G. rhamni
(No. 427) for instance, this was not the case, and the wing
standing next to the extra wing was normal. Both these con-
ditions are frequently found in cases of the occurrence of super-
numerary parts in series: for two members of a varying series
may clearly correspond jointly with a single member of the
normal series, or on the contrary a new member may stand ad-
jacent to members in all respects normal as in G. rhamni (No. 427.)
*422. Saturnia carpini $ , having a supernumerary hind wing. The
specimen is rather a small female. The right wings and the
left anterior wing are normal, but in the place of the left posterior
wing, there are two rather small but otherwise nearly normal
posterior wings. Of these the anterior is rather the larger and
to some extent overlaps the posterior. The costal border of the
posterior wing is folded over a little so that its width cannot

be exactly measured.

Greatest Greatest

length. width.

Right hind-wing normal 22'5 mm. 19 mm.
First left hind-wing 20*5 „ 14 „

Second left hind-wing 15'5 „ 11 „ about.

From the fact that the bases of these two wings are greatly
overgrown with hair, it is difficult to distinguish their exact points
of origin from the body, but so far as may be seen, the second
arises immediately behind and on a level with the first. The
neuration of each of the two small wings is identical with that
of a normal hind- wing. The scaling is perfect on both surfaces
of both wings, but is perhaps a little more sparse on the anterior
of the two abnormal ones. In colour the anterior abnormal wing
is rather light, but the posterior one is identical with that of
the other side. The markings on each of the wings are normal,
but are on a reduced scale in proportion to the size of the wings.
This is especially remarkable in the case of the ocelli, which are
both of a size greatly less than that of the ocellus of the normal
hind wing of the right side.

The two wings were in every respect true left hind-wings
and were in no way complementary to each other. [Specimen
in collection of and kindly lent by Dr Masox.]
423. Bombyx rubi J : 5th wing on left side. The additional wing
was placed behind the left posterior wing. It was of normal
structure as regards scaling and coloration. Its length was that
of the hind-wing but in breadth it did not exceed 6 mm. The

chap, xl] WINGS OF INSECTS. 283

insertion of this wing into the body was immediately above that
of the normal hind-wing. The extra wing bore 4 nervures, of
which 3 reached to the margin but one was shorter. The proper
hind-wing of the same side was rather narrower than that of
the other side and was not so thickly covered with scales, but
its neuration was complete and normal. Speyer, A., Stettiner
Ent. Ztg., 1888, xlix. p. 206.

424. Samia cecropia <£, having a fifth aborted wing. Bred in capti-
vity : ordinary size, expanding about 5^ inches : a smoky variety in
which red portion of transverse bands on wings is much narrowed.
Right primary and both secondaries normal in shape and marking.
Left primary in length from base to apex exactly the same as the right,
but in width from inner angle across to the costa is y3F of an inch less;
the markings are the same, but condensed into the narrower space.
Neuration normal in all wings. Left primary also somewhat narrower
at base, where it joins the body. The inner margin is in exact line
with its fellow; hence the costal line of the left primary is somewhat
posterior to that of the right primary. The supernumerary wing
emerges from the side of the collar and runs parallel to the normal left
primary. It consists mainly of the costal and subcostal nervures, a
small part of the median nervure and a strip of wing about i inch wide
which was much curled in drying. The supernumerary wing is in no
way connected with the normal one.

[The author regards this supernumerary wing as a repetition of the
anterior part of the left primary wing.] Strecker, H., Proc. Ac. Sci.
Philad., 1885, p. 26.

425. Limenitis populi, having four normal wings and a fifth wing
behind the left posterior one. This supernumerary wing was 20 mm.
long and 9 mm. wide. It slightly overlapped the left secondary and
was attached to it for a length of 12 mm., but its outer end was free.
It is described as exactly resembling the part of the secondary which
bears the three anterior nervures, and it is stated that both surfaces
were normal as regards scales and colouration. Rober, J., Correspond-
enzbl. d. ent. Ver. "Isis" z. Dresden, 1884, I. p. 31.

426. Vanessa urticae, having an additional hind-wing on the right
side. This structure is inserted into the thorax dorsal to and betice/i
the two normal wings. It is shorter and of about i the width of the
normal hind-wing. In colouring it is a close copy of the anterior third
of the hind-wing. Westwood, Trans. Ent. Soc, 1879, pp. 220 and
221, Plate. [Now in Brit. Mus.]

427. Gonepteryx rhamni with additional imperfectly developed hind-
wing on the right side. In this case the normal right hind-wing is
only about two-thirds of its normal size. It overlies the additional
hind-wing. The latter is coloured like the normal wing and bears an
orange spot. From the neuration of the two wings Westwood con-
sidered that the supplemental wing contained missing parts of the
normal wing.

Only two legs existed on the side of the abnormal wing, but for fear
of injury the specimen was not sufficiently examined to shew whether

284 MERISTIC VARIATION. [part i.

the missing leg had been broken off or whether the extra wing was in
its place. Westwood, ibid., p. 220.

A specimen of G. rhamni having five wings was caught at Brandon, Norfolk, in
Aug. 1873 by Mr J. Woodgate, and exhibited to the Ent. Soc. by Prof. Meldola,
Proc. Ent. Soc, 1877, p. xxvi. A similar specimen of this species was bought at
Stevens's auction-rooms and exhibited to Linn. Soc. by Prof. C. Stewart, in April,
1891. This specimen is now in Mus. Coll. Surg. Whether it is the same as that
taken by Mr Woodgate, or that described by Westwood, or not, I cannot say, but
possibly the references are all to one individual.

428. Lycaena icarus <£ . A coloured figure is given of a specimen
of this form with 5 wings from Taurus, Asia Minor. [No further
description is given. The figure is not very clear. It shews
however that all the wings are normal except the right anterior.
This wing is represented by two wings, which together are about
a third wider than the normal wing. The costal portion of the
foremost of these wings appears to be nearly normal in neuration,
and the posterior part of the hindmost seems to be also normal.
The two taken together shew several supernumerary nervures
as compared with the normal wing, but the details are not
shewn with sufficient clearness to justify a more precise statement.]
Honrath, E. G., Berl. Ent. Ztschr , xxxn. 1888, p. 498, To.f. VII.

429. Bombyx quercus J : specimen having 5 wings figured in
colour by Honrath, with statement that the left anterior wing
shews a double structure. [No further description given. The
figure shews the left anterior wing represented by two wings.
Of these the posterior appears to represent a nearly complete
anterior wing on a reduced scale. It bears the white ocellar mark
of the anterior wing. The pale-yellow submarginal band is
curved inwards over the ocellus upon the costal border as in a
normal wing and thus shews that the foremost wing is not merely
the separated costal part of this wing. The foremost wing is
anomalous. Its central half is rather darker in colour than that
of the normal wing and its peripheral half is pale in colour,
deepening towards the margin. It bears no ocellus. The neura-
tions cannot be made out from the figure with precision but the
two wings together contain many more nervures than the normal
anterior wing. The legs are not described.] Honrath, E. G.,
ibid., fig. 10.

430. Zygaena minos, having a fifth wing on the left side, inserted above and between
the normal wings. The neuration of this wing is peculiar. The colouring of the
supernumerary wing was that of the anterior wing. [Dr Rogenhofer kindly informs
me that the legs were normal.] Rogenhofer, A., Sitz.-Ber. d. zool.-bot. Ges. Wien,
1883, xxxn. p. 3-4, fig.

In the same place the following instances of five- winged Lepidoptera are given :
431 Orthosia laevis with an additional posterior wing on the left side, in the

' Museum of Pesth. Treitschke, Bd. vi. Abth. n. p. 407.

432. Tygaera anastomosis with a wing-like appendage to the left anterior wing in
' the collection of Ochsenheimer in Pesth.

433. Naenia typica with an additional posterior wing in the collection of Neustadt
at Breslau.

chap, xi.] HORNS. 285

434. Crateronyx dumi with five wings in the collection of Wiskott in Breslau.

435 Penthina salicella : left fore-wing about J wider than the normal right fore-

* wing. The apical border was markedly emarginated, giving it a bilobed appearance.

The nervures were as in the normal wing, except that the cells between the branches

of the subcostal nervure were enlarged. Kogenhofek, ibid. [I am indebted to Dr

Eogenhofer for a sketch of this specimen.]

[Palloptera UStulata (Diptera): specimen having a large upright
scale on the thorax. This abnormal structure is like a third wine in
appearance, and is fixed on the thorax, passing from the head, back-
wards between the wings. Its upper border is circular, and in all
respects it resembles the upper wing-scale of one of the Calypterous
Muscidce. Gercke, G., Wiener Ent. Ztg., 1886, v. p. 168.]

Horns of Sheep, Goats and Deer.

436. Sheep. Repetition of the horns in sheep is well known. The
best account is that of H. von Nathusius1 of which the following
is chiefly an abstract.

Commonly there is a pair of extra horns placed externally to
the usual pair, but there may be three pairs in all, and even
higher numbers are recorded, though Nathusius had seen no such
case. The numbers on the two sides may be different, two on one
side and one on the other, and three on one side and two on the
other being sometimes met with.

It is noticeable that in all cases the horns stand in a trans-
verse series, and not in a longitudinal series as they do in the
Four-horned Antelope (Tetraceros quadricornis). The bases of
the horn-cores are generally in contact, standing one outside the
other at the same transverse level on the skull. Nathusius
observed that in development the outgrowth for the horns of one
side is at first single, but afterwards divides into two or more
points, but he surmises that the division may appear earlier in
other cases.

The external horns are generally smaller than the internal
ones, but this is not universal. In some cases of two pairs of
horns a small fifth horn is placed between the external and internal
horns of one side.

In another form of double horn the horn-core of one side or
other may be a double structure, both cores being enclosed in a
single horn, which on being separated has a double-barrelled
appearance.

Several examples of permanently four-horned breeds occur in
various localities, being described as common in Cyprus and
notably in Iceland and other northern islands. Youatt (p. 169)
stated that there were two breeds of sheep in Iceland, the one
small and the other large, and that the greater part of both breeds

1 H. von Nathusius, Vortr. iib. Viehzucht u. Rcusenkenntniss, Th. n., Die Schaf-
zucht, 1880, p. 177, fig. 47.

286 MERISTIC VARIATION. [part I.

had more than two horns, some having eight. I am informed
however by Mr E. H. Acton, who has spent some time in the
country, that many-horned sheep are by no means common in
Iceland at the present day. In Kishtwar (district of S.E. Kashmir)
a breed of 4-horned sheep is carefully preserved, in which the
horns are as a rule very symmetrical, somewhat resembling
No. 438 \

Xathusius states that a four-horned ram does not always beget
four-horned offspring even when the ewe has the same character,
and the variation between father and son in respect of horns is
frequently considerable.

The best figures of many-horned sheep are those given by Buffon, Hist, nat.,
Vol. xi. Pis. 31 and 32 (3-horned and 4-horned); Youatt, The Sheep, pp. 141 and
171, copied from Buffon. Numerous other figures are referred to by Nathusius,
but few of them are satisfactory.

437. G-oat. A family of goats on an isolated farm near Bozen had
4 horns, which had been inherited for many generations. In most
cases the two ordinary horns were typical in shape and direction;
and in addition to these there were two lateral ones, which were
laterally curved, being sickle-shaped and bent into a semicircle.
Gredler, V., Korrespondenzbl. d. zool. min. Ver. Regensburg, 1869,
xxiii. p. 35.

'438. Rupicapra tragus (Chamois) : skull bearing two well-formed
and symmetrical extra horns. The cores of these horns were a little
outside and posterior to the normal pair. Alston, E. R., P. Z. S.,
1879, p. 802.

439 Capreolus caprea (Roebuck) : specimens having a supernumerary
beam are probably not very rare, and a number of such antlers were
shewn among the hunting-trophies exhibited by H. H. the Duke of
Saxe-Coburg-Gotha, and H. S. H. the Prince of Waldeck-Pyrmont at
the German Exhibition held in London in 1891. The normal antler of
the roebuck has a single beam rising vertically, then bifurcating, the
posterior branch again dividing. In the abnormal specimens from the
single burr of one side arose a supernumerary beam in addition to the
normal one. In one specimen, in which the supernumerary beam was
nearly as long as the normal one, the latter bifurcated as usual but
was rather more slender than that of the other side (Fig. 75 I.). In
another case (Fig. 75 II.), from the left burr, which was much enlarged,
arose (1) an innermost beam, in thickness and texture resembling that
of the normal right horn, though it was much shorter and bore no tine ;
(2) an external beam at once dividing into two almost equivalent
branches having about the same length as the innermost beam. In
such a case I know no criterion by which one of the three beams can
be certified to be the normal to the exclusion of the others. As in the
sheep and goats, the several horns resulting from subdivision seem to
be generally in or nearly in the same transverse plane.

1 Godwin-Austen, H. H., P. Z. S., 1879, p. 802.

CHAP. XI.]

HALIOTIS.

287

Fig. 75. Abnormal horns of Roebuck (Capreolus caprea), No. 438. ("When seen
by me the horns were fixed upon heads modelled in plaster.)

Perforations of shell of Haliotis.

44Q Haliotis gigantea (Japan) having two rows of perforations in the shell. In
addition to the ordinary row of perforations, of which 12 were present in this
specimen, there was a series of 8 additional perforations which began within an inch
of the apex. Of the normal series the last four remained open, but all the perfora-
tions in the abnormal row were closed with nacre. Specimen in Brit. Mus. Smith,
E. A., Ann. and Mag. of X. H., 1888 (1), p. 419.

441. Haliotis : two specimens, of different species, in which the perforations were
entirely absent, their place being taken by a continued convex, spiral rib, like the
second rib of Padollus. "Probably in this individual the mantle was without any
slit, and hence the malformation, the water being admitted to the gills by the slight
notch in front of the ribs, as in some Emarg inula, or Scuta." Gray, J. E., Proc.
Zool. Soc, 1856, p. 149.

442. H- albicans : several specimens in which the perforations were united to form a
continuous slit. The appearances were so uniform that Gray was disposed to think
that these specimens might represent a new genus, but on comparison with types
they seemed to belong to the species named. In some fossil genera (Scissurella) the
perforations are replaced by a more or less continuous slit over the mantle. The
specimens in question were greatly eroded and had a diseased appearance, ibid.
Plate.

CHAPTER XII.

linear series — continued. COLOUR-MARKINGS.

Ocellar Markings1, especially those of Lepidoptera.

Upon the bodies of animals belonging to many classes are
markings which consist of a central patch of colour surrounded by
a variable number of concentric rings of different colours. Such
markings are known as ocelli or eye-spots from their resemblance
to the pupil and iris of vertebrates. Eye-spots are perhaps best
known in Lepidoptera, but similar markings are not unfrequent in
other groups and especially on the feathers of Birds and in Fishes.

In one of the best known chapters in the Descent of Man 2 the
nature and mode of evolution of these markings is the subject of
a full discussion, the case of eye-spots on feathers being chiefly
taken in illustration. As is well known, Darwin by the compara-
tive method, comparing the eye-spots found in different species, on
the different feathers of the same bird, or on different parts of the
same feather, found that it was possible to construct a complete
progression from a plain spot to a fully-formed ocellus. Though
no one examining such a series can possibly doubt that the simple
spot and the fully-formed ocellus are really of the same nature and
that the one represents a modification of the other, there remains
nevertheless the difficulty that members of a series of parts cannot
be assumed to represent conditions through which the other mem-
bers of the same series have passed, and it is of course clear that
the conditions found in some forms do not necessarily correspond
with phylogenetic phases of other forms. In the present instance
however Darwin is not specially urging this view, but brings
forward the comparative evidence chiefly in illustration of the
possibility that such structures may exist in an imperfect state
and so may be conceived of as having had a gradual origin.

1 The evidence concerning eyespots of Lepidoptera is taken here because eyespots
when repeated in series, though borne on appendicular parts, are nevertheless
arranged chiefly with reference to the chief axis of symmetry of the body. In some
few forms, e.g. Taygetis, there is a conspicuous Minor Symmetry within the limits
of a single wing (the posterior), but this is not often the case.

2 Descent of Man, 1871, n. pp. 132—153.

chap, xii.] EYE-SPOTS. 289

Though doubtless the eye-spots of Birds are in their nature
not different from those of Lepidoptera yet their manifestations in
the latter are usually in some respects simpler than they are in
Birds. From the abundance of material also the Variation of eye-
spots is most easily studied in Lepidoptera and it is to them that
the present evidence chiefly relates.

In preface to the evidence a few remarks are needed to direct
attention to certain features in the mode of normal occurrence of
eye-spots and in the manner of their Variation.

On a survey of the facts it is at once seen that eye-spots are
extraordinarily variable both in number and size, some of the best
formed being occasionally absent, and large and perfect ocelli being
sometimes added in situations having normally no trace of such
marks. With this fact Darwin was well acquainted and he refers
to observations in illustration of it. In speaking of Gyllo leda he
concludes that from the great variability of the eye-spots " in cases
like these, the development of a perfect ocellus does not require a
long course of variation and selection ; ': and again, that bearing in
mind " the extraordinary variability of the ocelli in many Lepi-
doptera, the formation of these beautiful ornaments can hardly be
a highly complex process, and probably depends on some slight and
graduated change in the nature of the tissues." The facts to be
given and the circumstances attendant on the variation of ocelli
tend to support this conclusion.

Considered from the point of view of Meristic Variation the
chief feature in the manner of occurrence of eye-spots in Lepi-
doptera is the frequency with which they are repeated. A single
spot may be repeated in homologous places in both pairs
of wings ; in other cases there is a series along the margins
of one or both wings. Besides the repetitions thus occurring it is
especially worthy of notice that ocelli are very commonly repeated
on both surfaces of the wing (Satyridse, &c), the centres of the
upper and lower ocelli coinciding. It need scarcely be remarked
that this effect is not produced by transparency of the wing-mem-
branes and scales, but is an actual repetition, the scales of both
surfaces being so coloured as to form an eye-spot on each side, the
two having their centres coincident. In some cases, e.g. Saturnia
carpini (the Emperor Moth), the rings and centres of the upper
and lower ocelli have nearly the same colouring, but in the majority
e.g. Pararge megcera (The Wall), Erebia blandina, &c, the upper
and lower spots, though coincident, have quite different colours.
In considering the Variation of the spots these facts as to the
repetition of the spots should be remembered, for, as has been often
insisted on in other cases of repetitions, we are concerned with the
evolution of the seizes and not of one member only. Here there-
fore regard must be had to the degree of correspondence between
the variations of the eye-spots in the fore and hind wings, on the

b. 19

290 MERISTIC VARIATION, [part i.

upper and lower surfaces of the same wing, in the several eye-spots
along the margin of the same wing, or in all of these, as the case
may be. The evidence will shew that there is sometimes a close
correspondence between the variations of eye-spots in these several
positions.

But though these are the matters with which we have now
the more direct concern it will be convenient to speak at the same
time more generally of eye-spots. It should be remembered first
that there are eye-spots of various complexity. In the simplest
all the bands are circular, having one centre ; the ocellus is then
as a rule complete in one cell of the wing, though sometimes the
outer zones of colour overspread parts of the adjacent cells. In
some cases the spot is double, having two centres, the bands being-
disposed round them in an hour-glass shape. As to the visible
structure of eye-spots it can be seen with the microscope that the
colour of the eye-spot lies in the colours of the scales. The scales are
arranged in parallel rows running (with little crossing or anasto-
mosing) as nearly as possible at right angles to the nearest nervures,
being disposed in regard to them much as the circular threads of a
cobweb are in regard to the radial threads. Across these rows of
scales run the colour-zones, in no way limited or guided by them.
On the other hand it can be seen that the patterns are almost
wholly made up by the colours of single scales, each having its
own colour, particoloured scales being exceptional. The effect
thus seen is very like that of a mosaic picture made of similar
pieces, or of a design worked in cross-stitch on canvas, all the
stitches being in rows and each stitch having its own colour.

As regards the position of eye-spots it should be noticed that
the simpler sort, e.g. those of Morpho or of Satyridaa, are usually
placed in such a position that each of their centres is on the line of
one of the creases or fold-marks of the wing, and it sometimes
happens that these creases seem to begin from the centre of an
ocellus. From the fact that the creases for the most part run
evenly between two nervures, bisecting a cell, it commonly results
that the centre of the eye-spot is exactly halfway between two
nervures. The large spots on the hind wings of some Pieridas, e.g.
Parnassius apollo, are an exception to this rule.

In that cell of the hind wing which lies between the submedian
and first median nervures in many ocellated forms (Satyridse,
Morpho, &c.) there are two creases, and it is especially interesting to
notice that in this cell there are commonly two ocelli, one on each
crease ; but if there is only one ocellus its centre does not corre-
spond with the middle of the cell but is nearer to the first median
nervure, being placed exactly on the anterior of the two creases.
In spite of the excessive variability of ocelli, in for instance Satyr-
idse, it appears that they are not formed in situations other than
these, being so far as I have seen always on one of the creases \
1 These remarks refer to simple ocelli with one or more definite centres.

chap, xii.] EYE-SPOTS. 291

On looking at such a series of repeated ocelli as those on the hind
wing of Pararge ?negcera, from this fact that the ocelli are on these
creases or folds the question naturally arises whether the wing may not
have been, in its development, folded along these creases so as to bring
the ocelli into contact with each other like the fold-edges of a fan. If
this were the case it might be supposed that the repetition of the ocelli
was due to the action of some one cause on all the folded edges
together. As a matter of fact, however, so far at least as can be
judged from the condition of the wings in the pupal state before scales
or pigments are excreted, there is no such folding, but each wing is
laid smoothly out, and the increase in extent of the wings of the imago
is attained, not by a process of unfolding, but by a stretching of the
elastic wing-membranes on inflation from the trachea?. On the whole
it does not seem likely that the repetition of similar eye-spots on the
Lepidopteran wing arises in any way more immediately mechanical
than that by which other repeated patterns are elsewhere formed on
animals.

The Variation of eye-spots as already stated may be very great,
and examples are to be given both of the total absence of large
eye-spots present in the normal, and of the presence of perfect
eye-spots in abnormal places. Besides these extreme cases there
is immense Variation in the degree to which eye-spots are develop-
ed, and such variability is nearly always to be seen in any species
possessing simple ringed ocelli. In the manner of Variation of
ocelli the following things are noteworthy.

(1) The tvhole of an eye-spot, centre and various concentric
bands together, may be wanting ; conversely a tvhole new eye-spot
having the centre and all the bands pertaining to the normal eye-
spot of the species may suddenly appear upon a crease normally
bearing no eye-spot. Eye-spots therefore may come or disappear
in their entirety.

(2) If a number of specimens of some much ocellated species
are taken and compared, examples will be found in which some of
the normal ocelli are absent altogether. But besides these there
may generally be found specimens having an ocellus in a reduced
and imperfect condition. Speaking generally such reduction com-
monly occurs by diminution of the diameter of the whole spot ; but
if any of its component parts are wanting the centre is the first to
disappear, then the next innermost band, and so on. In Fig. 76 is
shewn a series of specimens illustrating this fact in the case of
Hipparchia tithonus. The eye-spot in its least form is represented
by a plain black patch. In the more complete condition a white
centre appears. A similar case in Morpho is shewn in Fig. 81.
Here on the right side a certain eye-spot is absent altogether,
while on the left side it is present in a reduced state ; the white
centre and the innermost broad black band are absent, and the
actual centre is of the yellow-red colour which in the normal eye-
spot of the species is the third colour from the centre. The spots

19—2

292 MERISTIC VARIATION. [part I.

on the upper surface of the hind wings of the Wall (P. megcera)
are an excellent illustration of these principles of Variation.

The principle here stated, though generally followed, is not
absolutely universal, and in other instances it occasionally happens
that even when of very minute size an eye-spot still retains all its
bands ; but the statement that the order of disappearance is from
the centre outwards and not the reverse is substantially true.
Some have expressed a belief that ocelli arise by the breaking up
of bands of colour, but this view finds no support in the facts of
Variation so far as the simple ocelli of such forms as Morplio and
the Satyridse are concerned ; for in its rudimentary condition a
circular eye-spot is in them a circular eye-spot still.

The fact just stated, that in the reduction of a circular ocellus
its central parts are the tirst to disappear, recalls phenomena seen
in many cases of disturbance propagated from a centre through a
homogeneous medium. A whole eye-spot may come, or it may go (as
seen in cases of Morpho), leaving the field of the cell plain and
without a speck. The suggestion is strong that the whole series of
rings may have been formed by some one central disturbance, somewhat
as a series of concentric waves may be formed by the splash of a stone
thrown into a pool. It is especially interesting to remember that the
formation even of a number of concentric rings of different colours
from an animal pigment by the even diffusion of one reagent from
a centre occurs actually in Gmelin's test for bile-pigments. Bile is
spread on a white plate and a drop of nitric acid yellow with nitrous
acid is dropped on it. As the acid diffuses itself distinct rings of
yellow, red, violet, blue and green are formed concentrically round it
by the progressive oxidation of the bile-pigment.

If the experiment is made by letting a drop of the acid fall on
a piece of blotting-paper wetted with bile, a fairly permanent imitation
of an ocellar mark can be made. It will be noticed that as in the
natural eye-spot, so here, the outermost zone appears first and the central
colour last. As also is usually the case in the ocellus, when all the
zones are formed, the centre may greatly increase in diameter without
any increase in the breadths of the circular zones, which merely get
larger in diameter, remaining of the same breadth.

There is of course no reason whatever for supposing that ocelli are
actually formed by the oxidation or other simple chemical change of
the pigments of the field, but this example is merely given as an
illustration of the possibility that a series of discontinuous chemical
effects may be produced in concentric zones by a single central disturb-
ance. Indeed, that the formation of an ocellus cannot be in reality of
such simplicity is shewn by the fact that the scales of the centres of
ocelli generally exhibit interference-colours (usually white or blue) and
are then wholly or partially without pigment, while in not a few cases
the centres of ocelli are deficient in, or destitute of, scales. It must
also be remembered that occasionally the colour of one of the outer
zones is repeated in an inner zone, which would scarcely be expected on
the analogy of the oxidation of bile-pigments.

(3) As in the case of Teeth at the ends of series, disappearance
of a member of a close series of eye-spots commonly occurs by the

chap, xii.] EYE-SPOTS. 293

loss of the spot standing at one of the ends of the series. This is
easily seen in P. megcera, &c. Likewise as was found in Teeth,
disappearance of such a terminal eye-spot is associated with
reduction in the size of the other members of the series, and
especially of those nearest to the place of the absent member.
If as in Satyrus hyperanthus and many others, the series is broken
into groups, then as in the case of heterodont dentitions containing
gaps, a new member may be added on to the end of either group.

(4) The condition of the ocelli may vary similarly and simul-
taneously in both anterior and posterior wings. In a series of
Satumia carpini for example I notice that the size of the ocelli
varies greatly, those of a particular female specimen in the Cam-
bridge University Museum being nearly a quarter larger than those
of the specimen having the smallest ocelli ; but the size of the
ocelli in the hind wings of each individual varies with that of
the ocelli in the fore wings not less closely than the size of the
right ocelli does with that of the left.

(5) This correlation between the wings of the two pairs is seen
also in the presence or absence of ocelli as exhibited for instance
in H. tithonus (Fig. 76). It is of course often very irregular, but
for our purpose it is even of consequence that such correlation
may occur sometimes.

(6) As mentioned, ocelli are often coincident on the upper and
lower surfaces. When this is so, the degree of development of the
spots on the one surface is generally an accurate measure of the
degree to which they are developed on the other surface. But in
species having spots developed thus coincidently on the two sur-
faces it can be found that, in varying, an ocellus always first
appears in its least condition either on one surface or on the other,
and not indefinitely sometimes on one and sometimes on the
other. In P. megcera, for example, ocelli of both pairs of wings
can be seen on the under surface when not formed on the
upper and conversely. Nevertheless there is always a close corre-
lation between the degrees of development on the two surfaces.

(7) Lastly, attention is called to the circumstance that in two
cases of great variation in ocellar markings there was a variation
in the neuration. In the first case, P. megcera, No. 458, the second
median nervure was absent from both fore and hind wings. In
the fore wing upon the line where it should be there was an eye-spot:
in the hind wing the eye-spots of the two cells which should be
separated by the second median were partially coalescent. In the
other case, S. carpini, No. 459, the large ocellus was absent from
each wing, and it is stated that a nervure was also absent, but of
this case no proper description has appeared, and it is uncertain
which nervure was absent. When however these facts are con-
sidered in connexion with the circumstance that ocelli stand on
the creases of the wings it seems likely that in some way unknown
the positions and perhaps even the existence of the eye-spots may

294

MERLSTIC VARIATION.

[part I.

be determined by the manner of stretching of the wing-membranes.
It must still be remembered that in the great majority of cases of
ocellar variation there is no change in the neuration.

As to the Junction of ocellar markings nothing is known, and I
am not aware that any suggestion has been made which calls for
serious notice.

*

443

Evidence as to Variation of Ocelli in Lepidoptera.

General variability of ocelli.

The following are chosen to illustrate the general variability of
ocelli in Satyridse. Any of the common forms, such as C. darus,
P. megcera, &c. shew similar variations. Generally speaking the
condition is bilaterally symmetrical, but somewhat asymmetrical
examples are not rare.

Hipparchia tithonus : from some 80 specimens taken in one

Fig. 76. Hipparchia tithonus <? , cases illustrating Variation in number of ocelli.
I. In f. w. the upper half of the large ocellus has a pupil, the lower has none :
in h. w. no ocellus. II. Both halves of large ocellus of f. w. have pupils, and the
h. w. has one ocellus. III. Pupils of large ocellus of f. w. are larger : h. w. has
two ocelli. IV. F. w. has a new ocellus and the large double ocellus is half- joined
to a second new ocellus. H. w. has two ocelli, one being placed otherwise than in
III. V. F. w. has two ocelli without pupils as well as the large double one. H. w.
has three ocelli. The wings of the other side corresponded near-ly though not
accurately. II. is the most frequent form.

(This figure was drawn with especial care from the specimens by Mr Edwin
Wilson.)

CHAP. XII.]

EYE-SPOTS.

295

f444.

ditch in the Cambridgeshire Fens on the same day the individuals
shewn in Fig. 76 were selected. These cases especially illustrate
the statements numbered (2) and (o), viz. the order of appearance
of the colours and the similar Variation of the two pairs of wings.
Satyrus hyperanthus : four specimens (Fig. 77) shewing

ill

II

IV

Fig. 77. Satyrus hyperanthus. Various conditions of ocelli. II. is the most
frequent form.

(From Newman's British Butterflies.)

different conditions of ocelli in this species from Newman's British
Butterflies. A form without ocelli is mentioned by Porritt, Ent.t
xvl, 1883, p. 188.

On one day I have myself taken all the forms shewn in Fig. 77
(except III.) and others in Monk's Wood, so that here no question
of seasonal or local difference is necessarily involved.

445 Chionobas. The North- American species of this genus [in general appearance
' somewhat resembling the British Hipparchia semele, the Grayling] are of a brown
colour having eye-spots on some or all of the wings. According to Strecker the
number of eye-spots varies extremely, and the following instances are given. The
species norma may have two spots on fore wings and none on hind wings ; two on
f. w. and one on h. w. ; one on f. w. and one on h. w. ; one on f. w. and none on h. w.;
three on f. w. and two on h. w. Of the species uhleri one of the types has three on
f. w. and four on h. w., the other has four on f. w. and five on h. w., the subapical
being very small ; other examples have only one on f. w. and two or three on h. w.
The species chryxus may have one on f. w. and none on h. w.; or two on f. w. and
one on h. w. Strecker, Cat. Macrolepid., p. 155.

446. Arge pherusa: a butterfly resembling the British Arge galathea, the Marbled
White, has a variety plesaum, in which the eye-spots of hind wing are wanting. ^

Specimen figured in which the left hind wing is a third smaller than the right
and lacks the eye-spots. Failla-Tedaldi, Nat. Sicil., i. p. 208, PI. xi. lig. 8.

296

MERISTIC VARIATION.

[part I.

MORPHO.

A number of species of this genus, for example, M. achilles,
menelaus, octavia, montezuma, &c. are marked upon the under
surface of both pairs of wings with large ocelli having four principal
zones in addition to the white central spot. Of the zones the
outermost is silvery, the next dark brown, the next either red or
some shade of yellow. Within this is a band of verv variable
width having a deep chocolate colour. When very broad, as in M.
montezuma or M. achilles, the inner parts of this band are irregu-
larly sprinkled with red scales. The centre is white or bluish-
white, some of the scales in its periphery being nearly always
distinctly blue. The centre is commonly not circular but is pro-
duced (especially in larger ocelli) in a direction at right angles to
the crease on which it stands. Fig. 78, I, taken from a normal
specimen of M. achilles, shews the usual positions of the eye-spots
in all the species whose variations are described below. The ocelli
on the fore wing are 3, on the hind wing 4. In speaking of them
the letters a, b, c, d, e,f, g are used as shewn in the figure. Between
a and b there is a cell normally bearing no ocellus, and between d
and e there are two such cells. The spot g as described on p. 90,
stands at the anterior side of its cell and not in the middle of it,
and a second spot gL may appear behind it in the same cell.

The following examples are taken from the series in the collec-

II

^-7

Fig. 78. Morpho achilles. Undersides of left wings. I. Normal. II. Specimen
wanting the spots a and c on both sides.

(From specimens in the collection of Messrs Godman and Salvin.)

CHAP. XII.]

MORPHO : EYE-SPOTS.

297

tion of Mr F. D. Godman and Mr O. Salvin, to whom I am much
indebted for permission to examine the specimens1.

447. Morpho achilles £. Specimen having the spots a and c en-
tirely absent (Fig. 78, II) and the spot g very small. This specimen
occurred together with t\vo normals from Para. Ten other normal
males seen, and also a specimen in Camb. Univ. Mus. having no c,
the spot a being also greatly reduced.

448. M. montezuma £ : 15 specimens have all the spots from a to
g of fair size. One specimen has a spot in the place av as shewn

Fig. 79. Morpho montezuma. Abnormal specimen having an ocellus on both
sides in the position ax (where an ocellus normally exists in Si. sulkowskii).
(From a specimen in the collection of Messrs Godman and Salvin.)

in Fig. 79. One specimen has a very faint a1 and gl : another lias
a1 as a small ocellus, and g indicated as a bulging of the spot g.

In Camb. Univ. Mus. are 4 normal males and one specimen
having both a1 and g1 marked somewhat as shewn in the case of
the abnormal M. octavia (Fig. 80).
449. M. octavia. Mr Salvin tells me that this form has a very
restricted distribution and is probably only a local form of M.
montezuma. In addition to 12 normal males the following were
seen, all being male. Specimen having gx as a spot of moderate
size ; another having g1 very small. In another a1 and gx were
both present as shewn in Fig. 80. Besides these is one having g
very small. All are from the Pacific slope of Guatemala. The
specimen figured is from El Reposo in this district, one of the
normals being from the same place.

1 In each of the figures the faint lines round the ocelli should be shewn as in
Fig. 81 ; they are omitted for simplicity.

298

MERISTIC VARIATION.

[part I.

Fig. 80. Morpho octavia: abnormal specimen having ocelli on both sides in
the positions a1 and g1 (where ocelli normally are in M. sulkowskii).
(From a specimen in the collection of Messrs Godman and Salvin.)

*450 M. menelaus </ : ten normals, and two having no a ; one
having left a absent and right a very faint, c and g both absent.
In addition to these, the specimen shewn in Fig. 81, having no c

Fig. 81. Morpho menelaus : abnormal specimen having no ocellus c in rt. f. w.
In left f. w. there is a small ocellus c, but it wants the two innermost colours of a
normal ocellus. Compared with a normal ocellus, as that at b of the same wing, the
abnormal has only the zones 1, 2 and 3, the latter colour forming the centre.

Fig. 78, I. may be taken as approximately shewing the normal for this species
also.

(From a specimen in the collection of Messrs Godman and Salvin.)

chap, xil] COMPLEX EYE-SPOTS. 299

on right side, while on the left the same spot is reduced as shewn
in the figure, the centre being of the colour normally constituting
the third band.

In connexion with the above cases it should be mentioned that
in another species, Morpho sulkowskii, one of the more transparent
species, the spots a1, a,, and gx are all normally present. The spot
c is however sometimes absent in this species. In M. psyche the
spot c is normally absent, though present in one specimen examined.

Complex ocelli.

Besides the simpler ocelli there are other forms of ocelli of
more complex structure, having two or more centres around which
the coloured zones are disposed without an accurate symmetr}7.
Such ocelli may be seen in Vanessa io or in Junonia, and it is
noticeable that they are no less variable than the simpler forms.
The following examples may be given.

Vanessa io. Looking at the eye-spot on the fore wing of the
Peacock-butterfly one can readily see that it is not a structure of
the same nature as the other ocelli that have been already con-
sidered. The eye-spot of the hind wing does not materially differ
from other eye-spots, being essentially a black spot surrounded by
a pale band and containing an irregular and incomplete centre of
blue. The eye of the fore wing on the contrary is not actually
made up of concentric markings but is quite exceptional, being
formed of a combination of patches of different colours. But
whether the eye of the fore wing is a true ocellus or not it is
nevertheless certain that its formation mav vary with that of the
eye of the hind wing, as the following examples testify.

451. Specimen, British; reared from a larva in captivity, having all the
eye-spots deficient (Fig. 82). On the fore wings the series of white
spots along the margin (on the creases) are present. The three which
lie within the field of the normal eye-spot are longer than usual. The
costal black mark is extended so as to cover the greater part of the

Fig. 82. Vanessa io, the Peacock butterfly, having all the four eye-spots
deficient (No. 451). (From Newman.)

300 MERISTIC VARIATION. [part I.

situation of the eye-spot. On the hind wings the eye-spots are entirely
obliterated and their place is taken by an ill-defined patch of pale
colour. Newman, Ent., 1872, \\ 105, Fig.

452. Similar specimen described by Goossexs, Bull. Ent. Soc. France,
S. 5, v. p. cxlix.

453 Similar specimen in Lord Walsingham's collection in Brit. Mus.

Here the blue and black of the eye-spots of the hind wing are altogether
absent. The black internal border of the spot is broader than usual,
and the place of the spot is lightish in colour. In the spot of the fore
wing the blue is deficient, the yellow is largely absent, but the white
spots are emphasized.
*454. Specimen in which the eye-spots on the hind wings are obliterated,
as in the foregoing : those of the fore wings are also similarly modified,
but the white spots of the marginal series are enlarged to a much
greater extent. Also another specimen in which the eye-spots were
partially deficient. These two specimens were from one brood reared
in Germany: of this brood none were typical, and several resembled
the specimens described. South, P., Ent., 1889, xxn. p. 218, PI.

455 Specimen figured in which the eye-spots are symmetrically absent

from both posterior wings. In this case both the greyish yellow
bordering of the eye-spots and the blue marks generally contained
within them are entirely absent. The ground-colour of the hind wings
is greyish brown, and upon this two black marks are placed in the
situation of the normal eye-spot and a series of small black lines occurs
round the margins of the hind wings. The eye-spots of the anterior
wings are modified in a peculiar manner which is not easily described.
Mosley, S. L., Varieties of Brit. Lepicl, Pt. m. PI. 2, Fig. 3.

456. Junonia clelia. Cram. In this species there are normally two ocelli in each
fore wing and a similar pair in each hind wing (Trimex, S. Afr. Butterflies, i. p.
214). In a series of nine specimens in the Cambridge University Museum very
great variations in the size of the ocelli appear. The posterior ocellus of each wing
is more constant in size than the anterior. One specimen wants altogether the
anterior ocellus of the hind wings, which in most specimens has a diameter of about
2*5 mm. In several the anterior ocellus of the fore wings is hardly visible.

457- Junonia coenia : the degree to which the two eye-spots of each wing are de-
veloped varies greatly. In a Californian specimen in Godman and Salvin's collection
the spots are all very large, while in a Granada specimen they are almost entirely
obliterated. Of four specimens in the same collection from the United States of
Colombia (but not from the same locality), one has scarcely a trace of the anterior
eye-spot of the fore wing, the second eye being very faint. In the hind wing the
anterior eye-spot is very faint and the posterior is absent.

The two following cases are important from the fact that in
each of them there is said to have been abnormality in neuration.

*458. Pararge megaera ^ (the Wall Butterfly) : specimen in
which the second nervure of the median vein is wanting in eacit
of the four wings. In the anterior wings the place which should
be crossed by this nervure is occupied by an extra ocellus (Fig. 83),
which is nearly as large as the normal large ocellus of the wing.
The normal ocellus itself is incompletely doubled. In the hind
wings, the two ocelli (2nd and 3rd), which in the normal insect
are separated by the missing nervure, are elongated towards each

CHAP. XII.]

EYE-SPOTS AND NEURATIOX.

301

other, so that their black borders touch and the usual central white
dots join into a line, one- twelfth of an inch long. On the under

Fig. 83. Pararge megcera, the Wall ; case described in No. 458. [This copy is
rather too light, and the banding on the hind wing is too distinct.]

(From Webb.)

side, the anterior wings have respectively six and five ocelli and
the hind wings five and six. The arrangement of the dark colour
on the upper surface of the anterior wing differs somewhat in the
direction of the pattern of the female. Webb, S., Entomologist,
1889, xxii. p. 289, Fig.

Saturnia carpini £ ; variety without eye-spots. (Fig. 84.)
This specimen was bred from a larva found with many others

Fig. 84. Saturnia carpini lacking the ocellar marks in each wing (No. 459).

(From Bond.)

feeding upon sallow in Sawston Fen, Cambridgeshire. " In the
colour and markings of the specimen there was perhaps nothing
worth notice excepting the absence of the ocellus in each wing and
also of one of the veins in each of the anterior wings."

About 50 larvae were collected at the same time on one large
sallow. One of them, a female, was destitute of scales1, but the
remainder of the specimens reared were remarkably fine. Bond,
F., Entomologist, x., 1877, p. 1, fig. [This is the specimen
mentioned by Humphreys, Brit. Moths, p. 20. It is unfortunate
that no further description is given, and the figure is not sufficiently
clear to enable one to see which nervure was absent. On the fore
wings a narrow, elongated patch of light colour was in the place of
each ocellus, and on the hind wings there was a somewhat wider

1 Partial deficiency of scales, occurring evenly over all the four wings, is not very
rare in S. carpini. I have myself reared two such specimens.

302 MERISTIC VARIATION. [part i.

and irregularly shaped patch of pale colour. If this specimen,
which was in the collection of the late Mr F. Bond, is still in
existence it is greatly to be wished that a proper description of it
should be published.]

460. Saturnia carpini £ : wings yellowish-grey throughout, with
the usual markings, save that on the fore wings there is no ocellus,
and on the hind wings is only a small black eye, without a border,
having a yellowish-grey central spot. Ochsenheimer, F., Schmet.
von Europa, 181(3, IV. p. 191.

From this evidence it is clear that the range of Variation of
ocellar markings in Lepidoptera is very great. It is especially to
be noticed that this variability affects no one family, or the species
of one geographical region, or one kind of ocellus exclusively,
though doubtless it is more marked in some than in others ; but it
seems rather to be a property belonging to ocelli in general. From
the fact that they can bodily come and go, it seems clear that, as
was suggested above, each ocellus is as regards its origin one
structure made up of parts in correlation with each other.

RAIIDiE.

The great variability of ocellar markings is probably not
peculiar to Lepidoptera, but I have no evidence sufficient to pro-
duce regarding the variability of ocellar markings in other forms.
I may however instance the case of the Raiidye, many of which
have been found marked with a large ocellar mark on the dorsal
surface of each pectoral fin. At different times such a mark has
been thought to characterize a certain species, but I believe it is
now generally admitted that it may appear as a variation in several
species. The best figure of this ocellar mark is that given by
Donovan (Brit. Fishes, 1808, v. PL cm.) in a Ray described under

461. the Linnean name Raid miraletus. On each "wing" was a large
spot, having a dark purple centre, surrounded by a zone of silvery
green enclosed by a broad dark boundary composed of five equi-
distant, contiguous spots of blackish purple. Donovan suspected
that the fish might be a variety of the Homelyn (R. maculata),
and it has been generally believed by other authors to have been
so. Donovan states that a similar eye-spot was seen by him in
various degrees of definition in several young Skates.

462. R. clavata, the Thornback, also sometimes has a large white
spot surrounded with black on the " wings." Day, Brit. Fishes, II.
p. 344.

Raia circularis, the Cuckoo Ray, has normally on each " wing "
a large black blotch banded with yellow and surrounded by yellow
spots. This structure may be absent as a variation. Day, Brit.
Fishes, II. p. 349.

chap, xii.] SIMULTANEOUS COLOUR- VARIATION. 303

Simultaneity of Colour-variation in Parts repeated in

Linear Series.

Reference was made (Introduction, Section V.) to that relation
subsisting between the several members of a linear series of
segments or other repeated parts, by virtue of which they may
resemble each other in respect of colour or pattern of colours
From the fact that the several members do in such cases often
bear the same colours or patterns it is clear that they must at
some time or other have undergone similar Variation. In order
to measure the possible rapidity of the process of evolution by
which such parts may have reached their present condition it is
important to ascertain the extent to which their several variations
may be simultaneous.

Variations in colour are of course Substantive variations and a
full consideration of their nature cannot be taken here. For the
present we are only concerned with the consequences of the fact
that the parts are repeated in series. As was pointed out in the
Introduction the problem of the resemblance between the colours
of such segments is only a special case of the same problem of
Symmetry which is again presented in bilateral or other Repetition.

Simultaneous colour-variation taking place abruptly in a large
number of organs, such as hairs, feathers, &c. is a very common
occurrence, and the part that repetition of structures plays in
producing the total effect is apt to be overlooked. In comparing
two varieties of some whole-coloured animal, a bay horse with a
chestnut for example, it must be remembered that the difference
is really made up of a simultaneous variation in the pigment of each
particular hair. Similarly if a caterpillar normally green appears
in a uniformly brown variety we may conceive the total change as
brought about by variation occurring simultaneously in the skin
of the several segments, or in some smaller units. But whatever
unit be taken, whether segment, or hairs, or cells, that all or any
particular groups of such units should vary together and in the
same direction is not a matter of necessity. That such simul-
taneity is not universal and that segments may vary independently
of each other is a matter of common observation, and indeed is
sufficiently proved by the occurrence of differentiation between
segments. Nevertheless the evidence goes to shew that between
parts repeated in series there may be a relationship of the kind
spoken of, though its causes, nature and limitations are unknown.
In the case of actual segmentation this relationship may appear
either in the simultaneous variation of the colour-patterns of the
segments, or of some one colour or patch borne by each, or by the
appearance of some unusual mark or patch on several of them at
once.

In some cases it happens that certain of the segments may
vary together, the rest remaining unchanged, and, as seen in

304 MEMSTIC VARIATION. [part i.

Chiton marmoreus, (q.v.), the segments thus undergoing the same
variation are not always even adjacent to each other.

The whole question is a very large one and it is not possible
here to do more than refer briefly to a few cases illustrating some
of its different aspects. Fuller treatment will be attempted in
connexion with the evidence of Substantive Variation.

463. As examples of a form whose segments in their colour-variations
manifest a very close agreement with each other, the Hirudinea may
be taken. Figures of numerous varieties of medicinal Leeches are given
by Ebrard. Xouvelle monogr. des Sangsues, 1857, and other cases are
represented by Moquin-Taxdox, Monogr. de la famille des Hirudinees,
1827 (see especially PI. v. fig. 1). As these figures testify, there is a wide
diversity both in the ground-colour and in the size, colour and manner
of distribution of the lines and spots with which it is decorated, but
so far as may be judged from the figures and descriptions the same
decorations are repeated on the various segments. It cannot be doubted
that a close scrutiny of the specimens would shew points of difference
even between adjacent segments but substantially the patterns are the
same for the segments of an individual. The patterns of the varieties
may thus, like patterns of ribbon, be each represented by a drawing
of a short piece of the body in the way adopted by the writers named.

As regards the larvae of Lepidoptera a good deal of information
bearing on this subject exists, and some of these results, especially
those relating to Sphingida?, are of interest 1.

'464. In ^he larvae of many species of Sphingidae there is a more or
less regular dimorphism in colour. Notable examples of this are
Acherontia atropos, Chozrocampa elpenor, C. porcellus and Macroglossa
stellatarum, in each of which the larva is known both in a light green
and in a dark form2. The dark form is the commonest in C. porcellus
but in A. atropos it is much rarer than the green form. Judging from
the figures, the ground-colour of the segments generally varies as a

1 The facts which follow are chiefly taken from Wilson, Larvce of Lepidoptera ,
1880; Weismanx, Studies in Theory of Descent, Eng. Trans., 1882; Poulton, Trans.
Knt. Soc, 1884, 1885, 1886, 1887; Buckler, Larva of Brit. Butterf. and Moths,
Vol. in. Eay Soc, 1887.

2 That this dimorphism is 'phytophagie ' is not very likely, but the possibility should
be remembered. It seems to be established that in many of the species the colour-
varieties are definite and largely discontinuous. Of 21. stellatarum Weismann (p.
250) bred 140 from one batch of eggs, and of these 49 were of the green form and 63
of the brown form, only 28 being transitional. The discontinuous character of the
variation was illustrated by one most remarkable specimen. In it the body was
particoloured, being partly of the green and partly of the brown form. The head,
prothorax, all the abdominal segments behind the 2nd, and the right side of the
remainder were brown, but the left side of the meso- and meta-thorax, of the 1st
abdominal, and part of the left side of the 2nd abdominal were green [according to
the figure 9 on PI. in., with which the description in the text, p. 249, differs slightly].
In A. atropos I know no account of any intermediate form. In most of the species
the dimorphic or polymorphic character appears in the later periods of larval life
and especially after the last moult; but in C. porcellus, according to both Weismann
(p. 188) and Buckler (p. 117) though the larva are of both kinds in the penultimate
state all or nearly all after the last moult turn to the dark form.

CHAP, xii.] LARVAE OF SPHINGID^E. 305

whole, shewing only slight differences in tint in different parts of the
body. To this there are certain exceptions, of which A. atropos is
especially remarkable. In the brown variety of this species the
abdominal segments have a dark ground-colour composed of shades
of brown, while the three thoracic segments in it are white "like linen"
(see Wilson, PI. vi.; Buckler, PI. xxi.; Poulton, 1886, p. 149;
Hammond, ZooL, 6282; Balding, Ent. Mo. Mag. xxn. p. 279; Girard,
Bull. Soc. ent. Fr., 1865, S. 4, v. p. xlix. &c).

Tn M. stellatarum though the ground-colour of the head and of all
the segments varies greatly it appears that the head and prothorax vary
in colour simultaneously with each other and are of one colour, while
the other two thoracic segments and the abdominal segments also vary
together but usually differ from the head and pro-thorax (see Weismann,
PI. in.).

In illustration of the degree to which simultaneity of Variation
is possible over considerable areas of the body the varieties in markings
are perhaps more important than those in ground-colour. Of such
changes simultaneously occurring in several segments there are many
examples.

4(3 5# In all the varieties of ground-colour in M. stellatarum the pattern
of the markings remains the same though of differing intensities
(Weismann, p. 248), but in the brown variety of A. atropos the pattern
is quite peculiar and cannot even be recognized as a representation of
the markings seen in the green form. Even the oblique stripes are
absent (Poulton, 1886, p. 149; see also authors quoted above). But
as in the ground-colour so in the markings, the abdominal segments
have one new pattern while the thoracic segments have another.
*466. The figures of larvae of Deiphila euphorbias given by Buckler and
by Weismann are especially interesting in this connexion, shewing
that in the complex variations of this polymorphic form the particular
pattern of the individual is carried out with little difference in each
segment behind the prothorax. Some of these changes are extensive,
but to be at all appreciated the figures must be referred to. In one
case all the triangles at the posterior part of each segment were red
instead of green as usual, and this change was found in many speci-
mens from one locality (see Weismann, p. 206, PI. v.). This identical
variation was known to and figured by Hubner (Weismann). In
one specimen from the same place as the last the second row of marks
which should occur just below the sub-dorsal mark of each segment
was absent throughout the whole line, and the ring-spots of the upper or
sub-dorsal row had, as a variation, a red centre or nucleus, well marked
in the posterior spots but fading away anteriorly. The occurrence of
these considerable changes is still more noteworthy if, as Weismann
states, the members of each batch are much alike. He remarks also
that the variability is great in some localities but little in others.

467. The larva of Deilephila hippophaes has a sub-dorsal row of red
markings upon a variable number of segments from the 7th abdominal
to the 3rd or even 2nd abdominal, increasing in size and distinctness
from behind forwards. The size of these markings differs greatly in
different specimens, varying from a mere dot to a distinct red spot
with a black ring. As the figures shew, there is a considerable cor-

B. 20

306 M ERISTIC VARIATION. [part i.

respondence between the segments in the extent to which the spots
are developed, though in each case they fade away in the anterior
segments (see "Weismann's tigs. 59 and 60).

468. Another interesting example of considerable uniformity in the
colour-variation of a series of segments is to be seen in Saturnia
carpini. In this species besides change in the tint of the green
ground-colour [two chief tints being found, one dark and one light]
there is immense difference in the amount of black pigment deposited,
most marked in the last two stages of the larva?. Good figures and
descriptions of these are given by Weismann (PI. vin.). Though no
two segments are alike and though there are differences perceptible
even between the two sides of most segments, yet the general scheme
of colour of each individual is carried out with fair constancy over
the several segments. As I have myself seen, the lightest and darkest
may both be reared from one batch of eggs and in the same breeding-
cage or sleeve.

469. The colour of the tubercles of S. carpini also varies greatly. They
may be light yellow, dark yellow, pink, violet, or white, but the yellow
and pink forms are the commonest. As I have myself observed, there
is generally a close agreement between the different tubercles of each
larva in point of colour. In a few specimens I have seen the tubercles
of the anterior and posterior segments pinkish, while the remainder
were yellow, but this diversity is exceptional. The importance of this
case is increased by the fact that Poulton (1887, p. 311) has found
that the offspring of a pair whose tubercles had been pink shewed a
high proportion of larva? with pink tubercles. The two parents were
from a lot of 80 larva? found together, of which only 3 had pink tubercles :
but of their 88 offspring 64 had pink tubercles.

470. The case of the occurrence of red spots on the larva? of Smerinthus
ocellatus and S. populi1 may be quoted as an instance of great irregu-
larity in the degree to which the segments agree in their colour-
variations. This well-known case is also of great interest as an
example of a parallel variation occurring in different species. The
larva? of both species are most commonly without any red spots, but
not rarely a number of red spots are present. In extreme cases each
of the spiracles is surrounded with red, and there is in addition a row
of red spots in the sub-dorsal region of all segments from the 1st
thoracic to 7th abdominal, and also a red spot on each clasper. The
number of spots, number of rows, the size and tint and distinctness of
the spots is exceedingly variable. In point of time the spots of the
3rd abdominal segment appear first and those of the 2nd thoracic
next (Poulton, 1887, p. 285, &c). Though in much spotted specimens
the spots may remain till the larva is full-fed, in some cases a few
spots appear at an early stage and are afterwards lost. Among the
individuals of the same brood there may be great diversity, some
having spots and others being without them (Poulton, 1887, p. 287).
In several cases a spot present on one side of a segment has been
found absent on the other side. As Poulton observes, it is especially

1 I have not referred to the case of S. tilice, as it is possibly of a different
nature.

chap. XII.] COLOURS OF CHITOXS. 307

remarkable that though there are no spiracular openings on the meso-
and meta-thoracic segments, yet in cases of extremely spotted larvae
there are red spots at the level of and continuing the spiracular series
of spots upon these segments also (S. ocellatus, Buckler, PI. xx.
tig. 1 a; Poulton, 1887, PL x. fig. 1. S. populi, Poulton, 1887, p. 286).
As an indication of an element of definiteness in this variation may
be mentioned the fact that in fully spotted larvae of S. populi the
sub-dorsal spot on the 7th abdominal seems to be always the smallest
in that row (Poqlton, 1887, p. 285; Wilson, PI. v. fig. 2a; Flemyng,
Ent, 1880, p. 243, &c).

In our present consideration the fact that these very large variations
sometimes occur simultaneously over a large range of segments and
are sometimes restricted to particular segments is of considerable
importance.

We may note that Weismann (p. 360) is prepared to believe that
these spots represent a new variation arising similarly and indepen-
dently in the different species of Smerinthus. As however is usual in
cases of considerable Variation an attempt has been made to lessen
the value of these indications of the magnitude of Variation by sug-
gesting that they may be of the nature of " reversion " (Poulton,
1884, p. 28). Apart however from a general reluctance to recognize
the possibility of the occurrence of large variations there seem to be
no special grounds for the suggestion here. It is nevertheless true
that in the case of the Smerinthus larvoe a complete disproof of the
hypothesis of "reversion" is wanting. This is only to be obtained in
cases (like that of D. euphorbice), in which a great number of complex
and mutually exclusive variations exist side by side. In the absence
of such complete refutation the hypothesis of reversion may still find
favour.

'471. Chitonidae. The following facts observed in certain Chitons
are given in illustration of the existence of a similar possibility
of simultaneous Variation between parts which are repeated in
series but whose repetition is not of the kind commonly included
in the term Metameric. Unfortunately the material at hand is
very limited and I do not know what might be the result of
further examination, but the facts seen suggest that the subject
is worth investigating.

The dorsal plates of Chitons are eight in number. Though
the colours and markings in different species are complex and
various yet in many species all the plates are alike or nearly so.
The question then arises do all the plates change colour together,
or do they change one by one, or otherwise ? From the few
observations made it seems that in this respect the species differ,
but variation uniformly occurring in all the plates seems to be
rare. This may perhaps be due to the constitution of such
specimens as separate species, but I saw little likelihood of this.
On the other hand in several cases the same variation was present in
more than one segment, and in particular there was strong evidence
that in some species the segments 2, 4 and 7 shew a noticeable

20—2

308 MERISTIC VARIATION. [part i.

agreement with each other in colour-variation. The specimens
are all in the MacAndrew Collection in the Cambridge University
Museum, and I have as usual simply followed the labelling of the
specimens.

C. arhustum, Australia. 10 specimens, of which the plates in 6 are nearly uniform.
In one there is a white band in the centre of each plate ; in 2 the plates are irregularly
coloured; in one the plates 1 and 6 agree in being broadly marked with white.

Cliiton hennahi, Peru. 4 specimens. 3 are uniformly dark brown; but in the
other specimen there is a strong tohite mark on the centre of plates 2 — 7, and a faint
one on plates 1 and 8.

C. elegans, Chili. 2 specimens. In one, complicated markings are repeated on
each plate nearly uniformly ; in the other specimen a much simpler pattern recurs on
each segment.

On the other hand, C. pellis-serpentis, New Zealand, 8 specimens: great di-
versity of markings and no uniformity among plates in 4 specimens, but in one
specimen plates 2 — 5 were black and the rest light-coloured. Similar want of uni-
formity among the plates in 2 specimens of C. incanus, New Zealand.

The evidence of agreement between segments 2, 4 and 7 in the following cases is.
very striking.

C. (Tonic ia) marmoreus, "Hebrides, &c." 18 specimens, all of a light brown
colour marked with dark red.

In 4 specimens the plates are uniformly marked or nearly so.

In 6 specimens plates 2, 4 and 7 are much darker than the others, being for the
most part of a uniform dark red.

In 5 specimens plates 2, 4, 7 and 8 are darker than the rest.

In 1 specimen plates 2, 4, 5 and 7 are darker than the rest.

In 2 specimens the central parts of most of the plates have dark markings, but
no segment is specially distinguished.

Of 18 specimens therefore 12 have plates 2, 4 and 7 darker than the rest.

Among 3 specimens of the same species from Gr. Manan (N. America) 2 are nearly
uniform throughout, but in one plates 2, 4, 7 and 8 are much darker than the rest.

C. (Tonicia) lineatus, 2 specimens. In one the markings on all the plates are
nearly similar, and the white wavy streaks characterizing the species are almost
similarly distributed on the sides of all the plates. In the other specimen these
lines are absent on the plates 2, 4 and 7, which are much darker than the rest ; but
the lines, though less extensive than in the first specimen, are present on plates
1, 3, 5, 6 and 8.

The preceding evidence may suffice to indicate the nature of
this important question of the degree to which the colour-variations
of parts repeated in Linear Series may be similar and simultaneous,
a question which, as must be evident, is of the highest consequence
in estimating the magnitude of the steps by which Evolution
may proceed. To the consideration of this matter it will be
necessary to return when the evidence of Substantive Variation
is considered.

Meanwhile it will not be forgotten that though we have only
spoken of this question in reference to colour and to Linear Series,
the same question arises also with regard to other variations and in
reference to all parts which are in any way repeated and resemble
each other, whether such repetition is strictly serial or not. In a
survey of any group of animals cases will be seen in which organs
in one region are repetitions of organs in another region though

chap, xil] SIMULTANEOUS VARIATION OF SERIES. 309

not necessarily in serial homology with them in any sense in
which the term is commonly used. Many such cases were spoken
•of by Darwin in the chapter on " Correlated Variability1" and are
now famous. The simultaneous colour- variations of the mane and
tail of horses2, the correspondence between the large quills of the
wings and those of the tail of pigeons3 and other birds are
among the most familiar of such cases.

When with such facts in mind we turn to some species which
differs from an ally in the presence of some characteristic develop-
ment or condition common to a number of its parts, in making
any estimate of the steps by which it may have been evolved it
must be remembered that it is at least possible that the common
feature characterizing these several parts may have been assumed
by all simultaneously. To take a single instance of this kind, the
species of the genus Hippocampus, the Sea-horses, have the
shields produced into more or less prominent tubercles or spines.
The back of the head is also drawn out into a prominent knob.
In^ an allied genus from Australia, Phyllopteryx, many of these
spines are provided with ragged looking tags of coloured skin,
like the seaweed which the fishes frequent4, giving the animal a
most fantastic appearance and no doubt contributing greatly to
its concealment [probably from its prey]. If in this case it were
nece>sary to suppose that the variations by which this form has
departejj from the ordinary Hippocampi had occurred separately,
and that -each spine had separately developed its tag of skin, the
number of variations and selections to be postulated would be
enormous ; but probably no such supposition is needed. We are,
as I think, entitled to expect that if we had before us the line of
ancestors of Phyllopteryx, we should see that many and perhaps
all of the spines which are thus modified in different parts of the
body had simultaneously broken out, as we may say, into tags of
skin, just as the feathers of the Moor-hen (Gallinula chloropus)5
may collectively take on the " hairy " form, or as, to take the case

1 Animals and Plants under Domestication, ed. 1885, n. chap. xxv.

2 As D,*$*vin mentions, simultaneity in the variations of the hair may be mani-
fested in size and texture as well as in colour. A bay horse was lately exhibited at
the Westminster Aquarium standing 16£ hands, having the hair of both mane and
tail of prodigious length. The longest hairs of the mane measured 14 ft. and those
of the tail 13 ft. It did not appear that the hair of the fetlocks or bo ly was unusual
in character, but these were kept closely clipped and nothing could be affirmed on
this point.

3 By the courtesy of Professor L. Vaillant I was enabled to examine a number
of specimens of the singular breeds uf Gold-fish from China in the Paris Museum of
Natural History. Some of these are characterized by the great length both of the
appendicular fins and of the caudal fin also. Measurement shewed that there was
a substantial correspondence between the lengths of these parts, those with long
appendicular fins having also very long tails. The correlation between these parts
is not however universal in Gold-fishes, and in many of the ordinary "Telescope"
Gold-fish the tail may be longer than that of a common Gold-fish of the same size,
though the length of the appendicular fins be not exceptional (v. infra).

4 Gunther, Study of Fishes, 1880, p. 682, fig. 309.

5 See Introduction, p. 55.

310 MERISTIC VARIATION. [part i.

of Radial Series, the petals of a flower may all together take on
the laciniated condition1.

Further study will indeed probably lead to the recognition of
a principle which may be thus expressed : that jxtrts which in any
one body are alike, which have, that is to say, undergone similar
Variation in the past, may undergo similar variations simid-
taneously; a principle which, if true at all, is true without regard
to the morphological position of the parts in question.

1 For cases see Masters, Vegetable Teratology, 1869, p. 67.

CHAPTER XIII.
linear series — continued.

Minor Symmetries : Digits.

All the cases considered in the foregoing chapters have il-
lustrated Variation of parts whose repetition is disposed in Linear
Series along the chief axis of the body, being thus arranged
directly and immediately with reference to the Major Symmetry
of the body. We have now to consider cases of the Meristic
'Variation of parts which are also repeated in Linear Series but
normally possess in some degree the property of symmetry partially
completed within the limits of their own series, thus forming a
Minor Symmetry.

Of Linear repetitions thus occurring there is a great diversity,
and evidence will here be produced regarding two of the chief
examples, namely, the digits of vertebrates and the segmentation
of antennae and tarsi of Insects.

In each of these groups of organs the parts are frequently
formed in such a way as to make an approach to symmetry,
about one or more axes within the limits of the appendage to
which they belong. This fact will be found to lead to conse-
quences apparent in the manner in which numerical Variation
takes place in limbs of the various types.

In these Minor Symmetries Linear Repetition may occur in
two forms : there may be repetitions of digits or other parts in
lines forming an angle with the axis of an appendage ; and there
may be repetitions in the form of joints &c. along the axis of the
appendage itself.

The cases of Variation in number of joints in the appendages
of Insects are chiefly interesting as examples of manifest Dis-
continuity in Variation, and from the conclusions which they
suggest as to the supposed individuality of segments. This latter
question arises also in considering the relation of the two pha-
langes of the pollex and hallux to the three phalanges of the
other digits, but the evidence which can be gained from a study

312 MERISTIC VARIATION. [part i.

of Variation with reference to this question is so intimately con-
nected with the subject of the variation of digits in general that
it cannot be considered apart. Other cases referring to repetitions
in the line of the axis of appendages will be taken in a subsequent
chapter.

In studying numerical Variation in the digits of certain animals,
especially the Horse and the Pig, we shall meet with forms of
Variation which are peculiar to structures having a bilateral
symmetry. In examining the evidence as to Meristic Variation
of Bilateral Series further reference to these cases will have to
be made, but it appears simplest to describe the facts in the first
instance in connexion with the subject of digits.

From the evidence as to Meristic Variation in digits I propose
to make a selection, taking certain groups of cases having a direct
and obvious bearing on the general problems of Variation. It
will be understood and should be explicitly stated that unless
the contrary is declared the principles of form which can be per-
ceived as operating in special cases are not of universal appli-
cation in the Variation of digits, but are enuntiated as applying
only to the special cases in which they are perceived. In the
human subject, for example, cases of polydactylism will be quoted
which when arranged together form a progressive series illus-
trating the establishment of a novel and curious Symmetry ; but
though these cases are valuable as illustrations of the way in
which the forces of Division and growth can dispose themselves
to produce a symmetrical result, yet it must always be borne in
mind that very many variations of the digits have been seen in
Man, whether consisting in increase in number of digits or in
decrease, of which the result is almost shapeless. The case of
polydactyle Cats is thus especially interesting from the fact that
in this animal the polydactyle condition, though differing in degree
of expression in various specimens, yet, in the greater number of
cases, occurs in ways which may be interpreted as modifications
of one plan, or rather of one plan for the hind foot and of another
for the fore foot.

I arrange the evidence primarily according to the animal con-
cerned, Cat, Man and Apes, Equidye, Artiodactyles, &c. To these
are added a few facts as to digital variations in Birds, but from
the scantiness of the evidence and the difficulty of determining
the morphology of the parts I have not found it possible to give a
profitable account of these phenomena in other vertebrates below
Mammalia.

In most of the groups increase in number of digits may be
seen to occur in several distinct ways ; and, just as in the case
of teeth, mammae, &c, it is possible to recognize cases of division
of single members of series, and cases of addition to the series

chap, xiil] DIGITS : CAT. 313

either at one of its ends (often associated with remodelling of
other members of the series) or in the middle of the series.

Reduction in number of digits, or ectrodactylism as it is often
called, is usually so irregular in the manner of its occurrence that
little could be done as yet beyond a recitation of large numbers
of cases amongst which no system can be perceived. For the
present therefore the interest of these observations for the student
of Variation is comparatively small and they are for the most
part omitted.

To the irregularity of ectrodactylism in general certain cases
of syndactylism are a marked exception and of these an account
will be given.

After stating the morphological evidence as to numerical
Variation in digits in the several groups, reference will be made
to some collateral points of interest concerning such variations.

There is a good deal of evidence respecting the recurrence
of digital variations in those lines of descent wherein they have
appeared. Facts of this kind have been frequently seen in the
case of Man, and other examples are known in the Cat, the Pig,
the Ox, Deer, Sheep, &c. References to these cases will be given.

It will be seen that the facts contained in this section of
evidence are of consequence rather as indicating the limits set
on Variation, and from their bearing on the question of the nature
of Symmetry and of Homology, than from any more direct appli-
cation to the problem of Species, but even this cannot be said
with much confidence.

There are in certain groups limbs such as the pes of Macro-
podidse or that of Peramelidae whose appearance forcibly recalls
what is seen in some teratological cases and the possibility that
they may have had such a sudden origin may well be kept in

view1.

Cat.

The apprehension of the chief features in the evidence as to
digital variation in the Cat will be made more easy if a general
account of the subject be given as a preliminary. In order to
understand the peculiar phenomena seen in the limbs of poly-
dactyle cats certain points of normal structure are to be re-
membered. Of these the most important relate to the claws
and their disposition with regard to the second phalanx ; for it is
by this character that the relation of digits to the symmetry of
the limb may be determined.

1 In the case named this is all the more likely from the circumstance that
according to Thomas, Cat. Marsup. Brit. 2Ius., p. 220, there is reason for supposing
that the extraordinary condition of the digits II and III was attained independently
in these two groups.

314 MERISTIC VARIATION. [part i.

Hind foot.

The phenomena seen in the case of the hind foot are in some
respects simpler than those of the variations in the fore foot, and
for this reason they may conveniently be described first.

If the phalanges of the index of the hind foot, for example, be
examined, it will be seen that the proximal phalanx is nearly
bilaterally symmetrical about a longitudinal axis, but that the
second phalanx is deeply hollowed out upon the external or fibular
side. Into this excavation the ungual phalanx is withdrawn when
the claw is in the retracted position. The retraction is chiefly
effected by a large elastic ligament running from the outside of
the distal head of the second phalanx and inserted into the upper
angle of the last phalanx (see Owen, Anat. and Phys. of Vert., III.
p. 70, fig. 36). The same plan is found in the digits II to V both
of the fore foot and of the hind foot. By this asymmetrical re-
traction of the claw a digit of the right side may be differentiated
at a glance from one of the left side, for the claw is retracted to
the right side of a right digit and to the left side of a left digit.
The importance of this fact will be seen on turning to the evidence,
for it is found that with variation in the number of digits there is
a correlated variation in their symmetry.

With respect to the tarsus little need be said. The proximal
part of the tarsus contains three bones, the calcaneum, astragalus
and navicular. The distal row consists of four bones, the cuboid
and three cuneiform bones. In the majority of polydactyle cats
that I have seen in which the tarsus is affected, the cuboid is
normal and the ecto-cuneiform is also normal and recognizable ;
internal to the latter there are three small cuneiforms articulating
with the navicular instead of two, making four cuneiforms in all.
In some specimens there is no actual separation between the two
innermost of these cuneiforms, but the lines of division between
them are clearly marked.

In the normal hind foot of the Cat there are four fully formed
toes, commonly regarded as II, III, IV and V, each having
three phalanges. In the place where the hallux would be there
is a small cylindrical bone articulating at the side of the internal
cuneiform. As usually seen, all the four digits are formed on a
similar plan, each having its claw retracted to the external or
fibular side of the second phalanx, the four digits of a right foot
being all right digits and those of left feet being all left digits.
The rudimentary hallux has of course no claw.

Starting from this normal as the least number of digits, it will
be found that a large proportion of cases are such that they may
be arranged in an ascending or progressive series. In this series
the following Conditions have been observed.

In the schematic representations of the limbs the words 'Eight' or 'Left'
signify that a digit is shaped as a right or as a left. The Roman numeral

chap, xiil] digits: cat. 315

indicates that the digit to which it is assigned has the tarsal or carpal relations of
the digit so numbered in the normal. For brevity each is described as a right foot.

I. The normal, consisting of four three-phalanged digits, each
retracting its claw to the external, viz. right side, and a rudimentary
hallux with no claw. In this foot therefore the digits enumerated
from the external side are

Eight. Eight. Eight. Eight. Eudiment.

V IV III II I

II. Five digits, each with three phalanges. Of these the
minimus and annularis borne by a normal cuboid are normal and
are formed as right digits. The medius is borne by a normal ecto-
cuneiform and is also a true right digit. Internal to this is a full-
sized digit having the relations of an index and borne by a bone
placed as a middle cuneiform. But the claw of this digit cannot
be retracted to the external side of the limb, for the second
phalanx is not excavated on this side. There is on the contrary a
slight excavation on the internal side of the second phalanx, but
this is very incomplete and the claw cannot be fully retracted,
being in fact almost upon the middle line of the digit when bent
back. This digit is thus intermediate between a right and a left.
Nevertheless it is truly the index of this right foot, for it has the
tarsal relations of an index.

Internal to this digit is another, which by all rules of homology
should be the hallux, but it has three phalanges and is fashioned
as a left digit, retracting its claw to the left (internal) side of the
digit. This digit (Fig. 85, II, d1) is borne jointly by two cuneiforms,
c1 and c2, as shewn in the figure. There is thus one cuneiform
more than there is in the normal. In this foot therefore the digits
enumerated from the external side are as follows : —

Eight. Eight. Eight. Indifferent. Left.

V IV III II I

Such a specimen is No. 472, right pes.

Between this state and the normal I have as yet met no inter-
mediate. It might perhaps have been expected that a foot having
four three-phalanged digits and a hallux with two phalanges would
be a common form of variation. Such a condition has not however
been seen, so far as I know.

III. The foot shewn in Fig. 85, 1 exemplifies the next condition.
In it the three external digits, which are structurally the minimus,
annularis and medius of a normal foot are normal in form, position
and manner of articulation with the tarsus. Internal to the
medius are three digits, of which the innermost has two phalanges
(Fig. 85, I, dl) and a claw which cannot be retracted, like the
pollex of the normal fore foot. The other digits, d3 and d2, are
fashioned as left digits, retracting their claws to the internal or
left side of the limb. It will be seen that of them d3 has the

316 MERISTIC VARIATION. [part I.

relations to the tarsus which an index should have. The tarsus is
as in the last Condition.

In the specimen seen, c1 and c2 were not actually separate from
each other, but there was a distinct line of division between them.

Here then the digits enumerated from the external side are as
follows : —

Eight. Eight. Eight. Left. Left Hallux-like

V IV III II digit digit

IV. The stage next beyond the last is shewn in Fig. 87, II.
[The drawing is from a left foot.] Here there are six digits, each
with three phalanges. The three externals are normal and true
rights as before. The other three are all formed as lefts. Tarsus
as before.

This foot may be represented thus : —

Eight. Eight. Eight. Left. Left Left

V IV III II digit digit

As far as I have seen the last or fourth Condition is the com-
monest. There are doubtless many variants on these plans.
No. 477 is an especially noteworthy modification of the third
Condition and the cases of the hind feet in No. 478 must also
be specially studied as not conforming truly to either Condition.

Forefoot.

I. The normal right fore foot has four digits II — V each with
three phalanges all differentiated as rights, and a pollex with two
phalanges, the last being non-retractile but bearing a claw. It may
be represented thus : —

Eight. Eight. Eight. Eight. Pollex.

V IV III II I

Departures from this normal are more irregular than they are
in the case of the hind foot. Those given in this summary being
only a selection. For the others the evidence must be examined.

II. One specimen, No. 474, has the four external digits normal.
The pollex however has three phalanges and is formed as a digit of
the other side, thus : —

Eight. Eight. Eight. Eight. Left.

V IV III II I

III. The next Condition seen was as follows: —

Eight. Eight. Eight. Eight.

V IV III II

d tj Q

-2 a 2

03 it Cj

rt O CO

Left Indifferent

digit digit

IV. In the majority of polydactyle cats the manus 1ms the
digits II — V normal in shape and symmetry. Internal to the
digit II are two digits more or less united in their proximal parts ;
sometimes the metacarpal only, sometimes the metacarpal and first
phalanx are common to both. Of these two digits the external,

chap, xiil] digits: CAT. 317

that is, the one next to the digit II, is in some degree shapeless
and imperfect, but the external branch is as a digit of the other
side in form. Internal to this double digit is a seventh digit,
sometimes with two phalanges, sometimes with three, but in either
case the claw is as a rule non-retractile, and the digit is in this
respect not differentiated as either right or left. Such a manus
may be thus represented (cp. Fig. 86 a left manus) : —

Eight. Right. Right. Right. Amorphous Left Indifferent

V IV III II digit digit digit

/ As regards the carpus its changes are like those of the tarsus.
When there are six metacarpals there are three carpals in the distal
row internal to the magnum. That next the magnum may be
supposed to be trapezoid, and the other two may be spoken of as
first and second trapezium. In correspondence the length of the
scapho-lunar is increased.

No comment can increase the interest of these curious facts.
In the pes, as has been stated, with change in the number of
digits there is change in the grouping and symmetry of the series
of digits, and in particular the digit having the relations of the
index or digit II is formed as the optical image of its neighbour
III instead of forming a successive series with it. There is thus a
new axis of symmetry developed in the limb, passing between the
parts which form the digits II and III of the normal.

The evidence of the above statements may now be given.

r472. Cat having the digital series of each extremity abnormal, being
that preserved in the Coll. Surg. Mus., Teratological Catalogue,
1872, Nos. 305 and 306.

Right pes (Fig. 85, II). Digits III, IV and V normal right
digits. Internal to these are two digits each having three phalanges
and claws. That lettered d1 is formed as a left digit but d2 is al-
most indifferent, the second phalanx being slightly hollowed on the
inside. Internal to the external cuneiform there are three small
bones, of which the inner two together bear the digit d1. [This is
the Condition II of the pes.]

Left pes has the same structure as the right so far as can be
seen from the preparation (in which the muscles remain). The
digits III, IV and V are normal left digits, but internally to them
there are two digits each with three phalanges, of which the
external is an indifferent digit, while the internal is formed as a
right. [Condition II of the pes.]

Left manus. The digits II, Til, IV and V are normal. But
the carpal of the distal series (trapezoid) which bears the digit II
is imperfectly separated from a similar bone placed internal to it.
This second part of the trapezoid bears a metacarpal which
articulates with a full-sized digit of three phalanges formed as a
right digit. From the external side of the first phalanx of this

318

MERISTIC VARIATION.

[part I.

digit there is given off a rudimentary digit, which has however a
complete claw, but its bones do not differentiate it as right or left.

II

ect cijl

Fig. 85. I. Right pes of Cat No. 473, shewing condition III of the pes.

II. Right pes of Cat No. 472 shewing Condition II of the pes.

as, astragalus, c1, c-, c3, three ossifications representing the ento- and meso-
cuneiforms of the normal, cb, cuboid, clc, calcaneum. d1 — cZ6, the digits numbered
from the inside, ect, cu, ecto-cuneiform. nav, navicular.

(From specimens in Coll. Surg. Mus.)

The " pollex", d\ has two phalanges and is rather slender. The
trapezium which bears it is not separated from the scaphoid.
(Fig. 86). [Condition IV of the manus.]

Right manus. This is exactly like the left manus so far as can
be seen from the dissection, except for the fact that the rudimentary
digit borne by the large digit external to the "pollex" is much
more reduced than in the case of the left manus. The digit which
supports it is fashioned as a left digit. [Condition IV of the
manus.]
473. Cat having digital series of all feet abnormal, being the
specimen in Mus. Coll. Surg., Teratol. Catalogue, 306 B.

CHAP. XIII.]

DIGITS : CAT.

319

Right pes. The digits III, IV and V (Fig. 85, I) are
normal and are fashioned as right digits. The cuboid and external

Fig. 86. Left manus of Cat No. 472, shewing Condition IV of the manus.
cu, cuneiform, d1 — d7, digits numbered from the inside, m, magnum, sclu,
scapho-lunar. Tp, trapezoid.

(From a specimen in Coll. Surg. Mus.)

cuneiform (cb and ect. cu) are also normal. Internally to the ex-
ternal cuneiform there is a long flat bone which is grooved in such
a way as to divide it into three parts (c1— 3) and each of these bears
a digit.

Of these digits, d2 and d3 have each three phalanges, but dl has
only two phalanges and may therefore be called a hallux. The
digits d2 and d3 are fashioned not as right digits but as left
digits, and their claws are thus retracted towards the internal side
of the second phalanges, which are hollowed out to admit of this.

The bones of the hallux are not thus differentiated as right or
left, for the claw is not retractile. The navicular is enlarged in
correspondence with the presence of the fourth cuneiform element
and the astragalus and calcaneum are normal. (Fig. 85, 1). [Con-
dition III of the pes.]

Left pes. This foot is almost exactly like the right. As in it,
the digits III, IV and V are normal and are left digits. Internal
to this are three digits, viz. a hallux and two long digits with three
phalanges which are both made as right digits. The bones of this
foot have not been cleaned. [Condition III of the pes.]

Right manus. This is formed on the same plan as the manus
of the last animal, differing from it in details of the carpus, chiefly
in the presence of two separate trapezial elements. The four digits
on the external side, II — V are shewn by their claws to be true

320 MERISTIC VARIATION. [part I.

right digits. They articulate in a normal way with the trapezoid,
magnum and unciform, and are thus clearly II, III, IV and V.
The metacarpals of the " pollex " and of the double digit corre-
sponding to d'2 and d3 of Fig. 86 articulate with two separate
carpal bones of the distal row. The external of these bears a
rather thick metatarsus which peripherally gives articulation to
two digits. Of these the internal is well formed and bears a claw
which slides up on its internal side, and thus shews it to be formed
as a left digit. The other is misshapen in its proximal phalanx which
perhaps contains two phalangeal elements compounded together
and aborted ; hence the relation of this digit to the symmetry of
the limb is not apparent. The claw and last phalanx are well
formed. The innermost carpal bone is nearly normal and bears
an almost normal " pollex." [Condition IV of the manus.]

Left manus. This foot has not been dissected, but from ex-
amination it appears that the digits II, III, IV and V are normal
like those of the right manus. As in it, there is a " pollex " with
two proper phalanges, but the metacarpal of the " pollex " is in its
proximal part united with the metacarpal of an imperfectly double
digit corresponding to d2 and d3 of Fig. 86. The division between
the two parts of this double digit is not so complete in the left
manus as it is in the right and from external examination it
appears that the phalanges of the two are not separate. There are
two claws of which one is rudimentary and the pads of the two are
separated only by a groove. There is nothing to indicate .whether
these digits are formed as right or left digits. [Approaches Con-
dition IV of the manus.]
*474. Cat having supernumerary digits. This specimen belonged to
the strain of polydactyle Cats observed by Mr Poulton (see No.
480) and I am indebted to Mr J. T. Cunningham for an oppor-
tunity of examining it.

Left manus. Five digits, the normal number. The " pollex '
however is a long digit, composed of three phalanges, which reaches
very nearly to the end of the index. The claw of this digit is not
retracted to the outside of the second phalanx, like that of a
normal digit, but to the inside, and the chief elastic ligament is on
the inside of these joints instead of being on the outside as in
a normal digit. This pollex therefore may be said to be fashioned
as a right digit, bearing the same relation to the others as a right
limb bears to the left. The flexors and extensors of this digit were
fully developed. The carpal series was normal. [Condition II of
the manus.]

Right manus. Six digits fully formed, one bearing an additional
nail on the third digit from the inside. Beginning from the outer
or ulnar side, there are four normal right digits, placed and formed
as V, IV, III and II respectively. Internal to these are two
digits, the outermost having three phalanges, being shaped as a
left digit and bearing a minute supernumerary nail in the skin

chap, xiii.] digits: CAT. 321

external to the normal nail. The innermost digit has two pha-
langes, and is formed like a normal pollex, excepting that its claw
was very deep and looked as if it were formed from the germs of
two claws united and curving concentrically. The carpus as
regards number of elements was normal, but the trapezium and
trapezoid were both of rather large size, and the pollex articulated
partly with the trapezium but chiefly with the downward process
on the radial side of the scapho-lunar. [This approaches Condition
IV of the manus, but in it the external of the two united digits is
only represented by the minute extra nail.]

Left pes. Six digits, each having three phalanges. The three
outer digits were formed as left digits, but the three inner digits
were shaped like right digits. The internal cuneiform is double
the normal size, but is not divided into two pieces. It bears the
two internal digits, of which the innermost is ankylosed to it.
[Condition IV of the pes.] Compare Fig. 87, II.

Right pes. Same as the left, except for the fact that the two
internal digits are completely united in their metacarpals and first
phalanges, and the cuneiform series consists of four bones, two of
which correspond to the internal cuneiform of double size described
in the left foot. (Compare Fig. 85, I, c1 and c2.) [Condition IV of
the pes, save for the union of the metacarpals of the two internal
digits.]

475. Kitten belonging to Mr Poulton's strain (see No. 480) and
kindly lent by him to me for examination. The specimen was
very young and the carpus and tarsus were not dissected.

Left manus. Six digits, all with three phalanges. The two
internal digits are separated by a space from the others so as
to form a sort of lobe. The claw of the innermost digit is re-
tracted on the top of the second phalanx and not to the side,
so that this digit is not differentiated either as a right or a left.
The next digit is a right and the four external digits (II, III,
IV and V) are normal lefts. [Condition III of manus.]

Right manus. Same as left.

Left pes. Same as left pes of No. 474 [sc. Condition IV oi
the pes].

Right pes : same as the left [Condition IV of the pes].

476. Cat having its extremities abnormal, the property of the
Oxford University Museum and kindly lent for examination;
bones only preserved.

Right pes. Like the left pes of No. 474, but c1 not separated
from c2. [Condition IV of pes.]

Left pes. Like the right, but c1 separate from c'\ [Condition
IV of pes.]

Right manus. The four external digits II — V normal. The
double digit like that of No. 472. The innermost digit with thn
b. 21

322

MERISTIC VARIATION.

[part I.

phalanges, but the claw not retracted to one side more than to
the other. [Condition IV of the manus.]

Left manus. The same as the right. [Condition IV of the
manus.]

*477. Cat having all extremities abnormal, also the property of the
Oxford University Museum.

Left pes. Like the left pes of case No. 474 [sc. Condition IV
of the pes] represented in Fig. 87, II.

Right pes a peculiar case (Fig. 87, I). The digits V, IV and
III are normal right digits. The digit II marked 3 in the figure is

e.cu

Fig. 87. Hind feet of Cat No. 477.

I. Eight pes not truly conforming to any of the Conditions numbered.

II. Left pes shewing the ordinary form of Condition IV of the pes.
Lettering as in Fig. 85. (From a specimen in Oxford Univ. Mus.)

very slightly differentiated as a right digit, but the excavation on the
external side is very slight, and the claw when retracted is almost on
the middle of the second phalanx. The digit 2 of the figure is a left,
and internal to it is a three-phalanged digit of which the claw is
not retracted into any excavation. [Not conforming to any of the
Conditions specified.]

478. Cat having all feet abnormal, kindly lent to me by Mr Oldfield
Thomas.

chap, xiil] digits : cat. 323

Left pes. Digits V, IV, III normal lefts. The next internally
(II) is a three-phalanged digit formed as a right. The next is
a thick three-phalanged digit with a partially double nail and
double pad. This is not differentiated as either right or left.
The innermost digit is a two-phalanged hallux-like digit, not
differentiated as right or left. [Not conforming to any condition
in my scheme.]

Right pes. The same as the left except that the digit II is
only slightly differentiated as a left. The next has a double nail,
and the innermost is hallux-like as described for the other foot.
[Not conforming to any condition of my scheme.]

Right manus. As in No. 472. "Pollex" with two phalanges.
[Condition IV of the manus.]

Left manus. Same as right, but the " pollex ': is only repre-
sented by a single bone not differentiated or divided into meta-
carpal and phalanges and bearing no claw. [Approaches Condition
IV of the manus.]

479. Cat. A left pes bearing abnormal digits. The digits II, III,
IV and V are normal and are true left digits. Internal to these
are two metatarsals which are united centrally and peripherally
but are separate in their middle parts. These two metatarsals by
their common distal end bear amorphous phalanges belonging to
three digits. There are two large claws and one rudimentary one.
[For details the specimen must be seen.] The navicular bone is
divided into two distinct bones, of which one carries the external
cuneiform and a small cuneiform for the digit II, the metatarsal of
which is rather slender and compressed in its proximal part. The
internal part of the navicular bone bears two cuneiforms, one for
each part of the united metatarsals. The digits borne by these
metatarsals are so misshapen that it is not possible to say anything
as to their symmetry. Mus. Coll. Surg., Terat, Catal., No. 306 A.
[This specimen does not conform to any of the Conditions of
my scheme.]

*480. In the case of the Cat the polydactyle condition has been observed
by Poulton (Nature, xxix. 1883, p. 20, figs. ; ibid., XXXV. 1887, p. 38,
figs.) to recur frequently in the same strain. A female cat had six toes
on both fore and hind feet. The mother of this cat had an abnormal
number of toes not recorded. The grandmother and great-grandmother
were normal. Two of the kittens of the 6-toed cat had seven toes both
on the fore and hind feet [no 7-toed pes among specimens examined 1 »y
me]. Many families produced by the 6-toed cat, and among them only
two kittens with 7 toes on all feet, but between this and the normal
numerous varieties seen. The abnormality is not in all cases sym-
metrical on the two sides of the body. The pads of the different toes
are sometimes compounded together. In some cases an extra pad was
present on the hind foot behind and interior to the central pad. The
second pad was sometimes distinct from the central pad and sometimes
was united with it. [From the figures it appears that the secondary

21—2

324 MERISTIC VARIATION. [part I.

central pad in the pes bore to the digits internal to the axis of sym-
metry a relation comparable with that which the chief central pad bears
to the digits III — V, but the secondary central pad is at a higher level
than the primary one.] It was especially noted that the details in the
arrangement of the pads were inherited in several instances.

The history of the descendants of the 6-toed cat was followed and
a genealogical tree is given shewing that the abnormality has been
present in a large proportion of them. This was observed in five
generations from the original 6-toed cat, so that including the mother
of the 6-toed cat the family has contained polydactyle members for
seven generations. It may reasonably be assumed that in most of these
cases the fathers of these kittens have been normal cats and a good deal
of evidence is adduced which makes this likely.

It was observed also that some normal cats belonging to this family
gave birth to polydactyle kittens. In the later period of the life of
the original 6-toed cat she gave birth to kittens which were all normal.

I know no case of reduction in number of digits or of syndac-
tylism in the Cat.

Man and Apes.

Increase in number of Digits.

Increase in the number of digits occurs in Man in many forms.
Among them may be distinguished a large group of cases differing
among themselves but capable of being arranged in a progressive
series like that described in the Cat. These cases are all examples
of amplification or j3roliferation of parts internal to the index of
the manus.

Taking the normal as the first Condition, the next in the
progress is a hand having the digits II — V normal, but the thumb
with three phalanges, or as the descriptions sometimes say, " like
an index." (Condition II.)

In the next condition a two-phalanged digit is present internal
to the three-phalanged " thumb." (Condition III.) In the next
Condition the digit internal to the three-phalanged " thumb " has
itself three phalanges. (Condition IV.) A variant from this oc-
curred in the left hand of a child (No. 488) of parent having hands in
Condition IV. In the child the right hand was in Condition IV, but
in the left there were the usual four digits II — V, and internal to
them two complete digits, each of three phalanges, but of these the
external had a small rudimentary digit arising from the meta-
carpus. Hence the hand may be described as composed of two
groups, the one containing four and the other three digits.

In one case, No. 490, the right hand was in Condition IV, but
the left hand was advanced further. For in it the metacarpal of
the innermost digit bore a 2-phalanged digit internally to its
3-phalanged digit. This may be considered as a Condition V.

chap, xiil] DIGITS : MAN. 325

The number of phalanges in the digits in these Conditions
may be represented thus. The || marks the metacarpal space.
(The hand is supposed to be a right.)

Condition I

2

| 33 3 3

II

3

| 3333

„ III

2 3

| 3 3 33

n IV

3 3

| 3333

v

2 3 3

| 3 33 3

Distinct from these Conditions are the states sometimes
described as " double-hand." In the full form of this there are
eight digits, each of three phalanges. The eight digits are
arranged in two groups, four in each group. The two groups
stand as a complementary pair, the one being the optical image
of the other ; or in other words, the one group is right and the
other is left.

Besides the double-hand with eight digits there are also forms
of double-hand with six digits, arranged in two groups of three and
three.

Lastly, there are cases of double-hand having seven fingers,
an external group of four and an internal group of three. Thus
expressed these cases seem to come very near that mentioned as
a variant on Condition IV, but in one and perhaps both of these
double-hands there was in the structure of the fore- arm and
carpus a great difference from that found in the only recorded
skeleton of Condition IV.

At first sight it would naturally be supposed that these double-
hands in one or all kinds stand to the other Conditions in the
some relation that Condition IV of the pes in the Cat does to the
other polydactyle conditions in the Cat. But the matter is
complicated by the fact that the evidence goes to shew that in the
human double-hands the bones of the arm and carpus may be
modified, and in Dwight's example of seven digits (No. 489) at all
events, and perhaps in other double-hands, an ulna-like bone takes
the place of the radius, or in other words, the internal side of the
fore-arm is fashioned like the external side. In the polydactyle cats
the bones of the fore-arm were normal, as are they also substantially
in cases of the human Conditions III and IV, which have been
dissected. Further, in some of the human cases of eight digits
the abnormality was confined to one hand, which is never the case
in the higher condition of polydactylism in the Cat, so far as I
know. These circumstances make it necessary to recognize the
possibility that some at least of the human double-hands are
of a different nature from the lower forms of polydactylism.
This subject will be spoken of again after the evidence as to the
variation of digits has been given (Chap. xiv. Section (4).)

326 MERISTIC VARIATION. [part I.

In addition to cases more or less conforming to schemes that
can be indicated are several which cannot be thus included. These
will be duly noticed when the more schematic cases have been
described. That any of the cases can be arranged in a formal
sequence of this kind is perhaps surprising, and the relations of
some of the Conditions, II and III for instance, to each other must
at once recall the principle seen already in other examples of
addition of a member at the end of a successive series of parts,
notably in the case of Teeth (see p. 272). It was then pointed out
that when a new member is added beyond a terminal member
whose size is normally small relatively to that of the normal
penultimate, then the member which is normally terminal is
raised to a higher condition. Now this same principle is seen in
Condition III of the polydactyle manus.

Attention must nevertheless be forthwith called to the fact
that a two-phalanged digit1 may be present internal to the thumb
(usually arising from it) though the thumb has still but two
phalanges. But generally these cases may properly be described
as examples of duplicity of the thumb ; and as was well seen in
the case of Teeth, any member of a series may divide into two
though the rest of the series remain unaltered. Duplicity of a
member without reconstitution of the series is to be recognized as
one occurrence, and change in number associated with reconstitu-
tion of other members especially, of adjacent members, is another.
In Teeth and other Meristic series these two phenomena are both
to be seen, though as was pointed out (p. 270) they pass insensibly
into each other.

Another feature to be specially mentioned in this preliminary
notice is the difference in the manner in which the higher forms
of polydactylism appears in the human foot from that seen in the
human hand. In the hand there is this strange group of cases
forming a progress from the normal hand to Condition V, besides
the distinct series of double-hands. Polydactyle feet on the con-
trary do not in Man, so far as they have been observed (with the
doubtful exception of Nos. 499 and 500), develop a new symmetry.

Cakes of Polydactylism associated with Change of Symmetry.
A. Digits in one Successive Series.

'481. Man having a "supernumerary index" on each hand. Left
hand. No" thumb " present. In its stead there is a digit having
three phalanges which " performs its office." The middle phalanx
was abnormally short. The first intermetacarpal space was not
great. [Degree of opposability not stated.] Right hand. In
addition to four normal fingers there was a three-jointed digit

1 A case in which a 3-phalanged digit was placed on the radial side of the pollex
is mentioned by Windle, Jour. Anat. Plnjs.. xxvi. p. 440, but has not yet been
described. No other such case is known to me. This perhaps should be classed
with double-hands. Cp. No. 502.

CHAP. XIII.]

DIGITS : MAX.

327

482,

which could be opposed to them and could perform all the move-
ments of flexion, &c. Internal to this three-jointed digit was a
rudimentary thumb having only one phalanx and no nail. [Re-
lations of metacarpals to each other not particularly described.]
Guermonprez, F., Rev. des mal. de Venfance, iv. 1886, p. 122, figs.
[Left hand Condition II; right hand almost Condition III.]

Girl having a three-jointed thumb, resembling a long fore-
finger. Annandale, Diseases of the Fingers and Toes, p. 29, PI. II.
fig. 19. [Condition II.]

483. Man having a thumb with three phalanges on each hand. Feet
normal. In the thumbs the metacarpal is 2 j- in. long; the first phalanx
If in., being longer than usual. The second phalanx is longer on the
radial side than on the external side, causing the distal phalanx to curve
towards the index. On the internal it measures J- in., in the middle
| in., and on the ulnar side \ in. The distal phalanx is 1 in. long.
When the left thumb is straightened it passes \ in. beyond the joint
between the 1st and 2nd phalanx of the index. In the right hand the
thumb scarcely reaches that joint. The utility of the thumb is not
impaired. A maternal aunt had a similar thumb on right hand.
Struthers, Edin. New Phil. Journ., 1863 (2), p. 102, PI. n. fig. 6.
[Both hands Condition II.]

*484. Father and three children, each having 3-phalanged thumbs shaped
as indices and not opposable. [Full description q.v.~\ Paternal grand-
mother had double-thumb. Farge, Gaz. hebd. de med. et chir., Ser. 2.
ii. 1866, p. 61.

*485. Man having the following abnormalities of the digits. (Fig.
88). Right hand. The number of digits was normal, but the

Fig. 88. Right and left hands of No. 485. Right hand in Condition II; Left
hand in Condition III. (After Windle.)

328

MERISTIC VARIATION.

[part I.

*

±86,

radial digit or thumb had three phalanges in addition to the meta-
carpal, all the articulations being moveable. Relatively to the
others their digit was placed as a thumb. Left hand. The digit
corresponding with the thumb was composed of three phalanges like
that of the right side, and though finger-like in form it was
functionally a thumb. On the radial side of this 3-jointed digit
there was a supernumerary digit composed of two phalanges articu-
lating with the metacarpal bone of the 3-jointed thumb. This
supernumerary digit had a well-formed nail. The 3-jointed thumb
of the left hand was longer than that of the right hand (measure-
ments given), Windle, B.C. A., Journ. of Anat. xxvi. 1891, p. 100,
PL II. [Right hand, Condition II ; left hand, Condition III.]

Man having 3 phalanges in the thumb of the left hand together
with a supernumerary digit. (Fig. 89.) This case in several
respects resembles the left hand of the subject described by Windle.
The four fingers were normal. The thumb stood in its normal
relations to them, but was finger-like in form, having three
phalanges in addition to the metacarpal. On the radial side of

Fig. 89.

Bones of left hand of No. 486, shewing Condition III.
(After Rijkebusch.)

this 3-phalanged digit there was a supernumerary digit, having
two phalanges and a separate metacarpal, which articulated with
the head of the metacarpal of the thumb and the trapezium. In
the carpus of this hand there was a supernumerary bone which is
described as an os centrale. The bones and muscles of this limb

CHAP. XIII.]

DIGITS : MAN.

329

are described in detail. The thumb and the supernumerary digit
were closely webbed together and were very slightly moveable.
Specimen first described by Rukebusch, Bijdr. tot de Kennis der
Polydactylie, Utrecht, 1887, Plates, and subsequently by Spronck,
Arch, neerl, XXII. 1888, p. 235, PL VI. — IX. [Condition III.]

*487. Woman having 6 digits on each hand and foot as follows. In each
hand the thumb has three phalanges, and internal to it articulating
with the same metacarpal is an extra digit having two phalanges
[measurements given] webbed to the three-phalanged thumb. [Con-
dition III of the manus.j Right foot has six complete metatarsals and
digits very regularly set, one of them being internal to but longer than
the hallux which has two phalanges as usual. The digit internal to it
has also two phalanges. Left foot has also an extra digit with two
phalanges longer than the hallux, placed internal to and articulating
with the metatarsal of the hallux which has two phalanges as usual.
Many members of family polydactyle [particulars given]. Struthers,
Edin. New Phil. Jour., 1863 (2), p. 93. [Note in this case that in the
feet the digits added internally to hallux are greater than it, and they
thus stand as the largest terms in the series, the other members being
Successive to them. The series thus does not decline from the hallux
both internally and externally in the way seen in most other cases of
extra digits on the internal side of the limb.]

488. Man having six digits, each with three phalanges, on each hand.

d1

Fig. 90. Bones of right hand of No. 488 shewing Condition IV.
n1 and n2 represent the scaphoid, lu, lunar, c, cuneiform, tm, trapezium.
td, trapezoid, m, magnum, u, unciform. acl, ac2 are supernumerary bones.

(After Eudinoer.)

330 MERISTIC VARIATION. [part I.

The digits were arranged in two groups, which were to some extent
opposable to each other. The digits II, III, IV and V stood in their
normal positions and were properly formed. In the place where the
thumb should stand there were two digits, each with three pha-
langes. Of these the external (rf2) was of about the length and
form of the index finger while the internal, d1, was a good deal
shorter and more slender. The bones of the carpus are shewn in
Fig. 88. The scaphoid was represented in the right hand by two
bones n1 and n2, and there were two accessory bones, ac1 and ac2
placed in the positions shewn. The two hands were almost exactly
alike, save for slight differences in the carpal bones [see original
figures], and for the fact that in the left hand the internal of the
two digits of the radial group was rather more rudimentary.
Rudinger, Beitr. zur Anat. des Gehororgans, d. venosen Blutbahnen
d. Schddelhohle, sotuie der ilberzdhligen Finger, Miinchen, 1876,
Plate. [Both hands in Condition IV.]

489. A female child born to the last case, No. 488, had the right hand
in the same condition as that of the father, while the left hand
differed from it in the presence of an additional rudimentary
finger arising from the ulnar side of the digit d\ This additional
finger bore a nail but it appeared to consist of two joints only and
to be attached to the metacarpus by ligamentary connexions.
Rudinger, ibid. [Right hand in Condition IV ; left hand depart-
ing from the Conditions enumerated. Compare with manus of
Cat, Fig. 84]

490. Man. Rigid hand bore six digits and metacarpals. The most
external digit was a normal minimus, succeeded by digits IV and
III webbed together. Next to III there was an index. Internal
to this and separated from it by a small metacarpal space was a
3-phalanged long digit much as in Windle's case, No. 481, and
internal to it is a 2-phalanged thumb of nearly normal form like
that of No. 485. Left hand bore seven digits but six metacarpals.
Minimus normal. IV, III and II webbed together. Internal to II
was a 3-phalanged digit much as in the right hand ; but internal
to this there was a metacarpal bearing two digits, an external
having 3 phalanges and an internal having 2 phalanges. Each
foot had six digits and six metatarsals (q. v.). Redescribed from
the account and figures given by Gruber, Bull. Ac. Sci. Pet., xvi.
1871, p. 359, figs. [Right hand Condition IV, left hand Con-
dition V.]

491. Child having six fingers on each hand. The fingers were united together. In
the thumb [? both] there were three phalanges and the length of the thumb was as
great as that of the "other fingers." Dubois, Arch, gener. de Med., 1826, Ann. iv.
T. xi. p. 148; this case is quoted by Geoffroy St Hilaire, Hist, des Anom., i. p. 227,
Note. [? Condition IV.]

491, d. New-born male child having on the right hand two "thumbs" each with three
phalanges. Oberteufer, J. G., Stark's Arch. f. Gebnrtsh., 1801, xv. p. 612. [Con-
dition IV.]

(No more cases known to me.)

*

CHAP. XIII.]

DOUBLE-HAND.

331

B1. Digits in two homologous groups, forming "Double-hands."

*492. Double-hand I. Seven digits in two groups of four and three.
Male : left arm abnormal, having seven digits arranged in two
groups, the one an external group of four normal digits, and the
other an internal group of three digits2. (Fig. 91.) Described
from a dried specimen in Mus. of Harvard Med. School. The man
was a machinist and found the hand not merely very useful to him
in his business, but he also thought that it gave him advantages
in playing the piano.

" The fore-arm consists of the normal left ulna and of a right one in
the place of a radius. The left one shews little that calls for comment,
excepting that there is a projection outward at the place of the lesser
sigmoid cavity to join a corresponding projection from the other ulna.
The upper surface of this projection articulates with the humerus. At
the lower end the styloid process is less prominent than usual, and the
head rather broad. The right or extra ulna is put on hind side before,
that is, the back of the olecranon projects forward over the front and
outer aspect of the humerus. If the reader will place his right fore-arm
on the outer side of the left one he will see that it is necessarv for the

I

; ■
: . .

. i* ho

■ '•

II

Fig. 91. I. The left band of No. 492 from the dorsal surface.
II. The humerus and two bones of the fore-arm at the elbow of the same c
0, olecranon. O2, the secondary " olecranon ". I, the inner condyle of the
humerus. I2, the second or external " inner condyle."

(After Dwight.)

ulna to be thus inverted if the thumbs are to toucli and the palms
to be continuous. This olecranon is thinner, flatter, and longer than
normal. The coronoid process is rudimentary. From the side of this
process and from the shaft just behind it arises the projection already

1 Every case known to me is given.

2 This is the case reported by Jackson, to Bost. Soc. of Med. hup.. 1852.

332

MERISTIC VARIATION.

[part I.

referred to which meets a similar one from the normal ulna [Fig. 89, II].
On the front of this there is a small articular surface looking forward
which suggests a part of the convexity of the head of the radius. The
upper articular surface shews a fissure separating it from the side of
the olecranon which is not found in the normal ulna. These projections
which touch each other are held together by a strong interosseous liga-
ment. The lower end of this ulna is very like the other, only somewhat
broader. The mode of union of the lower ends could not be seen without
unwarrantable injury to the specimen. There can hardly have been
any definite movement between these bones. Perhaps the ligaments may
have permitted some irregular sliding, but it is impossible to know.
These bones have been described first because their nature is very clear
and, once understood, is a key to the more difficult interpretation of the
lower end of the humerus."

The upper end of the humerus presented nothing noteworthy. A
detailed description and figures are given, from which it appears that
the lower end of the humerus had such a form as might be produced
by sawing off the greater part of the external condyle and applying in
place of it the internal condyle of a right humerus.

The carpus seen from the dorsal side had the structure shewn in the
diagram (Fig. 92). The proximal row consisted of three bones besides
the two pisiforms (pl and p2). There was a cuneiform at either side of
the wrist, and between them a bone evidently composed of a pair of
semilunars, having a slight notch in its upper border. At each end of

Fig. 92. Diagram of the carpal bones in the left hand of No. 492 from the
dorsal surface.

pis1, cu1, u1, m1, pisiform, cuneiform, unciform and magnum of the external or
normal half of the band consisting of four fingers ; pis*, cu2, u2, m2, the similar
bones for the internal group of three fingers. Zu1+2, the compounded lunar
elements corresponding to the two groups, x, bone placed as trapezoid.

(After Dwight.)

the second row is an unciform bearing the middle and ring fingers.
Next came two ossa magna very symmetrically placed, each bearing the
metacarpal of a medius. Between these is a bone which Dwight states

chap, xiil] double-haxd. 333

to have clearly represented the trapezoid of the left hand, bearing an
index finger. The metacarpals and phalanges needed no description.

The muscles are described in detail [^.v.]. Some of the features
in the distribution of the arteries and nerves are of interest, and 1
transcribe Dwight's account in full. It appears that, like the bones,
the vessels and nerves proper to the radial side of a normal left arm
have in a measure been transformed into parts proper to the ulnar side
of a right arm.

"The Arteries. The brachial divides at about the junction of the
middle and lower thirds of the humerus. The main continuation, which
is the ulnar proper, runs deeply under the band thought to represent
the pronator radii teres, to the deep part of the fore-arm where it gives
off the interosseous. Above the elbow there is a branch running
backward between the internal condyle and the olecranon. The inter-
osseous branches are not easy to trace. There seems to be an anterior
interosseous and three branches on the back of the forearm, one running
on the membrane and one along each bone. At least two of them share
in a network on the back of the carpus. Having reached the hand the
ulnar artery runs obliquely across the palm to the cleft between the
two sets of fingers, supplying the four normal fingers and the nearer side
of the extra middle finger. The other branch of the brachial crosses
the median nerve and runs, apparently superficially, to the outer side
of the fore- arm. It supplies the little and ring fingers and the corre-
sponding side of the middle finger of the supernumerary set. There is
no anastomosis in the palm between the superficial branches of the
two arteries. Each gives off a deep branch at the usual place, which
forms a deep palmar arch from which some interosseous arteries spring.
There is also an arterial network over the front of the carpal bones.
The arteries of the deep parts of the hand cannot all be seen.

The Nerves. The ulnar nerve proper pursues a normal course and
supplies the palmar aspect of the little finger and half the ring finger of
the normal hand. Near the wrist it gives off a very small posterior
branch, which is not well preserved, but which seems to have had less
than the usual distribution. The median nerve is normal as far as the
elbow, running to the inner side of the extra condyle. It is then lost
in the dried fibers of the flexor sublimis, from which it emerges in two
main divisions near the middle of the fore-arm. The inner of these soon
divides into two, of which one supplies the adjacent sides of the ring
and middle fingers and the other those of the middle and index fingers
of the normal hand. The outer division of the median supplies the
outer side of the index and both sides of the extra middle finger and
one side of the extra ring finger. One of the branches to the index
gives off a dorsal branch, and there is a doubtful one for the extra
middle finger. The musculo-spiral nerve passes behind the humerus as
usual. A nerve which is undoubtedly continuous with it emerges from
the hardened muscles over the fused outer condyles. It seems to be the
radial branch changed into an ulnar. It runs with the extra ulnar
artery to the hand and sending a deep branch into the palm, goes to
the ring linger. There is a detached branch on the other side of the
little finger which in all probability came from it. The deep branch
sends a twig along the metacarpal bone of the ring finger. It probably

334 MERISTIC VARIATION. [part i.

supplied the side of the ring linger left unprovided for, but this is
uncertain. Assuming this to have been the case, each ulnar nerve
supplies the palmar surface of one finger and a half, the median supply-
ing the remaining fingers of both hands. Unfortunately no dorsal
branches except those mentioned have been preserved."

Dwight, T., Mem. Boston Soc. of JV. H.. 1892, Vol. iv. No. x.
p. 473, Pis. xliii and xliv.

[This is a case of high significance. We shall come back
to it hereafter. Meanwhile it will be noted that in it we meet
again the old difficulty so often presented by cases of Meristic
Variation. In this fore-arm there is already one true ulna.
Internal to it is another bone also formed as an ulna. We
may therefore, indeed we must, call it an ulna. But is it
an " ulna " ? To answer this we must first answer the question
what is an ulna? Similarly, is the second pisiform a "pisiform,"
or is the second ulnar nerve an c< ulnar " nerve ? These questions
force themselves on the mind of anyone who tries to apply the
language of orthodox morphology to this case, but to them there is
still no answer. Or, rather, the answer is given that an " ulna," a
" pisiform " and the like are terms that have no fixed, ideal
meaning, symbols of an order that we have set up but which the
body does not obey. An " ulna " is a bone that has the form of an
ulna, and a " pisiform " is that which has the form of a pisiform.
If we try to pass behind this, to seek an inner and faster meaning
for these conceptions of the mind, we are attempting that for which
Nature gives no warrant : we are casting off from the phenomenal,
from the things which appear, and we set forth into the waste of
metaphysic]

493. Boy having abnormalities in the left hand as follows. The four
outer fingers II — V are normal in form and proportions. Internal to
these is firstly an opposable digit with a single metacarpus and single
proximal phalanx but having two distal phalanges side by side webbed
together. Internal to this partially double thumb are two digits in
series, each with a metacarpal and three phalanges, respectively re-
sembling the annularis and minimus of a right hand. Struthers, Edin.
New Phil. Jour., 1863 (2), p. 90, PI. n. fig. 5. [Not representing any
of the Conditions.]

494. Male infant, one year and five months, examined alive, having the right hand
abnormal, possessing seven digits, arranged in two groups, an ulnar group of
four and a radial group of three. Each digit had three phalanges, but the ring
and middle fingers of the ulnar group are webbed in the region of the proximal
phalanges. The ulnar group seemed to articulate with the carpus in the usual
way. The radial group probably formed joints with more than one facet on the
trapezium, and possibly also with a surface on the lower end of the radius. It
did not seem that the carpal bones were increased in number, for the right wrist
had the same circumferential measurement as the left, which was normal. The
lower end of the ulna did not seem to articulate normally with the carpus. The
elbow was also abnormal, and it seemed "as if the ulna were dislocated inwards."
Ballantyne, J. W., Edin. Med. Jour., 1893, cdli. p. 623, fig. [Possibly this
condition approached to that found in the last cases.]

495.

CHAP. XIII.]

DOUBLE-HAND.

335

Double-hand II. Eight digits in two groups of four and four.
Woman (examined alive) having eight fingers in the left hand
arranged as follows (Fig. 93). With the exception of the left arm
the body was normal. The limb was very muscular. The shoulder-
joint was natural. The external condyloid ridge of the humerus
was strongly defined. The muscles and tendons of the fore-arm
were so prominent that it was not easy to decide whether there
was a second radius or ulna, but Murray eventually came to the

Fig. 93. Left hand of No. 495. (After Murray.)

conclusion that there was no such extra bone. The fore-arm
could be only partially flexed. The eight fingers were arranged in
two groups of four in each, one of the groups standing as the four
normal fingers do, and the other four being articulated where the
thumb should be. There was no thumb distinguishable as such,
but it is stated that there was a protuberance on the dorsal side
of the hand, between the two groups of fingers, and this is con-
sidered by Murray to represent the thumbs, for according to his
view the limb was composed of a pair of hands compounded by
their radial sides. In the figure of the dorsal aspect which is given
by Murray taken from a photograph, this protuberance cannot be
clearly made out. The four radial fingers in size and shape
appeared to be four fingers of a right hand. In the radial group of
fingers, the" middle "and" jring " fingers (6 and 7) were webbed as
far as the proximal joints, and the movements of the fingers of this
group were somewhat stiff and imperfect. Between the t \v< » gn nips
of fingers there was a wide space as between the thumb and index
of a normal hand, and the two parts of the hand could be opposed
to each other and folded upon each other. The power of inde-
pendent action of the fingers was very limited. No single finger
could be retained fully extended while the other seven fingers
were flexed, but if both " index " fingers (4 and 5) were extended,

336

MERISTIC VARIATION.

[part I.

the other six fingers could be flexed, or the four fingers of either
group together with the " index " of the other group may be
extended, while the other three are flexed. The " index " fingers
could not be flexed while the other fingers were extended, nor can
the " little fingers " be extended while the others were flexed.
Murray, J. Jardine, Med. Chir. Trans., 1863, xlvi. p. 29, PL n.

496. Female child, five weeks, having a hand of eight digits on the right side
(Fig. 94). The digits were disposed in two groups of four in each. [No further

r*0^"

Fig. 94. Right hand of No. 496. (After Giraldes.)

description.] Giraldes, Bull. soc. de Chirurg., Paris, 1866, Ser. 2, vi. p. 505,
fig. The same case referred to again, Giraldes, Mai. Chir. des Enfants, 1869,
p. 42, Jig.
49^ Female child having right hand almost exactly like Murray's case, but without
' syndactylism. The two halves could be folded on each other. The four extra digits
articulated with an imperfect metacarpal which was annexed to the normal meta-
carpal [of the index]. Fumagalli, C, Annal. Univers. di Med. Milano, 1871,
vol. ccxvi. p. 305, fig.

Girl's right hand having eight fingers, represented in a wax model. Langalli,
La scienza e lapratica, Pavia, 1875 [Not seen : abstract from Dwight, I. c],

498. Double-hand III. Six digits in two groups of three and three.
Man having abnormalities of left arm as follows (Fig. 95). The
left hand was composed of six digits with three phalanges, which
were disposed in two groups of three digits in each. The two
middle digits were the longest (d3 and c/4), and the length of the
digits on either side of them diminished regularly. The appear-
ance was as of a hand composed of the middle, ring and little
fingers of a pair of hands united together. The two groups of
fingers were to some extent opposed to each other and all the
digits could be flexed and extended. The digit d3 though single
in its peripheral parts articulated with two metacarpals, its proxi-
mal phalanx having two heads. Upon the radial side of the

CHAP. XIII.]

DOUBLE-HAND.

337

carpus of this hand there was a soft tumour about 2'5 cm. in
height, resembling a cyst with a firm wall.

Fig. 95. Dorsal and palmar aspects of the left hand of No.
are numbered from the inside.

(After Jolly.)

498. The digits

The structure of the bones of the arm and fore-arm could not
be made out with certainty in the living subject, but it appeared
that the humerus was formed by two bones partially united
together.

As regards the skeleton of the fore-arm an ulna could be felt
extending from the upper arm to the processus styloideus. The
existence of a radius could not be made out with certainty, but a
second bone could be felt which was in very close connexion [with
the ulna]. Jolly, Tnternat. Beitr. z. wiss. Med., 1891.
499. Male child, three years old, twin with a normal female child,
having all extremities abnormal. Right hand. Six metacarpals
arranged in two groups of three in each group. Each bore a
three-phalanged digit, none resembling a thumb. The first and
sixth were alike, resembling a minimus, while the two median
fingers resembled middle fingers. On the radial side the three
digits were completely united together. The next was five, and
the two external to this were also united. Left hand. Like the
right, but all the fingers united together in two groups of three in
each group. Feet. Each foot had nine metatarsals and nine digit-,
the central being like a hallux and having two phalanges perhaps,
but thicker than a hallux. The externals were like minimi. The
four toes on each side of the " hallux " were united two and two.
The tarsus was of about double size. The right leg was shorter
than the left. Gherixi, A.,Gaz. med. ital.-lombard., 1874, No. .31.
p. 401, figs.

B.

22

338

MERISTIC VARIATION.

[part I.

Complex and irregular cases of Polydactylism associated with

Change of Symmetry.

*500. Man (examined alive) having abnormalities in the digits of hands
and feet (Fig. 96). The case is very briefly and inadequately described,
but the condition was apparently as follows.

Right hand. Beginning from the ulnar side, there were three
normal digits (6, 5, 4). Beyond the third of these, which must be

») '/]

>

■i)

f] /

>

si

1

;t

jr

6

ft

loJ

5

JJ v

3

2 ~3 *
Fig. 96. Hands and feet of No. 500. (After Kuhnt.)

chap, xiii.] COMPLEX POLYDACTYLISM : MAN. 339

regarded as the medius, there were two complete digits (3, 2) each
having three phalanges : and on the radial side of the innermost of
these digits there was a stump-like rudiment (1), apparently representing
another digit. [This case therefore differed from those of Win die and
Rijkebiisch in the fact that both the digits internal to the medius (m)
were disposed as though they belonged to a left hand, and Kuhnt, in
fact, states that each hand was, as it were, composed of parts of a pair
of hands, thus agreeing with Jolly's case, No. 499.]

Left hand. In this hand there were only five digits, each of which
had three phalanges. None of them was fully opposable, but that on
the radial side (1) could to some extent be moved as a thumb. Of
these five digits the middle one was the longest, and on each side of it
there were two similar digits, those next to the middle finger being the
longest and those remote from it being a good deal shorter and having
the form of little fingers, which Kuhnt considers them to have been.
[This hand is perhaps in Condition II.]

Right foot. The hallux (2, 3) was of abnormal width and its bones
were to some extent double, the ungual phalanx being completely so.
[The nail however is drawn as a single structure and the double character
of the toe was not apparent in its external appearance.] On the internal
(tibial) side of the hallux there were two supernumerary toes (1, 1)
having, so far as could be ascertained, a single metatarsus. The
number of phalanges in these toes is not distinctly stated.

Left foot. The hallux (3, 4) was to some extent double, like that of
the right foot. Internally to it were two supernumerary toes (1, 2)
having apparently a common metatarsal. [Of these the most internal
is represented as being very wide and resembling a hallux, but this
feature is not mentioned in the description and the number of phalanges
is not given].

[It is greatly to be regretted that no fuller account of this important
case is accessible. According to Kuhnt's view each hand and each foot
were structurally composed of parts of a complementary pair of hands
and feet. As regards the hands the facts agree witli this description
and with what has been seen in other cases, but the condition of tin1
feet is more doubtful, and without more knowledge of the details no
opinion can be given. It should be remembered that the original
description is very brief and Dr Kuhnt offers an apology for the im-
perfection of the figures.] Kuhnt, Virch. Arch, f path. Anat. u. Phy8.,
lvi. 1872, p. 268, Taf. vi.

501. Case of a foot with eight toes, stated to have resembled Kuhnt's
case (No. 501). Ekstein, Prager Wochens., No. 51, 1891.

502. Man whose right arm beside the normal hand bore an extra thumb
and finger. The two thumbs were united and had a common meta-
carpal joint. They were of equal size. They were flexed and extended
together and had the power of spreading apart. The extra finger was
beyond the extra thumb and was shaped like an index. Besides the
radius and ulna of the normal arm there was an extra radius on the
outer [1 internal] side of the normal radius. This bone had a joint of
its own at its elbow. The wrist was broad, suggesting the presence or'
additional bones. Nothing is said of a metacarpal bone for the new
index. Carre, Seance publ. de la soc. rog. <1> Mid., Ghir. et Pharm. de

0 0 o

340 MEMSTIC VARIATION. [part i.

Toulouse, 1838, p. 28. [Not seen by me. Abstract taken from D wight,
I.e., vide No. 492. Cp. p. 326, Xote.]
503. Girl, new-born, having the left foot "double," bearing eleven toes.
The left labium majus was twice as large as the right, and the left
leg and thigh were much thinner than the corresponding parts on the
right side [measurements given]. The extra parts were all on the planter
side of a foot which had toes of nearly normal shapes and sizes. This
foot was bent into a position of extreme talipes equino-varus, and the
great toe was bent so that it pointed inwards at right angles to. the
metatarsal.

Upon the plantar side of this foot there was a series of six well-
formed, small toes, arranged in a series parallel to that of the 'normal'
five, and having their plantar surfaces in opposition to those of the
latter. Of the series of six toes that facing the normal little toe exactly
resembled it. The second was the longest of the six, but did not
resemble a great toe. The third and fourth were equal in length, the
fifth and sixth being shorter, as are the external toes of a normal foot.
None of the toes were webbed. Bull, G. J., Boston Med. and Sury.
Jour. 1875, xciii. p. 293, fig. [This figure copied by Ahlfeld.
Missb. d. Menschen, PI. xx. fig. 2.]

[The case described by Graxdix, Amer. Jour, of Obstetrics, 1887, xx. p. 425,
Jig., is probably a case of a pair of limbs composing a Secondary Symmetry
attached to and deforming the limb belonging to the Primary Symmetry and
corresponding with that of the other side. The nature of this case will be better
understood when evidence as to the manner of constitution of Secondary Symmetries
has been given.]

"504. Macacus sp. A monkey, full-grown, having nine toes on the
left foot ; right foot normal, upper extremities not preserved. The
specimen is described as No. 307 in the Catalogue of the Terato-
logical Series (1872) in the Mus. Coll. Surg. (Hunterian specimen).
Though I am disposed to agree in the main with the view of the
nature of the specimen given in the Catalogue it is not in my
judgment possible to decide confidently in favour of this view to
the exclusion of all others. For this reason the specimen is here
described afresh. This is the more necessary as the account of
the Catalogue is incorrect in some particulars.

Extra parts are present in the limb and in the pelvic girdle.
(Figs. 97 and 98.) The names to be given to the parts depend on
the hypothesis of their nature which may be preferred. In general
terms it may be stated that the ventral or pubic border of the
girdle and the internal (tibial) border of the limb are nearly normal.
The external (fibular) border of the limb is also normal, but between
these there are in addition to the normal parts other structures,
whose true nature is somewhat uncertain.

The appearances may be realized best in the following way. Sup-
pose that two similar left feet lie in succession to each other, the
" posterior " having its hallux next to the minimus of the "anterior/'
so that the digits read I, II, III, IV, V, I, II, III, IV, V. Now if
the two feet could interjDenetrate so far that the minimus of the
" anterior " foot took the place of the hallux of the " posterior," this

chap, xiii.] POLYDACTYLE FOOT : MaCCLCUS.

341

second hallux not being represented, the condition of this specimen
would be nearly produced. In the same way the left pelvic girdle
is just what it would be if two left innominate bones were placed
in succession, the ischium of the " anterior " superseding the pubis of
the posterior. As in the foot, so in the innominate, of the portions
which coincide the parts belonging to the anterior are alone
represented. Something very like this was seen in the case, for
instance, of the imperfect division of vertebrae in Python, No. 7.

The chief difficulty attending this view of the nature of the
case is the fact that as regards the tarsus the "anterior" foot

h'-

.g*

It-

4&}

.fib1

Fig. 97. Macacus, No. 50-1, left leg.
C. S. M. 307.

7*1, head by which femur articulates.
lr, supernumerary head (?). gt, great tro-
chanter. gt2, " posterior " great trochanter.
It, lesser trochanter, t, tibia, fib1, " anterior
fibula." fib2, "posterior" fibula (?). clc,
calcaneum. As, astragalus, nav, navicular.
nav2, supposed second navicular, c1 — c6,
six cuneiform bones, c3, the ecto-cuneiform
of "anterior" foot, cb, cuboid.

'C3

342

MERISTIC VARIATION.

[part I.

lacks the external (fibular) parts of a tarsus, viz. the cuboid and
calcaneum. There is a cuboid, cb, and a calcaneum, c, for the
"posterior" foot, but none for the " anterior." The bone c3 might
of course be called a cuboid ; but if this is a cuboid there is no
ecto-cuneiform for the anterior foot. The account given in the
Catalogue avoids these difficulties by the statement that each foot
has three cuneiforms and a cuboid, declaring that there is a second
cuboid between the two sets of cuneiforms. This is nevertheless
incorrect, for the whole distal series in the tarsus contains onlv
seven bones and not eight. The mistake has no doubt arisen by
counting cs twice over. The Catalogue is also in error in neglecting
the fact that the tarsal articulation of the digit 2 is quite abnormal.
Similarly in the crus, there is no good reason to affirm that the
boney^1 is a fibula rather than a tibia. The Catalogue regards it
as a second tibia, but I incline to speak of it as the fibula of the
' anterior ' foot following the view already indicated. As I have
said, the leg is almost normal in the structure of its external
border and almost normal in its posterior border, but between
these the nature of the parts is problematical. All that can be
done is to describe the parts as they are seen.

Beginning at the external (fibular) border of the foot there is a
nearly normal series of three digits, 9, 8, 7, fashioned as V, IV and III

I II

Fig. 98. I. Innominate bone of Macacus, No. 504. i\ p, is1, t1, of1, ilium,
pubis, ischium, ischial tuberosity and obturator foramen of the supposed anterior
part of the girdle; the parts marked 2 being the corresponding structures of the
supposed posterior part.

II. Details of tarsus of the same. Digits numbered 1 — 9 from the inside.
A, astragalus, c, calcaneum. n1. navicular of "anterior" foot. n\ navicular of
"posterior" foot, cb, cuboid, c1 — cF', six bones placed as cuneiforms.

chap, xiii.] POLYDACTYLE FOOT : MoCOCUS. 343

respectively, the V and the IV articulating with the cuboid (cb) and
the III with an external cuneiform, c6, as usual. There is a middle
cuneiform, c5, bearing a digit, 6, which is almost exactly formed as a II.
Internal to this point the parts can only be named with hesitation.
The tarsal bone, c4, of the distal series internal to c5 is shaped like
another c5, but the digit which it bears rather resembles a minimus.
This is succeeded by a tarsal bone, c3, shaped like the external cunei-
form, c6, but it bears a digit of the length suited to an annularis.
Internal to this are two tarsal bones of the distal row, c2 and c\ which
bear three digits, 1, 2, and 3. Of these the most internal is undoubtedly
an internal cuneiform ; it bears firstly a slender but otherwise normal
hallux with two phalanges, and secondly, it contributes (abnormally for
an internal cuneiform) to the articulation of a digit, 2, which is thinner
than all the others and resembles rather a minimus than an index.
The digit, 2, also articulates with c2 which chiefly supports the third
digit.

Between the metatarsals of the digits 5 and 6 there is a considerable
space, owing to the fact that the head of the metatarsal of 6 is pro-
longed upwards like that of a normal metatarsal V.

In addition to those described are four other tarsal bones : firstly, a
calcaneum c, which is rather smaller than that of the normal right
leg. It articulates with the cuboid, cb, with the astragalus, A, and
with the bone, n2. The astragalus is very large in its transverse
dimension but its length is less than that of the normal astragalus.
Peripherally it bears two bones, firstly, a navicular, n\ and secondly.
a bone of uncertain homology, marked n2 in Fig. 96. The navicular
articulates with c\ c2 and c3, together with the bone n2. The latter, ri2,
articulates with c3, c4, c5, c6, and also with the cuboid, cb, the astragalus
and calcaneum and navicular. From its form and relations it is
probably a second navicular.

The bones of the crus are three. Firstly, a tibia, lib., which is
rather thinner than the normal bone and is somewhat bowed inwards.
Passing as a chord to the curve of the tibia there is a thin bone, fib .
which is tendinous in its upper part. External to this, articulating
with the external condyle of the femur there is a third bone. ji/>\
which has nearly the form and proportions of a normal fibula. All
three bones articulate with the large astragalus.

There is a small patella.

The femur is about half as thick again as that of the right leg. Its
head is nearly normal in form, articulating with the rather shallow
acetabulum. The lesser trochanter and the internal border of the femur
are nearly normal. Anteriorly and externally there are the following
parts. Upon the external border there is a projecting callosity, clearly
being a great trochanter in its nature. Internal to this there is a knob-
shaped, rounded protuberance, which in texture so closely resembles
the head of a femur that it is almost certainly of this nature. h is
rounded and smooth as though for articulation with an acetabulum,
though it stands freely. Between this tuberosity and the real head of
the femur there is a third tuberosity, apparently representing the end
of the great trochanter of that limb which lias been spoken of as
"anterior." The peripheral end of the femur is nearly normal on its
inner side, while on the outside it is considerably enlarged. The ex

344 MERISTIC VARIATION. [part i.

ternal condyle is thus much larger than that of the normal femur, but
there is in it only a very slight suggestion of a division into two parts.
The innominate bone has an ilium which anteriorly is normal, but
which posteriorly enlarges and to some extent divides into two parts, V
and i2. Of these the ventral part, i\ unites with a nearly normal pubis,
p, and bounds the shallow acetabulum with which the femur articu-
lates. The rest of this acetabulum is made up by the ischium, is1, of
the "anterior" limb, which together with the pubis bounds an obturator
foramen, of1. Dorsal to these parts the ilium has a partly separated
portion, i2, which forms part of the wall of a cavity apparently repre-
senting the acetabulum of the "posterior" limb. Dorsal to this a
complete ischium arises which bears a normal ischial tuberosity and
curves round a second smaller obturator foramen, of2.

In so far as the foregoing description involves conceptions of
homology it is merely suggestive, but the structure of the innomi-
nate bone leaves little doubt that the nature of the parts is much as
here described. Nevertheless the appearance of the digits 5 and 6
and of the tarsal bones c3 to c6 somewhat suggests that there is a
symmetry about an axis passing between the digits 5 and 6 ; but
if 5 were a minimus and if 6 were fashioned as an index, which it
is, the appearance of a relation of images would to some extent
exist in any case. This appearance is however confined to the
dorsal aspect of the foot and is not present on the plantar aspect.

This case, if the view of it proposed be true, differs from other
examples of double-hand (e.g. Nos. 491 to 499) in that the Repe-
tition is Successive and is not a Repetition of images ; for the
digits stand I, II, III, IV, V, II, III, IV, V, and not V, IV, III, II,
[I], II, III, IV, V as in those other cases. In this respect it is so
far as I know unique.

Those who have treated the subject of double-hand generally make reference
to the following records. Kueff, De conceptu, Frankfurt, 1587, PI. 41 ; Aldro-
vandi, Monstr. Hist., 1642, p. 495 ; Kerckrixg, Obs. anat., Amst. 1670, Obs. xx.
PL, but the descriptions are scarcely such as to be useful for our purpose. A case
quoted by Dwight, Mem. Bost. Soc.of N. H., iv. No. x. p 474, from du Cauroi, Jour.
des Scavans, 161)6, pub. 1697, p. 81 [originally quoted by Mor.vxd and misquoted by
many subsequent authors], is probably not an example of double-hand (see No. 522).

Cases of Polydactylism in Man and Apes not associated with

definite change of Symmetry.

From the evidence as to polydactylism in general the foregoing
cases have been taken out and placed in association as exhibiting
the development of a new system of Symmetry in the limb. It
will have been noticed that in all of them the external (ulnar or
fibular) parts of the limb remain unchanged, and the parts not
represented in the normal are on the internal (radial or tibial)
sides. In the remaining cases of polydactylism, which constitute
the great majority, there is no manifest change in the general
symmetry of the limb.

chap, xiil] DIGITS : MAN. 345

These general phenomena of polydactylism have been observed
from the earliest times and the literature relating to the subject
is of great extent. Most cases known up to 1869 [not including
Struthers' cases] were collected by Fort, Difformites des Doigts,
Paris, 1869, and independently by Grubeu, Bull. Ac. Sci. Pet,
xv. 1871, p. 352 and p. 460, and good collections of references have
subsequently been published, especially by Fackexheim. Jen.
Zeits., XXII. p. 343. Of the whole number of cases the majority
fall into a few types, and a great part of the evidence may thus be
easily summarized and illustrated by specimen-cases. The forms
of polydactylism thus constantly recurring may be dealt with
conveniently under the following heads.

(1) Addition of a single digit, complete or incomplete.

A. external to minimus, in series with the other digits.

B. in other positions.

(2) Duplication of single digits, especially of the pollex and

hallux.

(3) Combinations of the foregoing.

Besides these are a certain number of cases not included in
the above descriptions, and of them an account will be given under
the heading

(4) Irregular examples.

As bearing upon the frequency of the several forms of poly-
dactylism it may be stated that in this irregular group are
included all cases which I have met with that exhibit any feature
of importance in departure from the cases otherwise cited. For
the purpose of this list I have examined every record of polydactyl-
ism to which access could be obtained.

(1) A. Single extra digit external to minimus in hand or foot.

(a) Incomplete form.

This is one of the commonest forms of extra digit. In the great
majority of such cases the extra digit is not complete from the carpus
or tarsus but arises from the metacarpal or metatarsal, less often from
one of the phalanges, of the minimus. The attachment may be either
by a direct articulation upon the side of one of these bones, or they may
give off a branch bearing the extra digit. In a not uncommon form
of the variation the extra digit has no bony attachment to the hand,
but is a rudimentary structure hanging from some part of the minimus
by a peduncle. Of these several forms the following are illustrative
cases.

-A' Extra digit hanging from minimus hi/ a peduncle.

Nanus. Annandale", Diseases of Fingers and Toes, 1865, p. 30, PI. n. fig. 20;
Tarnier, Bull. Soc. de Chir., Paris, vi., 1866, p. 487; and numerous other examples.
Pes. Bcsch, quoted by Grcber, I.e., p. 470: this form in the pes is rare.

346

MERISTIC VARIATION.

[part I.

506. Extra digit arising from one of the phalanges of minimus.

Axxandale, I.e. ; Otto, Monstr. sexc. Descr., Taf. xxv. fig. 7; Cramer, Wochens.
f. d. ges. Heilkunde, 1834, No. 51, p. 809; Gaillard, Gaz. med,, 1862. This form
seems to be comparatively scarce.

507. Extra digit arising from metacarpus or metatarsus of minimus.

The great majority of cases are of this nature but exhibit many differences of
degree. The articulation may be on the side of the metacarpus V (see Morand.
Mem. Ac. Sci. Paris, 1770, p. 142, fig. 4; Coll. Surg. Mus., Catal, Teratol. Ser.',
1872, No. 308, and numerous other cases), or of the metatarsus V (see Grurer, I. c
p. 476, Note 28) but in the pes this is less common. Frequently also the articulation
of the extra digit is on the head of the metacarpus V (Gaillard, I. c.) or metatarsus
V (Mus. Coll. Surg., Terat. Ser., No. 310).

In the foregoing cases the extra digit articulates immediately with the side or
head of metacarpal or metatarsal, but sometimes in the manus and often in the pes
the digit articulates at the end of a branch given off by the metacarpus (Morand.
ibid., fig. 3, and numerous other records), or by the metatarsus (Morand, /. c;
Struthers, Edin. New Phil. Jour., 1863 (2), p. 89; Meckel, J. F., Handb. d. path.
Anat., ii. Abth. 1, p. 36, and many more.
5 OS Hylobates leuciscus (Fig. 99) having an extra digit in the left manus arti-

culating externally with the metacarpus V and in the right manus articulating with
a branch from it. Mus. Coll. Surg., Teratol. Ser., No. 307, A.

Fig. 99. Hylobates leuciscus, No. 508, minimus of right and left manus bearing
a supernumerary digit articulating with the metacarpals.

(From specimen in Coll. Surg. Mus.)

(b) Complete digit having metacarpus or metatarsus external

to minimus.

Extra digits external to the minimus are occasionally complete,
having a metacarpal or metatarsal and three phalanges, standing
truly in series with the other digits, but to judge from the records
this complete form is decidedly rare. In the first of the following
examples given it should be noted that the digit standing fifth,

CHAP. XIII.]

DIGITS : MAX.

34;

that is to say, as minimus, was itself rather longer than it should
be in the normal, thus illustrating the principle with regard to the.
Variation of a small terminal member of a Meristic Series on
becoming penultimate which was predicated especially in regard
to Teeth (see p. 272). In Morand's case the interesting feet of th<
partial assumption by the sixth digit of anatomical characters
proper to the minimus is commended to the attention of the
reader.

*i

.09.

*r

510.

Girl : one extra digit on the external side of each hand. The
normal little fingers are rather longer than usual and the extra lingers
have nearly the same length. Each has three phalanges. Neither of
the extra fingers can be moved separately from the finger adjacent to
it. In the left hand the extra finger is borne on a supernumerary meta-
carpal which lies parallel with the normal metacarpal V. Each extra
digit can be opposed to the pollex. In the right hand the extra finger
is borne on the enlarged head of the fifth metacarpal. Beraxger, Bull.
Soc. d>A?ithrop., Paris, 1887, Ser. 3, x. p. 600.

Man (parents normal, one brother had six digits on each extremity,
six other members of family normal) having an extra digit external to
minimus on both hands (Fig. 100) and both feet, in series with the
normal digits.

Left hand: unciform abnormally large, having two articular facets,
one for the metacarpal of the fifth and the other for that of the sixth
digit. The sixth metacarpal bears a digit of three phalanges of which
the second and third were very short. [It does not appear that V was
of increased length.] Bight hand : metacarpals normal in number, but
the fifth is very thick, having in its peripheral third on the external

R L

Fig. 100. Palmar views of the bones of the hands of No. 510.

(After Otto and Mokand.)

348 M ERISTIC VARIATION. [part i

surface an articulation for a short digit of three phalanges, the second
and third being very small. Feet : well formed ; cuboid of size greater
than the normal, bearing the proximal end of two united fifth and sixth
metatarsals. Each of these is separate peripherally and bears a digit
[of 3 phalanges to judge from the figure (fig. 6)] in series with the
normal toes, but shorter than the minimus.

Muscles. In the left hand the sixth digit was fully supplied with
muscles. There were two extra interossei and the extensor communis
sent tendons to the sixth digit. The abductor, the flexor brevis and
the flexor ossis metacarpi which in the normal are proper to the minimus
were all inserted into the sixth digit instead.

In the right hand the extensor communis gave a tendon to the sixth,
which also possessed a proper abductor, but the fifth had no special
extensor. Of the flexors the sublimis gave a tendon to each of the
digits index, medius and annularis, none to the fifth, but a small slip
to the sixth. The flexor profundus gave four tendons as usual, but
from that going to the fifth a small tendon passes off laterally and
piercing the sublimis is inserted as usual.

In both feet the muscles were similar. The extensor longus gave a

tendon to the sixth digit, and the extensor brevis does not. The flexor

longus has four tendons as usual, none going to the sixth digit ; the

flexor brevis has four normal tendons and an extra one for the sixth.

The two tendons proper to the fifth (minimus) go to the sixth. The

interossei are normal and there are only two lumbricales, one for the

second digit and one for the fourth. Morand1, Mem. de V Acad. Roy.

des Sci., Paris, 1770, p. 142, Figs. 1, 2, 4, 5 and 6. [The condition of

the muscles in regard to the fifth and sixth digits in this case is worthy

of special attention. If the morphologist will here propose to himself

the question which is the extra digit, he will find it unanswerable. In

the right hand, judging from the bones, it may seem evident that the

fifth with its complete metacarpal is the minimus and that the sixth is

a new structure ; but the condition of the feet and the right hand taken

with that of the left, make a series or progression from which the

similarity of the variation in each of the three states is evident; hence,

if it is thought that the most external digit in the right hand is the

extra part, it must also be held that the external or sixth digit in the

left hand is the extra digit. But this digit in respect of its muscles has

some of the points of structure peculiar to a minimus, while the fifth

digit or supposed minimus on the contrary is without these characters.

Hence neither digit is the minimus. Just as in the Condition III (see

p. 326) of the hand, we saw that on the presence of a digit internal to the

pollex, the pollex itself may be promoted to be a fingerdike digit with

three phalanges, so may the fifth digit be partially fashioned as a more

1 The .similar descriptions and figures given by Otto, I.e., PI. xxv. figs. 9 — 11,
Seerig, Vb. angeb. Verwachs. d. Finger u. Zelien, Ammon, Die angeb. Kr. d. Mensch.,
all refer, I believe, to this one original case of Morand's, though the fact is not
stated and though several authors (Gruber, &c.) quote thern as separate cases.
Seerig states that his figures are from preparations in the Breslau Museum. These
figures agree exactly with those of Otto, which again agree closely with those of
Morand but give more detail as to the carpi, taken no doubt from the actual
specimens which had been acquired by the Breslau collection. I have therefore
copied Otto's figures, though taking the important descriptions from Morand.

chap. XIII.] DOUBLE-THUMBS : MAX. 349

central digit on the presence of a digit external to it. If therefore it

be still called the "minimus" this term can only be applied to it by
virtue of its ordinal position. '

For other cases of complete digits in this position see Auvard, Arch, de Tocologie
xv. 1888, p. 633; Marsh, Lancet, 1889 (2), p. 739.

(1) B. Single extra digit in other positions.

Apart from cases of extra digit external to the minimus, cases of duplication of
the pollex or hallux (to be considered below), and cases of extra digits internal to
the pollex or hallux associated with change of symmetry of the digital Beries, the
remaining cases of single extra digit are very few. In other words, it is with digits
as with Meristic series in general, when a new member is added, the addition taking
place in such a way that homologies may be recognized, it is most often at on*
the ends of the series that the addition is made. Cases of extra digits in other
positions are in Man and Apes very rare, and even in some of the few recorded <
of a new digit arising on the inner side of the minimus (No. 511) it should be re-
membered that this inner digit is judged to be the extra one rather than the outer
mainly by reason of its smaller size. I can only give particulars of few such cases,
and of the remainder no details are available.

*511. Simia satyrus (Orang-utan), having a rudimentary extra digit arising from the
internal side of the minimus of each hand: feet normal. In the left manus the
minimus has all joints moveable as usual ; the first phalanx is normal, but the
second is bent outwards nearly at right angles, thus making room for an extra digit
arising from the first phalanx and directed inwards. This digit is fixed and has no
articulation and no nail, but it is in its outer part bent back again towards the
minimus with which it is webbed. The structure in the right manus is almost the
same but the extra digit is larger and in its outer part free from the minimus,
bearing a nail. Bolau, Verh. naturw. Ver. Hamburg, 1879, N. P. in. p. 119.
512. Woman: left pes bearing an extra digit articulating by an imperfect metatarsal
with outside of metatarsal of IV. The extra digit stands obliquely to the others,
sloping outwards and being attached by ligaments to the normal V. [The Cata-
logue states that the extra digit resembles a right digit, but I see no sufficient
evidence of this.] C. S. M., Ter. Cat. 312.

[A case perhaps similar to foregoing is briefly quoted by Gruber, I.e., p. 471,
note 83, as being in the Vienna Museum of Anatomy.]

512(2. Child: left metacarpal IV bore a supernumerary digit on external side. This
digit was shorter than the digit IV and was completely webbed to it. Broca,

*ki «)7 <luoted hJ Tort, I.e., p. 66.

' DiZb. Foetus (otherwise abnormal) : left hand bore extra digit attached by peduncle to
first phalanx of digit IV. The minimus was separated from IV by a metacarpal
space, standing almost at right angles to it. Hennig, Sitzb. naturf. Qes. Leipzig,
1888. Oct. 9.

[Ammon (Die angeb. Krankh. d. Hensch. p. 101, PI. xxn. fig. 7) describes a
rudimentary finger appended to the "ring-finger" and is so quoted by * rBUBl a; but
the figure apparently represents the appendage as attached to the minimus.]

(2) Duplication1 of single Digits, especially of the Pollex and Hollas.

*513. Duplication of the pollex or of the hallux is one of the commonest
forms of polydactylism and numerous cases have been described by all
who have dealt with the subject. It consists in the development of
two digits, complete or incomplete, in the position of the usually single
series of bones composing the pollex (or hallux). In the section dealing
with polydactylism associated with change of Symmetry (p. 326 we
saw how upon the appearance of an extra digit in this position the
thumb itself may have three phalanges. In these cases the extra digit
may properly be considered as arising in Successive Series with the

1 A few cases are thought by some to shew triplication of digits, but i:
doubtful whether there is a case of division of one digit into three really equivalent

digits, perhaps excepting the thumb of No. 521.

350 MEMSTIC VARIATION. [part i.

pollex. But in a large majority of cases of the presence of an extra
digit on the radial side, the thumb has two phalanges as usual. Upon
a review of the evidence it is I think clear that we shall be right in
considering that in most of these cases the extra digit is not really in
Succession to the thumb, but that the two radial digits together repre-
sent the thumb, the increase in number being achieved by duplication
and not by successive addition.

Most authors (Gruber, etc.) thus speak of these formations as
"double-thumbs" and recognize them as examples of duplicity, but it
should be remembered that this view of their nature is not consistent
with any statement that either of the two digits is the extra one. If
these thumbs are instances of duplicity then both together represent
the normally single thumb.

In clear cases of double-thumb the two thumbs are equal or nearly
equal in size and development, as commonly happens in cases of true
duplicity. Double-thumbs are known in every degree of completeness.
The division between the two may occur at any point in their length.
Thus the duplicity may be confined to the nail and first phalanx
(Otto, Monstr. sexc. Descrip., Taf. xxv. fig. 1 ; Birnbaum, Monatsschr.
f. Geburtsk., 1860, xvi. p. 467); or it may include both first and second
phalanges (Gruber, Arch. f. path. Anat. Phys.x xxxn. 1865, p. 223); or
both phalanges and the greater part of the metacarpal (Gaillard,
Mem. Soc. de biol., 1861, p. 325); or even the whole digit and meta-
carpus, the two thumbs separately articulating with the trapezium
(Joseph, quoted by Gruber, I. c, p. 463, Note 37). It would be
interesting to know which of these conditions is the most frequent, for
it is likely that between the degrees of this variation there is Dis-
continuity, but the point is not easy to determine. As regards records
the conditions first and last named are much the rarest, and the double-
thumbs with two sets of phalanges articulating with one metacarpal
constitute the majority of cases.

Sometimes the two thumbs are webbed together (Gruber, Bull. Ac.
Sci. Pet. xv. p. 480, fig.) sometimes they are separate and may be

Fig. 101. Eight hand having a thumb double from the metacarpus, shewing the
relationship of images between the- two thumbs. (After Annandale.)

CHAP. XIII.]

DOUBLE-THUMBS : MAN.

351

opposed to each other (Fackenheim, Jen. Zts., xxn. p. 358, fi". IV. ■
Axnandale, Diseases of Fingers and Toes, PI. in. fig. 25). This con-
dition is important as an indication that between these double-thumb-
there may be a relation of images (Fig. 101).

The duplicity may be and often is very different in decree in the
two hands, though it is very commonly present in both.

514. The description given of duplicity in the pollex applies equally to
the hallux, though of duplicity in the latter perhaps fewer cases are re-
corded. Here too the duplicity may be in all degrees of completeness.
An example from Anxandale (I. c, PL in. fig. 32) is shewn in Fig. 102.

Fig. 102. Feet of infant, No. 514, having thumb-like supernumerary digits
arising from the metatarsi of the great toes.

(After Annandale.)

Here a thumb-like extra hallux is borne on the inner side of the meta-
tarsal I. Several such cases are known (cp. No. 517).

5X5. Among the cases called by authors "double-thumb" are a certain
number in which the two thumbs are not equally developed, that on
the radial side being more rudimentary. In such a case we are entitled
to consider the radial thumb as an extra digit formed in Succession to
the normal thumb, and not as a double of it. In speaking of other
Meristic Series (especially mammae and teeth) we have seen that it is
not possible accurately to distinguish between cases of duplicity and
cases of change in number of the series by formation of another
member in the Succession. This is extremely well seen in digits. For
firstly several conditions intermediate between the two are recorded by
many authors (e.g. a case in which the radial thumb had two phalanges
"ankylosed" together [or rather not completely segmented from each
other]. Gruber, I.e., p. 480; cases in which the radial thumb had
only one phalanx, ibid., p. 482; Strutiiers, Edin. New Phil. J-->>r.,
1863 (2), p. 87; Boulian, Rec. de Mem. de Mid. milit., 1865, Ser. 3,
xiii. p. 67, jigs.); and besides this there are several examples in which
one hand bore a clear pair of double-thumbs, while in the other hand
there is an extra radial digit in succession to the normal thumb (e.g.

352 MERISTIC VARIATION. [part i.

Fackexheim, I.e., p. 359, fig. iv.). Thus do the two conditions pass
into each other, though some cases are clearly cases of duplicity and
some are clearly cases of extra digit in Succession1,

I know no case of unmistakeable duplicity in any digit but pollex or
hallux ; but no doubt a good many cases of extra digit arising from the
minimus may be of this nature (e.g. Annandale, PI. ill., fig. 28), though
it is more likely that the extra digit is in Succession.

In digits other than I or V the only case of possible duplicity known
to me as occurring in a limb not exhibiting one of the complex conditions
of polydactylism, are those of Streng ( Viertelja.hr sschrift f prakt. Heilk..
xlix. 1856, p. 178; original not seen by me; quoted by Gruber,
p. 476), being a case apparently of double medius on one metacarpal ;
and of Dusseau, Cat. Mus. Vrolik, No. 518, two terminal phalanges on
right medius (together with double thumb ; six fingers on left hand
and peripheral duplicity of hallux in each foot). Accompanied by
numerical Variation in other parts of the digital series such cases
of duplicity are known in a few other cases.

(3) Combinations of the foregoing.

Limbs not rarely present the forms of polydactylism already named
in combination. Such combination may be found in the same limb, or
one or more limbs may present one form, while another form may be
found in the other limb or limbs. Of these combinations the following-
three cases will be sufficient illustration.

Case of double hallux on each foot, and rudimentary digit attached by
peduncle to the minimus of each hand.

516. A female member of a polydactyle family [particulars given] had an abortive
supernumerary finger attached by a peduncle to the little finger of each hand. In
the feet the two great toes were each partially double. In the left great toe the
individual phalanges could be felt and there were two nails. In the great toe
of the right foot the adjacent sets of phalanges were inseparably united by their
lateral borders, forming one bone, which was correspondingly broadened. There
was only one nail which was notched in the middle of its free border. Mum, J.
S., Glasgow Med. Jour., 1884, N. S. xxi. p. 420, Plate.

Case of each extremity with double pollex or hallux and rudimentary
digit attached to minimus.

517. Female infant having thumb of each hand double, the two sets of bones lying in
the same skin and connective tissue. In the right hand the nails and phalanges of
each were quite distinct, but it was not certain whether the metacarpals were
separate or not. In the left hand the nails were not completely separate and the
phalanges of the two thumbs were less distinctly separate. To the first phalanx of
the little finger of each hand was appended a rudimentary bud- like finger, hanging
by a peduncle.

The feet resembled the hands. From the inner border of the metatarsal of each
great toe there proceeded a well-formed thumb-like toe with two phalanges. This
toe was set at right angles to the great toe and could be flexed and to some extent
opposed. On the external border of the right foot there was a small extra little toe
hanging by a peduncle from the metacarpal V. In the left foot the supernumerary
little toe was bound up with the normal little toe for its whole length. Hagenbach,
E., Jahrb.f. Kinderheilk., xiv. 1879, p. 234,^*. [Cp. No. 514.]

1 Compare with the largely similar series of phenomena seen in the foot of the
Dorking fowl (v. infra). But in it if the two hallucal digits are not a true pair it is
most commonly the inner that is the largest, conversely, to the general rule in
the extra digits arising from the pollex in Man.

chap, xiil] IRREGULAR POLYDACTYLISM : MAX. 353

Case of double hallux in combination ivith extra digits on external
side.

518. Man in Middlesex Hospital, 1834, having on the right foot two
toes articulating with the first metatarsal, and ou the left foot two toes
articulating with the first metatarsal, and also two toes articulating
with the fifth metatarsal. From the ulnar side of one of his hands
two fingers had been removed. In each hand the middle and ring
fingers were adherent throughout their length, as also were all the toes,
except the minimi. Five brothers and three out of four sisters of this
man had six toes on each foot and six fingers on each hand. The other
sister had seven toes on one foot and six on the other, and had two extra
fingers on each hand. London Med. Gaz., 1834, April, p. 65, figs.

(4) Irregular examples.

Thus far we have considered cases of polydactylisra that can be in
some degree brought into order and included in general descriptions.
There remain a small number of irregular cases each presenting special
features which make general treatment inapplicable. These cases are
instances of extremities, mostly feet, having seven, eight or nine digit-.
The descriptions of these cases are for the most part fragmentary, and
as the bones have been examined in only one of them (Moraxd) so far
as I am aware, the relations of the digits to each other and to the limb
are obscure. Speaking generally in these irregular examples there is
an appearance of division, possibly of duplication, of several digit-. It
should be noticed also that in some of them (e.g. Blasius, No. 520) the
digits did not lie evenly in one plane but were in a manner bunched up
so as to overlie each other. In such a case it would be interesting
to know whether the digits originally grew in one plane and were
afterwards shifted during growth, or whether the original Repetition
was thus irregular.

As all these cases differ from each other an adequate account of
them could only be given at great length, and by reproducing the
original descriptions in full, together with such figures as are attainable.
For these reasons it would not be profitable to introduce them here,
though in a study of the nature of Meristic Repetition it is important
to remember that these irregular cases exist. As illustrative of several
cases I have appended an account of two complex cases in the foot and
of one in the hand, giving references to such others as I am acquainted
with.

19*. Girl, set. 6, having abnormal toes on the left foot as follows (Fig. 103). The total
number of toes on the left foot was nine. From the position and form it appeared
that the digits (6—9) representing II, III, IV and V were normal, bat upon th<
radial side of these instead of a single hallux there were five toes. ( >f these 1 and 2
were imperfectly separated, articulating with the first metatarsal bj their first
phalanges, which were united to form a common proximal head. Bach had a
distinct second phalanx and in general form resembled a great toe having a separate
nail. The second metacarpal bore firstly a pair of toes, 3 and 4, which were still
less separate from each other than 1 and 2, the biridity being oonfined to the soft
parts. These two toes had one proximal and one distal phalanx in oommon. The
second metatarsal also bore an external digit, 5, which in form ratlin reaembli d a
normal third digit, being considerably shorter than »'• [and presumably oontaining
three phalanges]. The toes 1, 2, 3 and 4 were found alter amputation to be devoid
of muscles and presented onlv the terminations of the tlexor and extensor tendons

b. 23

354 MERISTIC VARIATION. [part i.

having their normal insertions. The toes 1 and 2 were supplied by the same flexor
tendon which bifurcates and passes to be inserted into the ultimate phalanx of each

/ H 0
Fig. 103. Foot of No. 519. (After Athol Johnson.)

by a separate slip. The vinculum by which it is attached is common to the two
bones. Johnson, Athol A., Trans. Path. Soc, ix. 1858, p. 427, fig.

520. Male infant having supernumerary toes on the left foot, The tarsus and meta-
tarsus were abnormally wide. The hallux appeared externally to be divided into
two. This duplicity was most marked in the second phalanx and appeared in a
slight infolding of the skin. The nail also shewed traces of duplicity. Next to the
hallux were two toes which were bent upwards and inwards. Of these the one
overlay the other. The uppermost was found after excision to have two sets of
phalangeal bones enclosed in the same skin ; these two articulated with a single
metatarsal bone. The lower toe was thought by Blasius to represent the digit II.
Next to this there was a rudimentary digit with a slightly developed nail. After
excision it was found that this toe contained a cartilaginous basis which was partly
segmented into two phalanges and articulated with a metatarsal. External to this
rudimentary toe were three normal toes, representing as Blasius supposes, the
digits III, IV and V. External to the putative V was another digit of the same size
and shape. Blasius, v. SiebohVs Jour. f. Geburtsh., xiii. 1834, p. 131, figs. 1 and
2 ; figures copied in Ahlfeld, Jlissb. d. Mensch., Taf. xx. fig. 11. [This foot appears
to contain parts of ten digits.]

521. Child having polydactyle hands as follows. In each hand the fingers were
webbed to the tips, each minimus having an extra nail. In the right hand the
pollex was triplicate, having three sets of phalanges and three nails, the whole being
in a common integument. In the left hand the pollex was duplicate, having two
sets of phalanges webbed together and two nails. Each member thus formed a
prehensile paw. In right foot little toe webbed to next toe. Some (not all) of
brothers and sisters had similar hands : father and grandfather had similar hands :
mother and grandmother normal. Harker, J., Lancet, 1865 (2), p. 389, ^.g.

522. The following are other examples of irregular polydactylism : Morand, Mem.
Ac. Sci. Paris, 1770, p. 139, figs. 8 and 9. (The same redescribed from Morand's
figure by Delplanque, Etudes Teratol., n. Douai, 1869, p. 67, PI. v. ; and again by
Lavocat, Mem. Ac. Sci. Toulouse, v. 1873, p. 281, PI. i., who takes a different view.)

Gruber, Mem. Ac. Sci. Pet., Ser. vn. Tom. n. No. 2 (fig. copied in Bull. Ac. Sci.
Pet., xv. 1871, fig. 6, and by Ahlfeld, Missb. d. Mensch., PI. xx. fig. 20).

Gruber, Bull. Ac. Sci. Pet., xv. 1871, p. 367, figs. 4 and 5.

Otto, I.e., PI. xxvi. figs. 8 — 11.

Froriep, Neue Notizen, d)c., Weimar, No. 67, 1838, iv. p. 8, figs. 4 — 8 (very brief
account of important case, copied by Ahlfeld and others).

Du Cauroi, Jour, des Scavans, 1696 (pub. 1697), p. 81 (quoted first by Morand,
afterwards wrongly quoted by many writers. Dwight, Mem. Bost. N. H. S., iv.

chap, xiil] REDUCTION OF DIGITS : MAX. 355

No. x. p. 474, supposes that this is a case of double-hand, palm to palm (as No. 503),
but the original probably means that two adjacent thumbs and two adjacent annu-
lares were united, the digits being all in one plane).

Popham, Dull. Quart. J. of Med. Sci., xliv. 1867, p. 481.

Dusseau, Cat. JIus. Vrolik, 1865, p. 457 (very brief, see p. 352).

Graxdelemext, Gaz. des hop., 1861, p. 553.

Lisfraxc (see Schm. Jahrb., xn. 1836, p. 263).

Eorberg, Jour. f. Kinderkr., xxxv. 1860, p. 426.

Mabjoltn, Bull. Soc. de Chir., 1866, Ser. 2, vi. p. 505, jig. (probably case of double-
hand).

Annandale, Bis. of Fingers and Toes, 1865, p. 39 (eight metatarsals on a foot
possibly associated with change of Symmetry).

Ibid., p. 35, figs. 41 and 49 (pollex with two sets of phalanges but three nails,
together with extra digit external to V). Cp. No. 521.

Heyxold, Vireh. Arch., 1878, lxxii. p. 502, PL vn.

Mason, F., Trans. Path. Soc., 1879, xxx. p. 583 (foot having eight metatarsals
and nine digits).

Melde, Ft., Anat. Unters. eines Kindes mit beiders. Befekt d. Tibia u. Poly-
dactylic an Hdnden u. Fiisseti, Inaug. Diss., Marburg, 1892 (important).

REDUCTION IN NUMBER OF DIGITS.

Though in reduction of digits the course of Variation is generally
irregular and the result often largely amorphous there are still features
in the evidence which may be of use to us, and a few selected cases are
of some interest. These features will be sjDoken of under the three
following heads, though for a general view of the subject reference
must be made to teratological works.

(1) Reduction in number of phalanges.

( 2 ) Syndactylism.

(3) Ectrodactylism.

(1) Reduction in number of phalanges.

As in certain cases of polydactylism it appeared that increase in the
number of phalanges in the thumb could be regarded as a step in the
direction of increase in the number of digits, so a reduction may be
thought to be a step towards diminution in the number of digits. But
though many cases of reduction in number of phalanges are recorded,
there is in them nothing which suggests that they may be fitted into a
series of gradual reduction comparable with the series of gradual
increase already described. It is indeed chiefly as illustrating the
possible completeness and perfection of Variation that these phenomena
have a direct bearing on the subject of Meristie Variation, The
following case is chosen as being especially regular and symmetrical.

*523. ^an having only one phalanx in each hallux, and two in each of the other
fingers and toes. The hands were almost exactly alike. The thumb had a
short metacarpal fin: long, and one phalanx (11 in.), the joint between them
being loose as if composed of soft tissue. Uy the length of the metacarpal (Sin.)
the index is longer than the other digits. The next two metacarpals have only half
that length. The metacarpal of V is l.lin. long, but from its obliquity does not
project so far as that of IV. The proximal phalanx of the index measnn I , mediae
I:, annularis 1, minimus 1^. The distal phalanx in index and middle |, ring and
little | in. In left hand the distal phalanx of index is proportionally short. r.
Except the index all the dibits present their usual proportions. The feet are well
formed as far as distal ends of metatarsals. The toes are short, pulpy and loosely
articulated. Each has two phalanges except the hallux, which has only cue. This
case was a twin with a normal male. An elder brother and younger sister have the

23—2

356 MERISTIC VARIATION. [part i.

digits similarly formed, but in the last the feet are also turned in. Struthers.
Edin. New Phil. Jour., 1863 (2), p. 100.

As an example of similar and simultaneous Variation in both extremities this is
an instructive case.

(2) Syndactylism.

Under this name have been described those cases in which two
or more digits are to a greater or less extent united together. In
their bearing on the morphology of Repeated Parts some of these
variations are very instructive. It will be found that the impor-
tant considerations in this evidence may be divided into two parts.
Of these the first concerns the manner of the variation and the
second to the position in which it is most commonly found.

The manner of union betiveen digits.

In many cases of union of digits the limb is amorphous ; with
these we have now no special concern. In simpler examples the digits
may be of normal form but some or all of them may be united by a
web of integument for a part or the whole of their length. (For
records of such cases see Fort, Axxaxdale, &c).
*524. But besides these cases of webbing are many in which the union
may be of a much more intimate character. Taking the cases together
a progressive series may be arranged shewing every condition, beginning
from an imperfect webbing together of the proximal phalanges to the
state in which two digits are intimately united even in their bones, and
perhaps even to the condition in which two digits are represented by a
single digit (see No. 529). That the latter condition represents a phase
in this series of variations does not seem to be generally recognized by
those who have dealt with the subject but it is impossible to exclude it.

The lower conditions of this variation are sufficiently illustrated by
Fig. 104, I and II (from Anxaxdale, Diseases of Fingers and Toes,
figs. 39 and 33), shewing cases of medius and annularis partially com-
bined for the whole of their length. A higher condition is shewn in
Fig. 104, III, in which the same digits are united so closely that their
external appearance suggests that only four digits are present in the
hand. In this specimen (Anxaxdale, I. c, p. 14) there were neverthe-
less five metacarpals, but the first phalanges of III and IV were united
peripherally and bore a second and third phalanx and one nail common
to them both. The same author (I. c. fig. 44) gives an illustration of
such a set of bones from Otto 1.

The following cases are interesting as occurring in Apes.

*525. Pithecia satanas (Monkey) : young male having the third and fourth digits of
the hand on each side completely connected by a fold of nude skin. The remain-
ing digits of the hands and feet were normal. Forbes, W. A., P. Z. S., 1882,
p. 442.
526. Macacus cynomologus : specimen having the fifth finger of the right hand
represented by a rudiment only. On dissection the first phalanx of the fifth finger
was found to be enclosed with that of the fourth. All the fingers of the abnormal
(right) hand were somewhat misshapen and bore several exostoses. [? congenital
variation] Fbiedlowsky, A., Verh. zool. hot. Ges. Wien, 1870, xx. p. 1017, Plate.

1 I have failed to find the original of this figure in Otto's works.

CHAP. XIII.]

UNION OF DIGITS : MAN.

357

Before going further certain points are to be noted. First, the
union as shewn in the figures is a union or compounding as of optical

I

D

IV

Fig. 104. Cases of syndactylism. I, II and III. A progressive series illus-
trating degrees in the union of medius and annularis in the hand. IV. Case of
union of index and medius of the foot. The union is incomplete peripherally.

(After Axxandale.)

images in Bilateral Series, and is not like that of parts in Succc»m\ <■
Series. Next, the union of the bones is more complete /» rxphi rally and
less complete centrally. The latter is a rule very commonly observed in
cases of the union of the bones of digits both in Man ami other mam-
mals. This statement is made without prejudice to the other let that
in the least state of syndactylism as manifested by union of the Bofl
parts, it is the most central phalanges which are united. Such a case
of partial union between II and T FT in the foot' is shewn in Pig. 1" 1. I V
(Axnaxdale, /. c, fig. 34). The rule that in the Lowest condition o!
syndactylism of the bones it is commonly at the periphery thai the
union is most complete is also difficult bo understand in connexion with

1 Compare several remarkable cases of this variation in one family, lb Clkbo,
M€m. hoc. Linn. Normandie, ix. p. xxvi.

358 MERISTIC VARIATION. [part i.

the fact that the division of digits in the lowest forms of polydactylism
appears also first in the peripheral phalanges. These phenomena appear
to be in contradiction to each other, and I am not aware that the fact
of the appearance of the digits early in the development of the limb
throws any light on the difficulty.

The number of digits which may be thus united is not limited to
two, and examples of intimate union between three and even four digits
are common.

The position of union.

*527. Those who have treated of this subject do not, so far as I am aware,
notice the fact that the phenomenon of Syndactylism most frequently
affects particular digits. From an examination of the recorded cases
it appears that in the hand there is a considerable preponderance of
cases of union between the digits III and IV. I regret that I have
not material for a good analysis of the evidence on this point, but I
may mention meanwhile that in a collection taken at random of some
thirty-five cases of hands having only two digits united (chiefly those
given by Fort and Annandale) over 25 are cases of union of the digits
III and IV ' ; in only one were the digits I and II united ; the digits
II and III in 1 4 cases ; the digits IV and V in 1 3 cases.

*528. On the other hand if two digits in the foot are united they are
nearly ahvays II and III.

If in the hand three digits are joined they may be either III, IV
and V, or (perhaps less commonly) II, III and IV. In cases of union
of all the digits II to V, the digits III and IV are often much more
intimately united than the others, and are often recorded as having a
common nail, while II and V have separate nails.

This question of the comparative frequency of the different forms of
syndactylism would probably repay full investigation, and to the study
of the mechanics of Division it would clearly be important. In the
meantime may be noted the fact that the evidence suggests the possi-
bility that we have here to do with a case of union of parts which are
related to each other as optical images, and that the digits II to V of
the hand constitute an imperfect Minor Symmetry within themselves.
The fact that the subjects of most frequent union in the foot are the
digits II and III, not the digits III and IV as in the hand, may be
connected with the fact that the hallux stands to the foot in a different
geometrical relation from that which the pollex bears to the hand and
that consequently the axes of Symmetry are different in it.

(3) Absence of digits (Ectrodactylism).

In the conditions already described though the digits are not all
clearly divided from each other yet no one wdiole digit can be supposed
to be absent. Even in the specimen shewn in Fig. 104, II, from the
presence of separate metacarpals III and IV the identity of the several
digits is still easily recognized. These simplest cases however by no
means exhibit all the phenomena. From a large group of cases the
three following are chosen as each illustrating a distinct possibility.

1 Owing to the ambiguity of some records as to the similarity of the condition
in the right and left hands I cannot give exact numbers.

chap, xiil] ONE DIGIT STANDING FOR TWO.

359

Upon the morphological questions arising out of these facts comment
will be made when the whole subject of numerical Variation of digits
is discussed.

*x

529.

Representation of digits II and III of the pes by one digit.

Man having four digits in the right foot as shewn in Fig. 105. The calcaneum.
astragalus, navicular, first (internal) cuneiform and cuboid were normal. The
navicular had on its peripheral surface three facets as usual. The second and third
cuneiforms were completely united to form one bone which bore no traces of its
double nature as shewn in the figure (c2 + c3). The peripheral surfaces of both form
one plane. Taking the four digits in order, the minimus has its normal form and
tarsal relations. The digit next to it has the normal form and relations of a dijnt IV.

n+m

Fig. 105. Bones of the right foot of No. 529. I,
apparently representing index and medius. IV, annularis.

hallux. 11^- III, digit
V, minimus, a, astra-
c3, bone apparently
representing the middle and external cuneiforms. (After Gruber.)

galus. sc, navicular, cb, cuboid, c1, internal cuneiform, c2

*x

530,

Internal to this is a metatarsal of abnormal thickness articulating with the single
bone presumably representing the external and middle cuneiforms. This metatar-
sus presented no trace of duplicity. It bore a digit of three phalanges of more than
normal thickness but otherwise normal. The hallux was normal, having two pha-
langes. Each of the other digits had three phalanges, but the 2nd and 3rd phalai.
of the minimus were ankylosed.

Of the muscles, the transversalis pedis, one of the lumbricales, one of the inter-
ossei dorsales and one of the interossei plantares were absent. The extensor and
flexor longus each had three tendons. [Detailed description of bones and soft parts
given.] Gruber, W., Virch. Arch. f. path. Anat. u. PJn/s., 1869, xi.yii. [p. :>04.

PI. VIII.

Single digit articulating with the cuboid [probably a ease of representation of

digits IV and V by one digit].

Man having four digits on the left foot as follows. The foot is well form
The digits I, II and III are normal and have normal tarsal relations. The fourth
digit has a well-formed metatarsal and three phalanges. The hones are perhaps
rather more robust than those of a normal fifth digit, but the nit tatarsal has the
normal tuberosity at the base strongly developed. This metatarsal articulates with
a cuboid of somewhat reduced size having only onv articular facet on it- peripheral
surface. The other parts were all normal, and even in the muscular BVstem only a
trifling abnormality was found. Parents normal. Stkintiiu.. C. P., Virch. Arch,
f. path. Anat. u. Phys., 1887, cix. p. 347.

360 MEMSTIC VARIATION. [part l

Reduction of digit IV of pes.

'531. [This case is introduced here for comparison with the last.] A left foot having
abnormalities as follows. Calcaneum, astragalus, internal cuneiform normal in size
and shape. The second cuneiform is rather broader than usual, but the surface
which it presents to the internal cuneiform has all the characters of a middle cunei-
form. External to this middle cuneiform is only one large tarsal bone in the distal
row. This bone presents no clear sign of duplicity, but from its form and relations
it appeared that it represented both the cuboid and the ecto-cuneiform. The hallux
and digit II have approximately normal relations. The large cuboid-like bone
bears externally a metatarsal agreeing in shape with a metatarsal V ; and internal
to this the same tarsal bone bears another metatarsal which upon its external side
gives off yet another metatarsal of reduced size. Each of the five metatarsals bore
a digit, but the digits of the minimus and of the slender IV were webbed together.
[Full details given.] Brenner, A., Virch. Arch. f. path. Anat. u. Phys., 1883, xciv.
p. '23, PL ii.

532. Besides these simpler cases there are very many recorded instances of reduction
in number of digits in which the identification of the parts is quite uncertain. From
the point of view of the naturalist it is worthy of remark that even in some of the
cases departing most widely from the normal form the limb though having only
three or perhaps two digits still presents an approach to a symmetry. Examples of
this kind are given by Guyot-Daubes {Rev. d' Anthropoid 1888, xvn. p. 541, figs.)
and by Fotherby (Brit. Med. Jour., 1886 (1), p. 975 figs. ) and many more. Fotherby's
record is interesting as relating to a family among whose members feet bearing only
two opposable claw-like digits of irregular form recurred for five generations. Evi-
dence relating to limbs of this kind is so obscure that it is not possible as yet to make
deductions from it, but there seems to be a general agreement among anatomists
that when two digits only remain one of them has the characters of a minimus.

Reference must be made also to the fact that in cases of absence of radius the
pollex is almost always absent. This seems to be established in very many cases.
The only examples of a pollex present in the absence of a radius known to me are
that of (jruber, Virch. Arch. f. path. Anat. u. Phys. 1865, xxxn. p. 211, and that of
Geissendorfer, Zur Casuistik d. congen. Radiusclefectes, Munch. 1890.

Horse.

Variation in the number of digits in the Horse1 has been
repeatedly observed from the earliest times. The mode of occur-
rence of the change is by no means always the same, but on the
contrary several distinct forms of Variation may be recognized.
On inspection the cases may be divided into two groups.

A. Cases in which the extra digit (or digits) possesses a distinct
metacarpal or metatarsal.

B. Cases in which the large metacarpal or metatarsal (III) gives
articulation to more than one digit.

Besides these I have placed together in a third group (C) two
very remarkable cases which cannot be clearly assigned to either of
the other groups. These instances are of exceptional interest from
the fact that in them is exhibited a condition intermediate between
those of the other two groups. We have seen repeatedly that

1 In the Mule two cases have been recorded, but in the Ass I know no instance
of polydactylism. Describing a polydactyle horse seen on a journey in Rio Grande
von Jhering (Kosjjios, 1884, xiv. p. 99) states that he believes polydactyle horses to
be much more common in S. America than in Europe, and that most persons who
have travelled much in that country have met with cases. Mules between the
jackass and mare are bred in great numbers, but he had heard of no case in a mule.

chap, xiil] digits: horse. 361

Meristic Variation may take place by division of single members
of Series, a phenomenon well seen in the B group ; and we have also
seen many cases of numerical Variation by addition to the Series
associated with a reconstitution, or more strictly a redistribution
of differentiation amongst the members of the series thus newly
constituted ; but here in these rare examples of the C group the
nature of the parts is such that it cannot be predicated that
the change is accomplished by either of these methods exclusively.
From such cases it follows that the two processes are not really
separable, but that they merge into each other. (Compare the
similar facts seen in regard to teeth p. 269, and mammae p. 1.93.)

A. Extra digits borne by distinct metacarpal or

METATARSAL.

The cases in this group may be subdivided as follows :

(1) Two digits, one being formed by the development of the
digit II.

a. Only three metacarpals or metatarsals (II — IV) as

usual. Common form : fore and hind limb.

b. Four metacarpals (? I — IV). Common form : anato-

mically described in fore limb only.

c. Five metacarpals (? I — V). Single case in fore limb.

(2) Tivo digits, one being formed by development of the digit IV.

Rare.

(3) Three digits; the digits II and IV both developed. Rare.

(4) Two digits; the digits II and IV both developed, III

aborted. Rare.

It will appear from the evidence that though the same varia-
tion is often present in the limbs of both sides this is not always
so. The fore and hind limbs also sometimes vary similarly and
simultaneously, but in other cases they do not. Different forms of
numerical Variation are also sometimes found on the two sides,
and not rarely the variation in the fore limb is different from that
in the hind limb.

(1) Two digits, one formed by development of the digit II.

a. Three metacarpals or metatarsals only.

To this division and to the next, (1) b, belong the greal majority
of cases of polydactylism in the Horse. Unfortunately most of the
records have .been made from living animals and contain do
anatomical description: in the absence of such particulars it is
not possible to knowr whether a given case belongs to this division
or to the next, and it thus is impossible to determine the relative
frequency with which the two forms occur.

The following are given as specimen cases.

362

MERISTIC VARIATION.

[part I.

Forefoot

*533. Horse of common breed, having a supernumerary digit on the
inner side of the right fore foot (Fig. 106).

Humerus and radius: no noticeable variation. Ulna a little
more developed than usual ; lower end slightly broken, having
probably reached to lower fourth of radius. The part of the
inferior and external tuberosity of the radius which is usually
supposed to represent the ulna is larger than in the normal form.

Fig. 106. Right fore foot of Horse,
No. 533.

A. The leg seen from in front.

B. The carpal bones enlarged.

M, magnum, sc, scaphoid, u, unci-
form. t'2, trapezoid, t1, supernumerary
bone not found in normal, represent-
ing trapezium. IV, the metacarpal re-
presenting digit IV. Ill and II, meta-
carpals bearing those digits respec-
tively. (After Arloing.)

Carpus consisted of eight bones, instead of seven as usual.
Scaphoid much larger than normal ; lunar, cuneiform and pisiform
normal. In the lower row the magnum and unciform have normal
relations, but in the place of the normally single trapezoid are two
bones, one anterior (f), the other posterior (t1). These together
bear the enlarged inner metacarpal (II). The posterior of these
bones had a short pyramidal process lying beside the inner meta-
carpal. This process was partially constricted off and is regarded by

chap, xiii.] DIGITS : HORSE. 363

Arloing as a representative of the metacarpal I, the carpal portion
of the bone being the trapezium.

The outer metacarpal (IV) was perhaps slightly larger than
usual.

The inner metacarpal (II) was greatly enlarged at its central
end, articulating with the twro bones t1 and t'2, and partly with the
magnum. In its central part this metacarpal was fused with the
large metacarpal (III) and above is united to it by ligamentous
fibres. Belowr it again separates from the large metacarpal and
is enlarged, bearing an additional digit of three phalanges, the
lowest bearing a hoof. [This hoof is not curved towards the large
hoof as in many specimens described, but is convex on both sides,
resembling the hoof of an ass.] The large central metacarpal was
flattened on the side adjacent to the enlarged metacarpal II. The
muscles, nerves and vessels are fully described (q. v.). Arloing.
M. S., Ann. Sci. Nat, ZooL, Ser. V. T. vm. pp. 61 — 67, PL

534. Foal having two toes on each fore foot. The father and mother of
this foal wrere both of the "variete chevaline comtoise." The foal in
question was the only one which this mare dropped and she died two
months afterwards. The foal wTas in nowise abnormal excepting for the
peculiarity of the fore feet. The carpus was normal and the external
metacarpal was rudimentary as usual and ends in a small knob. The
internal metacarpal is thicker than the external one and bears a digit
of three phalanges, the terminal phalanx bearing a small hoof. This
hoof is curved outwards towards the normal hoof. The ligaments and
tendons of the foot did not suffice to keep it stiff, and as the animal
walked, it not only touched the ground with the hoof but also with
the posterior surface of the phalanges. This led to inflammation of
the foot, in consequence of which the foal was killed. CORNEVIN,
Nouveaux cas de didactylie chez le chevcd, Lyons (1882?). [Xote that
this case differs from the last in the fact that the carpus was normal.]

A similar case in the right forefoot is given by Kitt. Dent. Ztsch.
f. Thiermed., 1886, xn. Jahresb., 1884 — 5, p. 57, Jig.

Hind foot.

Among the many accounts of polydactyle horses I know none
which gives an anatomical description of a case of a fully developed
digit II in the hind foot. The following case, indeed, is the only one
known to me in which an}^ facts respecting the condition of the
tarsus of a polydactyle horse have been ascertained. In it, as will be
seen, the digit II was not fully developed.

535. Horse having the metatarsal II enlarged and bearing a rudimentary
' digit (Fig. 107 B and C). In the left hind foot the arrangement was as

shewui in Figs. B and C. The metatarsal II was enlarged an. 1 articulated
with "two united cuneiform bones" [presumably one bone with indica-
tions of duplicity]. Internal to this digit was a " first cuneiform bone,"
but the digit I was not developed. The metatarsal II bore peripherally
a rudiment of a digit as shewn in the figure. The right hind foot was
similar to the left but it is stated that the "three small cuneiform

364

MERISTIC VARIATION.

[part I.

bones'' were serjarate1, as shewn in Fig. 107 C. The fore feet of the
same animal were in the condition described in (1) h. [See No. 537.]

Marsh, 0. C, Am. Jour. Sci., xliii

1892, pp. 340 and 345.

s'l " mr iv

Fig
A.
B.
C.

107. Limb bones of a polydactyle horse.

Left fore foot. No. 537.

Left hind foot. No. 535.

Tarsus of right hind foot from the inside.

three bones placed as
m, magnum.

No. 535.
n, navicular, cb, cuboid. 4, ecto-cuneiform. 1, 2, 3,
cuneiforms, td, trapezoid, tm, trapezium, u, unciform.

I, II, III, IV, numerals affixed to the metacarpals on the hypothesis that these
are their homologies. Cp. Fig. 108, which is lettered on a different hypothesis.

(After Marsh.)

b. Four metacarpals.

This condition is a higher manifestation of the variation seen
in the cases just given. In No. 533 the digit II was developed and
in addition the trapezium had appeared ; in the cases now to be

1 Marsh introduces this case in support of a contention that these variations are
of the nature of Reversion. Upon the same page appears the statement that "in
every specimen examined, where the carpal or tarsal series of bones were preserved
and open to inspection, the extra digits were supported in the usual manner," I. c,
p. 345 : this assertion is hardly in agreement with the previously stated fact that
the metatarsal II is supported by two cuneiform bones. On p. 349 Marsh comments
on the presence of five bones in the distal row of the tarsus, and from the expres-
sions used it is implied that five such bones had been met with in other polydactyle
hind feet. A number of alternative explanations are proposed ; (1) that the five
tarsals correspond "to those of the reptilian foot"; (2) that the first may be a
" sesamoid " ; (3) that the first may be a remnant of the first metatarsal, for such
a rudiment " apparently exists in some fossil horses." With conjectures of this class
morphologists are familiar. Into their several merits it is impossible to inquire, but
it may be mentioned that the real difficulty is not the presence of the cuneiform
marked 1, but the fact that the tarsal element of the digit II seems to have been
double, and that the digits in reality are not supported in the usual manner.

CHAP. XIII.]

DIGITS : HORSE.

3G5

given the digit II is extensively developed and the trapezium
bears a splint bone representing the metacarpal I, like that which
in the normal represents the digit II. This is a phenomenon
illustrating the principle seen in the case of teeth and other parts
in series (see p. 272), namely, increase in the degree of development
of the normally last member of a series correlated with the appear-
ance of a new member beyond it.

Nevertheless the same cases have sometimes been described
(e.g. Gatal. Mus. Coll. Surg.) on a different hypothesis. This is
illustrated by the lettering of Fig. 108. On this other view
the innermost carpal is considered to be the trapezoid and its
splint-bone is regarded as the original metacarpal II. The second
digit, ac, and its tarsal bone are supposed to be " accessory ': or
"intercalated." To these terms it is difficult to attach any
definite meaning. The proposal that some digits are to be
reckoned in estimating homologies and that others are to be
omitted is arbitrary, and, if allowed, would make nomenclature
dependent on personal choice. It is, as has been often pointed
out in foregoing chapters, simpler to number the parts in order as
they occur and to accept the visible phenomena as the safest index
of the methods and possibilities of Variation. Nevertheless, to
illustrate the point at issue I have introduced two cases of the
same Variation, the one, No. 536, lettered on the view advocated
by the Catalogue of the College of Surgeons, &c, the other, Xo. 537.

108.

Eight fore foot of Horse No.

530 from

acta

Fig.
behind. The upper surfaces of the carpal bones of the
distal row are separately shewn above. Specimen in
Coll. Surg. Mus., Ter. Cat., 304.

T, trapezoid, if, magnum. U, unciform. <u\ ac-
cessory carpal bone. II, III, IV, metacarpals, ocm,
accessory metacarpal.

This figure is lettered to illustrate the hypothi
adopted in the Catalogue, which is alternative to that
adopted in Fig. 107, A.

366 MEMSTIC VARIATION. [part i.

lettered on the other and in the case of polydactyle horses, more
usual method.
'536. Horse: right manus with extra digit (Fig. 108). The distal
row of the carpus is present. It consists of four bones, the unci-
form, magnum and two other bones. Of these that lettered T
on the view of the Catalogue must be supposed to be the normal
trapezoid, while ac is considered to be an intercalated bone, perhaps
an additional os magnum. The unciform bears a splint-bone,
namely mcp. IV. The magnum bears a fully-formed mcp. and
digit III. With the bone ac articulates a large and substantial
metacarpal with a digit of three phalanges and a hoof, while the
bone T bears another splint-bone, marked II in the figure on the
hypothesis that the digit ac is not to be reckoned. Cat. Mus. Coll.
Surg., Terat. Series, 1872, No. 304. As mentioned above, it would
be more consistent with fact to count the bone ac as trapezoid with
mcp. II and the bone T as trapezium with mcp. I.

.537. Horse having both fore feet (Fig. 107, A) as in the last case, the
hind feet bein^ in the condition described in the last Section, No. 535.
Marsh, Am. Jour. Sci., xliii. 1892, p. 3-40, Jigs. 3, 6, and 8.

538. Foal having right manus closely resembling the above, the other
limbs being unknown. The mcp. I was longer than the normal mcp.
II. In this case the metacarpal II was partially united to mcp. Ill at
the central end but was free from it peripherally. vVehenkel, J. M.,
La Polydactylie chez les Solipedes, from the Journal de la soc. r. des
sci. med. et nat. de Bruxelles, 1872, Jig. 2.

Probably the feet of a large number of polydactyle horses would be
found to be in this condition if examined. Marsh, I.e., mentions three
other cases known to him in Yale Museum.

c. Five metacarpals.

539. Horse having Jive metacarpals and one supernumerary digit in
the left manus, and four metacarpals with a similar supernumerary
digit in the right manus.

In the left manus with the trapezoid there articulated a well-
developed metacarpal II bearing the extra digit. Internal to this
was a trapezium bearing a splint-bone, 6 cm. long, 1'5 wide at
proximal end, representing metacarpal I [as in Section (1) b]
coalescing peripherally with III. On the external side of III the
splint-bone IV was present as usual. The case is remarkable from
the fact that external to the metacarpal IV there was another
rudimentary metacarpal, presumably representing V. This bone
was distinctly separated from IV at the central end, but was for
the most part united with it. Putz, Deut. Ztschr. f. Thierm., 1889,
XV. p. 224, figs. [The figures illustrating this paper are
carefully drawn. The representation of mcp. I is quite clear, but
the condition of the mcp. V cannot be well seen, as the whole foot
is represented with its ligaments, &c, which partly conceal the
structure. The whole account is very minute and gives confidence
in the statements.]

KKf

CHAP. XIII.]

DIGITS : HORSE.

367

*

The right manus of the same animal came into the possession
of the University of Graz and was described independently. In it
also the metacarpal II was developed and bore a well-formed digit.
There was also a rudimentary metacarpal I beside it, having a
length of 5 '7 cm., and a breadth of 1*5 cm. at the central end. [The
description is brief and makes no mention of a mcp. V : further
account promised.] Mojsisovics, Anal Anz., 1889, IV. p. 255.

(2) Two digits, one being formed by development of the digit IV.

Cases of this variation are ex-
ceedingly rare. No. 540 is the only
instance known to me in which a
proper account exists. Most writers
on the subject make a general state-
ment that such cases exist, but give
no references.
540. Horse, having a supernumerary
digit on the outside of each fore foot.
(Fig. 109.) The animal was from
Bagdad. The outer rudimentary
metacarpal (IV) was well formed and
of nearly even thickness throughout
its length. It bore a digit of three
phalanges and a well- formed hoof.
The hoof was elongated and is de-
scribed as being shaped like the hoof
of a cloven-footed animal. [The de-
scription is very imperfect, but two
good figures are given, from which
it may be gathered that the inner
metacarpal (II) was somewhat more
developed than in an ordinary horse;
and it appears that both the inner

and outer metacarpals were separate

throughout their course, but whether

they could be detached from the

large metacarpal or were ankylosed

with it is not stated. The carpal

bones are not described, but the

figure suggests that the unciform

was larger than it normally is. It

is not stated that the two feet were

alike in details. The large hoof

(III) is represented as of the normal

shape.] Wood - Mason, J., Proc.

Asiat. Soc. Bengal, 1871, p. 18, Plate.

Fig. 100. Right fore foot of Horse, No. 640, the ,.rtu->ci! metacarpal (IV
being developed, bearing a digit.

(After V\'<>"I»-Mason.)

Ill

368 MERISTIC VARIATION. [part i.

Wehenkel, I. c, p. 15, mentions a similar specimen in the Museum of the
Veterinary School at Berlin described by Gurlt, Mag. f. gesam. Thierh., 1870, p.
297 [not seen, W. B.].

(3) Three digits [1 the digits II and IV being both developed].

Examples of this variation are alluded to by many authors but I
know of no anatomical description. The following are all very im-
perfectly described.

541. Foal (foetus): left manus having three sub-equal digits; right
manus two digits and rudiments of a third more developed than usual.
Hind feet normal. Geoffroy St Hilaire, Ann. Sci. Nat., xi. 1827,
p. 224.

Similar case, Bredin, Froriep,s Notizen, xvm. p. 202.

542. Horse from Texas, having extra digit on inside of each manus,
and an extra digit both on the outside and on the inside of each pes
[external view only]. Marsh, Am. Jour. Sci., xliii. 1892, p. 344,

fig- ~-

543. Horse with both splint-bones bearing digits in each foot. Franck,
Handb. d. Anat., Stuttg., 1883, p. 228.

(4) Two digits ; the digits II and IV both developed, III aborted wholly or in
part.

Mention of these cases must be made in illustration of the possibilities of
Meristic Variation, but the parts were in all three instances so misshapen that the
animals could not have walked.

544. Foal having two toes on each foot, the developed toes belonging to the metacar-
pals and metatarsals II and IV, while the normally large III was not developed at
all in the fore feet and was in the hind feet represented by a wedge of bone only.

Hind feet. Left. Bones of leg and tarsus said to have been normal. Metatarsal
III represented by a wedge of bone fixed between the greatly developed metatarsals

II and IV. The wedge-like bone 5 cm. wide at upper end, having usual tarsal rela-
tions. Its length about the same as its width. Laterally it is united to the
metatarsals II and IV which curved round it till they met, and then curve away
from each other again. Each was about 20 cm. long and bears a misshapen digit
consisting of a proximal phalanx and a hoof-bearing distal phalanx. A small
nodule of bone attached to the proximal phalanx may or may not represent part of
a middle phalanx. Bight. Very similar to left, but the wedge-like III was rather
broader — [for details see original].

Fore feet. More misshapen and less symmetrical than hind feet : metacarpal

III not developed at all. The metacarpals II and IV curved towards each other and
crossed, giving an unnatural appearance to the feet. Eight foot. Cuneiform and lunar
united, and upon the surface of the bone formed by their union there was a groove
occupied by two parts of the tendon of the anterior extensor metacarpi passing to
mcp. II and IV respectively. Pisiform and scaphoid normal [this is not clear from
the figure]. Magnum absent. Unciform and trapezoid abnormal only in respect
of their relations, for whereas they should articulate with the magnum they do not
do so, for both magnum and mcp. Ill are not represented. Metacarpal II was
11 cm. long, mcp. IV being 19 cm. long. Each bore a digit with a hoof; the digit

IV having a proximal and a distal phalanx connected by a fibrous cord instead of a
middle phalanx. The digit II had a rudimentary distal phalanx only. Left foot
like the right, but with the mcp. and digit II more fully developed. [Muscles fully
described. It may perhaps be thought that there is not sufficient proof that the
developed digits are actually those normally represented by the splint-bones II and
IV, but the condition of the hind feet is practically conclusive that this is the right
interpretation.] Wehenkel, La Poly dacty lie chez les Solipedes, from J. de la soc. r.
des sci. vied, de Bruxelles, 1872, Plate.

545. Foal, in which the right anterior leg possessed two metacarpals and digits.

The radius, ulna and proximal series of carpal bones were normal. In the
distal series only two bones were present, viz., an inner bone corresponding to the
trapezoid, and a magnum. There was no separate bone corresponding to the

CHAP. XIII.]

DIVISION OF DIGIT I HORSE.

369

546.

unciform, but in its stead, the head of the outer metacarpal was continued upwards
to articulate with the cuneiform. Between the heads of the two metacarpals was
an irregularly quadrate bone which articulated with the magnum in the place where
the large metacarpal (III) should be. This bone however only extended a little
way, articulating at its outer end with a notch in the external metacarpal. [This i-
the author's view, but the figure strongly suggests that this quadrate bone may have
been originally in connexion with the external metacarpal and that it may have been
separated from it by fracture. If this were so, the large metacarpal would then not
be represented by a separate bone at all.] The outer metacarpal distally bore three
phalanges of irregular shape, flexed backwards and outwards. The inner metacarpal
articulated solely with the trapezoid. Peripherally it bore a callosity which was
due to the healing of a fracture. The phalanges of the inner metacarpal were three,
but the first was reduced in length, while the second was elongated and bent in a
sinuous manner. The ungual phalanx of this toe was cleft. [The author
regards this case as analogous to the foregoing one, No. 544, that is to say, as an
instance of development of the normally rudimentary lateral metacarpals to the
exclusion of the large one (III), and he considers therefore that the large metacarpal
(III) is only represented by the quadrate ossification which lay between the two
developed metacarpals.] Ercolani, G. B., Mem. della Ace. Sci. d. Istituto di
Bologna, S. 4, T. in. 1881, p. 760, Tav. i.fig. 11.

Foal in which the feet were all very abnormal. In the two fore feet the meta-
carpal of the normal toe (III) was very little developed, being however somewhat
larger on the left side than it was on the right. It bore no digit. The external
metacarpal bone (IV) of each fore foot attained a considerable length and bore a
small hoof-bone. In the left fore foot the inner metacarpal was present but reduced ;
in the right foot it was absent. Bight hind foot also had the external metacarpal
developed and bearing three small phalanges, but the central metacarpal (III) was
fairly developed, bearing however only two phalanges. Left liind foot was amor-
phous. Boas, J. E. V., Deut. Ztschr. f Thiermedecin, vn. pp. 271 — 275. [For full
description, measurements and figures see original.]

B. Cases in which metacarpal III gives articulation to

MORE THAN ONE DIGIT.

These cases are clear examples of the representation of a Bingle
digit by two. It will be seen besides that the
two resulting digits may stand to each other
in the relation of optical images (see Fig. 110)
and do not form a Successive Series, thus
following the common method of division of
structures possessing the property of Bilateral
Symmetry in some degree (cp. p. 77). All
cases of this variation known to me occurred
in the fore limb.

*z

o47.

Foal: a right fore foot figured from a specimen
in the collection of the Veterinary School of
Copenhagen (Fig. 110) has two complete digits
articulating with a single normal metacarpal bone.
The two digits are symmetrically developed ; each
consists of three phalanges and bears a hoof.
These two hoofs are well formed and curve to-
wards each other like those of Artiodactyles.
Boas, J. E. V., Deut. Ztschr. f. Thiermedecin,
vii., p. 277, Taf. xi.,jiy. 9.
548. Two fore feet of a foal, each being Irregularly
and unequally bifid. Boas, ibid., jigs. 7 and ^.

B.

t.rt

inf

Fio. IK'. Bight
for.' foot of Bora No.
547.

Mcp, peripheral
cml of metacarpal III.
est, external side. int.
internal Bide

i After Boas.)

24

370

MERISTIC VARIATION.

[part I.

549.

Filly, two-year old, which had been born with left fore foot cleft
like that of the Ox. Each of the two toes had three phalanges, which
were completely separate as far up as the metacarpophalangeal joint.
The division externally was carried to the same extent as in the Ox.
The lower end of the great metacarpal III felt as if bifurcated like
that of the Ox, so as to give separate articular support to the two toes.
Upper parts normal. The lesser metacarpals, II and IV, felt through
skin, seemed to terminate rather lower down in left foot than in right,
but this was uncertain. Animal examined alive. No attempt at

shoeing had been made, and hoofs

*

550.

having become elongated forwards

larger

was much larger or
New Phil. Jour..

had had their points sawn off. The whole foot
more spread than the other. Struthers, J., Edin
1863, pp. 279 and 280.

Horse: right fore foot having phalanges bifid (Fig. 111). The limb
was normal as far as the distal end of the metatarsal, except for some
exostoses. The proximal phalanx was short and
of great width; in its lower third it divided into
two divergent parts, the divergence being more
marked on the posterior face than on the anterior.
Each of these diverging processes bears a complete
second and third phalanx. The third phalanges
each bear hoofs, which are convex on the outer
sides but lit together on the opposed surfaces, the
external hoof being slightly concave on its inner
face, while the internal is slightly convex. On
the plantar surface, each toe bore a half -frog.
The two large sesamoids, normally present in the
Horse, are in this specimen united along their
inner borders to form a single bone, which was
placed behind the upper part of the proximal
phalanx. Two small sesamoids lay behind the
third phalanx. A good deal of exostosis had
taken place in all the phalangeal bones. Arloing,
M. S., Ann, Sci. Nat., Ser. V., Tome vin. pp.
67—69, PI.

551.

Mb

Sla

Fig. 111. Right
fore foot of Horse No.
550, from in front.

sc, scaphoid, tp,

552.

Foal : in right fore foot the large metacarpal divided
into two parts, each bearing a separate digit. The proximal
row of the carpus consisted of four normal bones, but the
distal row was composed of two bones only. The external
splint-bone (IV) was of normal proportions, but the internal
splint-bone (IIj had almost completely disappeared. The

large metacarpal (III) divided in its peripheral third into trapezoid. II, III,
two equal cylindrical branches, each of which bore a digit IV, metacarpals. Ilia,
composed of three phalanges and bearing a crescentic HI 6, internal and
hoof. These two digits were bent across each other in a external sets of pha-
shapeless way. Delplanque, Mem. Soc. centr. cVAgric. langes representing
du Dep. du Nord, s. 2, ix. Douai, 1866—18(37, p. 295,
PL III. fig. 5.

Mule, having two distinct toes on each fore foot. The
hoofs were shaped like those of the Ox. They were of
unequal length. Jolt, Comptes Eendus, 1860, p. 1137. [Perhaps a case belonging
to this section.]

the digit III of the
normal.

(After Abloing.)

chap, xiii.] DIGITS OF HORSE : SPECIAL CASES.

371

C. Intermediate casks.

m

trf

flWml

i*

IVT

We have now seen cases of increase in number of digits oc-
curring by addition to the series, and cases occurring by division
of III. It may at first sight seem impossible that there can be
any process intermediate between these two. Nevertheless the
word sufficiently nearly describes the condition of at least the first
of the following cases, and is to some extent applicable to the
second also. If the condition shewn in Fig. 112 be compared with
those in Figs. 106 and 110 it will be seen that it is really inter-
mediate between them.
*553. Horse (young): right manus with internal supernumerary digit.
The bones are not in place, but have been attached with wires.
The condition is as follows. The distal series of carpus remains ami
is normal or nearly so. Of the splint-bones, the inner (mcp. II) is
thicker than the outer mcp. IV, but it is very
little longer. The large metacarpal (III) is
almost, but not quite, bilaterally symmetrical
about its middle line. In the distal epiphysis
the asymmetry is distinct, the internal side of
the epiphysis being less developed than the
external side. This epiphysis bears a large
digit of three phalanges, but instead of being
bilaterally symmetrical, like the normal toe of
the Horse, each of the joints is flattened on the
internal side, the flattening increasing from the
first to the third phalanx. The hoof is greatly
flattened on its inner face.

Internally to the epiphysis of the digit III
there is a separate small bone, representing the
distal end of an inner metacarpal. This bone
bears a digit with two phalanges, and a hoof
which is flat on the side turned towards the
•other hoof, like that of a calf, though it only
reaches to the top of the larger hoof. The
first phalanx of this digit is imperfectly divided
by a suture into two parts. This division is not
that of the epiphysis from the shaft. This extra
digit may be thought to be that of mcp. II,
but it is clear that it was in part applied to
mcp. III. Note also that mcp. Ill is modified
in correlation with its presence. Coll. Surg.
Mas., in Terat Cat., No. 301.

The foregoing case well illustrates the inade-
quacy of the view on which an individuality is
attributed to members of the digital series.
The smaller digit in it is as regards

Fig, 112, Bight

maims of :i hoi

No. ").*)3, from behind,

m, magnum. I i tra-
pezoid. », unciform.

(From a -inrirnen
the Sym- in Coll. Surg. Mus.).

oi •>

_ 1 —

372

MERISTIC VARIATION.

[part I.

metry of the limb complementary to the larger digit. It is a
partial substitute for the inner half of the digit III. If the
visible Symmetry of the limb is an index of mechanical relations
in which the parts stood to each other in the original division of
the manus into digits it is possible that there may have been
a mechanical equivalence between the two digits.

554. Mule (between jackass and mare): foetus of about nine months having super-
numerary digits. Hind limbs normal. Fore limbs normal as far as peripheral
ends of metacarpals. Each manus consisted of three digits. Eight. Metacarpals
II and IV normal splint-bones. Metacarpal III normal as far as line of union with
its distal epiphysis. The inner part of the sheath of the epiphysis is continued into
a rod of fibro-cartilage which supports an extra toe. This rod of cartilage contains
a small ossification which represents, as it were, the proximal phalanx of this
internal supernumerary toe. Its outer end bears a small second pbalanx, and this
bears a small distal phalanx which was covered by a hoof. This extra toe, therefore,
is internal to the main continuation of the leg, commences from the line of union
between the large metacarpal and its epiphysis, and has three phalangeal joints.

The epiphysis of the large metacarpal supports a normal first
phalanx with which the second phalanx articulates. This
second phalanx is enlarged iuternally [details obscure] to
bear a small extra nodule of cartilage which appears to be
of the nature of an extra toe. The second phalanx also
bears a large third (ungual) phalanx. This ungual phalanx
together with the minute supernumerary toe borne by the
second phalanx are together encased in a common hoof, but
the hoof is divided by a groove into two distinct lobes,
corresponding with the division between the two digits
which it contains. The whole foot, therefore, has one free
internal toe and one large toe bearing a small internal one,
which are enclosed in a common hoof.

Left fore foot. Fig. 113. The small, lateral metatarsals
II and IV, and the large central metatarsal III are normally
constructed ; but from the inner side of the sheath of the
large metatarsal, upon the line of union between the bone
and its epiphysis, arises a fibro-cartilaginous rod, which
contains an ossification representing the proximal phalanx
of a supernumerary toe (lettered II in fig.). This rod of
tissue in its proximal portion is represented in the figure as
abutting on, but distinct from the end of the inner small,
lateral metatarsal. It bears a cartilaginous second phalanx,
containing a small ossification, which articulates with a
terminal (ungual) phalanx covered by a hoof.

The distal end of the large metatarsal articulates with

a large first phalanx, which at its proximal end is of normal

width. At about its middle point this phalanx bifurcates

into two parts, of which the inner, Ilia, is short and ends a

little beyond the point of bifurcation : it bears an ungual

phalanx only, which is encased in a hoof. The outer iimb

(III b) of the bifurcated first phalanx bears an elongated

second phalanx of somewhat irregular shape which carries a

larger ungual phalanx covered by a separate hoof. In this

foot, therefore, there is an inner toe consisting of three

phalanges attached to the inside of the large metatarsal : next,

the proximal phalanx of the large toe is divided longitudinally into two parts,

bearing (1) an internal toe having only the ungual phalanx and hoof; (2) an outer

toe which has a second and third (ungual) phalanx.

In the case of both feet, the hoof and ungual phalanx of the outer toe are turned
inwards, having an external curved edge and an internal straight edge; but the two
inner toes in each case are turned outivards, having their outer edges straight and
their inner edges curved. Jolt, A. et Lavocat, N., Mem. de VAc. des Sci. de Tou-
louse, S. 4, Tome in., 1853, p. 364, Plates. [Authors regard this case as proof of

Fig. 113. Left
fore foot of Mule No.
554.

IV, the external
splint-bone. Ill, the
chief metacarpal.
Ilia, Illb, internal
and external rudi-
mentary digits borne
by HI. II, a super-
numerary digit at-
tached to the inner
side of III.

(After Joly and
Lavocat.)

•chap, xiii.] DIGITS OF HORSE : SPECIAL CASES. 373

truth of certain views of the phylogeny of the Horse and employ a system of nomen-
clature based on these views. This is not retained in the abstract here given.]

ARTIODACTYLA.

In the domesticated animals of this order digital Variation is
not rare, being in the case of the Pig especially common. Such
variation has been seen in the Roebuck and Fallow Deer, but not
in any more truly wild form so far as I am aware. These varia-
tions may take the form either of polydactylism or of syndactylism.
Of the former a few cases are known in Ox, Sheep, Roebuck
Fallow Deer, and many cases in the Pig ; syndactylism has been
seen only in the Ox and in the Pig. The absence of cases of
syndactylism in the Sheep is a curious instance of the caprice
with which Variation occurs.

The phenomena of polydactylism in Pecora may conveniently
be taken separately from the similar phenomena in Pigs.

Polydactylism in Pecora.

At the outset one negative feature in the evidence calls for
notice. It is known that in the embryo Sheep rudiments of meta-
carpals II and V exist1 which afterwards unite with III and IV.
In view of this fact it might be expected by some that there would
be found cases of Sheep and perhaps Oxen polydactyle by develop-
ment of the digits II or V. In the Sheep only one case (No.
555) is known that can be possibly so interpreted; and in the I ).\
there is no such case unless Nos. 557, 558, and 559 should be held
by any to be examples of the development of II, a view attended
by many difficulties.

The two following examples are the only ones known t<> nit- in
which there can be any question of reappearance of a lost digit,
but in neither is the evidence at all clear.
*555. Sheep. Some specimens of a small Chilian breed had an
extra digit on the hind foot. It was not present in all individuals
and was not seen to be inherited; but normal parents were
observed to have offspring thus varying. [From the description
given I cannot tell whether the extra digit was internal or
external. Also, though said to have been on the hind foot, in
describing the bones the cannon-bone is twice called metacarpus;
probably this is a slip for metatarsus.] The digit was only
attached by skin. It contained a bent bone, of which the upper
segment was 20 mm. long, the lower 13 mm. Proximally the

1 Rosenberg, Z. f. w. Z., 1873, xxiii. pp. 126—182,^. It. Ac. Sometimes
these rudiments remain fairly distinct ;it the proximal end of the eannon-bone,
especially of the fore foot. See Xatiicsius, Die Sehafiucht, L880, pp. 187 and 1 13,
figs.

374 MERISTIC VARIATION. [part I.

cartilaginous head of this bone rested in a pit on the tendon of
the flexor brevis digitorum at the level of the end of first third of
the cannon-bone, and peripherally it bore an end-phalanx and
claw-like hoof, properly articulating. No splint-bones present.
[Other details given : it was suggested that the bent bone re-
presented an extra ' metacarpal ' and first and second phalanx.]
Von Nathusius, H., Die Schafzucht, 1880, p. 143.
556. Capreolus caprea (Roebuck), 2 yr. old, killed in district
of Betzenstein, having a slender fifth digit on the inside of each
fore foot. In the left there was a small, conical metacarpal
element, bearing a digit with three phalanges. The right extra
digit had a longer metacarpal piece with epiphysis, but in it
there were only two phalanges. Each bore a hoof of about the
size of those of II or V. The hoofs curved outwards. Bau-
muller, C, Abh. naturh. Ges. Numb., ix. 1892, p. 53, PL

Other cases of polydactyle Pecora mostly fall into two groups :

(1) Examples of limbs having three digits borne by a large
cannon-bone made up of three metatarsal or metacarpal elements,
grouped in one system of Symmetry. The axis of Symmetry is
then deflected from the normal position, and instead of falling
between two digits it approaches more or less to the central line
of the middle of the three digits. The degree to which this change
of Symmetry takes place corresponds irregularly with the extent
to wrhich the innermost digit is developed. This form is known in
the Ox only [? Goat].

(2) Limbs in which the series of digits has two more or less
definite axes of Minor Symmetry. Both of the systems of Sym-
metry thus formed are in addition arranged about one common
axis of Symmetry. The nature of this condition will be discussed
later. It occurs in Ox, Sheep, Roebuck and Deer.

(1) Three digits in one system of Symmetry.

*557. Calf. Right manus (Fig. 114) having three digits borne by a
single cannon-bone. This is an old specimen of unknown history
which was kindly sent to me by Mr W. L. Sclater for examination.

Of the carpal bones only the distal row remains, containing a trap-
ezoido-magnum and unciform not differing visibly from the normal.
The cannon-bone spreads at about its middle into three sub-equal parts,
each ending in a separate articular head bearing a trochlear ridge.
Between these articular surfaces the only point of difference was that
in that of the middle digit (b), the trochlear ridge was rather nearer to
the outer surface of the joint, not dividing it into two halves as usual
(see figure). The foramen for entrance of the nutrient vessel was in
the channel between the external and middle digits. This channel was
very slightly deeper than the corresponding channel between the
middle and inner digits. Each articular head bore a digit, well formed,

CHAP. XIII.]

DIGITS : PECORA.

375

of approximately similar lengths, having a hoof. The [hoofs of the
outer and inner digits curved to the middle line of the limb, like the

-n for

Fig. 114. Eight fore foot of a Calf, No. 537.

I. The whole foot seen from behind.

II. The bones from behind.

tpM. trapezoido-magnum. imc, unciform, n, for., nutrient foramen. J",
dotted outline shewing position of supposed rudiment of digit V. Sesamoids not
shewn.

normal hoofs of a cloven-footed animal, but the hoof ol the central toe
was convex on both sides. The two accessory hoofs were in place,
one on each side as shewn in the figure. The whole manus was very
nearly symmetrical about the middle line of this digit. It was notice
able that the out^r and inner hoofs were both father narrow in propor-
tion to the length of the limb, but the whole width y>i the fool was
rather greater than it should be. The small bone considered to repre
sent the digit A' articulates with the unciform as usual, being of normal
size. Each of the three digits was supplied with flexor and extensor
tendons.
558. Heifer having three fully developed toes on each hind limb.

The right hind foot described (Fig. 115). The calcaneum, astragalus
and cuboido-navicular presented no special abnormality. The cuneiform

376

MERISTIC VARIATION.

[part I.

Uc

559.

series usually consisting of two pieces in the Ox, were here represented
by one piece (c and c3), though externally the bone seemed to be in two
pieces. The internal portion (c) approximately corresponding in posi-
tion with the normal ento-cuneiform was imperfectly and irregularly
divided by a groove into two parts. The metatarsus or cannon-bone at
its proximal end was almost normal, but from about its middle it
spread out into three parts as shewn in the figure, each part ending in
an articular surface and bearing a digit, but the trochlear ridge for the
innermost digit (ac) was not quite so large as those for the others.
From the skeleton it seems clear that this innermost digit could not
have reached the ground.

Of the three hoofs the middle one was the
largest, the other two being nearly equal to each
other in size. The outermost hoof curved inwards,
and the innermost hoof curved outwards. The
middle hoof also curved outwards, but less so than
that of a normal digit III, being rather flatter
underneath, and having its two edges more nearly
symmetrical. The accessory hoofs ('ergots' of
French writers) were " in their usual place, on
either side of and behind the foot." This speci-
men was originally described by Goodman, Ne-
ville, Jour. Anat. Phys., 1868, Ser. 2, i. p. 109.

The skeleton of the foot is in the Cambridge

University Museum of Pathology.

In answer to my inquiries Mr G. Daintree of

Chatteris, the owner of this animal, kindly gave

me the following information. This cow was

bought in 1861 and from her a three- toed strain

arose, of which about ten generations were pro-
duced. The three-toed condition appeared in

both males and females, but no three-toed bull

was kept, so that the descent was wholly through
females. About two in three calves born of this

strain had three toes. In one case only were

there three toes on the fore feet. The third toe

was never walked on. The breed was got rid of

because it was at last represented only by males,

the last being sold in 1887. The beasts were as

good as any other cattle of the same class.

Calf.

ally resembling the last case

is nearly normal. The middle digit is very thick,

and is somewhat twisted and flexed. Its ungual

phalanx is not specially curved in either direction

but it is not truly symmetrical. The innermost

digit is thin and short and its ungual phalanx is the hypothesis that

not much curved. In this specimen there is a HI and IV represent

, . •■ j j, ,. . . . ,, ,. . , . these dibits ot the

decided appearance or division in the distal epi- normai and that ac

physis of the metacarpal of the middle digit is an accessory digit.

(?III). Coll. Surg. Mus., Terat. Series, No. 300.

gener-

Left manus having three digits,

?he external digit

uan

Km)

Fig. 115. Right
hind foot of heifer,
No. 558.

As, astragalus.
clc, calcaneum. c,
cs, parts of a large
united bone repre-
senting cuneiforms.

Ill, IV, ac, letters
affixed to illustrate

chap. XIII.] DIGITS : PECORA. 377

The following two cases are jjerhaps of the same nature as the foregoing.

560. Goat having three digits in each manus, described by Geoffroy St Hilaire,
Hist, des Anom. i. p. 689. The description states that a supernumerary toe was
placed between the two normal toes. The middle toe was one-third of the size of a
normal toe, but the lower part of the foot was larger than usual. This case was
probably like No. 557 ; for from the shapes of the lateral hoofs that case also might
seem to an observer at first sight to be an example of a toe " intercalated " between
two normal toes. But in No. 5G0 the middle digit was reduced.

561. Calf having a small supernumerary toe 'placed between the digits of the
right manus.' This toe had a hoof and seemed externally to be perfect, but on
dissection it was found to contain no ossification, but was entirely composed of
fibrous tissue and fat. Ercolani, Mem. Ac. Bologna, S. 4, in. p. 772. [Probably
case like last, the middle digit being still less developed.]

This case is probably distinct from the others given.

562. Calf: right fore foot having three complete metacarpals, each bearing a
digit of three phalanges. The two outer were disposed as in the normal, but the
innermost metacarpal was quite free from the others and its digit stood off from
the others [not grouping into their symmetry as in preceding cases] and having

an ungual phalanx [of ? pyramidal shape]. Delplanque, Etudes Teratol., Douai,
1869, n. p. '63, PI. II. Jigs. 2 and 3. [It is difficult to determine the relation of this
case to the others and I am not sure that I have rightly understood the form of
the inner digit ; but since this digit seems to be outside the Minor Symmetry
of the limb it is almost impossible to suppose that it can really be the digit II
reappearing. I incline to think that it is more likely that this digit belongs to a
separate Minor Symmetry. Compare the similar phenomena in Pigs, No. 570.]

On the foregoing cases some comment may be made. It may
be noted that the two first (Nos. 557 and 558) present two stages
or conditions of one variation. In No. 557 all three digits reach
the ground and the change of Symmetry is completed ; in No. 558
the internal digit is not so large in proportion and the plane of
Symmetry is not deflected so far.

As to the morphology of the three digits in these cases three
views are open on the accepted hypotheses. First, the internal
digit (if it be admitted to be the supernumerary) may be simply
a developed II. The existence of the normal accessory hoofs
practically negatives this suggestion, for there can be little doubt
that one of them represents II (v. infra, No. 579). The condition
of the cuneiforms in No. 558 suggests further that an element is
introduced into the cuneiform series between the almost normally
formed ento-cuneiform and the ecto-cuneiform. But if this new
element is the middle cuneiform, then the internal digit (Fig. 115,
ac) may still be II. But the innermost ergot is II in the normal.
Or is the inner ergot in this case I, and is this once more a case of tin-
development of a normally terminal member, II, and of the addition
. of I beyond it in correlation, as we saw in the Horse (see p. 364) ?
That such a correlation may exist is unquestionable, and it is not
clear that these cases are not examples of it. But even if this
principle be adopted here as a means of bringing these cases into
harmony with received conceptions it will presently be seen that
it still will not reconcile some other cases, notably those of the
presence of supernumerary digits in a Minor Symmetry apart from
that of the normal series. Yet if the conception of the digits as

378 MERISTIC VARIATION. [part I.

endowed with individuality be not of universal application, we shall
not save it even if by ingenuity we may represent the facts of the
present case as in conformity with its conditions.

On the other hand it may be suggested that there is a division
of some one digit, and undoubtedly in No. 559 there is a sugges-
tion that the innermost digit and the central digit are both formed
by division of III. But in the first place this view cannot so easily
be extended to Nos. 557 and 558, for in them there is practically
no indication that the digits are not all independent and equivalent.
The circumstance that the nutrient vessel enters between the
external and middle digits may perhaps be taken to shew that
they are III and IV ; but this vessel, if single, must necessarily
enter in one or other of the interspaces and there is no reason for
supposing that, were there an actual repetition of a digit, the
vessel must also be doubled, though doubtless repetition of vessels
commonly enough occurs with repetition of the organs supplied.

Next, the Symmetry of the foot, the development of the middle
digit to take a median place, the position of the accessory hoofs,
one on either side equidistant from the middle line of the manus,
all these are surely indications that this limb was from the first
developed and planned as a series of three digits, and not as a series
of two digits of which one afterwards divided. The series has a
new number of members, and each member is in correlation with
the existence of the new number remodelled.

It is no part of the view here urged to deny that a single digit,
like any other single member of a series, may divide into two (or
even into three) for this phenomenon is not rare. Probably enough
No. 559 is actually a case of such a division of the digit III. But
here in digits as in mammae, teeth, &c, the evidence goes to shew
that there is no real distinction between the division of one member
to form two, and that more fundamental reconstitution of the series
seen in No. 557, for the state of No. 558 is almost halfway between
them. In it we almost see the digit III in the act of losing its
identity.

(2) Limbs with digits in two systems of Minor Symmetry (Double-foot).

In dealing with these there are difficulties. The cases are examples
of limbs of Calves or Sheep hearing four or rive digits arranged in two
groups either of two and two, or of two and three. The members of
each group curve towards each other in such a wray that each group
has a separate axis of Symmetry (Figs. 117 and 118). In several such
cases the two groups are related to each other as right and left. Of
these facts two different views are possible. For first, a limb of this
kind may be a structure like the double-hands seen in Man (pp. 331 to
337), for it is certain that an almost completely symmetrical series of
parts is in those cases formed by proliferation of a series normally
hemi-symmetrical, howrever unexpected this phenomenon may be.

On the other hand it might be argued that one of the groups of
digits represents the normal, and that the other group is supernumerary.

chap, xiii.] DOUBLE-FOOT I PECORA. 379

For, as will be hereafter shewn at length in the case of Insects, super-
numerary appendages may grow out from a normal appendage and are
then a pair, being formed as a right and a left, composing a separate
Secondary Symmetry.

On the first view the digits of each group are in symmetry with
each other like those of the normal limb, the two groups also balancing
each other like the halves of a double-hand: on the other view one of
the groups would be supposed to be made up of a right and a left digit
III, or of a right and a left digit IV. The possibility of the second
view being true arises of course in the Artiodactyles from the fact that
in them the normal digits compose a bilateral Minor Symmetry.

There is nevertheless little doubt that the former account is the
right one and that neither group is a Secondary Symmetry ; for were
either of the groups really in Secondary Symmetry the supposed super-
numerary group should contain at least parts of four digits. Lastly,
some of the cases, as No. 566, are clearly of the nature of double limbs,
both groups having a common axis of Symmetry.

A further difficulty arises from the fact that most of these double
limbs are old specimens cut off from the trunk. There is therefore
no proof that such a limb is not that of a polymelian in Geoffroy St
Hilaire's sense. In other words, though it is practically certain that
neither of the groups of digits is itself a system of Secondary Symme-
try it is quite possible, and in some cases likely that the whole limb is
of this nature. In cases of duplicity, especially of posterior duplicity,
the two limbs of one or both of the united bodies frequently form a
compound structure somewhat resembling one of the double limbs here
under consideration. Hence it is not possible to include with confid-
ence great numbers of cases of double limbs described by various
writers or preserved in museums, for it is rarely that particulars re-
garding the rest of the animal are to be had. This difficulty applies to
almost all cases known to me and they are therefore given with this
caution. This objection of course does not apply to such a case as No.
564.

The following few cases will sufficiently illustrate the different forms of limbs
included in this section. They consist of two chief kinds ; first, limbs like Nos. 563
and 566, in which both groups contain two digits, and secondly, cases like No. 567, in
which one of the groups contains three digits, recalling the state described in the
last section (cp. Nos. 558 and 559). Besides these there are some cases of amor-
phous extra digits not here related.
563. Cow, full-grown, right fore foot with four digits arranged in two groups of two,
as sbewn in fig. 116. The carpus not preserved. No particulars as to the rest of the
animal. This specimen is in the Museum of Douai and is described in detail by
Dklplanque, Etudes Teratologiques, n. Douai, 1869, p. 30, PI. I. [The possibility
that this may be a limb of a pygomelian is not excluded.]

*564. Cervus dama (Fallow Deer). A female having each hind foot
double. The division occurs in the upper part of the tarsus, which
gradually diverges into two separate tarsi [? metatarsi] and two
separate feet. This doe had for several successive years dropped a
fawn with the same malformation, though she had been served by
several bucks. Ward, Edwin, Proc. Zool. Soc, 1874, p. 90.
565. Two cases, a Roebuck and a Deer, mentioned by Geoffroy St
Hilaire {Hist, des Anom., I. p. 697) are probably of this nature.

380

MERISTIC VARIATION.

[part I.

Fig. 116. Specimen stated by
Delplanque to have been the ri^bt
foot of a Cow (see No. 563). (After
Delplanque.)

Sheep, having four toes, each having three phalanges,
on each posterior limb (Fig. 117). In each case the toes
were arranged as two pairs, the hoofs of each pair being
turned towards each other. Each foot had four united
metatarsals, marked off from each other by grooves on the
surface of the bone, the division between the metatarsals
of each pair of toes being clearly marked at the peripheral
ends of the bones. In the case of each foot there were
parts of a pair of tarsi arranged in a symmetrical and com-
plementary manuer about the middle line of the limb.
In each tarsus there was a large bone having the structure
of two calcanea, a right and a left, united posteriorly ; the
upward prolongation, proper to the calcaneum, was present
on each side of this bone and projected upwards on each
side of the tibia. The astragalus of each foot was similarly
a bone double in form, uniting in itself the parts of a right
and left astragalus. The left foot had a single fiat bone
below the astragalus, representing as it were two naviculars
fused together ; and four bones in a distal row, representing
presumably two cuboids, and two cuneiform elements. In
the right foot also there was a single bone below the
astragalus, and four other bones arranged in a way slightly
different from that of the other foot. Ercolani, ibid., p.
773, Tav. n. figs. 7 and 8.

Fig. 117. Bones of left hindjfoot of a Sheep, No. 566 [q. v.] copied from Ercolani.
clc, clc, the two calcanea. a + a2, bone representing the two astragali, n + n'2,

tbe two naviculars, cb, cb, the two cuboids.

CHAP. XIII.]

DOUBLE-FOOT : PECORA.

381

[A case given by Ebcolani (I. c, p. 783, Tav. 11., figs. 9 and 10) of similar
duplicity in a lamb seems to be very possibly a case of double monstrosity. In this
animal the hind limbs were altogether absent.]

567. Calf, having five digits on one manus. There is nothing to shew positively
whether this specimen is a right or a left, and it is even possible that it is part of a
polymelian1. Carpal bones gone. Metacarpals four, disposed in two pairs. One
pair bear the digits d4 and d5 (Fig. 110), which

have a common proximal joint. Their ungual
phalanges curve towards each other, forming a
Minor Symmetry like those of a normal Calf.
The other two metacarpals bear three digits ; two
(d3 and d2) articulate with one metacarpal having
a divided epiphysis. The other metacarpal bears
a digit (d1) of full size curving towards d'2. The
ungual phalanges of d2 and d3 are nearly straight
[cp. Nos. 558 and 559.] C. S. M., Terat. Ser.,
No. 299.

568. Calf: left hind foot similar case : inner group
of tico toes curving towards each other and an
outer group of three toes of which the middle one
was almost bilaterally symmetrical while the hoofs
of the other two were each turned towards it. Five
metatarsals united but marked out clearly by
grooves. Tarsus much as in No. 566. Ercolani,
7. c, p. 774, Tav. i. fig. 8.

569. Calf: left hind foot a somewhat different case,
Drew, Commercium Litterarium, Nuremberg, 1736,
p. 225, Taf. in. fig. 2. [Description meagre, but
figure good. Beginning from the inside the five
toes turned (1) outwards, (2) outwards, (3) inwards,
(4) outwards, (5) inwards, respectively. There were
only four metatarsals, (3) and (4) being both borne
on one metatarsal.]

POLYDACTYLISM IX THE PlG.

Fig. 118. Manus of a Calf.
No. 567. d\ d2, d3, group of
three digits [? internal] ; d4, d\
group of two digits [? external].

570.

Of the great numbers of feet of poly-
dactyle pigs recorded or preserved in
museums all I believe are fore feet. No
case of a polydactyle hind foot is known to
me in the pig. All the cases are examples of proliferation upon the
internal side of the digital series. With very few exceptions the
variation takes one of two forms, consisting either in the presence of
a single digit internal to the digit II, or in the presence of tivo digits,
either separate or partially compounded, in this position. A very few
cases depart from these conditions2. The condition is very usually
the same or nearly the same in both fore feet.

One extra digit, internal to digit II.

Such a digit may either have a separate bone for its articulation in
one or both rows of the carpus (as Ercolani, /. c, PI. I. fig. 3), or it
may articulate with a half-separated extension of the trapezoid (as Coll.
Surg. Mus., Ter. Ser., 297 A), or with the metacarpal or other part of
digit II (very common), sometimes simply branching from this digit
without an articulation. In no case of which good accounts are to be

1 The Catalogue gives no indication on these points.

2 For example a 1. fore foot in which the -metacarpal of II. bears a rudimentary
digit on each side of the digit II, three in all. Ebcolani, Mem. Ac. Bol., 1881, PL
I, fig. 1.

38:

9

MERISTIC VARIATION.

[part I.

had does such a digit group itself into the Symmetry of the normal
manus ; but it stands apart, or is bent or adducted behind the other
digits, having a hoof which is irregularly pyramidal, curving in neither
direction especially. Such a digit has generally three phalanges, and
is of about the size of digit II, though not rarely it is large in size
approaching more nearly to III than to II (as Coll. Surg. Mus., Ter.
Ser.t 297).

Two extra digits internal to digit II%

This condition is not less common than the last. The two extra
digits are borne either by two separate extra carpal bones (Fig. 119, c\
c2), or by one carpal imperfectly divided (Ercolani, I. c, PI. I., Jig. 6);
or the metacarpals of the extra digits simply articulate against the
carpo-metacarpal joint of II (as in a specimen in my own possession).
The extra digits may be double throughout, or the two may be com-
pounded in their proximal parts (Ercolani, I. c, PL i., fig. 5 ; also case
in Oxford Mus.1, 1506, a, in which the two extra digits were ill-formed
and of unequal size, having a common metacarpal). Fig. 119 shews
such a pair of extra digits in their most complete form. The central
part of the metacarpal of II has either never ossified or has been
absorbed. As bearing on the question of the relations of parts in
Meristic Repetition the fact of most importance is the circumstance
that the digits III and IV retain their normal Symmetry, but the two

• I II

Fig. 119. Left manus of a Pig, No. 571.

I. View from in front. II. View from inside to shew the convergence of
d1 and d2 towards each other.

d1, d2, two extra digits placed internally, c1, c2, two extra carpal bones with
which they articulate, sc, scaphoid, lu, lunar, cu, cuneiform, t, trapezoid,
m, magnum, u, unciform. dz — d6, the digits II, III, IV, V.

1 For note of this specimen I am indebted to Mr W. H. Benbam.

chap, xiil] DIGITS : PIG. 383

extra digits form another Minor Symmetry of their own. It is perhaps
worth noting that the metacarpal of the digit lettered da in the form of
its head is nearly the optical image of that of III (d*), but this resem-
blance may be misleading and must not be insisted on. Coll. Surg.
Mus., Ter. Ser., 298.
572 Wild Boar. Two cases, apparently resembling the foregoing are

described, from external examination only, in the wild boar by Geoffroy
St Hilaire, Hist, des Anom., 1. p. 696.

Syndactylism in Artiodactyla.

This phenomenon is known in the Ox and is common in the
Pig. In all cases the variation consists in a more or less complete
union or absence of division between the digits III and IV. Among
the many records of digital variation in the Pig no case relates to
union between a lateral and a chief digit, but it is always the two
chief digits III and IV that are united. (Compare the case of
Man, p. 358.) In this case there is therefore an absence of a
division in the middle plane of a bilateral Minor Symmetry, and
the parts that remain united are related to each other as optical
images. The phenomenon is thus the exact converse of the
variation consisting in a division along a plane of bilateral sym-
metry which was seen in the Horses Nos. 547 and 550. As was
remarked in speaking of similar variations in Man, it is to be
noticed that if the union is incomplete, as it commonly is, the
peripJteral parts are the least divided, the division becoming more
marked as the proximal parts are approached.

In the normal Sheep according to Rosenberg1 the metacarpals
II and V are distinct in the embryonic state, afterwards completely
uniting with III and IV. The same is presumably true of the Ox ;
but whether this be so or not, the digits II and V are in the
normal adult not represented by separate bones in the hind foot,
and in the fore foot V only is represented by the rudimentary
* bone articulating with the unciform. Unusual interest therefore
attaches to the observations made by Bo AS and by Kitt of the
development of lateral metacarpals and metatarsals (II and V) in
Calves having III and IV united. Note also that in two of Kitt's
cases there was not only a development of lateral digits but also
indications of a division occurring in them. Besides this, in the
right fore foot of one solid-hoofed Pig (No. 585) there is a slight
appearance of duplicity in the ungual phalanx of the lateral
digit V.

On the other hand the reduction of accessory hoofs {ergots) in
Landois' case, No. 582, seems to be an example of a contrary
phenomenon ; for the connexion between the developed lateral
metacarpals and metatarsals in Kitt's case (No. 579) must be
taken as evidence that the accessory hoofs do really represent
II and V.

1 Rosenberg, A., Z.f. w. Z., 1873, xxm. pp. 126 — 132, figs. 14, &c.

384 M ERISTIC VARIATION. [part i.

*573. Ox. Young ox having the two digits of the right fore foot
completely united together. At the lower extremity of the large
double metacarpal (III and IV) of the normal limb a deep cleft is
present, which separates the two articular extremities of the bone.
In this specimen this cleft was represented only by a sort of
antero-posterior channel, at the bottom of which there was a
slight groove, which was all that remained as an indication of the
original double nature of the bone. At the back of this metacarpal
there were only three sesamoids instead of four, and in the central
one there was not the slightest trace of duplicity. This sesamoid
was placed opposite to the channel above mentioned. The two
first phalanges were entirely united, but the vestiges of this fusion
could be seen both before and behind and also in the two articular
surfaces by which the bone was in contact with the metacarpal.
The same was true of the second phalanges. The third phalanges
however were so completely fused and so reduced in size that they
had the appearance of a single bone. The two small sesamoids
were similarly united. The general appearance of this limb was
remarkably like that of the Horse. Barrier, Rec. mecL veter.,
1884, Ser. 6, Tome 13, p. 490. [No particulars given as to the
condition of the other feet of the same animal.]

574. Ox having right fore foot with a single large metacarpal and
one splint-bone [? Y]. The peripheral end of the metacarpal
had two articular surfaces closely compressed together, and these
two surfaces bore but one digit of three phalanges and one hoof
like that of a Foal. The preparation was an old one, and with
regard to the accessory hoofs there was no indication that could be
relied on. Kitt, Dent. Ztschr. f. Thierm., XII. 1886, Jahresb.,
1884—5, p. 62, Case No. III.

575. Calf: each foot having only one hoof. The phalanges, sesamoids, meta-
carpals and metatarsals, were all normal and the hoofs alone were united. The
cavity of the hoof was divided internally into two chambers, which were more
distinct in front than behind. Externally each hoof was slightly bifid in front, but
the soles of the feet were without trace of division. Morot, C, Bull, de la Soc.
de vied, vet., 1889, Ser. vn. T. vi. p. 39. Case I.

576. Calf: killed at 10 weeks old. The left fore foot alone was abnormal, having only
one hoof. Viewed from without, this hoof was like that of a young ass, but it bore
a slight median depression, which was about 3 cm. wide and only 1 to 2 mm. deep,
which was all that remained to shew its double structure. Internally the cavity of
the hoof was single, but a horny ridge was present on the inside in the region of
the depression. The two unequal phalanges were peripherally united into a single
bone, but were separate centrally, and the two parts were not quite symmetrical
[details given]. The other parts were nearly normal. Morot, C, I. c, Case 2.

*577. Ox. In a newly-born calf the following abnormalities were seen.
In the right fore foot there was a small well formed metacarpal
bone on the outside of the normal paired metacarpals, and a similar
but more rudimentary structure was also present on the inside of
the limb. The additional outer metacarpal bore two small phal-
angeal cartilages, and with them had a length of about 10 cm.,
but the supernumerary metacarpal on the inner side was more
rudimentary and bore no trace of phalangeal structures. The toes

chap, xiii.] syndactylism: ox. 385

borne by the normal metacarpal of the right fore foot were ab-
normal, inasmuch as the second and third phalanges were united
together. The first pair of phalanges were separate, but their outer
ends were modified so as to articulate with the single second
phalanx. The distal (third) phalanx bore a groove indicating its
double origin, but the second phalanx was without any such groove,
and was to all appearance a single structure.

The left fore foot also bore an outer and an inner supernumerary
metacarpal, but in this case it was the inner supernumerary meta-
carpal which attained the greatest size. This inner metacarpal
bore two small phalangeal bones, while the outer extra metacarpal
was more rudimentary and had no phalanges. The phalanges of
the two normal toes were separate in the left foot, but though the
bones were of the ordinary formation the two toes were enclosed
in a common hoof. Boas, J. E. V., Morph. Jahrb., 1890, p. 530,

figs-

Boas also states that in the museum of the Agricultural
School of Copenhagen are several instances of united toes in the
fore foot of the Ox, and that in all these specimens the outer
metacarpals (II and V) are larger than they are in normal
specimens, but are not so much developed as in the case just
described. Boas, I.e.
578. A case [sc. Ox (?)] is also mentioned in which the two normal
toes of the hind foot were united, and the median and distal parts
of the metatarsals II and V were developed, though they are
absent in the normal form. Boas, I.e.

*579. Calf having the digits of each foot united and bearing a single
hoof. The carpus and tarsus were not seen. Fore foot. The chief
digits, III and IV, were completely united in the fore limbs and bore
a single hoof, but, in addition to this variation, the metacarpals of the
lateral digits, II and V, were developed and ossified. The length of
metacarpal II was 9 cm. and its thickness at the proximal end was
T5 cm. Metacarpal Y had a length of 8 cm. and a maximum thick-
ness of 1*3 cm. at the proximal end. The metacarpal of the united
digits, III and IV, measured 13 cm. in length. The metacarpal V
was slightly bifid at its distal extremity, and here presented two
articular surfaces. With the internal of these there articulated a bone
measuring 2 cm. by 0-5 cm., and attached by fibrous tissue to the end
of this bone there was a cartilaginous nodule. The external end of
metacarpal V bore a rod-like piece of cartilage, 1 cm. in length. This
and the cartilaginous nodule of the other part of the digit together
formed the basis of one of the accessory hoofs (ergots), but the horny
covering itself was divided by a deep cleft into two imperfectly separate
parts. To the metacarpal of II was loosely articulated a bone 2*5 cm.
in length, to which a nodule of cartilage was attached. The end of this
digit was covered by an accessory hoof, which was imperfectly double
like that of V and contained a second cartilaginous nodule, which was
distinct from the first and was not supported by any proximal bone.
The union between the digits III and IV was complete, and the re-

b. 25

386 MERISTIC VARIATION. [part i.

suiting structure with its hoof was like that of the Horse. The artic-
ulations were perfectly mobile. At the ruetacarpo-phalangeal joint
there were two sesamoids only. [With this division in the lateral
digits on fusion of III and IV compare Pig, No. 585.]

Hind foot. The digits III and IV were united as in the fore feet,
but the single hoof was more pointed. The metatarsals II and V
were developed. The latter was 12-7 cm. long, and was united to the
large metatarsal above, but was free below, and was joined by a liga-
ment to its accessory hoof. That of II began in the middle of the
metatarsus, being cartilaginous and of about the thickness of a goose-
quill ; it was connected with the accessory hoof by a ligament only.
Kitt, Dent. Z. f Thierm., xil, 1886, Jahresb. 1884-85, p. 59, Case
No. I, Jin.
*580. Calf. Three of the feet had each one large digit (III and IV)
formed much as in the last case. But in the dried preparation it
could be seen that in each of these feet there were four accessory
hoofs, and connected with them several ossicles irregularly placed, re-
presenting phalanges 1 and 2 connected by ligaments with lateral
metacarpals. The fourth foot [which 1] had only three accessory hoofs,
but the phalanges 1 and 2 of the digits III and IV were partially
separated from each other, and there were two distal phalanges,
one for each digit ; but instead of being side by side, they were placed
one behind the other, both being encased in a single hoof. Kitt, I.e.,
p. 61, Case No. II.

581. Calf. A right fore foot having the two chief digits (III and IV)
represented by one digit with one hoof. The distal end of the common
metacarpal had two articular surfaces in close contact which bore a
digit in which there were only slight traces of duplicity. The meta-
carpal of the digit V was represented by two small bones, one beside
the upper and one beside the lower end of the large metacarpal.
These two ossicles were connected together by a ligament which is
prolonged downwards as far as the accessory hoof, and contains two
nodules of cartilage. On the median side of the foot there is no
rudiment of the metacarpal II, but the accessory hoof contains a
nucleus of partly ossified cartilage. Kitt, I.e., p. 63, Case IV.

582. Calf having a single hoof on each fore foot. In external appearance, the hoof
was a single structure, but its anterior portion shewed two projections which sug-
gested that it was really a double structure. The outer accessory hoof was present
on the right foot in a very much reduced form, but the corresponding structure of
the inner side of the foot was entirely absent, and a marked ' turning-point ' in the
hairs (Haancirbel) indicated the place where it should normally have been de-
veloped. In the left foot the accessory hoofs were in the same condition as in the
right foot, but the ' turning-point ' was not formed at all. There were no skeletal
structures corresponding to the accessory hoofs.

The skeleton of left fore foot was prepared. In it the metacarpal was 125 mm.
long, having a deep cleft on its anterior face, indicating the line of union of the two
metacarpals. The two articular heads, which in a normal animal of the same age
are separated from each other by about 5 mm., are in this specimen united by the
inner edges of their anterior borders. The proximal phalanges formed a single
bone, 32 mm. long. The division between the two bones was visible as a cleft on
the anterior surface, in which place the two ossifications were distinctly separated
from each other ; on the posterior surface the union between the two is continued
for half the length. The second phalanges formed a typically single bone, as did
also the distal phalanges which bore the hoof. The foramina for the two nutrient
arteries of the two toes remained double and entered the single bone, one on each

CHAP. XIII.]

SYNDACTYLISM : PIG.

387

583.

side. Landois, H., Verh. d. naturh. Ver. d. preuss. Rheitil., Bonn, 1881, S. 4, vin.
p. 127.

Pig. " Solid-hoofed " pigs have been mentioned by many
writers from the time of Aristotle. The fact that they have
been reported as occurring in many parts of the world makes it
likely that the variation has often arisen afresh. The first case
(No. 583) is the only instance of complete union of III and IV in
the pig that is known to me. The variation is most commonly
simultaneous in fore and hind feet. As seen, it occurs in many
degrees. Several specimens not separately mentioned below are in
the Coll. Surg. Mus. and other collections.

A fore foot and a hind foot of the same individual, in which the
two chief digits were completely united, viz. represented by a
single series of bones.

In each case the two chief metacarpals and metatarsals (III
and IV) were respectively represented by a single large bone, and
with each a single digit of three phalanges articulated. The bones
of these digits were straight, and not curved as they are in an
ordinary foot in which two toes are present. There was not the
slightest trace of duplicity, and the lateral digits were placed
symmetrically on either side. The sesamoids were two in number

A

B

Fig. 120. Bones of feet of solid-hoofed Pig, No. 583, from specimens in the
Museum at Alfort, described by Barrier.

A. Left manus from in front.

B. Left manus from behind.

C. Left pes from in front.

The numbers II and V indicate the digits so numbered in the normal.

25—2

388 MERISTIC VARIATION. [part i.

instead of four. The carpus and tarsus appear to have also been
changed in connexion with this unification of the digits, for in the
distal series at least the normal number of bones was not present.
[The feet had been cut off across the tarsus and carpus before
being received. By kind permission of the authorities at Alfort
I examined these specimens and made the sketches in Fig. 118.
I could not satisfactorily identify the bones of carpus and tarsus.
The proximal parts were covered by a large exostosis.] The
extensor of the phalanges ended in three tendons only, and the
same was true of the deep and superficial flexors. The central
tendon in each case however shewed signs of its double nature.
Barrier, Rec. mid. ve'ter., 1884, Ser. 6, Tom. xiii. p. 491.

584 A skeleton of a solid-hoofed pig exists in the Museum of the Royal
College of Surgeons of Edinburgh which was presented by Sir Neil
Menzies of Rannoch, Perthshire. Inquiries instituted by Struthers
(1863) elicited the following facts.

" The solid-hoofed pig has been well known and abundant on the
estates of Sir Neil Menzies at Rannoch for the last forty years.
Most, if not all of them, were black. They were smaller than the
ordinary swine, and seem to have had shorter ears. They liked the
same food and pasture as the common swine, and showed no antipathy
to herd with them. They were more easily fattened, though they did
not attain so large a size as the ordinary swine ; their flesh was more
sweet and tender, but some of the Highlanders had a prejudice against
eating the flesh of pigs which did not " divide the hoof," unaware
apparently that the Mosaic prohibition applied to all pigs. A male
and female of the solid-hoofed kind wTas brought to Rannoch forty
years ago, by the late Sir Neil Menzies, which was the commencement
of the breed there ; but I have not been able to learn Avhere they were
brought from. Although they did not breed faster than the common
kind, they multiplied rapidly, in consequence of being preserved, so
that the flock increased to several hundred.

" At first, care was taken to keep them separate, on purpose to
make them breed with each other, but after they became numerous
they herded promiscuously with the common swine. As might be
expected in a promiscuous flock, some of the young pigs had solid and
some cloven feet, but I am unable as yet to say whether any definite
result was ascertained as to the effect of crossing ; whether any experi-
ments were tried as to crossing ; or whether after the promiscuous
herding, some of the pigs of the same brood presented cloven and
some solid hoofs.

" No pig was ever known there with some of its feet solid and
some cloven ; nor, so far as is known, was there any instance of young
born with cloven feet, when both parents were known to be solid-
hoofed. The numbers diminished — for what cause is not apparent ;
so that last year there was only one or two — one of them a boar,
which died ; and now the solid-hoofed breed appears to be extinct in
Rannoch."

585. " Fore foot. — The distal phalanges of the two greater toes are re-
presented by one great ungual phalanx, resembling that of the Horse,

CHAP. XIII.]

SYNDACTYLISM : PIG.

389

but longer in proportion to its breadth. The middle phalanges are
also represented by one bone in the lower two-thirds of their length,
presenting separate upper ends for articulation with the proximal
phalanges. The proximal phalanges are separate through their entire
length. The whole foot above the middle phalanges presents the
usual arrangement and proportions in the hog." Middle Phalanges.
"There is no symphysis or mark indicating a line of coalescence of the
two phalanges. The surface across the middle is somewhat irregularly
filled up to nearly the level of each lateral part. Each half of the
phalanx, as indicated by the notch between the separate upper ends,
has the full breadth of the proximal phalanx above it." Distal
Phalanx. The middle part of this is raised above the lateral parts,
and is partially separated from them by a fissure on each side, giving
it an appearance as of the union of three bones. The end of the
phalanx is notched like that of the horse ; it bears no trace of
symphysis. ' ' The ungual phalanx of one of the lesser internal toes of
the fore foot presents a bifurcation reaching half the length of the
phalanx." See Fig. 121.

I. II.

Fig. 121. I. A right fore foot of a solid-hoofed Pig, No. 585, from in front.
The ungual phalanx of the digit V is bifid [cp. Nos. 579 and 580].

(After Struthers.)

II. Middle digits of foot of solid-hoofed Pig, No. 587. .r, an extra ossification
wedged in between the phalanges of III and IV. (After Elliott Coues.)

" Hind foot. In the hind foot only the distal phalanx is single....
There is no trace of double origin to the bone." Struthers, J., Edin-
burgh New Phil. Jourii., 1863, pp. 273— 279, Jigs.

586. A Pair of solid-hoofed pigs received by Zoological Society of London from Cuba
* in 1876. The sow gave birth to a litter of six [the solid-hoofed boar being presumably
the father]. The six young were three males and three females. The hoofs wen
solid like those of the parents in two males and one female : in the others the hoofs
were cloven as in the normal pig. The feet of one of the solid-hoofed males of thi>
litter were dissected, and it was found that "the proximal and second phalanges
are separated as usual, whilst at the extreme distal ends of the ungual phalanges

390 MERISTIC VARIATION. [part i.

these bones are completely fused together ; and, further, a third ossicle was developed
at their proximal ends, where they are not completely united, between and above
them " [cp. No. 587]. " It might have been imagined that the deformity was simply
the result of an agglutination along the middle line of the two completely-formed
digits ; but such is not the case, the nail-structure being absent in the interval,
where it is replaced by bone with a transverse cartilage below it. The nail is con-
tinued straight across the middle line of the hoof, as in the horse." Garbod, A. H.,
Proc. Zool. Soc, 1877, p. 33.

587. Domestic pigs having the two central hoofs compounded into a single solid hoof
have been known to occur several times in America. The two other toes remain
distinct in these cases. A breed of pigs having this character is said to have been
established in Texas, which transmits this peculiarity in a definite way. In this
breed the peculiarity is said to have been so firmly established that "no tendency to
revert to the original and normal form is observable in these pigs." A cross between
a solid-hoofed boar and an ordinary sow is said to produce a litter of which the
majority shew the peculiarity of the male parent. " On the sole of the hoof, there
is a broad, angular elevation of horny substance, apex forward, and sides running
backward and outward to the lateral borders of the hoof, the whole structure being
curiously like the frog of the horse's hoof. In fact it is a frog, though broad,
flattened, and somewhat horseshoe-shaped, instead of being narrow, deep and acute
as in the actual frog of the horse. This arcuate thickening of the corneous sub-
stance occupies about the middle third of the whole plantar surface of the foot."
The terminal phalanges are united together, and above this single bone is another
independent ossification lying between the second phalanges of the two digits, which
remain distinct. [Cp. No. 586.] Coues, Elliott, Bull. XI. S. Geol. Geogr. Surv., iv.
p. 295, fig.

588. Case resembling the above reported from Sioux City, Iowa, in which these pigs
were bred for some time and were advertised for sale, with the statement that they
were also of superior quality. Other cases given from different parts of the United
States. In one of these it is stated that one hind foot was thus formed [the others
being presumably normal]. Auld, R. O, Amer. Nat., 1889, xxiii. p. 447, fig.

589. Fig. In all four feet the digits III and IV partially united and covered by one
hoof. The metacarpals and first phalanges were separate in each case but the
second and third phalanges of the two digits were united together. The common
hoofs were not compressed laterally, as in some of the cases seen in the Calf, and
the small digits II and V were unmodified. Kitt, Deut. Zt. f. Thierm., xn. 1886,
Jahresb., 1884-85, p. 64, Case IV, figs.

POLYDACTYLISM IN BlRDS1.

The whole number of cases of Polydactylism recorded in
birds generally is small. The phenomena however seen in the
Dorking fowl are well worthy of attention and have scarcely been
adequately treated. I propose here to give an account of this
case, mentioning instances seen in other birds and indicating so far
as may be their relation to the facts of the Dorking.

Five-toed fowls have been known from very early times. The
character is now most definitely associated with the Dorking, though it
is also considered necessary in Houdans for show purposes. It is
likely that the latter breed derived the fifth toe from the Dorking.
Fifth toes may often be seen to occur in other breeds, but I cannot
quote a satisfactory record of their appearance in pure strains.

In the foot of an ordinary four-toed fowl the hallux articulates with
the tarso-metatarsus by a separate metatarsal. The hallux in such a
foot most often has two phalanges. In its commonest form the five-
toed foot departs from this normal in the fact that the hallucal meta-

1 See also the case of Rissa, p. 396.

chap, xiii.] DIGITS I BIRDS. 391

tarsus bears two digits instead of one. The morphological nature of
these digits is obscure. Some have judged that one of them is .1
" prse-hallux ; " Cowper ' sees in the internal toe the true hallux, and
argues that the digit commonly called the hallux is really the index ;
Howes and Hill2 consider that the normal hallux has split into these
two digits. The diversity of these views comes partly from an insuffi-
ciency of the area of fact over which the inquiry has been extended,
for it will be found that the conditions are very various and shade off
imperceptibly in several directions. As in all cases of Meristic Series,
the first question relates to the position of these digits in the system of
Symmetry of the limb. Are they in a Successive Series with the
other digits, or do they balance them ? Are they in Succession to each
other or do they balance each other as images 1

Turning to the facts with these considerations in view it will be
seen that no general answer can be given, but that the condition is
sometimes of the one kind and sometimes of the other. For there are
not merely two conditions, a four-toed and a live-toed, but there is a
whole series of conditions and according to the cases chosen so may the
question be answered. By examining a few score of fowls' feet many
sorts may be seen.

590. (1) The most usual five-toed foot is that figured by Cowpeb
(I.e., p. 2-19), in which the metatarsal of the hallux bears two digits, an
outer one of two phalanges and an inner of three phalanges. For pur-
poses of description let us call the outer the hallux. In this foot then
the hallux is the least digit, and the members of the digital series
increase in size on either side of it.

591. (2) But not rarely is found a state like the last save that the
inner digit is borne by the proximal phalanx of the hallux. This is
very common. The two digits may then be about equal in size, or
more often the hallux is the smaller.

592. (3) Hallux more or less perfectly divided into two digits with a
common base, having (a) two, or (b) three phalanges (as in Howes' case
Fig. 5). This state is practically that of the human "double-thumb"
(see p. 350), and, just as in that phenomenon, the duplicity may be of
various extent, often affecting only the nail and distal phalanx. f ><•-
tween the two parts of such a double digit there is often that relation as
of optical images found in human double-thumb, the curvatures of the
two parts being equal and opposite. But if both digits are of good -
and are separate up to the metatarsal this equality is rarely it ever found,
and one of the digits, generally the innermost, is the larger. In this
condition therefore there is a Succession from the hallux to the inner
digit just as in (1). So the condition of double-hallux, that is to say
the representation of one member of a series by two members in bi-
lateral symmetry, shades off' imperceptibly into the condition in which
a new member is formed in Succession to the terminal member.

It should be noted that this case presents a remarkable difference
from that seen in the like cases of variation on the radial Bide of the
hand of Man. In Man the states of true double-thumb are just as in
the Fowl; but if there is a difference or Succession between the two parts

1 Jour. Anat. Phys., xx. p. 593; and xxm. p. 242.
- Ibid., xxvi. p. 31)5, jigs.

392 MERJSTIC VARIATION. [pam I.

it is the external l which is the greater, being in several cases a three-
phalanged digit shaped like an index (see No. 486). Nevertheless in the
Fowl it is the internal which is the greater.

The conditions in the following cases are not far removed from those named
above.

593. Archibuteo lagopus (Rough-legged Buzzard): specimen in good condition
shot near Mainz, being otherwise normal. The toes of the left foot were placed as
usual in a bird of prey, but on the outside2 of the hind toe was a much smaller
accessor}- toe. This accessory toe was attached to the hind toe almost as far as the
base of the claw of the latter. The claw of the accessory toe was half the size of
that of the hind toe. In the left leg the muscles of the thigh and shank were less
developed than usual. Toes of right foot abnormally arranged, being all directed
forwards. The three normally anterior toes were on the inside of the series, and
the toe which should properly be single and directed posteriorly was double and was
directed anteriorly. These abnormally disposed toes were not functional. The
right leg was much more developed than the left, and it seemed as if the bird had
habitually stood on the right leg. vox Reichenau, W., Kosmos, 1880, vn. p. 318.

594. Gallinula chloropus (Moorhen): specimen killed in Norfolk in 1846. "Each
of the hind toes possessed a second claw, which in the right foot merely springs
from about the middle of the true toe, but in the left is attached to a second toe,
which proceeds from the original one, about half-way from its junction with the
tarsus." Extra toe and claw in each case attached outside2 of the true hind toe.
Guexey, J. H., and Fishek, W. R., Zoologist, 1601.

Guinea-hen having double hallux ; of the two digits the external 2 was the
longer. Geoffroy St Hilaire, Hist, cle Anom., i. p. 695.

Division of digits II and III.

595. Anas querquedula, L. (Garganey Teal): wild specimen having the left foot
abnormally formed. In it there was no toe occupying the place of the hallux, but
the digits II and III [using the common nomenclature] were partially bifurcated.
In the digit III, the extremity only was divided, but each part bore a separate nail
and there was no web between these secondary digits, which were somewhat irregular
in form. The digit II divided in about its middle into two nearly similar digits,
which were united by a web. The nails of these digits were hypertrophied. Erco-
laxi, Mem. Ace. Bologna, S. iv. T. in. p. 804, Tav. in. fig. 1.

596. (4) From the condition seen in (3) it might be supposed that
duplicity of the hallux is the least possible step in the progress of the
four-toed form towards the five-toed. It is only one of the least possi-
ble steps. For in a few cases upon the base of the digit recognizable
as the hallux, and standing in the normal place of the hallux, may be
found a minute rudiment of a digit, sometimes with a nail, sometimes
without. Between this and the well-formed fifth toe all conditions exist.

There are thus, as usual in the numerical variations of Meristic
Series, two least conditions, one being found in duplicity of a single
member, the other taking the form of addition of a rudimentary
member beyond the last member.

597. Passing now from the simpler conditions of the variation to the
more complex, several distinct states may be mentioned. The diverg-
ence from the normal may be greater either by the presence of two
extra digits, or by change in the position of the extra digit or digits.

1 The only case to the contrary is that mentioned by Wixdle, Jour. Anat. Phys ,
xxvi. p. -440, in which a three-phalanged digit stood on the radial side of a pollex.
This ease has not been described. See pp. 326 and 352.

2 In reading these records it should be remembered that owing to the backward
direction of the hallux the apparent outside is morphologically inside, and probably
this is meant in each case.

chap, xiii.] DIGITS : BIRDS. 393

Tico extra digits are said to be not uncommon in the Dorking but I have
myself seen only one case. A foot of this kind is figured by Cowper1,
and in it the appearance is as of an extra digit of three joints ( ? all
phalanges) arising internally and proximally to the hallucal metatarsal,
which already bears two small and sub-equal digits. In the case seen
by myself there was one large internal digit with three phalanges sepa-
rately articulating with the tarso-metatarsus, and the hallucal metatarsus
bore a digit divided peripherally, bearing two nails related as images.
Here therefore there was a double hallux, and internal to it a separate
digit.

598. The evidence regarding extra digits in other positions, though small
in amount, is of importance as a light on the morphology of these repeti-
tions of digits. We have seen that the ordinary extra digit is, with
the hallux, borne on the hallucal metatarsal. In one of Howes' cases
(I. c. figs. 2 and 3) this metatarsal instead of simply articulating with
the shank of the tarso-metatarsal ivas continued up to articulate also
with the tibio-tarsus. From this state the condition in which a separate
digit (or digits) articulates with the tibio-tarsus only is not far removed.
Of this condition I know no detailed account in the Dorking, though it
is referred to by Lewis Wright 2, but I have met with the following
cases in other birds. •

599. Aquila chrysaetos (Golden Eagle): having two extra toes borne by right
metatarsus [left foot is not described]. The two extra toes attached to upper part
of the back of the metatarsus. Each bears a full-sized claw which was curved
backwards and upwards. One of the toes bore six scutella on the morphologically
upper surface and four on the plantar surface. The other toe, which was more
completely united to the metatarsus along its whole length, bore only a single
scutellum on the plantar surface. The rest of the foot was normal. Jackel, A. J..
Zool. Gart., xv. 1874, p. 141, fig.

600. Pheasant: right foot bearing a thin and deformed digit articulating internally
with the distal end of tibio-tarsus. Hallux normal. Left not seen. Specimen
received from Mr W. B. Tegetmeier.

(301. Pheasant: each leg bears a large extra digit of irregular form attached to the
middle of anterior surface of tibio-tarsus. The two legs almost exactly alike, but in
one the digit is firmly and in the other loosely attached to tibio-tarsus. Specimen
kindly sent by Mr Tegetmeier.

602. Buteo latissimus S , having extra digit on right leg. the toe was well formed,
with two phalanges, bearing perfectly formed claw, loosely attached internally
to tibio-tarsus just above articulation with tarso-metatarsus. Coale, H. K., Auk,
1887, iv. p. 331, fig. [Cp. No. 593.]

603. Turkey having two imperfectly separate digits [? images] attached to process of
tibio-tarsus. Two cases differing in degree: hallux normal. Ercolani, Mem. Ac.
Bologna, Ser. iv. in. PI. in. figs. 2 and 3.

604. Pheasant: somewhat similar case, in which two such digits were similarly
placed, but one was large and the otber small. Ibid., fig. 4.

605. Larus leucopterus. For the following case I am indebted to Professor R.
' Ridgway, Curator of the Department of Birds, in the United States National

1 Cowper, J., Joum. Anat. Phys., xxm. p. 249.

2 "Perhaps the most difficult point in judging Dorkings, however, La to watch

against malformations of the feet which have been fraudulently removed ; for

the abnormal structure of the Dorking foot is very apt to run into still more abnor-
mal forms, which disqualify otherwise fine birds for the show-pen. Birds are not
unfrequently produced which possess three back toes, or have an extra toe high ap
the leg; or, in the case of the cock, with supernumerary spurs, which have been

known to grow in every possible direction We have on two occasions seen

prizes awarded to birds which shewed unquestionable traces of such amputation...."
The Illustrated Book of Poultry, 1886, p. 331.

394

MERISTIC VARIATION.

[part I.

Museum. The specimen is No. 76,221 in that collection, marked "Greenland,
Sept. 1877 ; Loc. Kumlien." The accompanying figures were kindly made for me

A

B

Fig. 122. Larus leucopterus, No. 605.

A. Eight foot seen from in front.

B. The same from the internal side.

C. Left foot from in front.

From a drawing of specimen in U. S. Nat. Mus., kindly made for me by Prof.
Eidgway's direction.

under Professor Eidgway's supervision and sufficiently shew its structure (Fig. 122).
[It will be seen that the hallux in A, the right foot, appears on the outside; this I
conceive is due to partial rotation to shew the abnormal toes.]

Besides these there are a few amorphous cases of extensive repetition of digits in
birds.

These facts shew how fruitless a work it is to try to find a
general statement which shall include all the cases. There is an
almost unbroken series of conditions starting from either duplicity
of the hallux, or from the presence of an internal rudimentary

chap, xiii.] DIGITS : LIZARD. 395

digit, up to a condition somewhat resembling that of " double-
hand " in Man. If the first digit behind the hallux is the prae-
hallux, what are the digits on the tibio-tarsus ? If on the other
hand the appearance of an extra digit internal to the supposed
hallux is to be evidence that this " hallux ,: is the index, it may
equally be argued that if two digits come up internal to the
" hallux " then the supposed hallux is the medius, and so on inde-
finitely. Again, though with Howes and Hill we may accept
the cases of double-hallux as evidence that an extra digit may
appear by division of the hallux, which is indisputable, we must
equally accept the cases Nos. 597 and 598 as evidence that extra
digits may grow directly from the tarsus or even from the tibia,
though the hallux remain single and unchanged. And between
these two there is no line of distinction ; they pass into each
other. Do not these things suggest that we are looking for an
order that does not exist ? Is it not as if we should try to name
the branches of a tree in their sequences ?

Possibly Continuous numerical Variation in Digits : miscellaneous

examples.

Under this heading are placed in connexion a few cases of
great interest. Whatever may be held as to the relation to the
problem of Species of the phenomena hitherto described, it can
scarcely be doubted that the following are instances of Variation
which at least may be of the kind by which new forms are evolved.

Great interest would attach to a determination whether the
reduction of the digits in these cases is a' continuous or a discon-
tinuous process, but unfortunately these phenomena have been
statistically studied by no one, and it is not possible to do more
than make bare mention of the fact that such Variation is known
to occur. There is no statistical evidence as to whether the indivi-
duals in any one locality may not fall into groups, dimorphic or
polymorphic in respect of the degree to which the digits are
developed (compare the case of the Earwig, Introduction, p. 40).
As an inquiry into the Continuity of Variation such an investiga-
tion would be exceptionally valuable. In the case, for instance, of
Cistudo mentioned below, such a statistical inquiry should surely
not be hard to make.

*606. Chalcides. This is a genus of Lizards belonging to the
family Scincidse. In several genera of this family the limbs are
reduced or absent, differences in this respect being frequent among
species of the same genera. (See Boulenger, Catalogue of Lizards
in Brit. Mus., 1887, m. pp. 398, &c.)

Mr Boulenger kindly shewed me a number of Lizards of the

.....

genus Chalcides from the shores of the Mediterranean basin which
strongly resemble each other in colour and general appearance, but
which contained almost a complete series of conditions in respect

396 MERISTIC VARIATION. [part i.

of the development of the limbs and digits, ranging from C. ocellatus
and C. bedriagce with pentadactyle limbs fairly developed, through
C. lineatus (tridactyle) and 0. tridactylus to C. guentheri in which
the limbs are minute conical rudiments. Amongst the species of
this series great individual variations occur.

607. Chalcides mionecton : normally four digits on each foot.
A specimen in Brit. Mus. kindly shewn to me by Mr Botjlenger
has on each hind foot five digits.

608. C. sepoides : Mr Botjlenger tells me that the normal num-
ber of digits on each foot is five, but that specimens occur having
four digits on each foot.

609. Cistudo. This genus includes the North American Box-
turtles as defined by Agassiz (N. Amer. Testudinata, Gontrib. to
N. H. of U. S., I. p. 444). These animals are widely distributed
to the E. of Rocky Mountains. On the hind feet of some of them
there are three digits, while others have four. Gray (P. Z. S.,
1849, p. 16) described two Mexican specimens which agreed in
having three large claws on the hind foot with no appearance of a
fourth claw, and even scarcely any rudiment of the fourth toe,
which was then believed to be present in the other members of
the genus. To this three-toed form he gave the generic name
Onychotria, but in Brit. Mus. Cat, 1855, he gave up this name as
a generic distinction, describing the Mexican form as Cistudo mexi-
cana, giving three toes on the hind foot as a definite character.

Agassiz in 1857 (I.e.) divided Cistudo into four species, giving
to the Mexican form the name C. triunguis, and he states that the
western and south-western type is remarkable for having almost
universally only three toes on the hind feet. The toe which is
missing is the outer toe and " it fades away so gradually that the
genus Onycliotria cannot stand." The form found from New
England to the Carolinas is called by Agassiz G. virginea = C. Caro-
lina, and he states that he received a three-toed specimen from N.
Carolina which agreed in all other respects with those from New
England.

Putnam (Proc. Boston, N. H. S., x. p. 65) stated that the three-
toed form found in the South is only a variety of C. virginea, and
that he had seen two specimens which had three toes on one hind
foot and four on the other.

610. Rissa1. The common Kittiwake (R. tridactyla) as found in

1 In illustration of the possible bearing of these facts on the problem of Species
reference may be made to the fact that among birds there are several examples of
species differing from their near allies by reason of the absence of the hallux.
Speaking of this feature in Jacamaraleyon tridactyla, Sclater observes: "In the
present bird we meet with another example of the same character [viz. a monotypic
form], and with one, perhaps, more isolated in its structure than any of those
above mentioned, Jacamaraleyon being notably different from all other members
of the Galbulidae in the absence of the hallux. At the same time we must be
careful not to put too high a value upon this at first sight seemingly important

chap. xiii. j DIGITS : K1TTIWAKE, ELEPHANT, &C. 397

this country and in N. Atlantic has no hallux, but only a small
knob without a nail in its place. No variation in respect of this
digit is recorded1. Birds not distinguishable from the Atlantic
Kittiwake occur in the North Pacific, but amongst these Pacific
specimens birds are found occasionally as rarities having a hallux
" as large as it is in any species of Larus " (Coues, p. 640). This
feature also exhibits gradatious. Specimens are described by
Coues and also by Saunders having the hallux including the
nail 2 in. long, with a perfect claw. These are given as extreme
examples. Saunders remarks that this hallux is small for the
size of the bird, stating that another species of similar size, L.
canus, had a hallux '5 in. long. Of these specimens of R. tridac-
tyla from Alaska one had the nail of the hallux developed, though
less so than in the extreme case. Saunders states further that the
variation is not always equal in extent on both feet of the same
individual : he considers that the extreme form is probably rare
and local. Coues, E., Birds of North-West (U. S. Geol. Surv.
Terr.), 1874, p. 646; and Saunders, Howard, P. Z. 8., 1878, pp.
162—64.
611. Rissa brevirostris : a species from the N. Pacific distinct from
R. tridactyla shews a similar variation in the development of the
hallux, though in a smaller degree. A specimen has no claw on
right hind toe and only minute speck on left ; another has no
hind nail whatever ; another has small black nails of unequal size
on the two hind toes. Saunders, H., I. c, p. 165.

(312. Erinaceus. E. europceus has a large hallux, while in E. diadema-
tus it is only 4 mm. in length, and in E. albiventris it is normally absent
in adults. An adult female S. albiventris had a minute hallux in
the left hind foot, represented by a claw and ligamentous structures,
the rjhalanges being absent2. In a female a few months old a minute
hallux with usual number of phalanges was present on both sides.
The presence or absence of a hallux has often been considered a suffi-
cient ground for the formation of a new genus. Dobson, G. E.,
P. Z. &, 1884, p. 402.

613. Elephas. In both the Indian and African elephant the
number of digits represented by bones is five, both in the fore and
the hind foot. The number of hoofs differs in the two species.
The African elephant has normally four on the fore foot and three

character, as the same feature occurs as is well known, not only in certain genera
of other allied families (such as Alcedinidre and Picida}), but even in a genus of
Oscines (Cholornis), in which group the foot- structure is generally of a very uniform
character." Sclater, P. L., Monograph of t he Jacamars and Puff-Bird*t 1879 -82,
p. 50.

1 Mr A. H. Evaxs has called my attention to a recent paper by Clarke (Ibis,
1892, p. 442) giving an account of a minute rudiment of the hallux in embryos of
R. tridactyla from Scotland.

2 Compare facts as to the loss of the hallux in Mungooses (Herpestida1), Thomas.
O., P. Z. S., 1882, p. 61.

398 MERISTIC VARIATION. [part I.

on the hind foot, and I am not aware that variations from this
number have been seen.

In the Indian elephant there is variation, and though I cannot
give any complete account of the matter the following particulars
may be of interest.

According to Buffox the ' Elephant ' has generally five hoofs
on both fore and hind feet, but sometimes there are four, or even
three1. He gives a particular case of an Indian elephant with
four hoofs on each foot, both fore and hind feet.

Tachard2, to whom Buffon refers, was desired by the French
Academy to notice on his journey in Siam, whether elephants had
hoofs, and he states that all that he saw had five on each foot.
Possibly the four- toed variety does not occur in Siam.

I am indebted to Mr W. T. Blanford for the information that
the natives of India attach importance to the number of hoofs,
and also for the following references. Hodgson3 gives a sketch
of elephants with four hoofs on each foot, marked " Elephas
Tndicus, var. isodactylus nob., Hab. the Saul forest," together with
the following note : " The natives of Nepal distinguish between
the breeds with four toes [sic] on all the feet and those with five
to four toes." Sanderson4 speaking of this says that some
elephants have but sixteen hoofs, the usual number being five on
each fore foot and four on each hind foot ; and that in the native
opinion 'a less number than eighteen hoofs in all disqualifies the
best animals.' Forsyth5 also alludes to the same fact.

Taken together these accounts seem to shew that five on the
fore foot and four on the hind foot is the most usual number, but
that both the number on the fore foot may diminish to four and
that on the hind foot may increase to five. Several text-books
mention the subject but I know no statistics regarding it. In
view of the different number characteristic of the African elephant
this variation has some interest. In particular it would be of use
to know whether the variation exhibits Discontinuity, and also
to what extent it is symmetrical.

Inheritance of digital Variation.

614. Recurrence of digital Variation in strains or families is frequent,
but though many observations on the subject have been made no
guiding principle has been recognized. To the general statement that
digital Variation, whether taking the form of poly dactyl ism or other-

1 Buffon, Hist. Nat., xxviii. p. 201. The mention of three hoofs must I think
refer to the African species, which Buffon does not distinguish from the Indian.
In the Cambridge Museum (Catal. 699) is an old preparation of the skin of an
elephant's foot having three hoofs. This is declared by the Catalogue to be the
fore foot of an Indian elephant. Perhaps this is a mistake.

2 Tachard, Voy. de Siam, 1687, p. 233.

3 Hodgson, B. H., Mammals of India, MS. in Zool. Soc. Library.

4 Sanderson, G. P., Wild Beasts of India, p. 83.

5 Forsyth, J., Highlands of India, 1872, p. 286.

chap, xiii.] INHERITANCE OF DIGITAL VARIATION. 399

wise, does very commonly appear in the offspring or kindred of the
varying individuals I can add nothing. It should be mentioned that
though in families exhibiting digital Variation the forms that the
change takes may differ (in some cases widely even among individuals
nearly related) yet on the whole the variation, if recurring at all, more
often recurs in a like form. This holds good apart from the rarity
of the particular form of variation. The facts described by Farge
(I.e., infra) are exceptionally interesting in this connexion. In the
family described by him duplicity of the thumbs occurred in the
paternal grandmother, while the father and three children had their
thumbs of the three-phalanged form as in No. 483. This case strikingly
illustrates the well-known principle that Meristic variability may
appear in the same strain or family under forms morphologically very
dissimilar.

Attention is also called to the circumstance that in the case of the
three toes in the ox (No. 558) the descent was wholly through females,
and the same was almost certainly true in the polydactyle cats (No. 480).
In the case of the syndactyle pigs the evidence of maintenance of the
variation in the strain is very clear (No. 584). See also No. 564.

As regards digital Variation in Man the following are the best
genealogical accounts :

Anderson, Brit. Med. Jour., 1886 (1), p. 1107. Billot, Mem. vied, milit., 1882,
p. 371. Boyd-Campbell, Brit. Med. Jour., 1887, p. 154. Fackenheim, Jen. Zte.,
1888. Fotherby, Brit. Med. Jour., 1886 (1), p. 975. Furst (see Canst. Jahresb., 1881,
p. 283). Harker, Lancet, 1855(2), p. 389. Lucas, Gm/s Hosp. Rep., xxv., p. 417.
Morand, Mem. Ac. Sci., 1770, p. 140. Muir, Glasg. Med. Jour., 1884. Pott,
Jahresb. d. Kinderh., xxi., p. 392. Potton1 quoted by Gruber from de Bansi .
Bull. Soc. d'Anthrop., 1863, iv. p. 616. Struthers, Edin. Neio Phil. Jour., 1863(2),
pp. 87 et seqq. Wolf, Berl. klin. Wochens., 1887, No. 32. Farge, Gaz. hebd. de
med. et chir., Ser. 2, n. 1866, p. 61. Case given Loud. Med. Gaz., 1834, p. 65.

Association of digital Variation with other forms of Abnormality.

(315, In the great majority of cases of polydactylism the rest of the bod}
is normal, the limb or limbs varying alone. There are however a cer-
tain number of examples of polydactylism in association with other
abnormalities ; as for instance with phocomely, cyclopia, double uterus,
hare-lip, defective dentition, defect of tibia, <kc, but there is nothing
as yet to indicate any special connexion between these several
variations. Diminution in number of digits and syndactylism is on
the contrary very often associated with general deformity and with
many forms of arrested development. To this no doubt is largely due
the fact that cases of ectrodactylism are commonly irregular, whereas
polydactylism is generally fairly regular in its manifestations, for
numerous cases of diminution in number of digits occur in bodies or
in limbs otherwise amorphous.

1 The notorious case of a village in Isere where the majority of the inhabitants
are said to have been polydactyle. Most modern writers on the subject quote this
statement but I have never found original authority for the fact. By some it is
referred to Devat, Du danger des mariages consanguins, 1862, p. 95, but I can rind
no mention of the facts in that work.

CHAPTER XIV.
Digits : Recapitulation.

In the remarks preliminary to the evidence of digital Variation
it was stated that this group of facts is interesting rather as bearing
on morphological conceptions than from any more direct relation
to the problem of Species. The indications to be gained from the
evidence will be treated under the following heads :

(1) Comparative frequency of digital Variation in different

animals.

(2) Particular forms of digital Variation proper to particular

animals.

(3) Symmetry in digital Variation.

(4) The manus and pes as systems of Minor Symmetry.

(5) Duplicity of limbs.

(6) Homceotic Variation in terminal digits when a new

member is added beyond them.

(7) The absence of a strict distinction between duplicity of

a given digit and other forms of addition to the
Series.

(8) Discontinuity in digital Variation.

(9) Relation of the facts of digital Variation to the problem

of Species.

(1) Comparative frequency of digital Variation in different animals.

In reviewing much of the evidence of Variation and especially
in the evidence concerning the variations of teeth it has been seen
that the frequency of these variations is immensely greater in some
classes or species than in others. This is remarkably clear in the
case of the variations of digits. Compare for instance the great
frequency of polydactylism in the Horse with the complete absence
of recorded cases in the Ass. It is true that the latter is the rarer
animal, but it might still be expected that some record would have
been found if the variation were as frequent in the Ass as in the
Horse. Again polydactyle Cats are certainly not very rare and
specimens are in several collections having been acquired at many

chap, xiv.] FREQUENCY OF DIGITAL VARIATION. 401

dates. On the other hand digital Variation in the Dog seems to
be confined to the formation of a hallux in the hind foot, and to
duplicity of hallux and pollex \ Similarly though digital Varia-
tion is so common in the Pig it is very rare in the Sheep, only
one or two clear cases being so far known to me. Note again that
polydactylism is common in the Fowl and has been often seen
in the Pheasant, while in other birds it is very rare.

Some one will of course remark that the Fowl is a domesticated
bird and the Pheasant is partially so ; but pigeons, ducks - and
geese3 are as much domesticated and in them digital Variation
does not seem to be known. The cases in Apes deserve mention
in connexion with this matter. One case of syndactylism was
quoted in Pithecia No. 525, a case of polydactylism in Macacus No.
504?, in Orang No. 511, and in Hylobates No. 508, and a case of
ectrodactylism in Macacus No. 526. These five cases surely
suggest that Meristic Variation is something more than a mere
result of high feeding or of " unnatural " conditions. It is not a
little strange that among Apes Meristic Variation should be
frequently met with in so many systems of organs.

(2) Particular forms of digital Variation proper to particular

animals.

Of more significance than the frequency with which digital
Variation recurs in certain animals is the frequency with which in
particular animals it approaches to particular forms, or to particu-
lar conditions in a series or progression of forms. This has been
seen in the Cat, Man, Horse, Pig, Ox, &c. In each of these the
mode of occurrence of Variation has in it something distinctive,
something that marks the phenomenon as in some way different
from the similar phenomena in other forms. Taking for instance
the curious series of cases found in the human manus, ranging

1 Both these variations are of course very common and may be seen in any
walk in the streets. The hallux is very frequently present in the Dachshund and
is common in Collies, Mastiffs and other large breeds. In the Mastiff dew-claws
(hallux) are not a disqualification (Shaw, Book of the Dog). In the St Bernard the
hallux is very often double, perhaps more often than not. This is largely due to
the fact that the monks of the Hospice considered the presence of the dew-claw of
the utmost importance and preferred it double if possible (Shaw, I.e.). The same
writer states that ' the more fully the dew-claws are developed the more the feet are
out-turned.' This fact suggests that there may be a change of Symmetry like that
in the Cat, but I have no observations on the point. I have several times seen
simultaneous duplicity of hallux and of pollex in the same individual (Dachshund,
&c). Other digital variations must be rare in dogs as there are hardly any recorded
cases. A problematical case of ectrodactylism is given by Baum, Deut. Ztochr. f.
TJiierm., xv. 1889, p. 709, Jig. [q. v.]. I once saw a mongrel Fox-terrier with no
pollex on either manus, but I was not satisfied that they had not been cut off,
though there was no suggestion of this.

- For an interesting account of a Duck with the webs of the toes almost wholly
absent see Mobius, Zool. Gart., xvm. 1877, p. 223. Another case of the same kind
Morris, F. 0., Zool., iv. p. 1214.

3 Pygomelian geese often recorded; e.g. Clelaxd, Proe. Phil. Soc. Glasg.,
xvm. 1886, p. 193,^.; Wyman, Proc. Bost/N. H. S., vm. 1861, p. 256.

b. 26

402 MERISTIC VARIATION. [part l

from the addition of a phalanx to the pollex up to the condition of
Nos. 488 or 490, and comparing them with the essentially similar
series of cases in the hind foot of the Cat, there is this remarkable
difference : that though both progressions lead up to a similar
kind of Symmetry in the series of digits, in the human manus
an approach is made to a system of Symmetry whose axis lies
internal to the index, while in the Cat's feet the axis lies external
to the index (see Section (4)). The series of forms in the manus
of the Cat is still more peculiar and is not like any case of poly-
dactylism in other animals.

(3) Symmetry in digital Variation.

From the evidence it will have been seen that digital Varia-
tion in most of its manifestations may be similar and simultaneous
in the limbs of the two sides of the body, though not rarely it
affects the limb of one side only ; and still more frequently the
form which it assumes on one side differs in degree from that found
on the other side. Considerable difference in kind between Varia-
tion on the right side and on the left is much rarer.

Almost the same statement may be made respecting simul-
taneity of Variation between the manus and the pes, though in
the pes the manifestation of Variation is rarely identical with that
in the manus of the same individual. Some variations, as for
instance duplicity of pollex and hallux, or extra digit external to
minimus, are not rarely found simultaneously in both pes and
manus, but there are many cases in which no such agreement is
found. The frequency of this simultaneous variation in the case of
syndactylism in the Pig may be specially noticed.

Certain variations in certain animals seem to be almost or
quite restricted either to hind limb or to fore limb. The form
taken on by the pes of the Cat upon increase in number of digits
is distinct from that assumed by the manus. The development of
the digit II in the Horse is much more common in the manus.
The extra digit (or pair of digits) in the Pig is so far as I know
seen only in the manus. On the contrary the three-toed state in
the Ox is found in the manus and also in the pes. Generally
speaking, M eristic Variation is much commoner in fore limbs than
in hind limbs.

One fact here calls for special notice. Though general statements
are hazardous, we are perhaps justified in affirming the principle
that large Meristic Variation, involving great departure from the
normal, very rarely affects exclusively one side of a bilaterally sym-
metrical body. In cases of variation in vertebra?, in spinal
nerves, in teeth, in the oviducts of Astacus, and many more, it is
seen that on the occurrence of great variation the change is seldom
restricted wholly to one side of the body, though the condition
reached by the two sides is frequently of differing degree. Now in

chap, xiv.] SYMMETRY IN DIGITAL VARIATION. 403

the extreme forms of double-hand as seen in Man there is a curious
exception to this principle. For in nearly all the extreme cases
the abnormality was on one side only, the other being normal.
This was seen in Nos. 492 — 500 and 501 — 503, and also in Macucus
No. 504. The case No. 500 is probably an exception to this general
statement. As to the significance of this absence of correspond-
ence between the right and left sides in extreme cases of digital
Variation I can make no conjecture. It has seemed that perhaps
in such cases the absence of symmetry between the two sides
of the body may be connected with the fact that in these extreme
forms of double-hand an approach is made to a bilateral symmetry
completed within the series of digits. But against this suggestion
must be noticed first the fact that a similar bilateral symmetry is
established in the six-toed pes of the Cat (Condition IV of the pes,
p. 316), but the variation is nevertheless found on both sides of
the body ; and secondly the case of double-foot in the lamb (No.
566), though for reasons stated this latter case may perhaps be
open to question.

(4) The manus and pes as systems of Minor Symmetry.

This is a subject to which it is most difficult to give adequate
treatment. Several of the phenomena have as yet been studied in
far too small a range of cases to justify sound generalization, and
with further knowledge the suggestions arising from the facts now
before us may not improbably be found to have been misleading
wholly or in part. Besides this there is a serious difficulty in
finding modes of expressing with clearness even those principles of
form which seem to underlie the phenomena. This difficulty pro-
ceeds first from the vague and contradictory character of the
indications, and next from the total absence of a terminology by
which diversities of symmetry and the form-relations of parts may
be expressed. Nevertheless it has seemed best to abstain from
the introduction of new terms until the ideas to be expressed
shall have been more clearly apprehended. It need scarcely
be said that the remarks which follow merely represent an attempt
to state some of the lines of inquiry along which the facts point.

On p. 88 mention was made of the fact that in a Bilateral
Symmetry the organs which occur as a pair, one on the right and
the other on the left, in so far as they are symmetrical are optical
images of each other, this relation of images being what is implied
by the statement that these organs are bilaterally symmetrical.
The hands and feet of vertebrates are organs of this kind, the
right hand and the right foot being approximately images of tin
left hand and foot respectively. But beyond their symmetrical
relations to each other in the Major Symmetry of the whole body
each manus and each pes may exhibit the condition of a Minor
Symmetry within the limits of its own series of digits. Not only
may each limb geometrically balance the limb of the other sid>-

26—2

404 MERISTIC VARIATION. [part I.

but its own external parts may more or less balance its own inter-
nal parts. This relation differs greatly in different animals, the
Minor Symmetry being nearly complete in the Artiodactyles and
in the Horse, but much less so in the human manus and pes, &c.
The matter now for consideration is the influence or consequences
of the existence of this symmetry in the Meristic Variation of
digits ; and conversely the light which the observed phenomena of
Variation throw on the nature of that relation of symmetry. It
will be seen that in some points the two halves of a bilaterally
symmetrical limb behave just as do the two halves of the bilaterally
symmetrical trunk, while in other points their manner of Varia-
tion is different.

Thus, the digit III of the Horse may divide into two halves
related to each other as images, bearing hoofs flattened on their
adjacent edges ; that is to say, the two resulting parts are formed
not as copies of the undivided digit, but as halves of it, a condition
never seen in division occurring anywhere but in the middle line of
a bilateral Symmetry.

In the syndactyle feet of the Pig or the Ox the converse pheno-
menon exists ; for the digits III and IV, which normally stand
as images of each other, are here wholly or in part compounded to
form a digit to which the uncompounded digits are related as
halves.

Thus far the connexion between the geometrical relations of
the digits and the modes of their Variation is clear and simple,
and does not differ from that maintained in the Major Symmetry.
But in proceeding further there is difficulty.

If, for instance, the manus or pes of a Horse possesses within
itself the properties of a bilateral Symmetry, then the splint-bone
II may be supposed to be in symmetry with the similar bone IV.
It would therefore be expected that on the occasion of the develop-
ment of II to be a full digit, the splint-bone IV would at least not
unfrequently develop, thus exhibiting that similarity and simul-
taneity of Variation which we have learnt to expect from parts in
symmetry with each other. Nevertheless such an occurrence
seems to be extremely rare. Then arises a further question: if
the digit II develop simultaneously, say in the two fore feet, would
the mechanical conditions of which Symmetry is the outward
expression be satisfied without a corresponding change in the
digit IV of the fore feet ? Is the frequent absence of symmetry
in the variation of the halves of the Minor Symmetry in any way
connected with the possibility that the two Minor Symmetries
together may be maintaining their relations to each other as parts
of a Major Symmetry ? Of course as to this we know nothing, but
the existence of this double relation should be remembered.

In several other phenomena of digital Variation the influence
of Symmetry is to be suspected. Reference may first be made to
the series of changes seen in the Cat's hind foot in correlation with

chap, xiv.] SYMMETRY IN DIGITAL VARIATION. 405

numerical change. The bones of this pes do not normally exhibit
any very clear bilateral symmetry \ Yet on the appearance of new
digits the foot is reconstituted and its parts are, to use a metaphor,
c deposited ' in a system of bilateral symmetry a whose completeness
is proportional to the degree of development of the new digits.
What may be the meaning of this extraordinary fact one cannot
yet guess. The fancy is constantly presented to the mind that there
is in the normal foot a condition of strain, that the balance between
the right foot and the left is a condition of imperfect stability, and
that upon the introduction of some unknown disturbance this
balance is upset and each foot settles down as a separate
system. But I see no way of testing this fancy and no way of
following it further.

Still more complex are the facts seen in the human hand.
There is here first the fairly complete series of conditions ranging
from the normal, through the three-phalanged thumb up to the
several Conditions in which extra digits upon the internal side of
the limb seem to have sprung up to balance the four normal digits ;
but on the contrary there is the exceptional case of the Macacque's
foot (No. 504) where the extra parts are, as I believe, external.
(Besides these there are the wholly distinct series of "double-
hands," which will be spoken of below.) The former cases taken
alone would certainly suggest that there is an imperfect balance
or system of symmetry subsisting between the thumb and the
four fingers of the normal manus, but to this suggestion there
are numerous difficulties which need hardly be detailed in this
preliminary glance at the phenomena.

With more confidence it can be maintained that the pollex
and perhaps the hallux of Man is in itself a Minor bilateral Sym-
metry, apart from the four fingers, for it may divide into equal
parts related as images. The same is true of the hallux of the
Dorking (p. 390), and probably of the extra digit or digits some-
times arising from the tibio-tarsus of the Turkey for example (see
No. 603).

Besides this the facts of the frequent syndactylism between the
digits III and IV of the human manus, taken in connexion with the
phenomena of the Pig and Ox, suggest that the four fingers may
have among themselves again a relation of the nature of Symmetry.

1 In the normal pes, though all the claws are retracted to the outside of the
second phalanges, yet the claws of digits III and IV rest close together, that of III
being external to its pad, while that of IV is internal to its pad, forming, so far, a
relation of images between these two digits. In the polydactyle foot it is a remark-
able feature that, though the bones are in symmetry about an axis passing between
II and III, the relation of the claws of III and IV to their pads remains almost
normal, still giving a superficial appearance of symmetry between these two digits.
(In the polydactyle pes the pads are mostly rather narrower.)

2 It will be remembered that this symmetry appears not merely in the lengths of
the several digits but in the manner of retraction of the claws and in the corre-
sponding form of the second phalanges, three digits being fashioned (in the case of
six perfect digits) as right digits and three as lefts.

406 MERISTIC VARIATION. [part i.

It has been mentioned that there is some evidence to shew
that in the human pes it is the digits II and III which are most
frequently syndactyle, even up to the point of being (in No. 529)
apparently represented by a single digit, and in this connexion
it will be remembered that in the polydactyle pes of the Cat
it is also between these digits that the new axis of Symmetry
falls.

These scanty allusions to the possible influences which Sym-
metry may exercise over Meristic Variation of digits will suffice to
indicate the nature of the problem to those who may care to
examine it. It is with hesitation that so indefinite a matter is
spoken of at all. Nevertheless it is likely that if any one can find
a way of interpreting these indications the result will be con-
siderable.

(5) Duplicity of limbs.

In the evidence as to the digits of Man facts were given
respecting the state known as Double-hand, and some similar
cases were referred to in Artiodactyles. In these instances the
digital series, and to some extent the limb, is in its new shape
made up of the external parts of a pair of limbs compounded
together in such a way that there is a partial duplicity of the limb,
the two halves being more or less exactly complementary to each
other and related as images1.

This phenomenon in its perfect form must be essentially
distinct from the other cases of increase in number of digits ;
for in the double-hands the limb developes an altogether new
bilateral symmetry (see especially No. 492). Between cases of
duplicity in limbs and the other forms of polydactylism confusion
can only arise when the nature of the parts is ambiguous.

As has been stated, in all certain cases of double-limbs the
two are compounded by their internal or pneaxial borders, but
the case of Macacque No. 504 was peculiar in the fact that there
was in it a presumption that the two limbs were not a pair but in
Succession.

In Arthropoda there are a very few cases of true duplicity in
appendages comparable with the double-hands. These cases will
be dealt with hereafter.

1 The fact that a structure naturally hemi-syminetrical, needing the limb of the
other side to balance it, may on occasion develop as a complete symmetry is most
paradoxical, but no other interpretation of the facts seems possible. The phenome-
non is of course comparable with that observed by Driesch in the eggs of Echinus,
where eacb half-ovum developed into a whole larva on being separated from the
other half-ovum (see p. 35, Note). It will be shewn that in almost every case in
which such an appearance is found in the extra appendages of Insects this appear-
ance is misleading, and that the extra parts have a Secondary Symmetry of their
own ; but no such way through the difficulty is here open.

chap, xiv.] DISCONTINUITY IN DIGITAL VARIATION. 407

(6) Homceotic Variation in terminal digits token a new member

is added beyond them.

This is a principle that has been several times seen in Meristic
Variation, and in Chapter x. Section 7, it was treated of at length
in the case of teeth. Some few illustrations of the same principle
occur among the evidence as to digits. It has been seen for in-
stance how that, upon the appearance of an extra digit on the
radial side, the digit which stands in the position of pollex may have
three phalanges and resemble an index (No. 485, &c). Similarly
it was found that upon the formation of a large digit externally to
the minimus the digit standing in the ordinal position of the
minimus may have an increased proportional length (No. 509).
Still more important is Morand's case (No. 510), in which the most
external digit had muscles proper to a minimus, while the digit
standing in the ordinal position of the minimus was without them.

The cases of extra digit in the Horse (No. 536, &c.) still more
clearly illustrate the principle, if the view of the nature of those
cases taken in the text be received.

It should be expressly stated that in digits, as in teeth, it is
not always that the terminal member is promoted on becoming
penultimate. Such promotion is indeed rather exceptional in
digits, but the fact that it may occur is none the less a phenome-
non of great significance.

(7) The absence of a strict distinction between duplicity of a
given digit and other forms of addition to the Series.

This subject has been so often spoken of in connexion with
special cases that it is unnecessary here to make more than brief
allusion to it. The same principle was shewn to be true of teeth
(p. 270) and of mammae (p. 193), and there is little doubt that it is
true of Meristic Series generally. Facts illustrating the matter in
relation to digits will be found in the evidence as to duplication of
pollex and hallux in Man (p. 351), as to duplication of the hallux in
the Fowl (p. 391), in the evidence of cases in the Horse of variation
intermediate between division of III and development of II (p. 371),
and in the cases of three-toed Cows (p. 377).

In almost all the animals in which any considerable range of
digital Variation is to be seen it is possible to find a series of cases
making an insensible transition from true duplicity, or division into
two equivalent parts whose positions and forms are such that they
maybe reasonably looked upon as both representing a normally single
member, up to the condition in which while the series contains a
greater number of members, each member nevertheless stands in
a regular Succession to its neighbour.

Upon the proper understanding of this proposition and upon
the recognition of its truth hang those corollaries before enuntiated

408 MERISTIC VARIATION. [part i.

touching the false attribution of the character of individuality to
members of Meristic Series.

(8) Discontinuity in digital Variation.

The evidence that the Meristic Variation of digits may be
discontinuous is often rather circumstantial than direct. If for
example in the case of the Horse any one chooses to suppose that
every polydactyle horse had in its pedigree an indefinitely long-
series of ancestors in which the size of the extra digit progressively
increased, it would not be easy to produce direct evidence that this
was not the fact. But as regards the human examples such evi-
dence is abundant, many of the most marked cases being the
offspring of normal parents and there can be no reasonable doubt
that the same would be found true of other animals.

But it may fairly be replied that until it shall have been shewn
that formations like those described as variations may be estab-
lished in a natural race or species the contention that the Varia-
tion of digits may be discontinuous is so far weakened. To this I
would reply by referring to the case of Cistudo, Chalcides, and the
other similar examples ; for though in respect of these forms the
evidence is sadly imperfect yet it plainly indicates that very
distinct and palpable variation may be found between different
individuals. And since it is actually known that there may in
these points be considerable differences between the two sides of
the body it may safely be assumed that at least the same differ-
ences may occur between parent and offspring.

We may therefore take it that there is in these cases some
Discontinuity of Variation, though until some one shall have
examined statistically such cases as that of the Box-turtles or of
the Kittiwakes, as to the magnitude of the Discontinuity it is not
possible to speak. If hereafter Discontinuity shall be shewn to
occur in many such cases it will be difficult to resist the sugges-
tion that similar numerical diversity elsewhere characterizing the
digital series of various forms may have come about by similarly
discontinuous Variation.

(9) Relation of the facts of digital Variation to the problem of

Species.

This relation is both direct and indirect : direct, inasmuch as
some of the conditions seen to occur as variations are not far
removed from those known as normals in other forms ; and indi-
rect, since those strange and paradoxically regular dispositions of
digits which are found among the variations bear witness to the
influence of the principles of Symmetry, and prove that there are
modes in which Variation may be controlled and may produce a
result which has the quality of regularity and order of form
independently of the guidance of Natural Selection.

chap, xiv.] DIGITAL VARIETY AXD SPECIES. 409

Of actual variations from the arrangement of digits character-
istic of one form to that characteristic of another there are as ye1
scarcely any examples. The cases given on pp. 395 to 39S being
the most evident.

For the rest, that is to say examples of arrangements happen-
ing as variations matching no normal, some may say in haste that
with their like Zoology has no concern. It would be convenient if
those who make this careless answer (as many do) would mark
the point at which it is proposed to begin this rejection of the
evidence of Variation. Few perhaps realize how impossible it is to
give a real meaning to these distinctions. As regards digits, for
instance, I suppose that no one who holds the doctrine of Common
Descent would refuse to admit the evidence of Variation as to the
hallux of Hedgehogs (No. 612) as exemplifying the way in which
species may be built up — if indeed species are built up of varia-
tions at all. And if this case is admitted, by what criterion shall
we exclude cases of the formation of a hallux in the Dog ? But if
these are not excluded it is difficult to shew good reason for
not admitting the case of the three-phalanged digit placed as a
hallux in the Cat (No. 472) with all the curious series of which that
is only the first term. Are we quite sure that because there is no
Carnivore with a three-phalanged hallux therefore such a creature
could not exist in nature ? Still more difficult is it to shew cause
why duplicity of the hallux should be set apart as a variation not
capable of being perpetuated or of becoming part of the specific-
characters of an animal, seeing that there is actual evidence both
in the case of the Dorking fowl and in the St Bernard dog that it
may become at least an imperfectly constant character.

In connexion with the subject of this section many suggestions
with special bearing on particular cases, both positive and negative,
will strike every reader. In the present imperfect state of the evidence
it would be premature to pursue these. It may however be well to
mention that several writers, especial ly Joly and Lavocat (No. 554).
have seen in the cases of divided digit III in the Horse an indication
that the digit III of the Horse corresponds with the digits III and
IV of the Artiodactyles. The evidence as to syndactylism between
these two digits in Ox and Pig would probably be considered t<»
give support to the same view. But while we may note that the
relations of the digits with the carpus and tarsus of these forms,
were comparative evidence absent, should absolutely prevent any
one from seriously maintaining such an opinion, nevertheless the
fact that such closely similar systems of Symmetry may thus aris<
independently of each other is of interest.

CHAPTER XV.

linear series — continued.

Minor Symmetries : Segments in Appendages.

Meristic Repetition along the axes of appendages is very like
that along the axis of the body. Just as particular numbers of
segments or repetitions along the axis of Major Symmetry charac-
terize particular forms, so particular numbers of joints characterize
particular appendages. Such numbers frequently differentiate
species, genera, or other classificatory divisions from each other.
In the evolution of these forms therefore there must have been
change in these numbers.

Those who are inclined to the view that Variation is always
continuous do not perhaps fully realize the difficulty that besets
the application of this belief to the observed facts of normal
structure. For in those many groups whose genera or species
may be distinguished from each other by reason (amongst other
things) of difference in the number of joints in some particular
appendage or appendages, will any one really maintain that in
all these the process by which each new number has been intro-
duced was a gradual one ? To take a case : even were evidence
as to the manner of such Variation wanting, would it be expected
that the Longicorn Prionidae, most of which have the unusual
number of 12 antennary joints, did, as they separated from the
other Longicorns which have 11 joints, gradually first acquire a
new joint as a rudiment which in successive generations in-
creased ? Or, conversely, did the other Longicorns separate from
a 12-jointed form by the gradual "suppression" of a division or
of a joint ? If any one will try to apply such a view to hundreds
of like examples in Arthropods, of difference in number of joints
in appendages of near allies — forms that by the postulate of
Common Descent we must believe to have sprung from a common
ancestor — he will find that by this supposition of Continuity in.
Variation he is led into endless absurdity. Surely it must be
clear that in many such cases to suppose that the limb came
through a phase in which one of its divisions was half-made or

chap, xv.] JOINTS OF ANTENNAE. 411

one of its joints half-grown, is to suppose that in the comparatively
near past it was an instrument of totally different character from
that which it has in either of the two perfect forms. But no
such supposition is called for. With evidence that transitions
of this nature may be discontinuously effected the difficulty is
removed.

The frequency of Meristic Variation in appendages is much
as it is in the case of body-segments. On the one hand there
are series containing high total numbers of repetitions little
differentiated from each other (e.g. the antennas of the Lobster),
and in these Meristic Variation is common ; on the other hand
in series containing few segments much differentiated from each
other, such Variation, though not unknown, is rare. Of the
latter a few instances are here offered. That the}7 are so few
may perhaps be in part attributed to the little heed that is paid
to observations of this class. Records of this kind might indeed
be hoped for in the works of those naturalists to whom the title
" systematic " has been given ; but unfortunately the attention
of these persons has from the nature of the case been drawn
rather to features whereby species may be kept apart than to
facts by which they might be brought together.

From the lack therefore of records of such variations their
absence in Nature must not lightly be assumed. To quote but
one case : in the common Earwig the numbers and forms of the
antennary joints are exceedingly variable, but in many special
treatises on Orthoptera, I cannot find that this variability is
spoken of, and if alluded to at all the only notice is given in
the form "antennas 13- or 14-jointed."

Antennae of Insects.

Prionid,e.

I am indebted to Dr D. Sharp for the information that the
number of antennary joints in certain Prionidse varies. In Longi-
corns generally the number of joints is constantly 11. Dr G.
H. Horn of Philadelphia who is specially acquainted with this
group, has kindly written to me that of six species of N.
American Prioni four species have 12 antennary joints constantly
in both sexes. Besides these he gives the following cases of
Variation. It will be seen that in both of these the normal
number is much greater than it is in the other species1.
*61G. Prionus imbricornis : females have very constantly 18 joints;
males have 18 to 20. A male in Dr Sharp's collection has only
17 joints in each antenna.

1 In Prionus imbricornis and P. fissicornis doubt may be felt whether the trifid
apex should be reckoned as one joint or as two, but this applies equally to each
individual. I have counted it as one.

412 MEMSTIC VARIATION. [part t.

*617. Prionus fissicornis: the female has 25, and the male 27 —
30, the note on the preceding species applying here.

618. Polyarthron. A Prionid beetle, in which the male has curious
many-jointed feather-like antennae, according to Serville has always
47 joints, but Thomson (Syst. Ceramb., 1866, p. 284) says the number
varies with the species and individually. A male in Dr Sharp's col-
lection has 45 joints in each antenna and a female has 31 in each.

619. Lysiphlebus is a Braconid (Hymenoptera) parasite on Aphides.
From a colony of Aphides on a bush of Baccharis viminalis 121 speci-
mens of Lysiphlebus were reared : of these 57 were males and 64 were
females.

The number of joints in the antennae varied as follows :

Males.

1 4 joints 18 specimens.

15 37

16 1 ....

15 on one side and 16 on the other 1

Females.

12 7

13 54

14 1

12 on one side and 1 3 on the other 2

In those having a different number of joints in the right and left
antenna?, the last joint of the antenna which contained the fewest
joints was longer than the last joint of the antenna with the larger
number of joints. Nevertheless this relation did not hold throughout :
for example in the case of the male with 16 joints, the last joint was of
the same length proportionally as that of the males with only 14 joints.
As a rule the specimens with fewer antennary joints are smaller than
the others.

Variations were also seen in coloration, in the proportional length
of the tarsi, and in the presence or absence of the transverse cubital
nervure, but none of the characters divided the sample consistently, it
was therefore inferred that the individuals belonged to one species of
Lysiphlebus, (L.citraphis, Ashm.)

From another colony of Aphides living on a rose-bush 58 specimens
of Lysiphlebus were bred, and no characters were found by which these
could be separated from those bred from the Aphis of Baccharis. In
the case of the second sample the joints of antennae were as follows :

Males.

14 joints 10 specimens.

15 19

14 on one side and 1 5 on the other 2

Females.

12 2

13 25

CHAP. XV.]

ANTENNAE : BEETLE.

413

The number of antennary joints is employed as a specific character
in the classification of Lysiphlebus by Ashmead, Proc. U. S. Nat. Mus.,
1888, p. 664). Coquillet, D. W., Insect Life, 1891, Vol. in. p. 313.

*620. Donacia bidens. (Phyt.) A female found by Dr D. Sharp
at Quy Fen in company with many normal specimens had in each
antenna eight joints instead of eleven as in the normal. As shewn
in the figure (Fig. 123) the antennae of the two sides were exactly

Fig. 123. Donacia bidens ? . I. Normal antennae, eleven joints in each.
II. Abnormal specimen, having eight joints in each antenna. No. 620.

alike, and the insect was normal in all other respects. I am much
obliged to Dr Sharp for shewing me this specimen.

Forficula auricularia, the common Earwig. In the various
species of Forficula the number of joints in the antenna? differs,
the numbers 11, 12, 13 and 14 being all found as normals in
different species1. As regards F. auricularia most authors give
14 as the number of antennary joints. Serville2 gives 13 or
14. A number of adult earwigs examined by myself with a
view to this question shewed that there is great diversity in
regard to the number of antennary joints. The whole matter
needs much fuller investigation but the preliminary results are
interesting.

The commonest number is 14, which occurs in perhaps 70 —
80 per cent. The next commonest is 13, which was seen in a
considerable number, while 12, and even 11 occur in exceptional
cases. Different numbers were frequently found on the two sides.

1 Brunner von Wattenwyl, Prodr. eur. Orth., 1882. The number in F. auri-
cularia is given by Brunner as 15, but I have never seen this number. It is no
doubt an accidental error. The same mistake is repeated by Shaw, E., Ent. Mo.
Mag., 1888—89, xxv. p. 358.

2 Suites a Buffon: Orthop., 1839.

414

MERISTIC VARIATION.

[part I.

*

As is usual with appendages the whole length of the antenna?
differed a good deal independently of the number of joints.
621. On comparing antennas with different numbers it seemed that
the proportional length of the first two joints was nearly the
same in all, but in the third joint there was great difference, as
shewn in Fig. 124. The left antenna in Fig. 124, I may be
taken to be the normal form with 14 joints. In it both 3rd and
4th joints are small. The right antenna of the same specimen
has 13 joints and in most of the 13-jointed antenna? the arrange-

Fig. 124. Various forms of antennas of adult Earwigs {Forficula auricularia),
all from one garden and taken at one time.

I. Specimen having the left antenna normally 14-jointed, and the right
13-jointed. No. 621.

II. Both antennae 13-jointed. No. 622.

III. Both antennae 12-jointed. No. 623.

IV. Bight antenna normally 14-jointed ; left antenna 12-jointed. No. 624.

Note that the rights and lefts are arranged as marked by letters r and I. The
antennae were so fixed for drawing in order to bring them side by side after the
bend from the first joint. This figure was drawn with the camera lucida by
Mr Edwin Wilson.

ment was much as shewn in this figure. As shewn, the 3rd joint
especially is here rather longer than in the 14-jointed form, but
several of the peripheral joints are also a little longer, so that

chap, xv.] antenna: earwigs. 415

though the 13-jointed antenna is not as a whole so long as the
14-jointed antenna of the same individual it is longer than its
first 13 joints.

622. But besides the common 13-jointed form occasional specimens
are as shewn in Fig. 124, II. Here both antennae are 13-jointed,
the 3rd joint being much longer, and the 4th a little longer than
the corresponding joints of the normal with 14 joints. Two
specimens were seen having this structure in both antennas, thus
presenting a difference which, did it occur in a form known from
but few specimens, would assuredly be held to be of classificatory
importance.

623. In another case (Fig. 124, III) each antenna contained only
12 joints, the 3rd, 4th and 5th being all of greater length than
in the normal.

624. Fig. 124, IV shews a case in which there was on the right
side a normally 14-jointed antenna but that of the left side was
12-jointed, agreeing nearly with those in Fig. 124, III.

In considering these facts the possibility that some or all the
abnormal states may result from or be connected with regenera-
tion must be remembered ; but from the frequency of the varia-
tions, from their diversity, and from the fact that symmetrically
varying individuals are not rare, it is on the whole unlikely that
all can owe their origin to regeneration. It will besides be
noticed that it is in the proximal joints that the greatest changes
are seen, and it must surely be rarely that these are lost by mutila-
tion.

The difficulty — indeed the futility — of attempting to adjust a
scheme of individuality among such series of segments must here
be apparent to all. We can see the change in number and the
change in proportions, and we are doubtless entitled to affirm
that the differences between these several kinds of antennae are
reached by changes occurring chiefly in the neighbourhood of
the 3rd and 4th joints ; but not only is there no proof that the
changes are restricted to these joints, but the appearances suggest
that there are correlated changes in many, and. perhaps in all of
the joints.

Tarsus of Blatta1.

:625. Among the families of the class Orthoptera the number oi

tarsal joints differ. In Forficularia the number of tarsal joints

1 In connexion with variation in the number of joints in legs I may mention the
case of Stenopterus rufus ? (Longicorn) described by Gadbatj de Kkkville as having
each tibia divided into two parts by an articulation [Le Naturaliste, 1889, B. 2, xi.
p. 9, fig.)} but upon examination it proved that each tibia had been sharply bent at
each of these points, and there was no real articulation. I have to thank M. Gadeau
de Kerville for lending me this insect together with many interesting specimens of
which mention will be made hereafter.

416

MERISTIC VARIATION.

[part I.

is 3, in Blattodea, Mantodea and Phasmodea 5, in Acridiodea 3,
in Locustodea 4, in Gryllodea 2 or 31.

The fact, originally observed by Brisout de Barneville58,
that in various species of Blattidse the number of tarsal joints
may vary from five to four is therefore of considerable importance
in a consideration of the manner in which these several forms
have been evolved from each other. The species in which Brisout
observed this variation were ten in number and belonged to four
genera of Blattidse.

At my suggestion Mr H. H. Brindley has made an extended
investigation of the matter and a preliminary account of the
results arrived at was given in the Introduction (p. 63). It was
found that of Blatta americana 25% of adults have one or

Fig. 125. I. Normal five-jointed left tarsus of Blatta americana.
tarsus of the same having four joints.

n

II. Right

more tarsi 4-jointed. In Blatta orientalis these cases amounted
to 15°/o > and of 102 B. germanica examined, 16 had one or more
4-jointed tarsi.

The abnormality occurred sometimes in one leg and sometimes in
another, being more frequent in the legs of the second pair than in those
of the first, and much more frequent in the third pair than in either.
In some specimens legs of the two sides were symmetrically affected,
but this was exceptional. Only one specimen has hitherto been met
with having all the tarsi 4-jointed. There was a slightly greater
frequency in females than in males.

When the examination of these abnormal tarsi was begun it was
supposed that the variation was congenital, but as explained in a note
to the Introduction (p. 65) doubt subsequently arose as to this. It is
well known that Blattidse like many other Orthoptera have the power
of renewing the appendages after loss, and Mr Brindley found by
experiment that when the tarsus of Blatta orientalis is renewed after
mutilation the resulting tarsus is 4-jointed. It was also found that
4-jointed tarsi were much more frequent in adults than in the young.
The question therefore arises, is the 4-jointed tarsus ever congenital 1

1 From Bbunneb von Wattenwyl, Prodr. europ. Orthop., 1882.
• Ann. ent. soc. France, s. 2, vi. 1848, Bull., p. xix.

CHAP. XV.]

tarsus of Blatta.

417

To this question a positive answer cannot yet be given ; but as about
200 young B. orientalis have since been hatched from the egg and no
4-jointed tarsus was found among them, while in every instance of
regeneration the new tarsus had four perfect joints, there is now a
presumption that the variation does not occur congenitally. On the
other hand it should be mentioned that the 4-jointed tarsus was seen
in 3 specimens, found by Mr Brindley, which by their size would be
judged to have been newly hatched. But even if the variation shall
hereafter be found to be sometimes congenital it is certain that this
occurrence must be very rare, and there can be no doubt that in the
majority of cases the 4-jointed tarsus has arisen on regeneration1.

As mentioned in the Introduction, the existence of the 4-jointed
tarsus, whatever be the manner of its origin, raises two questions. Of
these the first is morphological, relating to the degree to which the
joints exhibit the property of individuality, and the second is of a
more general nature, relating to the application of the theory of
Natural Selection to such a case of discontinuous change. The interest
of the case in its bearing on both of these questions arises from the
Discontinuity, which was complete. All the tarsi seen were either
5-jointed or 4-jointed, and in none of the latter was any joint ever
rudimentary, or any line of articulation imperfectly formed (except
in a single specimen having a deformed tarsus). There were 5-jointed
tarsi and 4-jointed tarsi : between them nothing.

Following the usual methods of Comparative Anatomy it must be
asked which of the 5 joints is missing in the 4-jointed tarsus'? With
reference to this question careful measurements of the separate joints
were made by Mr Brindley in 115 cases of 4-jointed tarsi occurring in
legs of the third pair in B. americana; and for comparison the separate
joints of 115 normal 5-jointed third tarsi of the same species were also
measured. (It is clear that the legs compared must belong to the same
pair, 1st, 2nd or 3rd, for there is considerable differentiation between
them. From this circumstance it was comparatively difficult to obtain
a large number of cases, and hence the smallness of the whole number
measured. But though of course statistics respecting a larger number
would be more satisfactory there is no reason to think that by exami-
nation of a greater number of cases the result would be materially
affected.)

In the two sets of tarsi the total length of each tarsus was reduced to 1-000, the
lengths of the joints being correspondingly reduced.

The arithmetic means of the ratios of the several joints to the whole lengths of
the tarsi to which they belonged was as follows :

Five-jointed form.

1st joint
•532

2nd joint
•156

3rd joint
•095

4th joint
•019

5th joint
■168

Four-jointed form.

1st joint
•574

2nd joint
•183

3rd joint
•061

4th joint
•179

1 The circumstance that in Mr Brindley's observations the variation was in all
species more frequent in females than in males, and that the frequency differed in

b. 27

418 MEEISTIC VARIATION. [part i.

The evidence derived from these numbers lends no support to the
expectation that any one particular joint of the 5-jointed form is
missing from the 4-jointed, or that any one joint of the 4-jointed form
corresponds with any two joints of the 5-jointed ; for if the numbers
are treated with a view to either of these hypotheses it will be found
impossible to make them agree with either. It appears rather that the
four joints of the 4-jointed form collectively represent the five joints of
the normal.

The other question upon which the statistics bear has already been
stated in the Introduction. In any appendage the ratio of the length
of each joint to the whole length of the appendage varies ; but if it
varies about one normal form it will be possible to find a normal or
mean value for this ratio, and the frequency with which other values
of the same ratio occur will be inversely proportional to the degree in
which they depart from the normal value. The curve representing the
frequency of occurrence of these values will then be a normal Curve of
Error. The form of this curve will indicate the constancy with which
the normal proportions of the tarsal joints are approached. If the
proportional lengths of the tarsal joints vary little then the curve
representing the frequency of their departure from their normal value
will be a steep curve, but if these proportions are very variable and have
little constancy, then the curve will be flatter. The probable error
will thus in the case of each value be a measure of the constancy with
which it conforms to its normal proportions. As explained in the
Introduction, upon the hypothesis that all constancy of form is due to
the control of Natural Selection, it would be anticipated that the
4-jointed tarsus, if a variation, would be very much less constant in the
proportions of its joints than the 5-jointed tarsus. It was however
found that as a matter of fact the proportions of the joints of the
4-jointed form were very nearly as constantly conformed to as those of
the joints of the normal tarsus.

The evidence of this is as follows. The total length of the 5-jointed tarsus being

L, and t1, t2, &c. being the lengths of its several joints, I, T1, T2, &c. representing

tl T1

the same measurements in the 4-jointed form, the ratios — &c, — &c, represent

J-J v

the proportional length of the several joints in each case. The values of these

ratios were then arranged in ascending order in their own series and the measures

occupying the positions of the first, second, and third quarterly divisions noted1

(indicated hereafter by Q1, M and Q3 respectively). The probable error or

t1 T1
variation of each ratio y , — , &c. will then be represented by the expression

Q3_ Ql

— - . Inasmuch as the joints are of different lengths, to compare the results

each must be converted into percentages of the mean length of the joint concerned.
These results are set forth in the accompanying tables.

the different pairs of legs may seem to point to the existence of some control other
than the simple chances of fortuitous injury. As regards the latter point it is
not unlikely that the legs of the third pair, being longer and less protected, may
be more often mutilated than the others.

1 As described by Galton, F., Proc. Roy. Soc, 1888-9, xlv. p. 137.

CHAP. XV.]

tarsus of Blatta.

419

Five-jointed tarsus.

tl

«-'

t*

t*

t5

L

L

L

T*

L

Ql

•521

•152

•095

•046

•162

M

•529

•156

•099

•049

•168

Mean error

as percentage

of M

•535
1-3

•160
2-6

•101
3-0

•051
5-0

•174
3-6

Four-jointed tarsus.

T1

rp'2

Ti

Ti

I

I

I

I

Q1

•565

•178

•060

•172

M

•575

•183

•064

•177

Q3

Mean error

as percentage

of M

•584
1-6

•189
3-0

•068
6-2

•183
3-1

It is thus seen that the percentage variation of the ratios of the
several joints to the total length is very little greater in the case of the
abnormal than it is in the normal tarsus.

As regards the longer joints these results are probably a trustworthy
indication of the amount of Variation, but in the case of the shorter
joints the errors of observation must no doubt be so great in proportion
to the smallness of the lengths to be measured that no reliance should
be placed on results obtained from them.

As evidence that in spite of the small number of instances examined
the general result is satisfactory it may be mentioned that the mean

Q3 + Qi

obtained as the value of — ^r— agrees fairly well in each case both

-j

with the value of M, the middlemost value, and also with the arith-
metic mean given above. It may therefore be taken that the curve is
regular and the series nearly uniform.

The correlations between the lengths of the joints and that of the
whole tarsus have also been examined by Mr Brindley using the
method proposed by Galton I.e., the results closely agreeing with those
obtained by the ordinary method here described1.

If the 4-jointed tarsus be a congenital variation the sig-
nificance of the fact that the abnormality is in its constancy to
its normal hardly less true than the type-form must be apparent

1 It is hoped that a fuller account of this subject will be given separately. I am
indebted to Mr F. Galton for advice kindly given when this investigation was
begun, and Mr Alfred Harker has most obligingly given much help in connexion
with it.

27—2

420 MERISTIC VARIATION. [part i.

to all. Yet even if, as now seems likely, the 4-jointed tarsus
be not a congenital variation but is rather a result of regenera-
tion, there is still difficulty in reconciling the now established
fact that the form of the regenerated part, though different from
the normal, is scarcely less constant, with any hypothesis that
the constancy of the normal is dependent upon Selection.

If it were true that the smallness of the mean variation of the

t1 ..."

ratio y , which is ultimately the measure of the constancy and
Li

truth to type of the 5-jointed tarsus, is really due to Selection
and to the comparative prosperity of specimens whose tarsal pro-
portions departed little from the normal, to what may we ascribe

Tl

the smallness of the mean variation of the ratio -j- ? Are we

to suppose that the accuracy of the proportions of the regenerated
tarsus is due to the Natural Selection of individuals which in
renewing their tarsi conformed to this one pattern ?

We are told that the struggle for existence determines every
detail of sculpture or proportions with such precision that in-
dividuals which fall short in the least respect are at a disad-
vantage so great as to be capable of being felt in the struggle,
and so decided as to lead to definite and sensible effects in Evolu-
tion. If this is so, should we not expect that individuals which
had suffered such a comparatively serious disadvantage as the
loss of a leg or of a tarsus, would be in a plight so hopeless that
even though some of them may survive, renew the limb and
even breed, yet, as a class, by reason of their mutilation they
must rank with the unfit ? Nevertheless we find not only that
there is a mechanism for renewing the limb, but that the renewal
is performed in a highly peculiar way ; that in fact the structure
newly produced differs from the normal just as species differs
from species, and is scarcely less true and constant in its pro-
portions than the normal itself.

Now if this exactness in the proportions of the renewed limb
is due to Selection, it must be due to Selection working among
the mutilated alone ; and of them only among such as re-
newed the limb ; and of them only among such as bred.
Moreover if the accuracy of the form of the renewed tarsus is
due to Selection working on fortuitous variations in the method
of renewal, and not to any natural definiteness of the variations,
the number of selections postulated is already enormous. But
this vast number of selections must by hypothesis have all been
made from amongst the mutilated — a group of individuals that
would be supposed to be at a hopeless disadvantage1.

1 The same dilemma is presented in all cases where a special mechanism or
device exists (and must be supposed to have been evolved) only in connexion with
regeneration. An instance is to be seen in the Lobster's antenna. As is well known
the antennary filament of the Lobster when lost is renewed not as a straight out-

chap, xv.] RADIAL JOINTS OF COMATUL^E. 421

One or more of the hypotheses are thus clearly at fault. A
natural, and I believe a true comment will occur to every one :
that probably the injured insects are not at any serious disad-
vantage, and that these mutilations perhaps make very little
difference to their chances. But can we admit that the loss of
a leg matters little, and still suppose that the definiteness and
accuracy of the exact proportions of the tarsal joints makes any
serious difference ?

The hypothesis, therefore, that the smallness of the mean
variation in the proportional lengths of the tarsal joints of the
4-jointed tarsus has been gradually achieved by Selection is un-
tenable, whether that 4-jointed tarsus be a product of regenera-
tion or a congenital variation. But if the accuracy with which
the abnormal conforms to its type be not due to a gradual Selec-
tion, with what propriety can we refer the similar accuracy of
the normal to this directing cause ?

Kadial joints in Arms of Comatul^e.

The number of radial joints above the basals up to the division of the rays in
Crinoids is usually constant in the genera. In Antedon and Actinometra there are
normally three such joints, the third radial being the axillary, and none of these
bear pinnules. Both increase and decrease in the number of radials has been
observed, but variations from this number are rare, more so than variations in the
number of rays. Carpenter, P. H., Chall. Rep., xxvi. Pt. lx. p. 27.

Antedon alternata: specimen having in one ray four radials, none bearing
pinnules or united by syzygy. ibid., PL xxxu.fig. 6.

Encrinus gracilis (fossil) : in one ray four radials. Wagner, Jen. Ztschr.,
1887, xx. p. 20, PI. ii. fig. 13.

Antedon remota, A. incerta, Actinometra parvicirra (Fig. 126); one
specimen of each of these species had one ray with only two radials. Carpenter,
I.e., PL xxix. fig. 6; PL xviii. fig. 4; PL lxi. fig. 1.

Fig. 126. Actinometra parvicirra, No. 628. Specimen having only two radials
in the ray marked x. (From P. H. Carpenter.)

growth, as the other appendages are, but when formed again it is coiled up in a
tight conical spiral which cannot be extended at all, but is kept firmly in place by
the shortness of the skin on the inner curvature. (For figure see Howes, Jour.
Anat. Phys., xvi. p. 47.) During the process of regeneration the antenna is very
soft, and were it extended it would from its great length be much exposed to injury.
At the next moult after renewal the new antenna is drawn out as a straight filament
like the normal, and its skin then hardens with that of the rest of the body. This
strange manner of growth occurs only on regeneration. It is hard to believe both

422 MERISTIC VARIATION. [part i.

Metacrinus. Some species have normally 5, others normally 8 radials. If there
are 5, the 2nd and 3rd are united by syzygy and bear pinnules; but if there are 8,
both 2nd and 3rd, and the 5th and 6th are thus united and bear pinnules. In
Plieatocrinus the number of radials is two, and this is also the case in one or two
fossil Comatulas. Pentacrinus has normally three radials like Antedon.
629. Pentacrinus mulleri: specimen having in one ray four radials, the 2nd and 3rd
united by syzygy, though bearing no pinnules. Carpenter, I.e.; and Chall. Rep.
xi. Pt. xxxii. p. 311, PI. XY.Jig. 2.

(1) that the number of individuals that have lost antennae — a serious injury one
may judge — and have renewed them, and have bred, can have been enough to lead
to the establishment by Selection of a distinct and highly special device to be
invoked solely on the occasion of mutilation of an antenna ; and also (2) that the
least detail of normal form is of such consecpience as to be rigorously maintained by
Selection.

CHAPTER XVI.

Radial Series.

Little need be said in preface to the facts of Meristic Varia-
tion in Radial Series. In them phenomena analogous to those
of the Variation in Linear Series are seen in their simplest form.
Just as in Linear Series the number of members may be changed
by a reconstitution of the whole series so that it is impossible
to point to any one member as the one lost or added, so may
it be in the Meristic Variation of Radial Series: and again as
in Linear Series, single members of the series may divide. Be-
tween these there is no clear line of distinction.

Next, as in Linear Series, Variation, whether Meristic or
Substantive, may take place either in single segments (quadrants,
sixths, &c), or simultaneously in all the segments of the body.
For instance, a single eye may be divided into two, or there
may be duplicity simultaneously occurring in all the eyes of the
disc (see No. b'34) and so on.

These phenomena are here illustrated by facts as to the
Meristic Variation of Hydromedusae and of Aurelia. The latter
is exceptionally variable and in its changes exhibits important
features.

Together with these facts as to Variation in Major Symmetries
is given an instance of similar Variation in the pedicellarise of an
Echinid, and it will be seen that in this case of a Minor Symmetry
the change is perfect and altogether comparable with those found
in Major Symmetries of similar geometrical configuration.

The best field for the study of the variations of Radial Series
is of course to be found in plants ; and in the Meristic Variations
of radially symmetrical flowers precisely similar phenomena may
be easily seen.

424

MERISTIC VARIATION.

[part 1.

I. CCELENTERATA.

*630. Sarsia mirabilis1: normally four radial canals, &c. (Fig. 127.
I and III). Out of many hundreds of N. American specimens
two were found with six radial canals, six ocelli, and six tentacles,

Fig. 127. Sarsia mirabilis. I and III, the normal form, with four radii, from
below and from above. II and IV, an abnormal form with six radii, from below
and from above respectively. (From Agassiz.)

symmetrically arranged (Fig. 127, II and IV). These specimens
were of larger absolute size than the normals. Agassiz, L., Mem.
Amer. Ac. Sci., iv. p. 248, PI. v. fig. 5.

1 Sarsia is the medusa of the Gymnoblastic Hydroid Syncoryne.

chap, xvi.] RADIAL SERIES : JELLY-FISH. 425

'G31. Sarsia sp. Among many thousands examined on the east

coast of Scotland one was found having six radial canals, six

ocelli and six tentacles. Romanes, G. J., Jour. Linn. Soc, Zool.,

xii. p. 527.
'632. Sarsia sp. A single specimen having five complete segments:

the only abnormality met with amoog thousands of naked-eyed

medusae observed, ibid., xiii. p. 190.

There is perhaps in the whole range of natural history no

more striking case of the Discontinuity and perfection of Meristic

Variation.

Is it besides a mere coincidence, that the specimens presenting

this variation, so rare in the free-swimming Hydromedusse, should

have been members of the same genus ?

633. Clavatella (Eleutheria) prolifera. This form has a medusa
which creeps about on short suctorial processes borne by the tentacles.
The number of these tentacles varies from 5 to 8. In the specimens
examined by Krohn1 the number was 6. Most of Claparede's2 speci-
mens had 8. Filippi3 found that the majority had 6 arms, but 15 per
cent, had 7. Those examined by Hincks4 never had more than 6.
Filippi considered that the difference in number was evidence that his
specimens were of a species different from Claparede's. I examined
many of this form at Concarneau and found six the commonest number
in the free medusae, but those still undetached frequently had 5,
possibly therefore the number increases with development. [See also
Cladonema radiatum, &c. Hincks, I.e., p. 65, &c]

Claparede states that the 6-armed specimens had 6 radial canals,
but the 8-armed usually had four though occasionally six, but never
eiidit canals.

In this case note not only the frequent occurrence of Meristic
Variation, but also the suggestion that particular numbers of tentacles
are proper to particular localities.

'634. Normally there is a single eye at the base of each arm. Claparede
figures (I.e. p. 6, PL i. fig. 7 a) a case of duplicity of an eye, and says
that specimens occur in which each eye is doubled, so that there are
two eyes at the base of each arm instead of one.

635. Stomobrachium octocostatum (.ZEquoridae) : variety found in
Cromarty Firth, |rds of size represented by Forbes (Monogr. Br.
Naked-eyed Medusce); ovaries bluish instead of orange, and without
denticulated margins. Tentacles arranged in double series, long and
short alternating, while in the type the series is single. The number
of large tentacles same as in type. Each smaller tentacle bears vesi-
cular body at base, without pigment or visible contents. The same
variety figured by Ehrenberg, Abh. Ah. Berl., 1835, Taf. vin. fig, 7.
Romanes, G. J., Jour. Linn. Soc. xn. p. 526. [Simultaneous Variation
of the several segments.]

With Nos. 634 and 635 compare the fact that in Tiarops poly-

1 Arch. f. Naturg., 1861, p. 157.

2 Beob. iib. Anat. u. Entw. Wirbelloscr Thiere, 1863, p. 5.

3 Mem. Ac. Torino, S. 2, xxiii. p. 377.

4 Brit. Hyd. Zoophytes, 1868, p. 71.

426 MERISTIC VARIATION. [part i.

diademata there are normally as a specific character four diadems
between each pair of radial tubes, making in all sixteen instead of
eight, which is the usual number in the genus. Romanes, G. J.,
Jour. Linn. Soc. Zool., XII. p. 525.

*636. Aurelia aurita. This form exhibits an exceptional frequency
of Meristic Variation. In the normal there are 16 radial canals,
4 oral lobes, 4 generative organs and 8 lithocysts. The de-
partures from this normal form have been described in detail
by Ehrenberg1 and by Romanes2.

Meristic Variation in Aurelia may occur in two distinct ways,
first in the degree to which there is complete separation between
the generative sacs, and second in actual numerical change.

Imperfect division of generative sacs.

In the commonest form of Aurelia there are four generative organs each
distinct from its neighbours, but in some specimens the generative epithelium is
continuous all round the mouth, and there is then one continuous generative
chamber, though opening by 4 openings as usual. (Such absence of complete sepa-
ration between some of the generative organs is not rarely seen in cases of numerical
Variation, v. infra.) Though the epithelium is then continuous it does not form
a true circle, but is sacculated to form 4 (as normally) 3, 6, or some other number
of incompletely separated parts. Ehrenberg (I. c, p. 22) saw a case in which there
were 6 such sacculations, three on each side being united and having one generative
pouch, but each of these pouches opened by 3 openings. There was thus a bilateral
symmetry, each half containing three lobes of ovarian epithelium incompletely
separated from each other. Complete union of all the generative organs was
very rare.

The specimens differ greatly with regard to the degree to which the generative
epithelium is folded off, and in the shapes of the generative organs. Commonly
the generative epithelium is of a horse-shoe form, the two limbs of the horse-shoe
not meeting each other; but in some specimens the two limbs may be to various
degrees approximated, so that each generative organ is kidney-shaped or even
roughly circular. (Cases figured by Ehrenberg, I.e., PI. n.) [Here note the
Simultaneous Variation of the single quadrants.]

Numerical Variations.

Of these the most striking and also the most frequent are variations
consisting in a perfect and symmetrical change in the fundamental
number of segments composing the disc. Normally there are four
quadrants (Fig. 128, I). Varieties are found having only half the usual
number of organs, the disc being made up of two halves, each contain-
ing one generative organ (Fig. 128, IV). Other symmetrical varieties
having three, and six, as their fundamental numbers are shewn in Fig.
128, V, and II. These figures are from Romanes. Symmetrical forms
having five segments and eight segments are described and figured by
Ehrenberg. As to the comparative frequency of these forms facts are
given below. In each of them all the parts normally proper to one
quadrant are repeated in each segment of the disc, the number of parts
being greater or less than the normal in correspondence with the funda-
mental number of the specimen.

1 Ehrenberg, C. G., Abh. k. Ah. Wiss., Berlin, 1835, pp. 199—202, Plates.

2 Romanes, G. J., Jour. Linn. Soc., Zool., xn. p. 528, and xm. p. 190, Pis. xv.
and xvi.

CHAP. XVI.]

radial series : Aurelia.

427

Next, the number of certain organs may vary independently of
other organs. For example as seen in Fig. 128, VI the radial canal

Fig. 128. Diagrams of various forms of Aurelia aurita, slightly simplified from
Eojianes. I. The normal. II. Symmetrical form with 6 radii. III. Two
additional chief radial canals in opposite interradii (where manubrial lobes also
were bifid) and substitution of two canals for one in another interradius.
IV. Form with two generative organs. V. Form with three generative organs.
VI. Symmetrical form in which the intergenital canals are all doubled, the others
remaining single. VII. Apparently upper half-disc arranged as for a symmetry of
four, lower half for a symmetry of six. VIII. One of the quadrants tripled (?).
IX. Form resembling VI. except that in one quadrant the intergenital canal is not
doubled. The descriptions are not altogether those of Romanes.

normally lying in a plane between each pair of generative organs may
in each quadrant be represented by two canals, and in correspondence
with this change the number of marginal organs is proportionately
changed in the quadrants affected.

But besides these changes symmetrically carried out in eacli quadrant
or in the whole disc, one or more quadrants or a half-disc may vary inde-
pendently. For example Fig. 128, VII, shews a specimen in which the
two upper quadrants are normal but the lower half-disc is primarily
divided into three. (In the case figured the parts of the lower half-disc

428 MERISTIC VARIATION. [part i.

are not quite accurately distributed). Similarly a particular quadrant
may be represented by two sets of parts or by three sets (Fig. 128, VIII),
the other three quadrants being normal or nearly so. I have seen a
case also in which the chief symmetry was arranged as for three seg-
ments (having 3 oral lobes), but one of the three segments was imper-
fectly divided into two.

In a case of 6 segments, 3 on one side may be large and the other 3
small, somewhat as in Fig. 128, VIII, but the whole disc was not circular,
the radius on the side of the large segments being the greater.

In the figures (after Romanes) all the discs are represented as
circles, but my own experience was that when there was not a truly
symmetrical distribution of the generative organs the half quadrant or
other segment in which the number of parts was greatest bulged out-
wards, thus exemplifying the general rule that when an organ divides
the two resulting parts are together larger than the undivided organ.

Besides those specified, there are also irregular cases, e.g., specimens
with 3 generative organs but 4 oral lobes and other parts in multiples of
4, but as Ehrexberg says in such cases it is generally possible to detect
that one of the generative organs is larger than the others or even
partially double. He also saw cases otherwise arranged in a symmetry
of 6, but having 22 chief radial canals instead of 24, &c. Also 14 radial
canals (instead of 12) were found in some cases of 3 generative organs.

As everyone will admit, it is impossible in regular threes, sixes, tfcc.
to say that any particular segment is missing or is added rather than
another.

Comparative frequency of the several forms.

*637. Among thousands of individuals seen by Ehrenberg only two were
8-rayed, 15 — 20 were 6-rayed, some 20 — 30 were 5- and 3-rayed, the
remainder being 4-rayed. In percentages, 90 are 4-rayed, 3 are 3-rayed
3 are 5-rayed, 2 are 6-rayed and 2 have other numbers.

The result of an attempt to ascertain these percentages in a great
shoal of Aurelia washed ashore on the Northumberland coast on 4 Sept.
1892 is given below. The radial canals were not counted, and the
numbers apply strictly to the generative sacs only. It will be seen
that the proportion of abnormals is lower than that given by Ehrenberg.

2 generative sacs 0

symml. : 3 oral lobes in 4 unbroken cases ...10 (O^0/,)

2 large, 1 small : 3 or. lobes 1

normal 1735

3 large, 1 small : 5 or. lobes 1

3

4
4
4
5
5
6
6
6
6
6

2 large, 2 small : 3 lobes 1

symmetrical 5 lobes in one 2

not quite symmetrical 1

sym. : 6 lobes in 2 unbroken cases 7 (0'39°/o)

not symmetrical 1

4 large, 2 small 1

4 large, 2 united : 6 lobes in 1 unbroken ... 2

3 large, 3 small : 6 lobes 1

1763

CHAP. XVI.]

RADIAL SERIES : PEDICELLARI^E.

429

There were therefore 1735 normals, 19 symmetrical varieties and 9
irregulars. It will be noted not only that the symmetrical varieties
are comparatively frequent, but also that the several forms of irregu-
larity were seen for the most part in single specimens only.

II. PEDICELLARI.E OF ECHINODERMS.

The number of jaws in the pedicellarias differs in different
forms of Echinoderms, and I am indebted to Professor C. Stewart
for information concerning them.

In Asteroidea the number of jaws is usually two, but in Luidia
savignii the normal number of jaws is three.

In the Echinoidea the number of jaws is usually three, but
in Asthenosoma the normal number is four.
638. Dorocidaris papillata : number of jaws in pedicellariae

I I

Fig. 129. Peclicellariae of Dorocidaris papillata.

I. Normal form with three jaws.

II. A pedicellaria with four jaws from the abactinal region.

(From Prof. Stewart's specimens.)

normally three as in Fig. 129, I, but occasionally four in pedi-
cellarise of the abactinal region, as in Fig. 129, II. [Note that the
variety is perfect and symmetrical.] For this fact I am obliged to
Professor Stewart, who kindly allowed this figure to be made from
his preparations.

639. Luidia ciliaris : pedicellariae nearly all with three jaws ; but
on Roscofif specimens a few having two jaws occur on the borders
of the ambulacral groove. In Banyul's specimens none such were
found in this position, but there is one in almost all the marginal
intervals. CuE"not, Arch. zool. exp., S. 2. V. bis, p. 18.

640. Asterias glacialis : occasionally ^ree-jawed pedicellariae like
those of Luidia are found among the normal two-jawed pedi-
cellarise. Cu£not, I. c, p. 23.

430 MERISTIC VARIATION. [part

III. Cell-Division.

*G41. It was purposed at this point to have introduced an account
of Meristic variations observed in the manner of division of nuclei
and cells ; but I have found that, to give adequate representation
of these facts even in outline, it would be necessary not only to
treat of a very complex subject with which I have no proper
acquaintance, but also greatly to enlarge the scope of this work.
But were no word said on these matters, indications most useful
as comment on the nature of Meristic Variation at large would
have to be foregone ; and unwilling that these should be wholly
lost I shall venture briefly to allude to so much of the matter as
is needful to shew some ways in which the facts of abnormal cell-
division can be used in reference to the wider question of Meristic
Variation.

We have been dealing with cases of Radial repetition, and we
have seen that with Variation in the number of parts the result
may still be radially symmetrical. It therefore becomes of interest
to note that in the case of abnormal cell-division the result of
numerical change may in like manner be radially symmetrical.
Cells which should normally contain two centrosomes and which
should divide into two parts have been seen to contain three centro-

I II

Fig. 130. Triasters. I. Tripolar division of nucleus in embryonic tissue of
Trout (after Henneguy1). II. Triaster from mammary carcinoma. Centrosomes
not shewn (from F lemming2).

somes (Fig. 130) prior to division into three parts, and the tri-
angle formed by the three centrosomes may be equiangular just
as may be the triangle of the segments of the abnormal Aurelia
(Fig. 128, V), or of the jaws of the normal pedicellaria of
Dorocidaris (Fig. 129). It is, I imagine, difficult to suppose
that the radial symmetry of each of these series of organs is

1 Heknegut, Jour, de VAnat. et Phys., 1891, p. 397, PI. xix. fig. 9.

2 Flemming, Zelhubstanz, Kern u. Zelltheilung, 1882, PI. viii. fig. v. after
Martin, Virch. Arch., 1881, lxxxvi. PI. iv.

chap, xvi.] SYMMETRY IN TRI ASTERS. 431

different in its nature, or indeed that it is anything but a visible
expression of the equality of the strains tending to part each
segment from its neighbours. (The case of the triaster is taken
as the simplest and most plainly symmetrical, but examples of
cells with greater numbers of centrosomes, sometimes dividing
symmetrically, have also been seen.)

For our purpose this fact is first of use as a demonstration of
the absurdity of an appeal to " Reversion " as a mode of escape
from the admission that variations in Radial Symmetry may be
total and perfect though the new number of segments is one
which presumably never occurred in the phylogeny ; for we need
scarcely expect that even conspicuous defenders of the doctrine
that all perfection must have been continuously evolved, will
plead that the cells of every tissue in which a triaster is found
did once normally divide with three poles. Yet if it be once
granted that the symmetry of these abnormal forms is a sudden
and new departure from the normal, it will not be easy to put the
other cases on a different footing.

Though we have repudiated all concern with the causes of ab-
normality, mention may be made of the fact that multipolar figures,
both regular and irregular, have been observed to result from the
action of reagents {e.g. quinine, Hertwig1). Such figures are of
course well known especially in the case of carcinomatous growths, and
as Hertwig observes, from the resemblance of these figures to those
artificially induced by chemical means it seems possible that these
pathological appearances may also be the result of some chemical
stimulus. But whatever be the immediate or directing causes of
abnormalities in cell-division, or of those other abnormalities in the
segmentation of Radial Series of larger parts, and whether any of the
causes in the several cases be similar or different, we can scarcely
avoid recognition that the resulting phenomena are closely alike2.

1 0. Hertwig, Die Zelle u. d. Geivebe, 1893, pp. 192—198.

2 See also a case of the presence of triasters in two bilaterally symmetrical
tracts of the blastoderm of Loligo [v. infra).

CHAPTER XVII.
Radial Series: Echinodermata.

As seen in the majority of adult Echinoderms the repeated
parts are arranged with a near approach to a Radial Symmetry
and it is thus convenient to consider their Meristic Variations
in that connexion. But it must of course always be remembered
that in their development these repetitions are in origin really
a Successive Series and not a Radial Series. The segments are
not all identical (as, in appearance at least, they are in many
Ccelenterates &c), but are morphologically in Succession to each
other, though there may be little differentiation between them.

In the case therefore of Variation in the number of segments,
resulting in the production of a body not less symmetrical than
the normal body, there must be in development a correlated
Variation among the several members like that seen in so many
cases of additions to the ends of Linear Series.

This circumstance should be kept in view by those who seek
in cases of numerical Variation, in Echinoderms to homologize
separate segments of the variety with those of the type, hoping
to be able to say that such a radius is added, or such other
missing. As in other animals, this has been attempted in Echino-
derms, and though I know well that in the complex subject of
Echinoderm morphology I can form no judgment, yet it is difficult
to suppose that the same principles elsewhere perceived would
not be found to hold good for Echinoderms also.

All that is here proposed is to give abstracts of facts as to
Variation in the numbers composing the Major Symmetries.
It will of course be remembered that though the fundamental
number in Echinoderms is most commonly five, other numbers
also occur as normals, {e.g. four in the fossil Tetracrinus, six
in some Ophiurids, &c. Examples will be given of total change
from five to four and to six, and so on. It is besides not a
little interesting that of the normally 4-rayed Tetracrinus both
o -rayed and 3-rayed varieties should be known.

Besides the examples of total Variation there are a few cases
of incomplete Variation in which there is a fair suggestion that

chap, xvil] RADIAL SERIES : HOLOTHURIOIDEA. 433

a particular ray is reduced in size (Nos. 680 and 681, &c). There
are also two cases of imperfect division of a ray in an Echinid
(Nos. 688, &c), while in Asteroids &c. this condition is common. It
is of importance to observe that just as in Linear Series abnormal
divisions of members of the series are commonly transverse to the
lines of Repetition, so in radial forms the divisions of rays are
commonly radial.

The evidence is complicated by the fact that in many
Echinoderms extensive regeneration can occur, and in some
genera reproduction by division of the disc and subsequent
regeneration is almost certainly a normal occurrence1. Never-
theless it cannot be doubted that the variation seen in Echini,
in Asterina, in the discs and stems of Crinoids, &c, are truly
congenital. Similarly, though in Asterias &c. reduction in the
number of arms might otherwise be thought to be due to mutila-
tion, it cannot be so in Echini &c.

HOLOTHURIOIDEA.

Cucumaria planci : among 150 half-grown specimens found
at Naples five were 6-rayed. Ludwig, H., Zool. Anz., 1886, IX.,
p. 472. [These specimens are described in detail.] To determine
which is "the intercalated ray" the following ingenious reasoning
is offered, and as a good practical illustration of the conception
of the individuality of segments as applied to an Echinoderm
we may well consider it.

1 It is likely that several of the Ophiurids and Asteroids which normally have
more than 5 arms undergo such fission. Lutken ((Efvers. Dansk. vid. Selsk.
Fork., 1872, pp. 108—158 : tr. Ann. and Mag. N. H., 1873, S. 4, xn. pp. 323 and 391)
gave an account of this phenomenon. Ophiothela isidicola (Formosa) generally
has 6 arms, rarely equal, usually 3 large opposite to 3 small ; specimens common
with only 3 arms, with appearance as if corresponding half-disc cut off. There
can be no doubt that the animal divides and that the other 3 arms are renewed.
The same phenomenon has been seen in other small 6-armed Ophiurids, especially
of genus Ophiactis, but Liitken never saw any trace of it in any normally 5- rayed
species of the genus. There are indications that the division occurs once when the
animal is very small and again when it is adult or nearly so. In Ophiocom<i pumila
the small specimens have 6 arms, while the adults have 5. Probably therefore
division only occurs in the young, the last division being followed by the pro-
duction of 1 or 2 arms instead of 2 or 3.

Division is probably not a usual occurrence even in Ophiurids having more than
5 arms. Ophiacantha anomala has normally 6 arms, and 0. vivipara has 7 — 8,
but no such appearances are known in them.

Similarly there is evidence [figs, given] that certain Asteroids having normally
more than 5 arms viz. Asterias problema Stp. [ = Stichaster albulus], A. tenuispina
&.c. undergo fission; but there is no reason for believing that other many-armed
Asteroids divide. The Solasters have many rays, Asterias polaris has (5, but no
signs of division are seen in them.

An account is also given of the comet-like specimens of Ophidiaster cribrarius.
occasionally found, having one long arm, at the adoral end of which are present
4 or 5 arms as mere tubercles or as half-grown structures. This phenomenon is
well known in Linckia multiflora, in which doubtless the separate arms may break
off, each reproducing complete disc and arms. [See also as to Stichaster albulus,
Asterina wega, &c, Cuenot, L., Arch. zool. exp., V. bis, 1879—90, p. 128; and as
to Linckia, Sarasin, Ergeb. naturw. Forsch. auf Ceylon, 1888, X. lift. 2.]

b. 28

434 MERISTIC VARIATION. [part i.

In the normal there are 5 radii and interradii, and 10 tentacles :
in the abnormals there are 6 and 12 respectively. In half-grown
normals the 3 ambulacra of the ventral trivium have more tube-feet
than the 2 ambulacra of the bivium ; also the pair of tentacles corre-
sponding to the central radius of the trivium are smaller than the rest.
In the abnormals 3 ambulacra have more tube-feet and are separated
by narrower interradii than the rest, and of them the central has the
least pair of tentacles : therefore these are the 3 radii of the ventral
trivium, and of them the central is the central of the normal. The
structure of the calcareous ring bears out this correspondence. The
central radius of the ventral trivium is therefore not the intercalated
radius.

In the 6-rayed specimens there is thus a ventral trivium and a
' dorsal trivium.' (There were 2 Polian vesicles in 3 specimens, 3 in
one and one in the other, but in the normal also these vary in number.)
The stone- canal was single in all ; but in one of them it could be seen
that the canal arose in the interradius to the left of that which bore the
madreporic plate, suggesting that the radius thus crossed was super-
numerary ; for in a normal the interradius of the dorsal mesentery is
in the centre of the bivium. In a normal there are in the calcareous
ring two radials on either side between the dorsal mesentery and the
ventral median radius. In 4 of the abnormals (to which alone what
follows refers) there were 3 such radii on the left and 2 on the right,
while in the 5th specimen there were 3 on the right and 2 on the left.

The respiratory trees of the normal are in the right interradius
of the bivium and in the left interradius of the trivium. In the 6-rayed
they are in the left interradius of the ventral trivium and in the lower
right interradius of the dorsal trivium, agreeing with the normal and
shewing that the right radius of the ventral trivium is not an intercalated
one. Next, the mesentery in its course traverses in the 6-rayed form
4 radii and 3 interradii, the lower right interradius of the dorsal trivium
with its 2 adjacent radii alone being free. In the normal, 3 radii and
2 interradii are thus traversed, the right bivial interradius and its 2
adjacent radii being free. Therefore the right radius of the dorsal
trivium and of the ventral trivium are not intercalated. The central
radius of the ventral trivium has already been excluded ; therefore the
intercalated segment is either the middle or the left of the dorsal, or
the left of the ventral trivium.

In a normal, the mesentery which is attached to the alimentary
canal at that place where its upward portion again turns downwards
comes from that interradius which bounds the ventral trivium on the
left. This is the case also in the abnormals, and therefore the left
radius of the ventral trivium is not intercalated. Of the two remaining
radii the left of the dorsal trivium is in nowise abnormal, but the
central dorsal radius is abnormal in that it is crossed by the sand-canal,
therefore the central dorsal is the intercalated radius.

And since in four cases there were three radii in the calcareous
ring on the left, between the interradius of the stone-canal and the
central of the ventral trivium, and two on the right, therefore the new
segment is in them intercalated on the left of the median interradius of
the bivium ; while in the fifth specimen the intercalation has been made
on the rigid of the same interradius.

chap. XVII.] VARIATION IN HOLOTHUKIOIDEA. 435

Now all this argument rests on the premiss that the several
members of a series of differentiated parts cannot undergo a
Substantive Variation in correlation with Meristic change in the
total number of members constituting the series. It is assumed
that there can be no redistribution of differentiation.

This assumption has now in many cases of Linear Series been
shewn to be false. To refer to one of the simplest cases, there
is, in the case of the Frog, evidence that the peculiarities of the
9th vertebra may be wholly or in part transferred to the 10th
vertebra, when by Meristic Variation there are 10 vertebras
(Nos. 56, 57 and 60), and the like has been shewn in many other
examples (cp. No. 35). The functions (as indicated by the struc-
tures) of the vertebras may be redistributed on the occasion of
Meristic Variation.

Will anyone affirm that similar redistribution of differentiation
may not happen in the Meristic Variations of Echinoderms ?

Variations in organs of Holothurioidea. Lampert calls attention to the
great variability found in this group and the consequent difficulty in distinguishing
specific characters from individual abnormalities. These variations often take the
form of alterations in the number of organs. For example, the distribution of
the tube-feet is liable to great alterations during the lifetime of individuals. In
some forms (as Thyone and Thyonidium) the feet are confined to the ambulacral
areas in the young animal, but are distributed over the whole body in more mature
individuals ; and in species of the genus Stichopus, though the tube-feet are
arranged in rows, yet in old individuals this arrangement may become obliterated.
On the contrary, in others, as for example, Holothuria graeffei, the arrangement
of the feet in thoroughly mature specimens is still most sharply defined.

The number of tbe tentacles is generally a multiple of five, and such cases
as Amphicyclus and Phyllophorus in which other numbers are found, are rare.
In these forms the tentacles are said to vary both in number, position and size,
but the number is always about 20. The case of Thyonidium nwlle is cited as
an extreme case. Of this species 4 specimens had 20 tentacles arranged in a paired
manner as in typical Thyonidia ; other specimens had 20 tentacles of similar
length ; others had from 16 to 19 tentacles of nearly equal lengths, and others
again had from 19 to 21, which instead of being disposed in pairs were placed
irregularly, some being larger and some smaller.

Of all the organs, the Cuvierian organs are the most variable and they are
of little value for purposes of classification. Their number is very inconstant
and they may even be absent altogether. It is impossible to distinguish any
circumstances whether of locality or of structure in which the individuals without
Cuvierian organs differ from the others which possess them. The two chief ap-
pendages of the water vascular ring, namely Polian vesicles [cp. No. 642] and the
stone- canal are usually constant when they are single, but in rare cases there
are exceptions even to this rule. If however more than one of these organs is
normally present, it may generally be assumed that there is no constancy in
their numbers, and in such cases the number of the Polian vesicles is especially
variable. A few species have been recorded in which, from a single Polian vesicle,
secondary ones are formed by lateral outgrowths.

The calcareous plates are of all the organs the least liable to variations, but
in certain cases they are stated to change with age.

Lampert, K., Die Seeivalzen, in Semper's Reisen im Archipel der Philippinen,
1885, iv. in. pp. 6, 13, and 174; also in Biol. Centrabl. v. p. 102.

Crinoidea.

Variation from the pentamerous condition has been many times
observed, though considering the vast number of specimens collected

28—2

436 MERISTIC VARIATION. [part i.

it must be a rare occurrence. In Tetracrinus the four-rayed condition
is normal, and it is an especially interesting circumstance that in this
form Variation to both a five-rayed and to a three-rayed condition has
been observed. For nearly all the references to the following facts I
am indebted to the useful collection of evidence on the subject given by
Bather, F. A., Quart. Jour. Geol. Soc., 1889, p. 149.

Four-rayed varieties of five-rayed forms1.

044. Holopus rangi. This genus was originally described from a
4-rayed specimen by d'Orbigny, Mag. de ZooL, 1837, CI. x., PL in.
Subsequently, 5-rayed examples were obtained and this condition was
found to be normal (see Carpenter, Chall. Rep., XL, Pt. xxxn., p. 197).

645. Eugeniacrinus : departure from 5-rayed condition very rare.
Among many hundreds of calyces in Brit. Mus. one only is 4 rayed,
Bather, I. c., p. 155.

646. E. nutans : 4-rayed specimen at Tubingen figured in Quenstedt's
Atlas to Petrefacteuk. Deutschl. Taf. cv., figs. 179 — 181. Another case
Goldfuss, Petrefacta Germanice, I., p. 163, PL I., fig. 4, now in Poppels-
dorf Mus., Bour. (Bather).

647. E. caryophyllatus : 4-rayed specimen seen at Stuttgart. Such
a specimen [Hhe same] Rosinus, Tentaminis de Lithozois...Prodr. &c,
tab. in. (Hamb. 1719). Another case Goldfuss, I.e., fig. 4: now in
Poppelsdorf Mus. (Bather).

648. Pentacrinus : a 4-rayed stem-joint from the Chalk, Mantell, G.
A., Geol. of Sussex, 1822, p. 183 : now in Brit. Mus., E. 5501 (Bather).

649. Pentacrinus jurensis : 4-rayed specimen. The stalk had only
4 sides, one being quite flat. This flat side had an articulation for a
cirrus, de Loriol, P., Paleont. Franc. Terr, jur., Ser. 1, Paris, 1886,
p. 112, PL cxliv., fig. 6.

650. P. subsulcatus : 6 joints of a 4-rayed stem, ibid., p. 117, PI.
cxlv., fig. 2.

651. P- dumortieri: 8 joints of a 4-rayed stem, ibid., 1887, p. 186,
PL clxii., figs. 6 and 6 a.

652. P- dubius : 4-sided stem quite regular. Basle Mus., Bather, I.e.,
p. 168.

653. Balanocrinus subteres : 4-sided stem quite regular, ibid.
(354. B. bronni : "the articular surface shows 4 sectors quite regularly

disposed ; this peculiar character is continued over the whole series of
joints, 26 in number." ibid.

655. Encrinus fossilis : a 4-rayed calyx, &c, v. Strombeck, A.,
Ztschr. d. deut. geol. Ges., I., 1849, p. 158 et seqq. See also Palceonto-
graphica, 1855, iv., p. 169, PL xxxi. figs. 1 and 2.

656. E. fossilis : two 4-rayed calyces with mutilated arms, v. Koenen,
Abh. k. Ges. d. Wiss., Gottingen, 1887, xxxiv. Phys. Kl., p. 23.

657. Antedon rosacea : 4-rayed specimen, Carpenter, P. H., Chall.
Rep., xxvi. Pt. lx. p. 27. Four-rayed Japanese specimen, ibid.
Another in Brit. Mus. ibid.

1 4-sided stem joints undetermined. Pusch, Polens Palaont., 1837, p. 8, PI. n.
fig. 8, a, b, c, d. See also Austin, Ann. and Mag. N. H., 1843, xi. p. 203.

chap, xvil] VARIATIONS IN CRINOIDS. 437

658. Actinometra paucicirra : 4-rayed specimen, ibid. " In all
these [Nos. 657 and 658] the anterior ray (A) is missing, so that the
mouth,' instead of being radial in position is placed interradially between
the rays E and B." Carpenter, I. c.

Compare the following case of imperfect change towards the 4-rayed
state :

659. Cupressocrinus crassus : abnormal calyx (now referred to this
species, see Bather, I. c, p. 169) has one segment of the calyx reduced
in size and bearing no radial plate or arm. This reduced segment is
covered in by the adjacent segments so that the calyx as a whole is
regularly 4-sided. Goldfuss, Nova Acta Ac. C. L. C, 1839, xix. p.
332, PL xxx., figs. 3 a and b [cp. No. 665].

Six-rayed varieties of five-rayed forms.

660. Actinometra pulchella : doubtful case of six rays, Carpenter,
I. c.

661. Antedon sp. Six-rayed specimen. "The additional ray is in-
serted between the two of the right side (D and E)." Carpenter, I. c.

662. Rhizocrinus lofotensis : 6-rayed specimen. Four and six rays
stated to be more common in Rhizocrinus than in other recent Crinoids ;
seven rays are also found, but very rarely. In Pentacrinus no 6-rayed
specimen seen. Carpenter, P. H., Chall. Rep., xi. Pt. xxxn. p. 38,
PI. viii. a, figs. 6 and 7.

f663. Pentacrinus jurensis (probably) : stalk with 6 sides. [Fig.
represents two adjacent lobes of the stalk as smaller and closer
together than the rest, suggesting that perhaps these two may cor-
respond with one lobe of the normal.] de Loriol, I.e., PL cxliv. fig. 7.

664. P. jurensis : 6-sided stalk having two adjacent lobes larger than
the others, ibid., fig. 10.

The following is a case of imperfect change towards the six-rayed
state :

665. Sphaerocrinus geometricus : abnormal specimen having the
basal plate irregularly six-sided by reason of the flattening of the
external angle of an infra-basal piece. Three of the sides are normal
and each of these bears a normal parabasal ; but of the other three
sides two are rather shorter than the normal sides and each of them
bears a somewhat smaller parabasal. Upon the sixth side between
these two, is a still smaller parabasal. The radials are five as usual,
but one of them articulates with the smallest parabasal and in con-
nexion with this its form is changed [for details see original figure].
Sculpture, &c. normal. Eck, H., Verh. naturh. Ver. preuss. RheinL,
1888, Ser. 5, v. p. 110,^.

Three-rayed and five-rayed varieties of a four-rayed forni.

*666. Tetracrinus moniliformis : normally 4-rayed (as shewn in
Fig. 131, I.). A 3-rayed basal from the same locality, Birmensdorf
(Fig. 131, II.). A 5-rayed basal from Oberbuchsitten (Fig. 131,

438

MERISTIC VARIATION.

[part I.

III.), de Loriol, P., Me'm. Soc. paleont. Suisse, 1877 — 1879, p. 245,
PL xix. figs. 39 6, 40 a, 41a.

E

III

Fig. 181. I. Normal four-rayed basal of Tetracrinus moniliformis (from Birmens-
dorf). II. A three-rayed basal of the same species from the same locality as I.
III. A live-rayed basal of the same species from Oberbuchsitten.

(After P. de Lokiol.)

•667. Cupressocrinus gracilis. This form has normally a 5-rayed
calyx, and a 5-sided basal plate containing only 4 canals round
the central canal (Fig. 132, I.). Varieties have been seen in which

GOT a.

Fig. 132. Cupressocrinus gracilis. The normal form of the basal is shewn in
I. A form with five canals round the central is represented in II, and in the
specimen shewn in III there are three peripheral canals. See No. 667 a.

(After L. Schdltze.)

there are 5 (Fig. 132, II.), or 3 (Fig. 132, III.) such peripheral
canals. The stalk is normally 4-sided, but in the varieties it is
either 3- or 5-sided in correspondence with the number of canals.
C. elongatus : stalk may be either 4- or 5-sided. The
species G. inflatus has normally 3 canals in the (circular) stalk.
Schultze, L., Denkschr. Ah Wiss., Math.-nat, CL, 1867, xxvi.
pp. 130 and 136, PI. I. fig. 2 b, and PI. III. figs. 2 c and 2 i [Cp.
No. 667.]

Abnormalities in the manner and frequency of branching in the arms of Crinoids
leading to great numerical variation have been often recorded. See Carpentek,
Chall. Rep., xxvi. Pt. lx. p. 28; id. Phil. Trans., 1866, Pt. 2, p. 725 PI., also a case
of twelve arms in Antedon rosacea, the abnormality not being symmetrical, Dendy,
Proc. h. Phy.8. Soc. Edin., ix. p. 180, PL; also case of A. rosacea having abnormal
branches in two arms symmetrically placed with regard to the axis. Bateson, W.,
/'. /.. S. , L890, p. 584, tig. 4 (now in Coll. Surg. Mus.). The abnormal arms were
/>._. and ex of the usual nomenclature, as shewn in Fig. 133. For details see original
description.

*6G9. Encrinus liliiformis : amongst other abnormalities case
given in which one of the radii bore only one arm. V. Strom-
beck, Palceont, IV. p. 169, PL xxxi. fig. 3.

668.

CHAP. XVII.]

ASTEROIDEA.

439

ASTEROIDEA.

670. Symmetrical change in number of rays is common in some
of the forms. Asterias rubens and A. glacialis are frequently
seen with 6 or with 7 arms symmetrically arranged, and I have

, mouth

anus

Fig. 133. Antedon rosacea having two arms abnormally divided. Tbe figure A
shews the relations of the two abnormal arms, b2 and elt to the mouth and anus. B
shews the arm b2. (From Proc. Zool. Soc.)

440 MEBISTIC VARIATION. [part i.

seen one with 8. Individuals with 4 arms occur, but are much
less common than those with 6. I have seen Asterina gibbosa
with 4 rays, and a specimen (Scilly) given me by Mr S. F. Harmer
has 6 rays, of which 2 are a little nearer together than the others
(suggesting division of a ray). Mr E. W. MacBride tells me that
he has seen several 6-rayed specimens of this species. Mr E.
J. Bles kindly tells me that he dredged a 4-rayed Porania
pulvillus in the Clyde estuary. There appeared to be no trace
of a fifth ray and the specimen was as nearly as possible sym-
metrical.

The following cases exhibit special points.

671. Asterias glacialis : specimen with 8 rays possessed 3 madre-
porites. Couch, J., Charlesworttis Mag. of N. R., 1840, iv. p. 34.

(372. Asterias rubens : G-rayed specimens frequent atWimereux. In
several of these there are two sand-canals terminating at a common
madreporite. Giard, A., Comptes rendus, 1877, p. 973; cp. id. C. R.
soc. bid., 1888, p. 275.

673. Partial division of an arm is fairly common in Asteroids, but less
common I believe than the total variation in number, though I know
no statistics on this point. For a figure of Asterias (Hippasterias)
equestris L. with a bifid arm, presenting no appearance as of regener-
ation see Tiedemann, Zeitschr.f Phys., 1831, iv. p. 123, Plate 1.
The two following are peculiar cases.

6 / 4. Cribrella oculata : one of the arms bearing a branch, not as a
radius, but about (in dried specimen) at right angles to the normal arm,
the property of Prof. C. Stewart, who kindly shewed it to me.

675. Porania pulvillus, Gray (a Starfish): Specimen 5 cm. in diame-
ter, having five short rays. The ray opposite the madreporite when
viewed from the aboral surface is seen to be distinctly bifurcated at

1/

v^i.'i\\ &

\ Mm* &*&a*~-s

s.

Fig. 134. Porania pulvillus, No. 675, having the arm opposite the madreporite
abnormally divided as shewn at x and y. (From a sketch kindly sent by Prof.
Hbbdmak.)

chap, xvii.] ECHINOIDEA. 441

about 1 cm. from its termination. The ambulacral groove of (Fig. 134)
this abnormal ray divides into two branches at a distance of 2 cm.
from the edge of the mouth. One of these branches runs along one of
the forks of the ray to its extremity without further complication ;
but the other branch, belonging to the second fork, divides again 2 mm.
from the first bifurcation, so as to form two tracts which unite with
one another 3 mm. further on, thus inclosing a small piece of the ordi-
nary integument in an ambulacral area. Finally, this ambulacral area
divides once more close to the tip of the ray. There are no signs of
injury or disease in the specimen. Hekdman, W. A., Nature, 1886,
xxxi. p. 596. [I am indebted to Professor Herdman for the accom-
panying diagram of this specimen.]

ECHINOIDEA.

In the Echinoids there are (1) cases of total Variation to a
4-rayed form with 4 ambulacra and 4 interambulacra1: (2) cases
of partial or total disappearance of a definite ambulacrum or
interambulacrum, which can be named either because part of
it is present, or because two sets of similar plates thus become
adjacent: (3) a case of total variation to a 6-rayed form : (4) cases
of imperfect reduplication of a radius, thus forming an imperfectly
6-rayed form.

(1) Total Variation to a Grayed form.

676. Cidarites coronatus?: 4-rayed regular specimen (Fig. 135).
Meyer, A. B., Nova Acta G. L. C, xvm. 1836, p. 289, PL xm.

Fig. 135. Cidarites coronatus ? No. 676, a regularly 4-rayed specimen from
oral surface. (From A. B. Meyer.)

*677# Echinoconus (Galerites) subrotundus : 4-rayed specimen in
Woodwardian Mus. (Fig. 136). The ambulacral and interambulacral
areas are relatively wider than in a normal of the same size, the space
of the areas that are wanting being as it were shared among those that
are present. Apical disc roughly rectangular, and seems to be com-
posed of 4 perforated basals (genitals) and 4 perforated radials (oculars).
The basal plate corresponding to the posterior unpaired interambulacral
area is perforated, though normally imperforate. Statement made that

1 CuiNOT, Arch, tie Biol., 1891, xi. p. 632, says that Echinoconus vulgaris
has been seen with only three radii, but no authority is given.

442

MERISTIC VARIATION.

[part I.

the parts missing are those which lie on the left side of a line drawn
through the middle of the anterior single ambulacrum and the posterior

na

1

*

>-// ....

'^ ■/■':[:

< vv1 v- -•■/ •>

• •

L

'

-<

r~

V

-.

Fig. 136. Echinoconus subrotundus having 4 rays, No. 677. (From Roberts,
Geol. Mag., 1891.)

1. View of apical system. 2. Seen from side. 3. From apex. 4. From below.
aa, anterior ambulacrum [?]. mp, madreporite. ai, anal interradius.

The parts are lettered after Roberts.

unpaired interambulacrum, but it is not possible to say which of the
paired areas of this side are wanting, as the pores in the ambulacral
plates round the peristome are indistinctly shewn. Roberts, T., Geol.
Mag., 1891, Dec. ill., vni. p. 116, figs.
678. Discoidea cylindrica : a 4-rayed specimen, absolutely sym-
metrical. There are only 4 oculars corresponding with the 4 ambu-
lacra. Cotteau, G., Pal. /rang., 1862 — 67, VII. p. 31, PI. 1011, figs. 6
and 7. [This is exactly like Roberts' case No. 677 and is illustrated
by beautiful figures (q.v.). Cotteau in describing it says that the
anterior ambulacrum is wanting. It is difficult to see any sufficient
reason for the determination that this ambulacrum in particular is
wanting. For in this case there are only 4 sets of interambulacral
plates as well as 4 ambulacral areas in perfect symmetry. The anus
of course lies between two ambulacra ; and as the whole number is
even and the radii are symmetrically arranged, there is thus no ambu-
lacrum in the plane of the anus. Hence the suggestion that it is the
anterior ambulacrum which is wanting. But if by Variation an
Echinid has 4 symmetrical radii it would always seem that the

chap, xvii.] ECHINOIDEA. 443

anterior ambulacrum was missing, whether it be the anterior ambu-
lacrum, or the left anterior, or the left posterior that is wanting, or
even if all 4 new ambulacra correspond with all 5 of the normal.]

(379. Amblypneustes sp. (S. Australia): four specimens, each with four ambulacra
[no description or statement as to symmetry]. Haacke, Zool. Anz., 1885, p. 505.
(See No. 687.)

(2) Partial or total disajipearance of a definite ambulacrum or

inter ambulacrum.

*680. Echinus melo, having only four complete ambulacral areas (Fig.
137). The specimen is not spherical, for the apical system is warped
over in one direction and the oral pole is pulled in an opposite direction,
while the shell is much higher in the region of the apical system than
it is at the opposite side. There are only four ocular plates, which are
subequal, the madreporic plate and the plate opposite to it being some-
what larger than the other two. The genital plates are also four.
Only four ambulacral areas leave the apical system, and at that point
they are almost symmetrically disposed. Lower down however a
triangular series of plates bearing ambulacral pores is intercalated
between the plates of one of the interambulacral systems which it
divides into two. This intercalated series is of course the representa-
tive of the ambulacral area which is wanting at the apex of the shell.
The five ambulacra are nearly symmetrically disposed round the oral
surface just as theyb^r ambulacra are round the apical system. This
transition from a tetramerous to a pentamerous symmetry is effected
by complementary changes in the amount of divergence of the rays as
they pass down the shell. Examination shews that the ambulacrum
which is thus partially absent is the right posterior. Philippi, Arch. f.
Naturg., in. p. 241, Plate.
681. Amblypneustes formosus : a 4-rayed specimen having a
somewhat asymmetrical test. One of the interambulacral regions is
abnormally wide, and at about 9 plates down the side of the test in this
region a wedge-shaped piece composed of several partially distinct
plates bearing 7 pairs of ambulacral pores. This fragment doubtless
represents the deficient ambulacral area. The apical system consists of
10 plates. The two genital plates of the abnormal area are reduced in
size, and the ocular plate between them is abnormally large. Consider-
ing the madreporic plate as indicating the right anterior interambula-
crum, it appears that it is the left anterior ambulacrum which is thus
deficient. The height of the shell at the abnormal side is less than at
the other. Bell, F. Jeffrey, Jour. Linn. Soc, xv. p. 126, Plate.

In each of the foregoing the missing ambulacrum is actually at some
place represented by plates of ambulacral character, and the shape of
the test is greatly changed in correlation with the partial disappearance
of the radius. The following cases differ, in that in them one ambula-
crum is wholly wanting in the affected radius, and the interambulacra
are contiguous with each other. Curiously enough in two of these
specimens the symmetry is changed little or not at all. The cases in
Hemiaster were all Algerian fossils l.

1 Besides those here given in the text, Gauthier in the same place describes
an interesting case of symmetrical reduction in the two posterior ambulacra of
Hemiaster africanus.

*

444

MERISTIC VARIATION.

[part I.

II

Fig. 137. Echinus melo, No. 680, having the right posterior ambulacrum
partially absent, a, anterior ambulacrum, ra, la, right and left anterior ambu-
lacra, rp, Ip, right and left posterior ambulacra. I. View from apex. II. View
from oral surface. (From Philippi.)

chap, xvil] ECHINOIDEA. 445

g§2# Hemiaster batnensis : specimen in which the left posterior
ambulacrum is not present, and the ambulacral groove is only indicated
by a shallow depression, beyond which there are some rounded pores
which continue the ambulacral area beyond the fasciole. The corre-
sponding ocular seems to be absent. The test is of normal form, but
the median suture of the right posterior interambulacrum is not quite
straight. Gauthier, M. V., Comptes rendus de I'Ass. pour Vav. des sci.,
1885, xiii. p. 258, PL vn. fig. 1. '

(383. H. batnensis : very similar case of absence of right anterior
ambulacrum and corresponding genital and ocular plate, ibid., fig. 3.

(384. Hemiaster sp. : left anterior ambulacrum wanting and is gone
without trace. There are only 4 oculars and 3 genitals. In corre-
spondence with this variation there is considerable change in symmetry
of the test, which is irregular, the anterior and right anterior ambu-
lacra being deflected from their normal courses. [See details.] Ibid.,
figs. 4 and 4 bis. [Here, where there is a clear differentiation between
the several ambulacra, it is doubtless possible to affirm that such a
definite ambulacrum is missing, for the two interambulacra are left
adjacent to each other.]

685. Echinus sphaera (O. F. Miiller): specimen described in which
the left posterior interambulacral series of plates is almost entirely
absent. The details of the structure are as follows : the genital plate
which stands at the head of the left posterior interambulacrum is
reduced in size in all directions ; but the two ocular plates which should
be separated by it are somewhat enlarged, bearing several extra tuber-
cles, and meet together peripherally to the genital plate. The series of
interambulacral plates which should begin from this genital plate are
represented by a rudimentary row of small tubercles : the ambulacral
systems which are normally separated by these plates are consequently
almost contiguous. The rudimentary interambulacral series widens
somewhat at a short distance from the apical series and forms a small
island of interambulacral structure bearing 4 large tubercles. Beyond
this, viz. at a point placed about ^ the distance from the apex to
the oral surface, the two ambulacra again unite and are continued as a
single ambulacrum of double width. Doxitz, W., Midler's Arch, f
Anat. u. Phys., 1866, p. 406, PI. xi.

(3) Case of total Variation to a Q-rayed form.

*686. Galerites albogalerus(P) : a regularly 6-rayed specimen having
six symmetrical ambulacra and interambulacra (Fig. 138). Meyer,
A. B., Nova Acta Ac. Cces. Leop. Gar., xvm. 1836, p. 224, PI. xiii.

Fig. 138. Galerites albogalerus, No. 686. A six-rayed specimen. (After
Meyer.)

446

MERISTIC VARIATION.

[part I.

(387. Amblypneustes (S. Australia): 6-rayed specimen [no description or statement
as to symmetry]. Haacke, W., Zool. Anz., 1885, p. 505. (See No. 679.)

(4) Cases of imperfect reduplication of a radius.

'688. Amblypneustes griseus : having one of the ambulacra doubled
(Fig. 139); the apical system was normal. The width of the anterior
ambulacral region was almost double that of the others : it contained
two ambulacra lying side by side, each, as usual, composed of a double
row of plates with an ambulacral area and two poriferous zones. The

is.aPca

Fig. 139. Amblypneustes griseus, No. 688. Specimen having the anterior
ambulacrum doubled. I. The test seen from the apex. II. Details of anterior
ambulacrum shewing combined poriferous zones between A and A. The dotted line
bisects the ambulacrum of double width. (After Stewart.)

areas and external poriferous zones are like those of a normal ambula-
crum ; but the poriferous zones which touch one another are fused
together, with the pores irregularly arranged. The combined porifer-
ous zones are not quite equal to the sum of two normal ones. The
whole of this area, formed of the union of two ambulacra, projects as a
ridge which is continued down the whole of the side of the shell.
Stewart, C, Jour. Linn. Soc, xv. p. 130, PI.

689. Hemiaster latigrunda : right posterior ambulacrum double, the
two resulting ambulacra are closely adjacent peripherally and a small
interambulacral area is formed between them in their more central
parts. There are 6 oculars but no extra genital. Gauthier, /. c, tigs.
5 and 5 bis.

690. Hemiaster batnensis : right anterior ambulacrum double, the
two ambulacra are in contact through all their length. Cotteau, Pal.

frarig., 1869, p. 150, PI. xx., and Gauthier, I. c.

[For interesting evidence as to variation in the number of genital pores on the
costals in several genera of Echini, see Lambert, Bull. Soc. Yonne, 1890, xliv. Sci.

chap, xvil] ophiuroidea. 447

nat., p. 34; also Gauthier, Comptes rendus Ass. fr. pour Vav. Sci., Toulouse, 1887,
and other references given by these authors.]

Ophiuroidea.

Individuals with various numbers of arms are often seen,
especially in the genera Ophiothela, Ophiocoma, Ophiacantha and
Ophiactis, and in many of the species there are most usually
six arms. In these forms the evidence as to Meristic Variation
is complicated by the circumstance that in several of them change
in the number of arms may take place in the ontogeny, by division
and subsequent regeneration (see note on p. 433).

CHAPTER XVIII.
Bilateral series.

Of the organs repeated in Linear Series whose variations have
been illustrated, many are bilaterally repeated also ; but thus far we
have considered them only in their relations as members of Linear
Series. It now remains to examine the variations which they
exhibit in virtue of their relation to each other as members of
a Bilateral Series.

Meristic Variation in this respect is manifested in two ways.
A normally unpaired organ standing in the middle line of a bi-
lateral symmetry may divide into two so as to form a pair of
organs ; and conversely, a pair of organs normally placed apart
from each other on either side of a middle line may be com-
pounded together so as to form a single organ in the middle
line.

In animals and plants nothing is more common than for
different forms to be distinguished from each other by the fact
that an organ standing in the middle line of one is in another
represented by two organs, one on either side. The facility there-
fore with which each of these two conditions may arise from the
other by discontinuous Variation is of considerable importance.

Admirable instances of the bearing of this class of evidence upon
the question of the origin of Species are to be seen in zygomorphic
flowers. Veronica for example differs from the other Scrophulariacea?
especially in the fact that it has only one posterior petal, instead of
two posterior petals one on each side of a middle line. But there is
evidence not only that forms having normally two posterior petals
may as a discontinuous variation have only one such petal, placed in
the middle line, but also that the single posterior petal of Veronica may
as a variation be completely divided into two. Similarly the single
anterior petal of Veronica may also as a variation be divided into two,
thus giving three posterior and two anterior petals as in for example
Salpiglossis1. In these cases, which might be indefinitely multiplied,

1 An account of several discontinuous variations in the structure of zygomorphic
corollas was given by Miss A. Bateson and myself. Jour. Linn. Soc, 1892, xxvm.,
Botany, p. 386.

chap, xviii.] BILATERAL REPETITION. 449

there is thus a clear proof that so far as the variations in number and
symmetry are concerned, the transition from the one form to the other
may be discontinuous.

Analogous phenomena in animals are so familiar that general
description of them is for the most part not needed, and an
account will only be given of a few less known examples both
of union and of division of such parts. Besides these strictly
Meristic Variations in the amount of separation between the two
halves a few examples are introduced in further illustration of
the relationship that subsists between the two halves of a bilateral
animal.

In considering the evidence both of median union and of
division it must be remembered that the germs of most of the
organs in question are at some time of their developmental history
visibly double, and that when organs that should normally unite
to form single median structures are found double in older stages,
this duplicity is strictly speaking only a persistence of the earlier
condition. But to appreciate this comment it should be extended.
For, in every animal in which at some period of the segmentation
of the ovum, the plane of one of the cleavages corresponds with
the future middle line, all median organs must in a sense be paired
in origin, and the distinction between paired and median organs
is thus seen to be only one of the degree or amount of separation
between the symmetrical halves. Nevertheless the evidence of
Variation bears out the expectation that would be formed on
examination of normal diversities between species or larger groups
both in animals and plants, namely that whenever structures are
geometrically related to each other as optical images, insta-
bility may shew itself as Variation in the degree to which such
parts unite with or separate from each other. It is remarkable
that this instability appears as much in the case of organs bi-
laterally symmetrical about an axis of Minor Symmetry as it does
in the parts paired about the chief axis of Symmetry of the
whole body.

Examples of such Variation in bilaterally symmetrical parts
of a Minor Symmetry have been already given in the case of
the feet of the Horse and of the converse phenomenon in the
feet of Artiodactyles (q.v.).

A good illustration of the way in which duplicity about an
axis of Minor Symmetry may pass into the unpaired condition
is seen in the case of ocellar markings on bilaterally symmetrical
feathers. By comparing different feathers on several species of
Polyplectron, Darwin found that it was possible to find most of
the gradations between the complete duplicity shewn in Fig. 140,
I, where each half of the feather bears an almost symmetrical
ocellus, and the partially confluent condition shewn in Fig. 140, II,
which is not far removed from the state of the ocellus in the
Peacock's tail-coverts, where the whole ocellus has no peripheral

b. 29

450

MERISTIC VARIATION.

[part I.

indentation and is very nearly symmetrical about the rachis of
the feather, though each of its halves has no axis of symmetry.

I II

Fig. 140. I. Part of tail-covert of Polyplectron chinquis, with the two ocelli of
nat. size. II. Part of tail-covert of Polyplectron malaccense, with the two ocelli
partially confluent, of nat. size.

(From C. Darwin, Descent of Man, 1871, n. p. 139, figs. 54 and 55.)

Attention should be called to the fact that abnormal division along
a middle line may in many cases represent one of two different pheno-
mena which are not readily distinguishable. For when a normally
single organ is represented by two, standing on either side of a middle
line it is often possible that there may be not only a division of the
organ but a partial duplicity of the axis. These two conditions are of
course morphologically distinct ; for in the case of division of the organ
only, the two parts are still in symmetry about the original axis of
Major Symmetry of the body, but in the case of duplicity of the axis
there are two equivalent axes of symmetry, about which each half is
separately symmetrical. But though this distinction is in a sense a
real one it cannot be applied to cases of duplicity occurring in any
organ whose halves assume a bilaterally symmetrical form when sepa-
rate. For example in the case of the foot of the Horse, or of the
hjemal spines &c. of Gold-fishes (v. infra), when division occurs, each of
the two halves is only hemi-symmetrical, and this duplicity is no more
evidence that the axis is double than is the ordinary double condition
of the vertebrate kidney; but in the case of duplicity of the central
neural canal in Man for instance, or in the case of the tail-spine of
Limulus described below, it is not clear that there is not a partial
duplicity of the axis.

Division or absence of union in Middle Line.

Most of the organs which in a vertebrate stand in a median
position have been seen more or less often in a divided condition.

chap, xviii.] MEDIAN DIVISION: GOLD-FISHES. 451

Examples of such division in the middle line were, I believe, first
put together by Geoffroy St Hilaire, and a very full collection
of the evidence seen in Man is given by Ahlfeld1. The organs
most often divided are the sternum, neural arches, uterus,
penis, &c, and of these, specimens may be seen in any patho-
logical collection. Organs more rarely divided are the tongue 2,
epiglottis3, uvula4, and central neural canal5. The following are
special cases of variation consisting in a median division.

Division of caudal and anal fins in Gold-fishes.

•691. Cyprinus auratus (Gold-fish). The following account of the
multiple fins of Gold-fishes in China and Japan is taken chiefly
from Pouchet6 and Watase7. There is evidence to shew that these
animals were first imported to Japan from China.

Three distinct breeds of Gold-fishes are kept in Japan. The
first, called " Wakin " has a slender body closely resembling that of
the common carp. The second "Maruko or Ranckiu" has a very
short body, being in some cases almost globular in shape and
in it the dorsal fin is generally entirely absent. The head is
usually disfigured by rough-looking protuberances of the skin
which often attain a considerable size.

The third or "Riukin" has a short body with a rounded ab-
domen. Of all the breeds, this has the most beautiful tail which
is very large and often longer than the rest of the body.

Gold-fish breeders of the present day can freely produce the
" Riukin" or "Maruko " from the " Wakin." Various intermediate
forms between the above-mentioned breeds exist.

In all gold-fishes, irrespective of the breed to which they belong,
the tail-fin is, above all other parts, subject to the greatest varia-
tion. It is to be found in one of the following three states ;

(1) It is vertical and normal.

(2) It may consist of two separate halves ; each of these
halves is to all appearance a complete tail and the two tails pass
backwards side by side, but are united dorsally at the point where
they join the body.

(3) The two tails thus formed are united by their dorsal
edges to a variable degree and their lower edges may be bent
outwards, so that the two combined tails come to be spread out
into a three-lobed, nearly horizontal fin.

1 Ahlfeld, F., Mush. d. Menschen, 1880.

2 Partsch, Brest. Arztl. Ztsch., 1885, No. 17 ; Pooley, Amer. Jour., 1872, N.S.,
cxxvi. p. 385 [from Ahlfeld, p. 119].

3 Manifold, W. H., Lancet, 1851(1), p. 10; French, Ann. Anat. Surg. Soc.
Brooklyn, N. Y., 1880, ii. p. 271 [not seen], from Cat. Libr. Surg. -gen. U. S.
Army.

4 Trelat, Gaz. des H6p.t 1869, No. 125 [for others v. Ahlfeld, Abschn. n. p. 175],

5 Wagner, J., Mull. Arch. Anat. Phys., 1861, p. 735, PI. xvn. A.

6 Pouchet, G., Jour, de Vanat. et phys., vn. p. 561, PI. xvu.

7 Watase, S., Jour. Imp. Coll. Sci. Tokio, i. p. 217, Plates.

29—2

452

MERISTIC VARIATION.

[part I.

Besides the caudal fin, the anal fin undergoes remarkable

Fig. 141. Caudal and anal fins of Gold-fish (Cyprinus auratus).

I. Normal tail, seen from side. t>, dorsal lobe, d, ventral lobe. II. Abnormal
form divided as far as the notochord. v' v', two ventral lobes, d' d\ two dorsal
lobes. III. Abnormal form, the two ventral lobes, v' v', separate. IV. Pen-
ultimate vertebra of normal Carp (C. carpio). n.s, neural spine, h.s, haemal spine.
V. Penultimate vertebra of a Gold-fish with trilobed caudal fin. h'.s', double
haemal spine. VI. Diagram of transverse section through region of anal fin of
normal Gold-fish. VII. Similar section through a specimen having the anal fin
doubled, i.s, interhaernal spine. /. r, fin ray. n, bony nodule. i.s',f'.r', n', corre-
sponding parts doubled. (After Watase.)

variation. It is either median and normal ; or it may be distinctly
paired (Fig. 141, VII).

There are all stages of caudal and anal fins, intermediate be-
tween the normal and the completely paired states. Thus the
tail-fin with its lower portion alone in a double state, or the anal
fin with either its anterior or posterior portion double and the
remainder single, is of quite common occurrence. These different
conditions of the two fins combine in various ways in different
individuals thus giving rise to manifold varieties of form.

This doubling of the tail-fin consists essentially in a longi-
tudinal splitting of the morphologically lower lobe of the tail.
The first step in the process of doubling is seen in the case of
gold-fishes in which there is a slight longitudinal groove in the

chap, xviil] MEDIAN DIVISION : GOLD-FISHES. 453

ventral margin of the tail-fin. This groove may be extended up
through all the rays of the lower lobe of the tail, which then
consists of two tails side by side. The small dorsal lobe, which
lies above the notochord, is never involved in the jwocess, but always
remains single. There is therefore in this case no doubling of
the axis of the body. Examination of the skeleton shews that
in those fishes which have two tails the haemal spines of the last
three vertebrae are longitudinally split1 and diverge to carry the
two tail-fins (Fig. 141, V).

Pouchet lays stress on the fact that the size of each of the
paired tails is greater than that of the normal tail of a Gold-fish ;
but as Watase states that in the variety "Riukin" the tail may
be as long as the body, it is clear that this hypertrophy may exist
without any repetition.

In cases where the anal fin is doubled the process is exactly
the same, resulting from a longitudinal splitting of the rays of
which it is composed. This may only affect the outermost parts
of the fin or may be carried up further so as to divide the inter-
hsemal spines, in which case the two anal fins arise from the
body wall at separate points and diverge from each other.

Pouchet, who has extensively studied the history of Gold-fishes
in Europe, believes that it is almost certain that those which were
brought to Europe in the eighteenth century were all more or
less of the double-tailed order. He refers especially to the figure
given by Linnaeus2 representing the double-tailed form as a normal.

Pouchet states that the evidence goes to shew that this
anomalous race is not maintained in China by any rigid selec-
tion. He quotes a Chinese encyclopaedia to the effect that the
double-tailed Gold-fish is found in running streams, and gives
the evidence of Kleyn3, a missionary in China during the
eighteenth century, who states that "In fluvio Sleyn Gyprini
sunt qui caudam habent trifurcam et a piscatoribus Leid-brassen
vocantur, quasi diceres aliorum Cyprinoram conductor es."

Though the duplicity of the hasmal spines may be unaccompanied by other
variations it should be noticed that the extraordinary "Telescope ', Gold-fish not
unfrequently has also the double tail-fin. In the Telescope Gold-fish the eyes
project from the orbit to a greater or less extent, in the extreme form being
entirely outside the head and attached by a small peduncle only. The various
forms of abnormal Gold-fishes are generally to be seen in large quantities in
the shops of the dealers in aquariums &c. which abound near the Pont Neuf in
Paris. One of these dealers told me that he bred considerable numbers of them
every year, and that in fish from the same parents there was little uniformity,
many normals being produced for one that shewed any of the extreme variations.
It is recorded that of the Gold-fish hatched in Sir Robert Heron's menagerie about
two in five were deficient in the dorsal fin and two in a hundred or rather more had
a "triple" [sc. three-lobed as described above] tail-fin, and as many have the anal

1 It should be observed that there is no want of original union between the
hasmal spine3, for these close in the haemal canal as usual. The phenomenon is
thus altogether different from that of spina bifida in the neural spines.

2 Fauna suecica, 17-15, p. 331, PI. II.

3 Kleyn, Miss., v. p. 62, Tab. xm. fig. 1 [not seen], quoted by Baster, Opusc.
subsec, Harl., 1762, p. 91, note.

454 MERISTIC VARIATION. [part I.

fin doubled. The deformed fishes were separated from the others but did not
produce a greater proportion of varying offspring than the normals (Ann. Mag.
N. H., 1842, p. 533).

For a magnificent series of plates illustrating the various forms of Gold-
fishes see Billardon du Sauvigny, Hist. nat. des Dorades de la Chine, Paris, 1780.
[In Brit. Mus. copy text wanting ; I do not know if it ever appeared.]

Division of median structures in Coleoptera.
The following list includes every case known to me.

I. Epistome.

692. Anisoplia floricola (Lam.): Algerian specimen having the
epistome (chaperon) completely divided into two parts in the middle
line. Attention is called to the fact that this is a normal character
in certain genera of Lamellicorns, for example, Diphucephala and
Inca. Fairmaire. L., Ann. Soc. ent. France, 1849, Ser. 2, VII.
Bull., p. lx.

II. Pronotum1.

In Coleoptera the pro-thoracic shield or pronotum is normally
a single plate continuous from side to side. The following is a
list of cases in which this structure wras composed of two lateral
parts. In Nos. 695 and 706 the division was not completed
through the whole length of the shield. The two halves were
in most cases symmetrical, but in Nos. 700 and 703 they were
unequal.

As is shewn by No. 704 &c, there is in these variations more
than a mere fault of union between two chitinous plates, for in
this case the adjacent or inner edges of the plates were beset
with yellow hairs such as occur on the anterior and posterior
margins of the normal pronotum. In No. 703 again the adjacent
edges of the two plates are everted and form definite margins.

693. Melolontha vulgaris (Lam.), prothoracic shield consists of
two symmetrical pieces which do not meet in the dorsal middle
line. The prothorax is greatly reduced in length and the head con-
sequently is almost in contact with the scutellum (Fig. 142, I).
Kraatz, G., Deut. ent. Ztschr., 1880, p. 341.. PL u. fig. 8.

Fig. 142. Melolontha vulgaris, the Cockchafer, two cases of division of prono-
tum. (After Kraatz. )

1 With these cases compare the following : Hydrobius fuscipes, specimen
having pronotum formed into three lobes, one being central, and two lateral. The
lateral lobes projected from each side as considerable expansions. Kraatz, G.,Deut.
ent. Ztschr., 1889, p. 222, fig. 21.

chap, xviii.] MEDIAN DIVISION: BEETLES. 455

694. A male, closely similar case (Fig. 140, II., ibid., 1877, xxr.
v.5l,Taf.i.fig.2.

695. A male in which the pronotum was similarly divided, but
the division was not quite complete, de la Chavigxerie, Ann.
Soc. ent. Finance, 1846, Ser. 2, iv., Bull., p. xviii., PL II., fig. II.

696. An almost identical specimen (male). Mocquerys, Coleop.
anorm., 1880, p. 140, fig. [Now in the Rouen Museum, where
I have examined it.]

697. Another case ; extent of division not specified. Staxxius, Milll.
Arch. Anat. Phys., 1835, p. 304.

698. Oryctes nasicornis £ (Lam.) : anterior part of pronotum
divided into two parts by a longitudinal suture : posterior part
of pronotum undivided. Head normal, ibid., PL V. fig. 7.

699. Onitis bison (Lam.) : pronotum divided in the middle by a
longitudinal suture, the lateral pieces being raised up. ibid.

700. Heterorhina nigritarsis (Lam.) : specimen in the Hope Col-
lection at Oxford having the pronotum completely divided into two
somewhat unequal halves, of which the left is the largest. The
posterior angle of each of the pieces does not occupy its normal
position, but lies internal to the outer border of the elytron.
Owing to this disposition the mesothorax is exposed for a short
distance on each side and for a considerable extent in the
centre.

701. Attelabus curculionides (Rhyn.) : specimen of moderate size ;
head, elytra and legs normal. Structure of prothorax peculiar in that
the two lateral halves do not meet in the middle line, leaving
betwixt them a membranous space. The prothorax is shortened
and the head is pushed back into the thorax as far as the level
of the eyes. The edges of the plates of the prothorax are well
formed and properly finished. Scutellum present, but is not at
all concealed by the prothorax. Drechsel, C, Stettiner ent. Ztg.,
1871, xxxii. p. 205.

702. Chrysomela fucata (Phyt.) : Pronotum divided centrally into
two parts, each of which is triangular. The parts of the head and
scutellum which should be covered by the thoracic shield are
thus exposed. Krause, Stettiner ent, Ztg., 1871, xxxir. p. 137.

703. Telephorus nigricans (Mai.) : the pronotum is divided into
two unequal halves. The left half is nearly twice as large as the
right, and projects beyond the middle line, covering a part of the
right side of the prothorax. The right portion is small and very
concave. Both of these two parts of the pronotum are everted
at their edges to form a definite margin. The margins are con-
tinued all round each piece, and thus two margins are adjacent
in the contiguous parts of the plates. This specimen was kindly
lent to me by M. H. Gadeau de Kerville.

704. Carabus scheidleri: thorax dorsally covered by two com-
pletely separate and symmetrical plates, whose inner edges are
beset with yellow hairs [as the anterior and posterior margins

456 MERISTIC VARIATION. [part i.

normally are]. The rest of the animal was normal. Kraatz, G.,
Berl. ent. Ztschr., 1873, xvn. p. 430, fig.

705. Carabus lotharingus : thoracic shield divided in centre to
form two triangular pieces which only unite at a single point.
The head is drawn back into the thorax. Duponchel, Ann. Soc.
ent. France, 1841, S. 1, X., Bull, p. XX., PL

706. Lixus angustatus (Rhyn.): thoracic shield partially divided,
present a deep emargination both before and behind [description
not quite clear]. Doue, Ann. Soc. ent, France, 1851, ix. Bull.,

p. LXXXII.

III. Metasternal plates.

~07. Rhizotrogus marginipes $ (Lam.) having the abdomen de-
formed in a svmmetrical manner. Looked at from the ventral
surface the metasternal plates are seen to be divided in the middle
line by a deep depression so that the abdomen consists superficially
of two lobes ; these two lobes are united together in the last
segment in which the metasternal plate is undivided. The two
lobes are of equal size and the longitudinal depression which
divides them is shewn in the figure to be regularly and sym-
metrically formed. The animal is otherwise normal. [No dis-
section was made.] Baudi, L. V., Bull. Soc. Ent. Ital., 1877, ix.,
p. 220, fig.

IV. Pygidium.

708. Melolontha vulgaris (Lam.) : pygidium bifid, two cases.
Kraatz, G., Deut. ent. Ztschr., 1880, p. 342, PL II., figs. 4 and
4 a; and ibid., 1889, p. 222, PL I., fig. 19.

■j-qq A case of "double proboscis1' is recorded in Sphinx ligustri. The specimen
was a pupa, and through the pupal skin it could be seen that the two mandibles
had not united to form the single proboscis, but were divaricated. Kraatz, Deut.
nit. Ztschr., 1880, xxiv., p. 345, rig.

Miscellaneous cases of doubtful nature.

T 1 0. Ascidians. Prof. W. A. Herdman tells me that he has several
times met with Ascidians having a supplementary lateral atriopore.
He regards this as a retention of a larval character, since in the young
there are two atriopores which in normal individuals afterwards unite
dorsally.

711, Limulus polyphemus : large specimen found at Fort Macon, N.
Carolina, having a forked caudal spine (Fig. 143). This variation is

Fig. 143. Limulus polyphemus No. 711, having forked caudal spine.

(After Packard.)

chap, xviii.] MEDIAN DIVISION : MISCELLANEOUS.

457

probably very rare. Packard, A. S., Mem. Bost. N. II. S., 1872, n. p.
201, .$7.
712. Palamnaeus borneensis (Scorpion) : specimen in which the
terminal poison-spine was double, as
shewn in Fig. 144. The two halves
were not quite equal and there was no
opening of a poison-gland on the shorter
spine. This specimen, which is in the
Brit. Mus. was kindly shewn to me by
Mr R. I. Pocock.

Chirocephalus £ : specimen hav-
ing the generative sac with two horns
instead of one. [Normally there is only
one such horn which forms a median
downward prolongation of the ovisac.
No further description.] Provost, B.,
Mem. sur les Chirocephales, p. 232 ; in

71;

Jurine's
1820.

Hist, des Monocles. Geneva,

Fig. 144. Double poison-spine
of a Scorpion {Palamncem borne-
ensis). I. From dorsal side.
II. From ventral side. ??, the
spine which bore the openings of
the poison-glands.

714. Buccinum undatum. A number of specimens were formerly obtained from
Sandgate in Kent1, having the operculum double. Sometimes the two opercula
were separate, sometimes united. Many specimens of this variation are in the
collection of Dr A. M. Norman, who kindly shewed them to me. The shells and
opercula alone remain and consequently it is not now possible to determine the
position of the line of division relatively to the morphological planes of the animal ;
but, from the fact that in several instances the two opercula were related to each
other as images, it seems likely that the division was in the longitudinal median
plane, though this must be uncertain. Moreover in one of Dr Norman's specimens,
from the fragment of dried flesh adhering, it appeared that the apex of the foot
might have been bifid. Four cases are shewn in Fig. 145. In two of them (I and
II) there is a fairly close relation of images, while in III this relation is less clear
and in IV it is practically destroyed, though it is of course quite possible that this
may be the result of unequal growth. Several of these opercula are much contorted
and without any very definite shape.

II I

w.

HE

Fig. 145. Cases of duplicity in operculum of Buccinum undatum, from
specimens in the collection of Dr A. M. Norman. I and II nat. size. Ill and
IV enlarged. Ill and IV were kindly drawn for me by Mr J. J. Lister.

1 See Jeffreys, J. G., Ann. Mag. N. H., 1860 (2), p. 152.

458 MERISTIC VARIATION. [part i.

It was intended to have introduced here some account of the
curious and very rare cases in which, for a greater or less region of
the spine, corresponding half-vertebrae, on either side of the middle
line, are not united together in their proper order, but I fear this
would be too great a digression. For references on the subject see
Leveling, Obs. anat. rarior., Norimb., 1787, Fsc. 1, cap. in. p. 145,
Tab. v.; Sandifort, Mils, anat, Leyden, 1835, IV. p. 74. PL
clxxviii. ; Reid1, Jour, of Anat., 1887, xxi. p. 76, fig.; Guy's
Hosp. Rep., 1883, p. 132.

Union or absence of Division in the Middle Line.

This phenomenon is the converse of that described above.
Examples of median union are found in many organs of different
kinds. In vertebrates such union is especially well known in the
case of the eyes, the ears, and the posterior limbs, producing the
cyclopic, synotic and symmelian conditions respectively.

Each of these is of some interest to the student of Variation by
reason of the symmetry and perfection with which the union takes
place. In the cyclopian the degree to which the two eyes are com-
pounded presents all shades intermediate between the perfect duplicity
of the normal and the state in which the eye-balls are united in the
middle line of the forehead and have one circular cornea2. These
variations are closely comparable with those of the eye-spots on feathers
referred to on p. 449 ; for there also all stages are seen between a pair
of eye-spots placed one on either side of a middle line and complete
union to form one eye-spot bisected by the middle line. There is of
course no normal vertebrate having the eyes thus united in the middle
line, but as Meckel has remarked, the case of the cyclopian is not
essentially different from that of the Cladocera in which the compound
eyes, paired in other Crustacea, are united to form a single median eye.
The cases No. 718 and 719 of median union of the compound eyes of
Bees may also be considered in this connexion.

A very similar series of variations occurs in regard to the ears of
vertebrates, which in the synotic or cephalotic condition are compounded
in the middle line to a varying degree3. Such union of the ears is
especially common in the Sheep, cyclopia being most frequent in the
Pig. Dareste4 states that the first beginning of the cyclopian condi-
tion appears in the Chick as a precocious union of the medullary folds
in the region of the fore-brain, occurring before the optic vesicles are
fully formed from it. The degree to which the union of the eyes is
complete then depends on the earliness with which the folds begin to
meet relatively to the time of budding off of the optic vesicles. Dareste5
also declares that the cephalotic state is similarly first indicated by a
premature union of the folds in the region of the medulla, taking place

1 A ease in Man, resembling No. 7.

2 For an extensive collection of cases illustrating the various degrees of cyclopia
see especially Ahlfeld, Missb. d. Mensch., Abschn. n. 1882.

3 For figures see e.g., Otto, Mus. anat. path. Vratisl., PI. i. fig. 5, PI. in. fig. 2
(Lambs) ; Guerdan, Monats.f. Geburtsk., x. p. 176, PI. i. (Man) and many more.

4 Comptes rendus, 1877, lxxxiv. p. 1038.

5 I. c, 1880, xc. p. 191.

chap, xviil] MEDIAN UNION : KIDNEYS. 459

before this part of the brain has widened out. In this way the auditory
involutions are approximated. This account however cannot apply to
all cases of union of ears; for the compounded ears are sometimes on
the ventral side of the neck, as in Guerdan's case1.

The body of the symmelian ends posteriorly in an elongated lobe
made up of parts of the posterior limbs compounded together by homo-
logous parts. The two femora are usually united to form a single bone,
the tibiae are separate and the two limbs are again compounded in the
tarsal region. The axial parts posterior to the hind limbs are always
greatly aborted2.

Union of the kidneys in the middle line (Fig. 146), forming the
" horse-shoe kidney " of human anatomists, is a similar phenome-
non. As to the mode of development of this variation I know no
evidence. Usually the kidneys together form a single horse-shoe
shaped mass of glandular tissue, the union being posterior3 ; very

Fig. 146. Kidneys united in the condition known as "horse-shoe" kidney
(Man). In this specimen there were three renal arteries on each side.

(From Guy's Hosp. Rep., 1883.)

1 See note 2, p. 458.

2 See especially, Meckel. Arch. Anat. Phys., 1826, p. 273; Geoffroy Si
Hilaire, Hist, des Anom., ed. 1837, n. p. 23; Gebhard, Arch. Anat. Phys., l^ss,
Anat. Abth., p. 164 (good fig.). To the determination of the morphology of the
hind limb the structure of the symmelian monster is of unique importance, but I do
not know that it has had the notice it deserves from comparative zoologists.
From the manner of union of the parts of the two limbs may be obtained a positive
proof of the morphological relations of the surfaces of the two limbs to each other.
In a symmelian the feet are united by their fibular borders, the minimi being
adjacent, the halluces exterior, and the combined plantar surfaces ventral. The
great trochanters are dorsal, being often united into one in the dorsal middle line,
and the patellae are also dorsal, being also not rarely partly compounded. From
these facts, even were other indications wanting, we have a proof that if the hind
limbs were laid out in their original morphological relations to each other (as the
tail-fins of a Crayfish may be supposed to be) the halluces would be external and
anterior, the minimi internal and posterior, the flexor surfaces of the thigh and
crus and the plantar surface of the (human) foot would be ventral and the extensor
surfaces of the thigh and crus and the dorsum of the (human) foot would be dorsal.
This is of course affirmed without prejudice to any question of phylogeny ; but that
these must be the ontogenetic relations of the parts is clearly proved by the symmelian.

3 Sometimes anterior, e.g. Odin, Lyon mid., 1874, No. 12 [from Constat?*
Jahresb., 1874, i. p. 19] ; and Freund, Beitr. z. Geburtsh. u. Gyn., iv. 1875 [from
Canstatt's Jahresb., 1875, p. 340].

460

MERISTIC VARIATION.

[part I.

rarely the posterior ends of the kidneys are joined by a bridge of
ligamentous tissue1.

A remarkable case, in which the union of the two kidneys
was very complete and only indications of duplicity remained, is
given by Pichaxcourt, Gaz. hebd., 1879, p. 514.

*7

715

Illustrative Cases.

To these familiar instances are added a few less generally
known.

Capreolus caprea (Roebuck): specimen having the two horns
compounded in the middle line, forming a common beam for almost
the lower half of the horn (Fig. 147). This specimen was exhibited
among a large series of abnormal horns in the German Exhibition
beld in London 1891. Casts of it are in the Brit. Mus. and Camb.
Univ. Mus.2.

* >v '

Fig. 147. A Roebuck (Capreolus caprea) Xo. 705, having the horns com-
pounded to form one.

716. Limax agrestis : specimen having the upper tentacles united
into one in the middle line. The eyes were paired as usual.
Forbes and Haxley, Hist. Brit. Moll, iv. p. 288 and I. PI. JJJ,
fig. 4.

1 See Gruber, Virch. Arch., 1865, xxxn. p. 111.

The original is at Darmstadt.

chap, xviii.] MEDIAN UNION: EYES. 461

717. Helix hispida : specimen in which the tentacles were united
together. They were adherent throughout, excepting for a slight
cleft at the end, about one line in length. A shallow longitudinal
suture was visible between the two. The animal and shell were
otherwise normally formed. Roberts, G., Science Gossip, 1886,
xxii. p. 259.
*718. Apis mellifica (Honey-bee): a worker having the two com-
pound eyes continued up so as to unite on the top of the head
(Fig. 148). The union between the eyes of the two sides was com-
plete. There was no trace of any groove or division between them
and the resulting structure was perfectly symmetrical. In a
normal the three simple eyes are arranged in a triangle between

CE~~~^1

Fig. 148. A worker Bee (Apis mellifica) No. 708, having the two compound
eyes united across the middle line, seen from in front, and from the side.
CE, the united compound eyes. Oc, a single structure representing the three
simple eyes of the normal. (After Stannius.)

the upper edges of the compound eyes, but in this specimen they
were united into a single structure which was symmetrically placed
in the middle line in front of the united compound eyes (Fig, 148,
Oc). The body thus formed by the union of the simple eyes was
a round projection beset with long yellowish hairs.

In a normal male the compound eyes are much larger and are
in contact with each other at the top of the head, but the division
between them is sharply defined. In a normal worker, however,
the compound eyes are widely separated.

The facetting and the hairs on these eyes were normal and the
animal was in all other respects properly formed. STANNIUS,
Muller's Arch, Anal Phys., 1835, p. 297, PI.
'719. Apis mellifica having the compound eyes completely and
symmetrically fused. This individual was either a young and
abnormally developed queen, or else a worker. Its structure was in
several respects abnormal. The third pair of legs are like those
of the workers, as is shewn by the structure of the first joint of
the tarsus, the brush of hairs on the outside of the leg is not so

462 MERISTIC VARIATION. [part i.

much developed as in the workers, and this feature suggested that
perhaps the specimen may be a young and abnormal queen. The
abdomen is small and seems to have been arrested in its develop-
ment, but its shape is that of the abdomen of the workers. The
last segment of the abdomen is elongated, triangular, and slightly
grooved in the middle of the posterior border, so as to permit the
passage of the sting. The wings are more like those of a queen or
worker than those of a male ; for in the latter they generally
greatly exceed the abdomen in length. The thorax is small,
narrow, and contracted more than in the normal form, being also
less convex. The space between the wings is less than in a fully
developed bee. The antennas are mutilated, but seem to have
been normal ; but their last joints are slightly reddish brown as
they are in females, whether workers or queens, and not black as
they are in drones. The two compound eyes were completely
fused together in the middle line, across the place in which the
simple eyes ought to be found. The simple eyes are not present
at all. Lucas, H., Ann. Soc. Entom. France, S. 4, viii. 1868, p.
7: 37, PI.

CHAPTER XIX.

bilateral series — continued.

Further illustrations of the Relationship between

Right and Left Sides.

I. Variations in Segmentation of the Ovum of Loligo.

The following facts, taken from Watase1, are introduced in
further illustration of the mode of occurrence of bilaterally symme-
trical M eristic Variation.
*720. Loligo pealei. In the blastoderm the nucleus is placed eccen-
trically, being rather nearer to the posterior pole, as shewn in Fig.

a. v.

Fig. 149. Diagrams illustrating variations in segmentation of a Squid.
(Loligo pealei).

I. Normal unsegmented ovum, n, the nucleus eccentrically placed. A, anterior.
P, posterior. L, left. R, right. II, III, and IV. The shaded portions shew areas
in which in some specimens nuclear division was precocious. V. In the two
shaded areas triasters occurred in one specimen. VI. The hlastomeres of the
shaded areas in one specimen were not divided from each other. 1, 2, 3, successive
planes of division, ar, anterior right quadrant, pr, posterior right quadrant.
ar', pr', &c. areas separated off by the third segmentation-furrow. (After Watase.)

1 Watase, S., Jour, of Morph., iv. 1891, p. 247, Plates.

464

MERISTIC VARIATION.

[part I.

149, I. The first furrow, 1, 1, divides the blastoderm into two
halves and corresponds with the future longitudinal middle line.
The second furrow, 2, 2, is at right angles to this, dividing the
blastoderm into anterior and posterior halves, and the third
furrow, 3, 3, passes as shewn in Fig. 149, V.

In the subsequent segmentations various irregularities were
seen in single eggs, some of the variations being bilaterally sym-
metrical while others were confined to a particular half or to a
particular quadrant. For example, in some ova the nuclei of the
cells formed from the left half of the blastoderm, excepting those
next the median axis posteriorly (Figs. 149, II and 150, I), began
to divide before those of the right side and reached an advanced
stage of karyokinesis while the nuclei of the right half were still
resting. The nuclei of each half kept time very nearly (for details
see original figures). This curious variation was seen in three
(perhaps four) ova all taken from one mother.

In another the nuclei of the two anterior quadrants al, ar, in
their divisions kept ahead of those of the posterior quadrants.
Fig. 149, IV. represents an ovum in which the nuclei of the right
posterior quadrant on the contrary divided before those of the 3
other quadrants.

Another variation is shewn in Figs. 149, VI and 150, II. There
the four blastomeres shaded had either been never fully divided
from each other or had subsequently fused together symmetrically
on each side.

/ IT

Fig. 150. Variations in segmentation of ovum of Loligo pealei. I. Case in
which the nuclei of cells of the left half of the blastoderm began to divide pre-
cociously. II. Case in which the blastomeres of the areas ar' and al' were not
distinct from each other. (After Watase.)

Fig. 149, V, illustrates another remarkable Meristic variation
which symmetrically affected the portions shaded. In both of
these shaded segments the nuclei divided into three by triple
karyokinesis, forming " triasters."

chap, xix.] LATERAL HOMOEOSIS. 465

II. Homoeosis in cases of normal Bilateral Asymmetry.

In proportion as an animal is bilaterally symmetrical the right
side is an image of the left. Nevertheless in many substantially
symmetrical forms there is asymmetry in the condition of some
one or more organs present on both sides. (This asymmetry, in
the cases to be considered, is of course distinct from that due to
asymmetrical disposition of unpaired viscera, such as the heart and
liver of vertebrates, &c.) In several of these cases there is evidence
that both sides may on occasion assume the form normally proper
to one only.

Some one will no doubt be prepared with the suggestion that
these variations are reversions : with this suggestion I shall deal
after the facts have been recited.

Spiracle of Tadpole.

721. Pelobates fuse us : a tadpole, 7 cm. long, having two spiracles
symmetrically placed (Fig. 151), one on the right side and the other on
the left1. [No details given.] H^ron-Royer, Bull. soc. zool. Fr.t ix.

Fig. 151. A tadpole of Pelobates fuscus, having, as a variation, two spiracular
openings, No. 721. (After Heron-Royek.)

1884, p. 162, j%. [In the normal there is only one spiracle, that of
the left side. In Pipa and Dactylethra two spiracles are normally
present. See Wyman, Proc. Bost. N. H. S., ix. p. 155; Wilder, Am.
Nat.y 1877, xi. p. 491 ; Boulenger, Bull. soc. zool. Fr., 1881, vi. p. 27.

Tusk of Narwhal.

722. Monodon monoceros (Narwhal). In normal males the left tusk
alone is developed while the right remains abortive in its alveolus. In
the female both tusks are in this rudimentary condition. No reliable
record (1871) of a specimen having the right tusk only developed, but
in eleven cases from various sources the two tusks were both developed,
and in several of these the two were of about equal length. The
normal asymmetry of the skull is not affected by the presence or
absence of the teeth. Clark, J. W., P. Z. S., 1871, p. 42, figs, (full
literature); see also Turner, W., Jour. Anat. Phys., 1871, p. 133 and
1874, p. 516.

Ovary and oviduct of Fowl.

It might be anticipated that development of the right ovary and
oviduct in birds would be a frequent form of Variation, but as a
matter of fact very few such cases are recorded. In consideration of

1 In the same place is recorded a case of a tadpole of this species having the
spiracle on the right side instead of the left, perhaps a case of situs inversus.

b. 30

466 MERISTIC VARIATION. [part i.

the large numbers of birds, wild and domesticated, annually dissected
in laboratories it may perhaps be concluded that these variations are
exceedingly rare1.

728. Hen having a small right ovary in addition to the left ovary. The
left oviduct was normal, but the left ovary was partially transformed
into sacculated tissue. [Full histological details of the structure of
both ovaries given.] The hen had partly assumed the plumage of the
cock, having four sickle-feathers and other characters proper to the
male. Brandt, Z.f. w. Z., xlviii. 1889, p. 134, Pis.

724. Hen having a normal left oviduct and in addition a partially
developed right oviduct which formed a large thin-walled cyst dis-
tended with gas. C. S. M., Ter. Cat., 1872, 455.

Proboscis-pore of Balanoglossus
and ivater-pores of larvce of Asterias.

♦725. Balanoglossus kowalevskii. The anterior or proboscis-body-
cavity is continued backwards into the proboscis-stalk as two hollow
horns. In this and most other species the left of these alone acquires
an opening to the exterior at the proboscis-pore. In B. kupfferi alone
there are two such pores, one opening into each of the two horns2. A
specimen of B. kowalevskii in which both horns thus opened to the
exterior was seen by Morgan, T. H., Jour, of Morph., 1891, v. p. 442.
72G. Asterias vulgaris. The Bipinnaria larva as commonly seen
resembles the usual Tornaria in having a left water-pore only. In
several larvae 3| to 4 days old the presence of two such water-pores, a
right and a left, symmetrically placed, has been observed by Field and
Brooks. The right pore subsequently closes. This condition is be-
lieved by Field to represent not a variation but a normal phase of
development [though further confirmation is needed]. Field, G. W.,
Q. J. M.S., 1893, xxxiv. p. 110, PL xiv. figs. 22 and 23.

Variations in Flat-fishes.

A curious series of variations bearing on the relations of the
right side to the left occur in Pleuronectidse. The evidence on
this subject was collected by Steenstrup3 in 1863.

Flat-fishes are normally coloured on the upper side and are
without chromatophores in the skin of the lower side4. Variations
in colour occur in two ways ; the upper side may be white like the
lower, or on the contrary the lower side may be coloured like the
upper. The former change cannot well be distinguished from
other cases of albinism5 and does not call for special notice here.

1 In view of the cases of the Crayfish and the Cockroach mentioned in the
Preface, much stress cannot be laid on this consideration.

2 Spengel, J. W., Mitth. zool. Stat. Neap., 1884, v. p. 494, PI. xxx. fig. 2.

3 Steenstrup, Overs, k. Dansk. vid. Selsk., 1863, p. 145, abstr. by Wyville
Thomson, Ann. and Mag. X. H., 1865 (1), p. 361.

4 In some species the coloured side is normally the right, in others the left,
reversed specimens being common in some species (P. Jlesus), rare in others. The
reversed condition concerns only the head, skin, muscles, &c, and there is no
transposition of the internal viscera.

5 Evidence collected by Steenstrup. Gottsche (Arch. f. Naturg., 1835, n. p.
139) states that P. platessa is not rarely wholly white on both sides. I have never

chap, xix.] FLAT-FISHES. 467

The converse variation, by which the lower side assumes the
colour of the upper side is important in several aspects.

Interest has of late been drawn to this subject especially through an experiment
recently made by Cunningham1, who found that of a number of young flat-fishes
reared in a vessel illuminated by mirrors from below, some became partially marked
with pigmented patches on the lower side. The suggestion was made that this
pigmentation was induced by the direct action of light. It is of course impossible
here to enter into the theoretical questions raised in connexion with this subject
and this account will be confined to description of the colour- variation as seen in
nature and of the singular variation in structure commonly associated with it.
Mr Cunningham has obligingly advised me in connexion with this subject.

Pigmentation of the lower side has been seen in Rhombus
maocimus, R. Icevis, Pleuronectes flesus, P. platessa, P. oblongus,
Solea vulgaris [?] and probably other forms. Attention is drawn
to one feature in these changes which from our standpoint has an
important bearing. When the underside of a flat-fish is pigmented,
it is often not merely pigmented in an indefinite way but it is
coloured and marked just as the upper side is. There are, I know,
many specimens upon whose undersides a brownish yellow tint is
either generally diffused or restricted to patches, but when there
is pigment of a deeper shade, as in all the well marked cases of
the variation, the colour and markings are closely like those of the
upper side. For example, a Plaice (P. platessa) sent to me by Mr
Dunn of Mevagissey is fully coloured over the posterior half of the
lower side ; but there is not merely a general pigmentation, for the
coloured part of the lower side is marked ivith orange markings
exactly like those of the upper side.

More than this : it was found by passing pins vertically through
the body that there was in the case of most of the spots a close
correspondence in position behveen those of the upper and those of
the loiver side. There were 13 spots on the coloured part of the
lower side, which extended slightly beyond the line of greatest
width. Of these, 13 spots on body and fins coincided exactly with
those of the upper side ; 2 coincided nearly ; 2 were not repres-
ented on the upper side ; and 2 spots of the upper side were not
represented on the lower. From these facts it is clear that in
" double " flat-fishes we have an instance of symmetrical variation
of one half of the body into more or less complete likeness of the
other half, resembling other cases of Homceosis in Bilateral Series
already noticed.

This is made the more evident by the fact that in the two best
described specimens of "double" Turbot (No. 727) not merely did the
lower side resemble the upper side in point of colour, but upon it were
also present the bony tubercles normally proper to the dark side, being
only slightly less well developed on the lower side than on the upper.

succeeded in seeing an entirely white specimen, though individuals partially white
on the upper side are not rare. See also Zool, pp. 4596, -1914. Zeugopterus puncta-
tus white on both sides, Day, Brit. Fishes, n. p. 19.
1 Cunningham, J. T., Proc. Roy. Soc, 1893.

30—2

468

MERISTIC VARIATION.

[part I.

(Such a development of tubercles1 on the lower side may however occur
without any correlated change of colour.) It is also stated that in
the " double " turbots the muscles of the lower side are thicker than
they normally are, thus approximating to the upper side, a feature
that may be taken as an indication that the manner of swimming is
different from that of normals.

A flat-fish having pigmentation on the lower side does not
necessarily present any other abnormality'2. The Plaice, for in-
stance, just mentioned, was, colour apart, quite normal. But
some specimens of flat-fishes darkly coloured below present in
addition a very singular structural variation. This consists essen-
tially in the presence of a notch of greater or less depth occurring
below the anterior end of the dorsal fin above the eye (Fig. 1 52). By
this cleft the anterior end of the dorsal fin is separated from the
back of the head and is borne on a process or horn project-
ing anteriorly so as to continue the contour of the body above the

Fig. 152. Head of a Brill (Rhombus Icevis) having the dorsal fin separated from
the head as described in the text. (From Yarrell.)

1 The literature relating to discontinuous variations consisting in the presence
of bony tubercles upon the blind side of Rhombi is extensive. See especially
Demidoff, Voy. dans la Russie Merid., 1840, in. p. 534, Pis. 28, 29 and 30.
Steixdachner, Sitzb. Ak. Wiss. Wien, 1868, lvii. (1), p. 714. Rathke, Mem. Ac.
Sri. P6t.t 1837, in. p. 349. Gunther, Cat. Brit. Mm. Fishes, iv. p. 409. These
cases will not be confounded with those of supposed hybrids between R. maximus
and R. lavis, which bear upon both sides scales of various sizes.

- I know no detailed description of a flat-fish wholly pigmented on the underside,
having the dorsal fin normal, but numerous authors (Gottsche, Duhamel, &c.) make
mention of such cases. Since this chapter was written I have seen two recent papers
on the subject by Giard (Comptes rend. Soc. Biol, 1892, S. 9, iv. p. 31 and Nat. Sci.,
1893, p. 356) contributing further evidence on the subject and giving new cases in
the Turbot. According to Giard, of flounders (P.Jiesus) at Wimereux 3 °/0 are fully
coloured on the blind side, in addition to many that are piebald. This must be a
very much higher proportion of abnormal specimens than is found in English
fisheries.

chap, xix.] FLAT-FISHES. 469

head. Steenstrup states that the variation has, he believes, been
observed in all flat-fishes1 except the Halibut (Hippoglossus).

In several but not all cases of this abnormality the eye belong-
ing to the lower side was not placed in its normal position on the
upper surface, but stood in an intermediate position on the top of
the head, so that it could be partially seen in profile looked at from
the " blind " side. It seems possible that the pigmentation of the
" blind " side is in some way correlated with some abnormal delay
in the shifting of the eye and a consequent continuation of the
power of receiving visual sensations from this side.

The abnormality of the dorsal fin is in accordance with this suppo-
sition. To understand the nature of this condition it must be remem-
bered that the form of the flat-fish is derived from the usual "round"
form by two principal changes. (1) By a twisting of the head the eye
is brought over from the blind side to the upper side. (2) The dorsal
tin is extended forwards above the eye thus shifted ; for as Steenstrup
and Traquair2 have shewn, this anterior extension of the dorsal fin is
not in the morphological middle line. It is in fact an anterior repeti-
tion of the series of dorsal fin-rays along the new contour-line of the
body, and occurs irrespective of the fact that the tissues with which it
is there associated are not median at all.

Steenstrup and Traquair shewed plainly that it is insufficient to
suppose that there is a twisting of the head, for this does not explain
the presence of the dorsal fin in the position in which it is found,
curving along that which ivas once the side of the head. Traquair sug-
gested that these relations could be attained by two processes ; ( 1 ) a
twisting of the head so as to bring over the eye from the future
"blind" side, and (2) a forward growth of the dorsal fin along that
which is then the upper contour-line of the head. These processes
have now been actually seen by Agassiz5 in several Pleuronectidre.
The first observation of a specimen at the stage when the eye is on the
top of the head and the dorsal fin is not yet extended, seems to be that of
Malm4 and there can be little doubt that the normal development
proceeds in this way5. It has been pointed out by many writers that
if the upper eye were to remain in an intermediate position on the top
of the head, and the dorsal fin were then to grow forwards, arching
over it, the condition of these abnormal forms would be reached. That
this is what has actually occurred in them seems likely.

A number of difficult questions are thus raised as to the histological

1 The evidence as to the Sole seems to be doubtful (v. infra).

2 Traquair, Trans. Linn. Soc, 1865, xxv. p. 2(33.

3 Agassiz, Proc. Amer. Ac. Sci. 1878, xiv. p. 1, Pis.

4 Malm, (Efvers. k. Sven. Vet. Ac, 1854, p. 173, see Ann. and Man. N. H. 1865
(1), p. 366.

5 Allusion should be made to the fact that in the genus " Plagusia" the dorsal
fin acquires its forward extension at a time before the shifting of the eye occurs.
When the time for this change comes the eye of the future bliud side passes under
the dorsal fin and above the skull, through the tissues from one side of the head to
the other. This was first observed by Steenstrup, and afterwards by Agassiz in
great detail and the fact can hardly now be questioned. This mode of development
is peculiar to " Plagusia" though when Steenstrup wrote he expected that the same
would be found to occur in other Pleuronectidse.

470 MERISTIC VARIATION. [part I.

processes by which the dorsal fin comes to stand where it does. We
are accustomed to think of the repetition of the fin-rays as being an
expression of the fundamental segmentation of the trunk, accessory to
it no doubt, but still of the same nature and histologically dependent
upon it. The extension of this repetition along the morphological side
of the face is thus an anomaly.

Further comment on the nature of the variation will be made
after the chief cases have been given.

*727. Rhombus maximus (Turbot). Two specimens respectively 9 in.
9 lines and 7 in. 6 lines in length, 7 in. 6 lines, and 5 in. 6 lines broad.
Both sides of a similar coffee-brown colour. The smaller had a
yellowish white spot, about 1 in. square, on the operculum of the lower
side. The colour was more uniform than usual and the dark spots
normally found on the fins of the Turbot were absent. Both sides
irregularly beset with horny tubercles, only slightly more developed on
the upper than on the lower sides. Fine scales were also found deep
in the skin of both sides. All fins except the dorsal were normal in
form and position. The dorsal fin was anteriorly detached from the
head, being borne on a horn-like projection. The separation between
the head and dorsal fin was continued backwards as a semi-circular
notch to a level behind the eyes. Upon many of the fin-rays of the
dorsal, anal and caudal fins there were 1 — 7 small knotty elevations of
the size of poppy-seed. In the smaller specimen these elevations were
smaller, and on the caudal fin absent. The left eye had its normal posi-
tion, but the right eye [of "blind" side] was placed on the top of the
head, but in such a position that it could scarcely have seen any thing
not directly over it. [See further details given.] Schleep, Isis, 1829,
p. 1049, PL in.

Similar specimen Couch, Fishes Brit. Isl., in. p. 157. Dried speci-
mens in Brit. Mus., Newcastle Mus., &c.

*728. Very good figures of such a Turbot are given by Duhamel du
Monceau (Traite general des Pesches, 1777, III. Sect. ix. p. 262, PI. III.
figs. 3 and 4). The under side was of nearly the same colour as the
upper and the tubercles generally found on the upper side only were
present on the lower side also, though of smaller size. A slight notch
separated the dorsal fin from the head ; but the upper eye is figured as
in its normal place, not being on the top of the head, and it wTould of
course be invisible from the "blind" side. [This important case is
referred to by Steenstrup, but seems to be unknown to others, who
attribute the separation of the dorsal fin to the persistence of the eye on
the top of the head.]

729. A young turbot, similarly coloured on both sides, having the eyes
still symmetrical, swimming on edge, is figured by McIntosh, Fishes of
St. Andrews, 1875, PI. vi. figs. 5 and 6. Prof. Mcintosh kindly
informed me that these "double" individuals swim on edge much
longer than usual.

730. Rhombus laevis (Brill). Specimen presenting similar characters. The lower
(rt.) side of a uniform dark colour with exception of a white patch on operculum.
The right pectoral fin was whitish. The under side was rather darker than the
upper and the mottling present on the upper side was entirely absent from the
under side, which was without marking or spot. This is very probably a post-

chap, xix.] FLAT-FISHES. 471

mortem change. Right pelvic fin dark, but the left was whitish, speckled with
black. Nostrils normal. The eye of the right (blind) side was placed almost
entirely on the left side, but not completely so, for it could be seen to some extent
in profile from the right side. The notch separating the dorsal fin from the head
was rounded, and extended to about the level of the posterior margin of the left eye.
There were about 6 chief fin-rays borne by the prominence above the eye. The fish
seemed to be in all respects healthy and well grown. Paris Mils., numbered
#90 #310. [This specimen was kindly shewn to me by Prof. Vaillant.]

Similar specimen, also having white patch on operculum Duhamel du Monceau,
7. c. See also Fig. 152, from Yarrell, Brit. Fishes, 3rd ed., i. p. 613.

The specimen described by Donovan (Brit. Fish., 1806, iv. PI. xc.) under the
name " Pleuronectes cy clops" was in Steenstrup's opinion a young Brill having this
variation. In this specimen the right eye is seated on the top of the head and is
seen in profile from the right side. The right side was coloured like the left, but
was not so dark. The dorsal fin began behind the right eye. This specimen was
found in a rock-pool "inveloped in a froth" said to have resembled cuckoo-spit.

731. Zeugopterus punctatus (Muller's Topknot). This fish is very liable to mal-
formations of the anterior end of the dorsal fin, causing it to form an arch over the
eyes. Yarrell (quoting Couch), Brit. Fish., 3rd ed., i. p. 6-18.

732 "Platessa oblonga" De Kay (American Turbot) ; specimen having both sides

darkly coloured; upper eye placed on the top of the head; dorsal fin separated by a
notch. Storer, Mem. Amer. Ac. Sci., vm. p. 396, PI. xxxi. fig. 2 b.

733. Pleuronectes platessa (Plaice) : specimen completely and similarly pigmented
on both sides far from rare. In a specimen thus coloured the ' tubercula capitis '
were as strongly marked on the one side as on the other. In several examples the
anterior end of the dorsal fin was separated, from the head, Gottsche, Arch. f.
Naturg., 1835, n. 1, p. 139.

734 Pleuronectes nesus (Flounder) : several specimens found at Birkenhead, having
' a deep notch of this kind above the eyes. These fishes were 'very dark brown
(almost black) on both sides.' In the length of the fins these examples differed
somewhat from the Flounder, Higgins, Zoologist, 1855, p. 4596, fig. Specimen of
this kind figured by Traquair, Trans. Linn. Soc, 1865, xxv. p. 288, PI. xxxi. figs. 8
and 9. See also Nilsson, Skandin. Fauna: Fiskama, Lund, 1855, p. 621; Couch,
Brit. Fishes, 1864, in. p. 198.

735. Solea vulgaris. Many authors mention Soles coloured on both sides, but I
know no good description of one. Yarrell (I. c, p. 669) says "we have not seen
the Solea Trevelyani of Ireland (Sander's News-letter, 16th April, 1850). It is
dark-bellied and is described as bearing a projection on the head like the monstrosity
figured on p. 643." Duhamel du Monceau (/. c, PL I. figs. 3 and 4) represents a
sole darkly coloured on both sides. The dorsal fin is shewn in its normal state,
not separated from the head. No special description is given, and as the author
does not state that he had himself seen such a sole the figure was perhaps not
drawn from an actual specimen. A sole with the under side piebald is described in
Zool. x. p. 3660.

In connexion with this evidence Steenstrup refers to a small flat-
fish, Hippoglossus pinguis, found in a few localities in Scandinavian
waters, having a form almost intermediate between a "flat" and a
"round" fish. The eye of the "blind" side is exactly on the top of
the head and can be seen in profile from the blind side. The blind side
is nearly as muscular as the upper side, and its skin is yellowish-brown
in colour and is only slightly paler than that of the upper side. The
dorsal fin begins behind the eye, not arching over it. Steenstrup
looked on this creature as representing in a normal form the "double
condition presented as a variation in the cases we have been speaking
of. See description and figures in Smit's edition of Fries, Ekstrom
and Sundevall's Hist, of Scand. Fishes, 1893, pp. 416 and 417.
Smit makes a new genus, Platysomatichthys, for this animal.

472 MERISTIC VARIATION. [part i.

Comment on the foregoing cases.

In the cases preceding many will no doubt see manifest examples of
Reversion. There is a sense in which this view must be true, for it can
scarcely be questioned that if we had before us the phylogenetic series
through which the Flat-fishes, the Narwhal, &c. are descended, it would
be seen that each did at some time have a bilaterally symmetrical
ancestor. But, for all that, in an unqualified description of the change
as a reversion the significance of the facts is missed. By the state-
ment that a given variation is a reversion it is meant that in the vary-
ing individual a form, once the normal, reappears. The statement more-
over is especially intended to imply that the definiteness and magnitude
of the step from normal to variety is due to the circumstance that
this variety was once a normal. It is meant, in fact, that the great-
ness of the modern change can be explained away by the suggestion
that in the past, the form now presented as a variation, was once built
up by a gradual evolution, and that though in its modern appearance
there is Discontinuity, yet it was once evolved gradually.

Now the attempt to apply this reasoning, especially to the case of
the "double " Flat-fishes, leads to difficulty. "We may admit that in so
far as the varieties are bilaterally symmetrical they represent a normal.
Their bilateral symmetry, as a quality apart, may be an ancestral
character, if any one is pleased so to call it. But that in the contem-
porary resumption of a bilateral symmetry we have in any further sense
a reappearance of an ancestral form is very unlikely.

First it might be fairly argued that it is improbable that there was
ever a typical flat-fish having ori'both sides the peculiar pigmentation
of the present upper sides of the Pleuronectidse of our day. Such a
creature would be highly anomalous. But even if in strictness we
forego the assumption that since the evolution of Flat-fishes there has
never been an ancestor fully pigmented on both sides, there still
remains the difficulty that each species may in the "double" state have
upon its lower side the specific colour proper to its own upper side. A
notable instance of this has been mentioned in the Plaice (p. 467); and
here not only was the pigmentation of the lower side, as far as it went,
like that of the upper, but the spots were even almost bilaterally
symmetrical. It is true that the lower side does not in every case copy
the upper in colour, but it may do so ; and, in proportion as it does so
in different species, so far at least are the changes not simply revers-
ions ; for the several patterns of Turbot, Plaice &c. are mutually ex-
clusive and it can hardly be supposed that each species had separately
a "double" ancestor having the present specific pattern on both sides.

The outcome of this reasoning is to shew that the hypothesis of
Reversion in the strict sense is an insufficient account of the actual
variation in these Flat-fishes, and in the production of these varying
forms there is thus a Discontinuity over and above that which can be
ascribed to Reversion. The facts stated in connexion with the Plaice
(p. 467), especially the symmetry of the spots, probably indicate the real
nature of this Discontinuity, and raise a presumption that in the new
resemblance of the lower side to the upper we have a phenomenon of
Symmetry resembling that Homceosis shewn to occur between parts in

chap, xix.] LATERAL HOMCEOSIS : COMMENT. 473

Linear Series. In the Flat-fish the right side and the left have been
differentiated on different lines, as the several appendages of an Ar-
thropod have been, but on occasion the one may suddenly take up all
or some of the characters, whether colour, tubercles or otherwise, in
the state to which they have been separately evolved in the other.

What may be the cause leading to this discontinuous change we do
not know. That it is often associated with a delay in the change of
position of the eye of the " blind " side seems clear from the frequent
detachment of the dorsal fin in these cases. But it should be borne in
mind that even in such examples the eye may still eventually get to
its normal place, though probably it was delayed in the process and so
led to detachment of the fin. Taken with the fact that the young
" double " turbots swim on edge longer than the normals it must be
concluded that the bilateral symmetry of colour is associated with
reluctance or delay in the assumption of the asymmetrical state, but
more than this cannot be affirmed.

I do not urge that the same reasoning should be applied in other
cases, but the possibility must be remembered. In the Narwhal, for
instance, it is perhaps unlikely that there was ever an ancestor which
had two tusks developed to the extent now reached by the left tusk of
the male ; but if there ever were any such form, it is hard indeed to
suppose that it could have been connected with the present species
by a series of successive normals in which the right tusk gradually
diminished while the left was of its present size. On the whole it
seems more likely that when the right tusk now develops to be as
long as the left, it is taking up at one step the state to which the left
has been separately evolved.

However this may be, the fact that such Homoeosis is possible
should be kept in view in considering the meaning of such cases as that
of a Tornaria with two water-pores. For while on the one hand we
may suppose that Balanoglossus kupfferi with its normal pair of water-
pores is the primitive state and that the varying Tornaria is a revers-
ion, on the other hand B. kupfferi may be a form that has arisen by a
Homceotic variation from the one-pored form, and of this variation
Balanoglossus No. 725 may be a contemporary illustration1.

1 The following interesting example of a similar Variation has appeared since
these pages were set up. Eledone cirrhosa : specimen having not only the third
left arm developed as a hectocotylus, as usual, but the third right arm also. The
right had 57, the left 66 suckers, but otherwise they were alike. Appellof, A.,
Bergens Museums Aarbog, 1893, p. 14.

CHAPTER XX.

Supernumerary Appendages in Secondary Symmetry.

Introductory. — The Evidence as to Insects.

Of all classes of Meristic variations those consisting in repeti-
tion or division of appendages are by far the most complex and
the most difficult to bring into system. There is besides no
animal which normally presents the condition seen in the varia-
tions about to be described, though there may be a true analogy
between them and phenomena found in colonial forms. It has
nevertheless seemed well to introduce some part of this evidence
here for two reasons. First the subject is a necessary continuation
of the evidence as to digits, which would otherwise be left incom-
plete ; secondly it will be shewn that though many of the cases are
irregular and follow no system that can be detected, there remain
a large number of cases (being, indeed, the great majority of those
that have been well studied) whose form-relations can be put in
terms of a simple system of Symmetry. Thus not only are we
introduced to a very remarkable property of living bodies, but also
the way of future students of Variation may be cleared of a mass
of tangled facts that have long been an obstacle ; for on apprehen-
sion of the system referred to it will be seen that cases of repeti-
tion in Secondary Symmetry are distinct from those of true
Variation within the Primary Symmetry and may thus be set
apart.

Arrangement of evidence as to Repetition of Appendages.

In the first instance I shall give the evidence as to Secondary
Symmetries in Insects and Crustacea, prefacing it with a prelimin-
ary account of the system of Symmetry obeyed by those cases
which I shall call regular, and explaining the scheme of nomen-
clature adopted. Besides the regular cases of extra parts in
Secondary Symmetry there are many irregular examples which
cannot be shewn to conform to the system set forth. Of all but a
few of these, details are not accessible, and of the rest many are

chap, xx.] SECONDARY SYMMETRY: PRELIMINARY. 475

mutilated or so amorphous that the morphological relations of the
surfaces cannot be determined.

Over and above these there remain a very few cases of
Repetition of parts of appendages where the arrangement is cer-
tainly not in Secondary Symmetry, but is of a wholly different
nature, exemplifying in Arthropods that duplicity of limbs already
seen in the human double-hands (p. 331) and in the double-feet of
Artiodactyles (p. 378). Genuine cases of this kind are excessively
rare ; but owing to hasty examination great numbers of cases have
been described as instances of duplicity, though in reality the
supernumerary parts in them can be shewn to be of paired struc-
ture. To emphasize the distinctness of these cases they will be
made the subject of a separate consideration. Logically they should
of course be treated before the Secondary Symmetries ; but their
essential features may be understood so much more readily if the
latter are taken first that I have decided to change the natural
order.

In continuation of the evidence as to Secondary Symmetry in
Arthropods will be given a brief notice of similar phenomena in
vertebrates. This evidence is comparatively well known and
accessible and I shall attempt no detailed account of it, referring to
the facts chiefly with the object of shewing how the principles
found in Arthropods bear on the vertebrate cases.

It will then be necessary to consider how repetitions in Second-
ary Symmetry are related to other phenomena of Repetition.
Lastly something must be said with regard to the bearing of these
facts on the general problems of Natural History.

Preliminary account of paired Extra Appendages in
Secondary Symmetry (Insects).

Supernumerary appendages in Insects are not very un-
common, perhaps 120 cases of this kind being recorded1. Nearly
all known examples are in beetles, but this may be due to the
greater attention paid to the appendages in that order. They
do not seem to appear more often in one family than in another,
but perhaps the rarity of instances in Curculionidye is worth
noting. They are found in both sexes, in all parts of the world,
and in species of most diverse habits.

Supernumerary parts may be antenna?, palpi or legs. (Extra
wings are probably in some respects distinct. They have al-
ready been considered. See p. 281.) Extra appendages may
be either outgrowths from the body in the neighbourhood of
the part repeated, or, as in the great majority of cases, they
occur as outgrowths from an appendage, extra legs growing from
normal legs, extra antenna: from antenna1, &c. In every case
there are two essentials to be determined : first the constitution

1 Not including some 110 cases of alleged duplicity of appendages given later.

476 MERISTIC VARIATION. [part L

of the extra parts, and secondly the symmetry or relation of form
subsisting on the one hand between the extra parts themselves,
and on the other between the extra parts and the normal parts.

In few cases of extra appendages arising from the body
itself have these essentials been adequately ascertained.

For brevity I shall describe the phenomena as seen in extra
legs. The same description will apply generally to the antennae.
Recorded cases of extra palpi are very few, but probably are not
materially different.

Structure of Paired Extra Legs.

The parts composing extra legs do not as a rule greatly differ
from those of the normal legs which bear them. Though in
many instances extra legs are partially deformed, they are
more often fairly good copies of the true leg. Not rarely the
extra parts are more slender or a little shorter than the normal
appendage, but in form and texture they are real appendages,
presenting as a rule the hairs, spurs, &c. characteristic of the
species to which they belong.

The next point is especially important. The parts found in
extra legs are those parts which are in the normal leg peripheral
to the point from which the extra legs arise, and, as a rule no
more. Though in extra legs parts may be deficient or malformed,
structures which in the normal leg are central to the point of
origin of the extra legs are not repeated in them1. For instance,
if the extra legs spring from the trochanter they do not contain
parts of the coxa, if from the second tarsal joint, the first tarsal
joint is not represented in them, and so on.

Extra legs may arise from any joint of the normal leg, and
are not much commoner in the peripheral parts than in the
central ones, but there is a slight preponderance of cases be-
ginning from the apex of the tibia. It is rather remarkable that
cases of extensive repetition are not much less rare than others,
the contrary being for the most part true of the limbs of vert-
ebrates.

It does not appear that extra legs arise more commonly
from either of the three normal pairs in particular.

Supernumerary legs of double structure are sometimes found
as two limbs separate from each other nearly or quite from the
point of origin, but in the majority of cases their central parts
may be so compounded together that they seem to form but one
limb, and the essentially double character of the limb is not then
conspicuous except in the periphery. For example it frequently
happens that the femora of two extra legs are so compounded
together that they seem to have only a single femur in common,

1 Particular attention is therefore called to one case of extra antennas, which
did actually contain parts normally central to the point of origin. (See No. 804.)

chap, xx.] SECONDARY SYMMETRY I PRELIMINARY. 477

and careless observers have often thus declared them to be two
legs with one femur. Similarly the two tibiae or the two tarsi
may be more or less compounded. In the case of Silpha nigrita
(No. 769), the two extra legs which arose from a femur were
compounded throughout their length, having a compound tibia
and tarsus (see Fig. 167). Even in cases when the two extra
legs appear to arise separately it will generally be found that
they articulate with a double compound piece of tissue which
is supernumerary and is fitted into the joint from which they
appear to arise. This is especially common in cases of two extra
tarsi, which seem to spring directly from a normal tibia. As a
matter of fact in all such cases these extra tarsi articulate with
a supernumerary piece of tissue, as it were let into, and com-
pounded with, the apex of the normal tibia. These bodies are
themselves double structures, composed of parts of two tibiae.
In determining the morphology of the limbs they are of great
importance, but unfortunately they are not generally mentioned
by those who describe such formations. But though extra parts
are generally present in the leg centrally to the point from which
the extra legs actually diverge, it should be expressly stated
that if this point is in the periphery of the leg, the central
joints are normal : if for example, there are two extra tarsi,
there may be parts of two extra tibial apices, but the base of
the tibia, the femur, &c. are single and normal.

Symmetry of Paired Extra Legs.

To appreciate what follows it is necessary to have a distinct
conception of the normal structure of an insect's leg, and to
understand the use of the terms applied to the morphological
surfaces.

If the leg of a beetle, say a Carabus, is extended and set at right
angles to the body, the four surfaces which it presents are respectively
dorsal, ventral, anterior and posterior. In the femur, tibia and tarsus
the dorsal is the extensor, and the ventral is the flexor surface. The
anterior surface is seen from in front and the posterior from behind.
(The terms ' internal ' and ' external ' are to be avoided as they de-
note different surfaces in the different pairs.) Difficulty as to the use
of terms arises from the fact that as the beetle walks or is set in
collections, the legs are not at right angles to the body but are rotated
on the coxa?, so that the plantar surface of the first pair of legs is
turned forwards, but the plantar surfaces of the second and third pairs
are turned backwards1.

1 Attention is directed to the fact that in a beetle there is a complementary
relation not only between the legs of the right and left sides but also imperfectly
between the legs of the first pair and those of the second and third pairs, which are
in some respects images of the first leg of their own side. For instance, in Gerambyx
(see Fig. 160) the trochanter of the fore leg is kept in place by a process of the coxa
which goes down behind it, but the corresponding process in the second and third
legs is in front of each trochanter. Again in Melolontha &c. the tibial serrations of

478 MERISTIC VARIATION. [part I.

Extra legs may arise from airy one of the morphological
surfaces, but more often their origin is in a position intermediate
between them, e.g., antero-ventral, or postero-dorsal.

The next question is that of the determination of parts which
are extra from the parts which are normal. Two extra legs
spring from a normal leg. The appearance is often that of a
leg single proximally, but triple peripherally. All three limbs
are often equally developed and at first sight it might well be
supposed that the three collectively represent the single leg of
the normal.

In many cases of Meristic Variation I have contended that the
facts are only intelligible on the view that there has been such
collective representation. But in these Secondary Symmetries
this supposition is [? always] inadmissible. On closer examination
it is generally more or less easy to see that the three legs do not
arise in the same way, but that one arises as usual while the
other two are, as it were, ingrafted upon it. It is thus possible
in all but a very few cases to determine the normal leg from
the others by tracing the surfaces from apex to base, when it
will be found that some surface of the normal is continuous
throughout the appendage while those of the extra legs end
abruptly at some part of the normal leg.

Nearly always besides, as has been mentioned, the extra legs
are more or less compounded together at their point of origin
even if separate peripherally. In a few very exceptional cases
it happens that one of the extra appendages is compounded
with the normal and not with the other extra appendage. A
remarkable case of this in an antenna may be seen in Melolontha,
No. 800, and in a leg in Platycerus caraboides, (q.v.)

We have now to consider the positions of the paired extra
legs in regard to the normal leg and in regard to each other. At
first sight their dispositions seem entirely erratic ; but though it is
true that scarcely two are quite identical in structure, yet their
divers structures may for the most part be reduced to a system.
This system, though far from including every case, still includes a
large proportion and even the remainder do not much depart from
it except in very few instances. The comprehension of the general
system will also greatly help to make the aberrant cases appreciated
with comparatively few words. For simplicity therefore, the con-
sideration of exceptional cases will be deferred and the principles
stated in a general form. It will be remembered that we are
as yet concerned only with doable extra legs.

When extra appendages, arising from a normal appendage, are
thoroughly relaxed and extended, the following rules will be

the first legs curve backwards, but those of the other legs curve forwards. This
circumstance is mentioned lest it might be thought to have been neglected in what
follows, but this complementary relation has nothing to do with that which will be
shewn to exist between the extra legs.

chap, xx.] SECONDARY SYMMETRY : RULES. 479

found to hold good with certain exceptions to be hereafter
specified.

I. The long axes of the normal appendage and of the

two extra appendages are in one plane : of the two
extra appendages one is therefore nearer to the axis
of the normal appendage and the other is remoter
from it.

II. The nearer of the two extra appendages is in structure

and position formed as the image of the normal
appendage in a plane mirror placed between the
normal appendage and the nearer one, at right angles
to the plane of the three axes; and the remoter append-
age is the image of the nearer in a plane mirror
similarly placed between the two extra appendages.

Transverse sections of the three appendages taken at homo-
logous points are thus images of each other in parallel mirrors.

As the full significance of these principles may not be at once seen
it may be well to add a few words of general description. The relation
of images between the extra legs is easy to understand. They are a
complementary pair, a right and a left. This might indeed be pre-
dicted by any one who had considered the matter.

The other principles, which concern the relations of the extra legs
to the normal leg, are more novel. For first it appears not that either
of the extra legs indifferently may be adjacent to the normal, but that
of the extra pair the adjacent leg is that which is formed as a leg of
the other side of the body. If therefore the normal leg bearing the
extra legs be a right leg, the nearer of the extra legs is a left and the
remoter a right. This principle holds in every case of double extra
appendages of which I have any accurate knowledge, where the struc-
ture of the parts is such that right limbs can be distinguished from
left.

But perhaps of greatest interest is the fact that the inclination of
the surfaces of each extra leg to those of its fellow and to those of the
normal are determined with an approach to uniformity in the manner
described.

These principles of arrangement may be made clear by a simple mechanical
device (Fig. 153). A horizontal circular disc of wood has an upright rod fixed in its
centre. This rod passes through one end of a vertical plate of wood which can be
turned freely upon it as an axle, so as to stand upon any radius of the horizontal
circle. The head of the axle bears a fixed cog-wheel. In the vertical wooden plate
are bored two holes into which two rods each bearing a similar cog-wheel are
dropped, so that each can rotate freely on its own axis. The three cog-wheels are
geared into each other. They must have the same diameter and the same number
of teeth. Three wax models of legs are fixed on the head of each wheel as shewn in
Fig. 153. In that figure, R represents the apex of the tibia and tarsus of a normal
right leg. The anterior surface is dark, and the posterior is white. The anterior
and posterior spurs of the tibia are shewn at A and P. SL and SR represent the
two supernumerary legs, SL being a left, SR a right. (They are supposed to arise
from the leg R at some proximal point towards which they converge.) When the
wooden plate is put so that the arrow points to the word "Posterior" on the disc,
the models will then take the positions they would have if they arose from the
posterior surface, all the ventral surfaces coming into one plane. If the arrow be

480

MERISTIC VARIATION.

[part I.

set to "Ventral" the two supernumeraries will turn their dorsal surfaces to each
other, and so on. The model SL thus rotates twice on its own axis for each

Fig. 153. A mechanical device for shewing the relations that extra legs in
Secondary Symmetry bear to each other and to the normal leg from which they
arise. The model R represents a normal right leg. SL and SR represent respect-
ively the extra right and extra left legs of the supernumerary pair. A and P, the
anterior and posterior spurs of the tibia. In each leg the morphologically anterior
surface is shaded, the posterior being white. R is seen from the ventral aspect and
SL and SR are in Position VP.

revolution round R, but the surfaces of the model SR always remain parallel to those
of the model R. In every possible position therefore each model is the image of its
neighbour in a mirror tangential to the circle of revolution. In the figure the models
have the position they should have if arising postero-ventrally. Here the plantar
surface of SL is at right angles to the plantar surfaces of the other two legs.

Since at each radius the relative position of the legs differs, it is
possible to define these positions by naming the radius. This will be
done as shewn in Fig. 154. In this diagram imaginary sections of the
legs are shewn in the various positions they would assume at various
radii. The central thick outline shews a section of the normal leg, a
longer process distinguishing the anterior surface from the posterior.
The radii are drawn to various points D, A, V, P, representing
the dorsal, anterior, ventral and posterior positions respectively. In-
termediate positions may be marked by combinations, DA, VVP,
&c, using the system employed in boxing the Compass.

On several of the radii ideal sections of the extra legs are shewn in
thin lines, the shaded one being the nearer and the plain one the
remoter. M1 and M2 shew the planes of the imaginary mirrors.

The manner in which the pair of extra limbs are compounded with
each other in their proximal parts, and with the normal limb at their

chap, XX.] SECONDARY SYMMETRY : SCHEME.

481

point of origin is most extraordinary. It does not appear that the
surfaces compound together along any very definite line or that the

II

Fig. 154. Diagrams of the relations of extra legs in Secondary Symmetry at
various positions relatively to the normal leg from which they arise.

The legs are represented in transverse section, the morphologically anterior side
of each heing indicated by the longer spur. The section of the normal leg, in
which the radii converge, is shewn with a thick black line. The section of the
nearer extra leg in Diagram I is shaded, while the remoter is blank. The radii
shew them in various positions, anterior, posterior, dorsal, ventral, iv/c. relatively to
the normal leg.

M1, the plane of reflexion between the nearer extra limb and the normal.
M'2, plane of reflexion between the nearer and the remoter extra limbs.

Diagram II is constructed in the same way to illustrate special cases of extra
legs arising anteriorly or posteriorly. If the two extra legs diverge from each other
centrally to the tibial apex each tibial apex is then complete, as on radius A of
Diagram I. In Diagram II are shewn two degrees of composition of the two
tibial apices, illustrating how, in cases of complete composition, the extra parts may
consist wholly of two morphologically posterior or anterior surfaces according as
they arise posteriorly or anteriorly to the normal leg. (See for instance Nos.
750 and 764.)

line of division between the several limbs is determined by the normal
structure of the limbs. The homologous parts seem to be compounded
at any point, almost as an object partly immersed in mercury com-
pounds with its image along the line to which it is immersed, where-
ever that line may be.

b. 31

482 MERISTIC VARIATION. [part i.

From this some curious results follow. For instance, if two extra
limbs arise anteriorly and are separate at their tibial apices, they
bear four spurs as shewn at radius A in the upper diagram of Fig. 154.
But if the two are fully compounded at the tibial apices in the anterior
position the compounded limb will only have two spurs, both being
shaped as anterior spurs (as shewn in the lower diagram) and con-
versely for the posterior position (see No. 764). The parts, in fact,
where the pair may be supposed to interpenetrate (dotted in the diagrams)
are not represented.

Those who have described these phenomena have in consequence
often made the following error. Observing a limb giving off' a morpho-
logically double limb with a common proximal part subsequently sepa-
rating into its two components, they speak of this as a "primary
and secondary dichotomy." When the facts are understood it is clear
that there is no dichotomy between the extra legs and the normal, for
the parts are not equivalent and the normal is undivided.

Such are the principles followed. It ivould not be true to
assert that these rules are followed with mathematical jyrecision,
but in the main they hold good. Special attention will be given
to cases departing from them, bat the number of such cases is
small. The cases of slight deviation from the schematic positions
are besides mostly those of extra limbs in the Positions A and P,
and generally the deviation in them takes the same form, causing
the ventral surfaces of the extra parts to be inclined to each
other downwards at an obtuse angle instead of forming one
plane.

In all cases possible I have examined the specimens myself,
and I am under obligation to numerous persons who have very
generously given me facilities for doing so. Amongst others I
am thus greatly indebted to M. H. Gadeau de Kerville, Dr G.
Ivraatz and Dr L. von Heyden for the loan of many valuable
insects, and also to Messrs Pennetier, Giard, Dale, Mason, West-
wood, Waterhouse, Janson, Harrington, Bleuse, &c. In this part
of the work I am under especial obligation to Dr D. Sharp, for
without his cooperation it would not have been possible for me
to have undertaken the manipulations needed. He has most
kindly given up his time to the subject, and in the case of almost
every one of the specimens examined at Cambridge I have had
the benefit of his help and advice.

Of cases not seen by me few are described in detail sufficient
to warrant a statement as to the planes in which the parts stood,
but sometimes the figures give indications of this. Some of the
accounts are quite worthless, merely recording that such an
insect had two extra legs : in such cases I have thought it
enough to give the reference and the name of the insect for
statistical purposes. But every case known to me is here re-
corded : there has been no rejection of cases.

The cases will be taken in order of the Positions, beginning

CHAP. XX.]

EXTRA LEGS : POSITION V.

483

with the Position V and taking the other radii in order, going
round against the hands of a watch.

Cases of Extra Legs in Secondary Symmetry.

(1) Position V.

*736. Carabus scheidleri % : pair of extra legs having a common
femoral^ portion arising from the trochanter of the right fore leg
(Fig. 155). This case is of diagrammatic simplicity. The troch-

Fig. 155. Carabus scheidleri, No. 736. The normal right fore leg, R, bearing
an extra pair of legs, SL and SR', arising from the ventral surface of the coxa, C.
Seen from in front. (The property of Dr Kraatz.)

anter bears a normal leg (R) articulating as usual. Immediately
ventral to this articulation there is a second articulation upon a
small elevation. This bears a double femur made up of jDarts
of a pair of femora compounded by their dorsal borders. The
double femur has thus two structurally ventral surfaces opposite
to each other.

The apex presents two articular surfaces in the same plane
as that of the normal leg, each bearing a tibia, both tibiae flexing
in the same vertical plane.

Since the double femur of the extra legs stands vertically
downwards at right angles to the normal femur, it will be seen
that both the extra tibiae flex upwards, but one of them is a
left leg (SL), bending to meet the normal leg, while the other
is a right (SR')} bending towards the ventral surface of the body.
The tibia of the left extra leg is a little shorter than that uf
the normal, and the tibia of the right extra leg is a little longer
than it. All three tarsi are thinner than a normal tarsus; and
the claws are a good deal reduced in the case both of the normal
and the right extra leg, while in the left extra leg they are absent
altogether. This is an example of a pair of extra legs arising

31—2

484 MERISTIC VARIATION. [part i.

in the position marked V in the Scheme and having precisely
the relations there shewn. Specimen first described by Kraatz,
G., Berl. ent. Zt., 1873, p. 432, fig. 9. I am greatly indebted to
Dr Kraatz for an opportunity of examining it.

737. Carabus marginalis : penultimate joint of left hind tarsus is en-
larged and presents two articular surfaces, a proximal one on the
ventral surface, and another at the apex. The latter bears the normal
last joint with its claws. From the proximal articular surface arises a
thick joint shorter than the normal last joint, bearing at its apex two
pairs of claws set back to back, as in the Position "V. Specimen rede-
scribed from Kraatz, G., Deut. ent. Zt., 1880, xxiv. p. 344, PI. n. fig. 29.

738. Carabus granulatus <f , left posterior tibia bearing an amor-
phous rudiment of two extra tarsi arising from the ventral surface of
its apex. The apex of the tibia is produced at the dorsal border to
form an irregular process which bears a tarsus of normal form but
reduced size and immediately ventral to this tarsus is a pair of tibial
spurs. Ventral to these spurs is another deformed pair of spurs and
below them again is a deformed 3-jointed rudiment which probably
represents two tarsi. Ventral to the rudiment of the extra tarsi is
a third deformed pair of spurs. It was not possible to recognize the
surfaces of the tarsal rudiment, but the presence of tvw extra pairs of
spurs indicates plainly that the extra parts are morphologically of double
structure ; and as the spurs indicate the morphologically ventral sur-
faces, it follows that the surfaces adjacent in the extra tarsi are
dorsal. This specimen was originally described by Dr L. Von Heyden,
who was so good as to lend it to me for examination, see Deut. ent. Zt..
1881, xxv. p. 110, fig. 26.

739. Prionus coriarius (Longicorn) : three legs in region of right
posterior leg. The proximal relations not quite clear and hence it is
not easy to distinguish the normal. Presumably it was the most dorsal.
This le<2r was of normal form but of reduced size and it wanted the
claw-joint. Internal to it, arising by a double coxa, trochanter and
femur, were the other two legs. The remoter wras a normal right, but
the nearer was a left leg of reduced size, slightly crooked and lacking
three apical tarsal joints. The compound femur was just as in No. 736.
The normal leg must either have been the most dorsal or the most
ventral. If the former, the extra parts are in the Position V ; if the
latter, they are in the Position D, but in this event the normal would
be compounded with one of the extra legs. [Kedescribed from descrip-
tion and figure given by Krause, Sitzb. nat. Fr. Berl., 1888, p. 145, y?^.]

740. Melolontha vulgaris ? (Laraellicorn) : right posterior femur bears a super-
numerary pair of limbs having a double tibia in common. The supernumerary
parts are rather smaller than the normal ones. [The position of origin and
symmetry, according to the figure, must have been approximately V.] Kolbe, H.
J., Naturic. Wochens., 1889, iv. p. 169, fig.

741. Carabus perforatus <? : from the ventral or plantar surface of the 5th tarsal
joint of left hind leg project an extra pair of claw-joints compounded in Position V,
each bearing a pair of claws, set back to back. This is a diagrammatic case, well
and clearly described by Asmuss, Monstr. Coleop., 1835, p. 54, Tab. IX.

CHAP. XX.]

EXTRA LEGS : POSITION VAA.

(2) Position VAA.

485

742. Feronia (Pterostichus) miihlfeldii % (Carabidse) : left
middle tibia bearing two supernumerary tarsi arising by a
common proximal joint (Fig. 156). As in other cases of super-
numerary tarsi arising from the tibia, the apex of the tibia
itself is really a triple structure, containing parts of the apices
of a pair of tibiae in addition to the normal apex. This is shewn
by the presence of three pairs of spurs, &c. The additional
parts are in this case anterior and ventral to the normal apex
and a complementary pair. All three are completel}* blended
together, forming in appearance a single apex. The relations of
the three component parts are almost exactly those indicated
in the Scheme for the Position VAA.

743,

Fig. 156. Pterostichus miihlfeldii, No. 742. Semidiagrammatic representation
of the left middle tibia bearing the extra tarsi upon the antero-ventral border of the
apex. L, the normal tarsus; R, the extra right; L' the extra left tarsus. (The
property of Dr Kraatz.)

The two extra tarsi (R, L') arise by a common proximal joint
of double structure having two complete ventral surfaces inclined
to each other as in the Position VAA. Peripherally to this the
two tarsi are separate. The tarsus which is nearer to the normal
tarsus is perfect, and stands in the schematic position. The
second joint of the remoter arises in the position shewn for VAA,
but its apex is slightly shrivelled and in consequence the re-
mainder of this tarsus, though perfect in size and form is thrown
a little out of position. This specimen was kindly lent to me
by Dr Kraatz, and was originally described and figured by him
in Dent, ent. Zt, 1877, xxi. p. 56, fig. 21.

Aromia moschata J (Greece) (Longicorn) : right anterior
tibia enlarged at apex bearing anteriorly a supernumerary pair

486 MERISTIC VARIATION. [part i.

of tarsi. The widened apex bears three supernumerary spurs of
which the middle one is thicker than a normal posterior spur.
This is no doubt a double spur representing the two posterior
spurs of the extra tibia?. The other two extra spurs are ordinary
anterior spurs. The relative positions of these spurs are exactly
those marked VAA in the Scheme. Of the extra tarsi 3 joints
only remain and the two tarsal series are so closely compounded
that superficially they seem to form one tarsus only. In their
first joints the inclination of the ventral surfaces to each other
is at an acute angle, thus departing from the Scheme, but in
the second and third joints, where they are more separate from
each other, the inclination is at approximately the same angle
as that of the lines joining their respective spurs. Specimen
in General Collection of the British Museum.

744. Carabus graecus ^ : trochanter of right middle leg bears a super-
numerary pair of legs having trochanter, femur, tibia and 1st tarsal
joint common. The coxa of the normal leg is enlarged and the trochan-
ter has two heads, of which the anterior belong to the extra pair of legs.
The femur of the extra pair is a single piece but is morphologically
double, presenting two structurally anterior surfaces and two structurally
ventral surfaces, the latter being inclined to each other at an angle of
about 120°. From the apex of this femur there arises a double tibia,
also composed of two anterior and two ventral surfaces. This fact is
especially clear in the case of the tibia and is proved by the arrange-
ment of the spines and spurs. In a normal tibia there are two spurs,
one posterior and one anterior, and the posterior spur is longer than
the anterior. Now in this tibia there are three spurs, two shorter ones
at either margin of the apex, and one longer one with a bifid point
between them, which is clearly therefore a pair of "posterior spurs not
completely separated from each other. This view of the structure of
the double tibia is equally evident from the arrangement of the
remainder of the spines on its surfaces. In it the inclination of the ven-
tral surfaces is about the same as in the femur, but is perhaps rather
more acute. The 1st tarsal joint is similarly a double structure. Its
apex presents two articulations, but while the posterior bears a com-
plete 4-jointed continuation, the anterior bears only a single aborted
joint, from which possibly some portion has been detached, but this is
not certain.

The relations of the parts are a little obscured by the fact that the
normal tibia is slightly bent. The double part of the trochanter lies
very nearly anterior to the single part but it is also somewhat dorsal
to it. This gives to the base of the double femur a trend dorsal wards:
but from the base the femur curves ventralwards so that the nett
result is that its apex is actually ventral to the apex of the single
femur when both limbs are extended. This curve of course gives the
femur an abnormal form which is increased by the fact that it is
perceptibly shorter than the single femur. Now the relative position
of the pair of extra limbs is that marked VAA, and as it stands when
extended the apex of the double femur and the peripheral parts of the
double limb stand in the Position VAA with regard to the single limb ;

CHAP. XX.]

EXTRA LEGS : POSITION A.

48'

*

but as has been mentioned, by the curvature of the double femur its
base is somewhat dorsal to the single limb. This specimen was very
kindly lent to me by Dr L. Yon Heyden and was first described and
figured by him in Deut. ent. Zt., 1881, xxv. p. 110, fig. 25.

(3) Position A.

745. Eurycephalus maxillosus (Longic): right anterior femur
divides at base into two parts, of which the posterior bears ;i
normal leg. The other part of the femur is bilaterally sym-
metrical, being made up of the anterior surfaces of two femora,
for both sides present the same convexity (Fig. 157), neither
being flattened as the posterior surface of a normal first femur
is. With the apex of this joint ar-
ticulates a bilaterally symmetrical
tibia of extra width, bearing a 1st
and 2nd tarsal joint, each of nearly
double width.

The 2nd tarsal joint bears two
3rd tarsal joints, which are both
much wider than the normal 3rd
joint of the tarsus. (This is exag-
gerated in the diagram.) One of
these in 1891 bore a perfect ter-
minal joint with a pair of claws ; but
the terminal joint and claws of the
other side were gone, though Moc-
querys' figure shews that they were
originally present. Mocquerys' state-
ment that "la cuisse anterieure du
cote droit se bifurque des son origine
en deux branches ayant chacune le
volume dune cuisse normale" is mis-
leading, as suggesting that the two
femora are similar, while upon closer
examination they are seen to be
dissimilar. Here a pair of extra legs
arising from the anterior surface of
the normal limb, are compounded
together as in the position marked
A in the Scheme. Specimen origin-
ally described by Mocquerys, Col.
anorm., 1880, p. 54, fig.

'746. Eros minutus (Malacoderm):

divided at apex, forming two apices (Fig. 158). The posterior
apex bears a normal tarsus. The anterior apex bears a double
tarsus having the first three joints simple (3rd being enlarged).
The 4th joint is of nearly double width and bears peripherally
two claw-joints each with a pair of claws. From the structure

Fig. 157. Eurycephalus maxil'

losus. Right anterior leg bearing
an extra pair arising from the
femur. 22, the normal right. SL,
supernumerary left. SB, super-
numerary right, p, posterior sur-
face, a, anterior surface of normal
femur, a', <i'\ the two structurally
anterior surfaces of the extra le^r-.
(In Rouen Mus.)

right

anterior

tibia slight lv

488 MERISTTC VARIATION. [part i.

of these it was clear that they are a pair. When extended the
three plantar surfaces are not truly in a horizontal plane, as they

Fig. 158. Eros minutus, No. 746. The right fore leg seen from dorso-posterior
aspect. P, posterior face. A, anterior face. This figure was drawn from the
microscope and has been reversed. (From a specimen the property of Dr Mason.)

should be in Position A, but they are nearly so. This deviation
is exaggerated iu the figure. Specimen very kindly lent by
Dr Mason.

747. Aleochara msesta (Staph.) : middle left tibia has two articulations at apex.
The posterior bears a tarsus normal in form but without claws. The anterior bears
an extra tarsal series with a pair of rudimentary terminal joints, each having a pair
of claws. Of this double tarsus the 3rd and 4th joints are not distinctly separated.
The parts are in Position A. Specimen kindly lent by Dr Mason*.

748. Meloe proscaraba-:us <? (Heteromera). The apex of the femur of right hind
leg is extended on the anterior side so as to form a second apex in the same hori-
zontal plane. With this second apex articulates the common head of a pair of extra
tibiae each bearing a complete tarsus. As usual they are a right and a left respectively.
The two extra legs are twisted out of their natural position so that they turn their
ventral surfaces upwards. The tibia which in origin is remoter from the normal
tibia is moreover bent over the nearer tibia so that it stands actually nearer to the
normal tibia. In this way the morphological relations are obscured, but nevertheless
on tracing the ventral surfaces up to the point of articulation with the femur it is
clear that they arise in the normal position and that they have the relations marked
in the Scheme for the Position A, which is their position of origin. As this case is
a somewhat obscure one, I may add that Dr Sharp, who has kindly examined this
specimen, gives me leave to state that he concurs in the above description. This is
the specimen described by von Heyden, Isis, 1836, ix. p. 761 and by Mocquerys,
Col. A norm. p. 52, Jig., and was kindly lent to me by Dr L. von Heyden in whose
possession it remains.

749. Cetonia opaca (Lamell.): [right fore leg bears a pair of extra terminal tarsal
joints very nearly in Position A, arising from 4th tarsal joint. All the claws are
turned ventralwards, but those of the extra joints are turned away from each other
as well as downwards]. Mocquerys, I.e., p. 61, fig.

r750. Prionus coriarius % (Longicorn), having parts of a super-
numerary pair of tarsi arising from the middle right tarsus,
and also a similar double structure arising from the posterior

CHAP. XX.]

EXTRA LEGS : POSITION A.

489

right tarsus (Fig. 159). This is a very important case as a clear

II I

Fig. 159. Prionus coriarius, No. 750. I. Apex of tibia of right hind leg with
its tarsus. II. Similar parts of right middle leg. (The property of Dr von Heydeu.)

PS, AS, posterior and anterior tibial spurs belonging to the normal leg. A'S',
A"S", the spurs of the extra legs, all structurally anterior spurs. A, anterior
surface. V, ventral surface. (The property of Dr von Heyden.)

illustration of the mode in which double supernumerary limbs
may be compounded together so as to closely simulate a single
limb. Each of the extra parts in this case in the original account
was described as a single extra limb, but as will be shewn, each
is really composed of parts of a complementary pair. Cases of
this kind suggest very strongly that other cases of supposed single
extra limbs are really instances of double extra limbs in which the
duplicity is disguised.

490 MERISTIC VARIATION. [part I.

Right hind leg (Fig. 159, I), the tibia is dilated towards the
apex which presents dorsally two emarginations instead of one
as usual. On the ventral aspect of the apex there are two whole
spurs PS, A"S" and a double one AS, A'S', between them.

These spars give the key to the nature of the structure. The
proximal tarsal joint gives off a process on its anterior side and
is then continued to bear a normal termination as shewn in the
figure. The process from the first tarsal bears a second tarsal
from which the termination has been broken off. The extra parts
are as in the figure, being covered ventrally from edge to edge
with papillae, and having no longitudinal cleft in the middle line
like the normal tarsus.

Looking at these tarsal joints alone, the real nature of the
extra parts does not appear, for the anterior and posterior surfaces
of the normal tarsi are not differentiated from each other, and
hence it is not possible to say of what parts the supernumerary
limb is made up. Fortunately, however, the tibial spurs are
normally distinguishable from each other, for the anterior spur
is a short spur while the posterior is a long thin spur. Now the
spurs present in this case are firstly one long posterior spur PS,
and then three short anterior spurs, of which two are united for
part of their length .4$, A'S'. The extra spurs are thus both
anterior spurs, that of the extra tarsus which is nearer to the
normal being united to the normal anterior spur. Hence this
case is a case of a supernumerary pair of appendages compounded
together in the Schematic Position A, having the posterior sur-
faces adjacent and suppressed.

Right middle leg. (Fig. 159, II.) In this case there would
have been more difficulty in making out the real nature of the
parts ; for in the normal middle leg the anterior spur is not so
much differentiated from the posterior one as it is in the hind
leg : but having this case for comparison it is easy to see that
this also is a case of a pair of appendages similarly compounded
in Position A. This case differs from that of the hind leg in
the fact that the parts are not so fully formed, and especially
the anterior spur of the nearer extra tarsus is scarcely separated
from the anterior spur of the normal. By turning the specimen
over in the light however, its form can be made out to be that
shewn in the figure. When the specimen was received by me
the parts present were as shewn in the figure, but when originally
described by vox Heydex there was a third joint in the extra
appendage which was small and elongated, and to all appearance
it was the original termination and nothing had been broken off.
For the loan of this specimen I am indebted to Dr L. VON Heydex,
who originally described and figured it in Dent. ent. Zt., 1881,
xxv. p. 110, Jigs. 27 and 28.

In the two following cases there was nothing to differentiate

chap. xx.J EXTRA LEGS: POSITION DA A. 491

the normal limb from the two supernumeraries, and the Position
may either have been P or A.

751. Foenius tarsatorius (Ichneumon): tibia of left posterior leg bears a pair of
supernumerary limbs. This is rather a remarkable case by reason of the k'reat
similarity in the modes of origin of the three limbs, whence it is difficult to
determine positively which is the normal one. The tibia divides into three parts
which lie in a horizontal plane and are separate from each other for about ^ of the
length of the tibia. Of these the anterior is a good deal more slender than the other
two which are similar and about of normal size. The middle of the three is shewn
by its spurs to be a right limb. Each bears a complete tarsus The ventral surface
of the most anterior tibia is horizontal while those of the other two are not quite so,
but converge downwards at a very obtuse angle. From this fact, and from the
equality in size between them, it seems probable that the two posterior limbs are
the supernumerary pair. The Position is therefore very nearly P or perhaps A.
This specimen was described by Mr Harrington in Can. Ent., 18U0, p. 124,
who was so kind as to lend it to me.

752. Agestrata dehaanii (Lamellicorn) : the coxa of the right anterior leg has two
articulations, one anterior and the other posterior. With the anterior there articulates
a single trochanter, bearing a normal right leg. The posterior articulation bears a
large structure which is composed of two trochanters united together. This double
trochanter bears two legs and is placed in such a way that the two do not lie in the
same horizontal plane ; but the posterior extra leg is in the same horizontal plane
as the normal leg while the anterior extra leg is wedged out towards the ventral
surface, between the normal leg and the posterior extra leg. The posterior extra
leg is a normally shaped right leg having its structurally anterior surface forwards
as normally. The anterior extra leg is fashioned as a left leg and the surface of it
which is structually anterior faces backwards towards the other extra leg. These
two are therefore a complementary pair, having their structurally anterior surfaces
adjacent: all three legs are normal and similar in form, size and colour. [Specimen
kindly lent by Mr E. W. Janson.]

(4) Positions DA A and DA.

*753. Cerambyx scopolii (Longicorn.) : pair of extra legs arising
from the coxa of the right anterior leg. As this is a remarkably
simple and perfect case it will be well to describe it in some
detail, as it will serve to illustrate the arrangement of such cases
in general.

A normal leg of such a beetle as Cera/mhyx consists of coxa, tro-
chanter, femur, tibia and four tarsal joints. To a proper understanding
of the mode of occurrence of the extra legs in this case it is essential
that the forms of these parts and their mode of movement with regard
to the body and to each other should be accurately known.

Of the large, irregularly pear-shaped coxa only the hemispherical face
is seen from the exterior. It is chiefly enclosed by embracing out-
growths from the sternum, forming a socket in which it can be rotated
like a ball. Upon its broad, exposed surface it is itself hollowed out
to form a socket for the ball of the trochanter. For our purposes it is
necessary to find some means of distinguishing the anterior face of the
coxa from the posterior face. The structure which at once enables us
to do this is the process (Fig. 160, p), which goes down from the coxa
to embrace the neck of the ball of trochanter and lock it into its socket.
Now in the case of an anterior leg, this process is posterior to the
trochanter (but in a middle or hind leg it is anterior to the trochanter).
The next point to be considered is the position of the femur. The

492

MERJSTIC VARIATION.

[part I.

femur itself is flattened antero-posteriorly, having two broad surfaces,
morphologically anterior and posterior, and two narrow surfaces which
are extensor and flexor surfaces, or morphologically dorsal and ventral.
By rotation of the coxa the whole leg may assume a great variety
of positions, and it is thus of the utmost consequence that the nature of
the surfaces be truly recognized. If the front leg be placed with the

III

SL< m

Fig. 160. Cerambyx scopolii. No. 753. I. The whole beetle seen from ventral
surface. II. Details of right anterior coxa bearing extra trochanters and legs.
In this figure the legs are rotated so as to shew that SB is an image of SL.
III. The same, placed so as to shew that SL is an image of R.

p, process of coxa locking in the trochanter, srp, sip, corresponding processes
for the extra trochanters. (From a specimen belonging to M. H. Gadeau de
Kerville.)

chap, xx.] EXTRA LEGS : POSITION DA A. 4.93

femur at right angles to the body it may either be placed so that the
ventral surface is downwards, or by rotation of the coxa through 90 J
the broad posterior surface may be downwards. The rotations of the
middle and hind legs are complementary to this.

In the abnormal specimen the extra pair of legs arise from
the anterior side of the normal coxa, forming with it a solid mass
and preventing its free rotation in its socket, so that the normal
leg can scarcely be moved from the first position with the
ventral surface downwards. The common coxal piece is about
half as large again as the normal. Posteriorly it bears the tro-
chanter of the normal leg, which is of full size and of proper pro-
portions. The process of the coxa locking in the ball of the
trochanter is posterior, as in the normal front leg.

Anteriorly the legs SL and SR articulate with the coxa by
separate trochanters. Each is separately closed in by a process
of the coxa, sip and srp, respectively. Of these processes that
of the leg SR is posterior, but that of SL is anterior. Hence
the two legs are complementary to each other, and SR is a right
leg while SL is a left. This complementary relation is main-
tained in all the other parts of these legs. In size the two extra
legs are rather more slender than the normal leg.

It was explained in the introduction to the subject of super-
numerary legs that the relations of form between them depend
upon the surface of the normal leg from which they arise. Here
the point of origin is chiefly anterior to the normal leg, but is
also slightly nearer to the extensor or dorsal surface of the coxa.
This is not at first sight evident owing to the rotation of the
normal leg due to the great outgrowth from its anterior surface ;
but nevertheless if the plane of the ventral surface of the normal
femur were produced, it would pass ventrally to the ventral
surface of the remoter extra leg SR, and therefore this leg is
morphologically dorsal to the leg R. The positions of the extra
legs are approximately those of the Scheme for the radius marked
DAA, and while the surfaces of SR are parallel to those of R
when both are extended, the surfaces of SL are inclined slightly
to them as in position DAA. In the enlarged Figure III the
coxa is rolled forwards so as to exhibit the relation of images
between R and SL, and the figure II shews the coxa rolled
back to shew the similar relation between SR and SL.

For the loan of this beautiful specimen I am great!}* obliged to
M. Henri Gadeau de Kerville.

754. Harpalus rubripes (Carabidte) : left posterior tibia bears a supernumerary pair
of tarsi. The apex of the tibia is widened and presents two articulations, of which
the posterior bears a normal tarsus. The anterior articulation bears a pair of complete
tarsi having proximal joints compounded. The two extra tarsi are a complementary
pair, the posterior being fashioned as a right. The surfaces adjacent in these two
tarsi are structurally posterior surfaces, but they are a little supinated, so that the
ventral surfaces are also partly turned towards each other. The position of origin
and the relations of the surfaces to each other are almost exactly those which are

494 MERISTIC VARIATION. [part I.

indicated in the Scheme for the position DAA. This specimen was described by M.
A. Fauvel (Rev. (VKtit., 188(J, p. 331) and was kindly lent by him for further
examination.
755. Chrysomela banksii iPhytophagi) : right hind tibia bearing an extra pair of
tai-si. The border of the tibia which corresponds in position to the ventral or flexor
border of the normal tibia is covered with the hairs which characterize it in the
normal limb; but the ojjposite border of this abnormal tibia is similarly covered
with hairs, shewing that the anterior parts of at least two tibiae are included in it.
A rigid process projects from the wide apex of the tibia. Upon the inner side of
this process is the articulation for the tarsus, which from its direction and position
appears to be the normal tarsus of the limb. Outside the process articulates a
slightly smaller tarsus, which from its form and from the plane in which it moves
is a left tarsus, flexing away from the normal one. At a point slightly external to
this is the third tarsus, which is again a right tarsus and moves in a plane comple-
mentary to the middle one. The two are therefore a pair. The position of origin
lb anterior and dorsal, being nearly that marked DA, but the relative positions of
the extra tarsi are approximately DDA. As to the nature of the tibial process I can
make no conjecture. (Fig. 161.)

Fig. 161. Chrysomela banksii, No. 755. View of right hind tibia from posterior
surface. A normal right hind tibia is shewn for comparison. (From Pruc. Zuol.
Soc, specimen the property of Dr D. Sharp.)

This specimen is the property of Dr Sharp, who was good enough to lend it to
me. It was briefly described and figured by me P. Z. S. , 1890, p. 583, but 1 was not
at that time aware of the complementary relation existing in these cases and failed
to notice the somewhat inconspicuous differences which are evidence of it in this
case.
756. Hylotrupes bajulus (Longic): right middle tibia bears a suj^ernumerary
pair of limbs having proximal parts in common. From the antero-dorsal surface of
the base of the normal tibia, there arises a slender tibial piece which is not so long
as the normal tibia and bears no spurs. At the apex of this supernumerary tibia,
which is doubtless a double structure, articulate a pair of tarsi having their
first and second joints compounded together. After the second joint the twro tarsi
separate from each other and each bears a pair of claws. The relative position of
the two tarsi when they separate from each other is almost exactly that marked DA.
It should be mentioned that the supernumerary parts central to the 3rd tarsal joints
are not fully formed, being deficient in thickness, and the transverse separation
between the 1st and 2nd tarsal joints is incomplete. Specimen first described by
Mocquerys, Col. anorm., 1880, p. 53, fig. I am indebted to Dr L. vox Heydex
for an opportunity of examining it.

(5) Position D.

*757. Aphodius contaminatus <£ (Lamellicorn.) : left middle tibia
bearing two supernumerary tarsi which stand very nearly in the
position DDP, being rather nearer to D. The relative positions
are shewn in Fig. 162. The articular surface at the apex of the
tibia is extended along an elongated process which projects on
the dorsal side of the tibia. Upon this extension of the apex
articulate two extra tarsi. They stand with their ventral or

CHAP.

XX.]

EXTRA LEGS : POSITION D.

495

758.

LT.

plantar surfaces facing each other, and the tarsus RT is placed so
that its dorsal surface is
very nearly opposed to the
dorsal surface of the normal
tarsus LT, and the three
tarsi thus flex almost in the
same vertical plane. It is
to be observed, however,
that the tarsus LT is not
actually in the same plane
as the other two, but is a
little deflected from it so as
to flex rather more towards
the posterior surface of the
line than it would do if it
stood actually as L'T stands.
This may be made clear by
reference to the Scheme
(p. 481) : for while the two
extra tarsi are placed re-
latively to each other as if
they were in the position
D, the position of RT to
LT is that which it would
have if it stood in DDP.

In this species the mid-
dle tibia in the male bears
one large spur, namely, the
posterior one, while the an-
terior spur is rudimentary.
PS in the figure represents Fm 162 AphoMug containinatuSf No. 757>

the large posterior spur of left middle tibia bearing extra parts. LT,

EPS & LPS.

singh
of suture
b is seen
(Specimen the

iding posteriorly 0i u± ana jlt correspo
and between the two extra sPur Fs of normal, x, x, line

tarsi represents their two between these two spurs The limb is

. i ill from the posterior surface -

posterior spurs. 1 he double property of Dr Kraatz.)

nature of this spur is seen

when it is examined from the anterior side, for upon that surface

it is marked by a longitudinal ridge-like suture. This specimen

was first described by Kraatz, JJeut. ent. Zt, 1876, xx. p. 378,

fig. 13, and I am indebted to Dr Kraatz for an opportunity of

examining it.

Galerita africana (Carab.) : (Fig. 163) right middle leg normal as far as the last
tarsal joint, which bears three additional claws arising dorsally to the normal pair.
The extra claws are three in number, two of them being small and standing at the
anterior border of the limb, while at the posterior border there is one claw of larger
size. This larger claw is really a double structure, which is clearly shewn by the

496 MERISTIC VARIATION. [part i.

presence of two channels on its concave surface. Position of origin is therefore D,
while the inclination of the extra pairs of claws to each other is about that required

A.

Fig. 163. Galerita africana, No. 758. Apex of right middle tarsus. A,
anterior. P, posterior. V, ventral. (Specimen in Rouen Mus.)

for the position DDA ; for the planes of the two pairs are not parallel but incline
to each other at an acute angle. Specimen originally described by Mocquerys, Col.
unarm. , p. 64, fig.

(6) Position DP.

759. Pyrodes speciosus (Longic.) ; having two supernumerary legs
articulating with the thorax by a common coxal joint, which is
distinct from the coxa of the left middle leg, but is enclosed in
the same socket with it. In this remarkable case the normal
leg is complete, though slightly pushed towards the middle line.
The socket in the mesothorax is enlarged posteriorly and dorsally
so as to form an elongated, elliptical articulation, which lies ob-
liquely, so that its ventral end is anterior to its dorsal end. The
anterior and ventral end is occupied by the coxa of the normal
leg, while the coxal joint of the two extra legs fills the space
dorsal and external to it. Both are capable of being moved
independently in the relaxed insect. The extra legs articulate
with their coxa by a common double trochanter which has two
apices, from which point the legs are distinct. Their position
is dorsal and posterior to the normal leg, being practically that
marked DP in the Scheme, and the relative positions of the
extra legs are very nearly those indicated for the Position DP.
The leg nearest the normal leg is of course a right leg in structure,
and its plantar and a little of its structurally anterior surfaces
are turned posteriorly. On the other hand, the remoter leg is
a true left leg and the ventral surface of its femur is placed
almost exactly horizontally. All three legs are complete, but
they are a little shorter and more slender than the middle leg
of the other side.

This specimen is in the Hope Collection at Oxford.

CHAP. XX.]

EXTRA legs: position dp.

497

*

7 gO. Carabus irregularis J ; left middle leg and right hind leg bear-
ing supernumerary tarsal portions. In the left middle leg, Fig. 164, I,
the 2nd tarsal joint is short and thick ; the 3rd joint is partially double,
as shewn in the figure. One of its apices bears a tarsus of reduced
size, and the other apex, which is postero-dorsal, bears a double tarsus
having common 4th and 5th joints. The 5th joint of the latter bears
two pairs of claws which curve ventrally and partly towards each
other. The figure I shews the appearance from the ventral or concave
side of the claws, while the figure II is drawn from the convex or
dorsal side. The disposition and small number of the spines on the
ventral side of the extra 5th joint shew that the ventral surfaces are
partly suppressed, and in fact that the surfaces which are adjacent in
the extra tarsi are in part ventral surfaces. This view is also borne
out by the direction and curvature of the claws. Eelatively to each
other and to the normal the extra parts have nearly the Position DP.

7-°

III

Fig. 164. Carabus irregularis. I. Semi-diagrammatic view of left middle leg
from antero-ventral surface. I1, the claws of normal left tarsus, r, I2, claws of extra
tarsi compounded together. lhl, hair marking the dorsal surface between the claws.
A, anterior. P, posterior. II. Dorsal view of apex of extra tarsus rh, Ur, two hairs
marking dorsal surfaces. III. Dorsal view of right hind leg. c'c', c"c", claw-like
spines, perhaps representing extra claws. (Specimen the property of Dr Kraatz.)

The right hind tarsus has the form shewn in Fig. 164, III. The 3rd,
4th and 5th joints are not fully separated from each other. Both the
4th and 5th joints bear extra parts, but their nature is obscure. The
5th joint is partly double, and the anterior part bears two shapeless
claw-like spines (c'c). The 4th joint bears a similar pair of claw-like

b. 32

498 MEBTSTIC VARIATION. [part i.

structures of smaller size (c"c"). Probably these should be considered
as rudiments of extra tarsi ; but if this view is correct, it appears that
two extra tarsi are present, arising from different joints. For the loan
of this specimen I am indebted to Dr G. Kraatz, who first described
and figured it in Deut. ent. Z&, 1877, XXI. pp. 57 and 63, tig. 27.

•rgj Chrysomela graminis (Phy tophagi) : the femur of the right middle leg bears a

supernumerary pair of legs attached to the posterior and dorsal side of its apex.
At this point' there is an articulation with which the single proximal part of the
extra pair of tilme articulates. This- piece, which is common to the two super-
numerary tibia?, is a sub-globular, amorphous mass from which the two tibia?
diverge. " Each of the two tibia? bears a complete tarsus, except that the most
posterior has only one claw. In colour the two supernumerary tarsi differ from the
normal, being brown instead of metallic green, but the tibia? are normal in colour.
From the shape of the articulations and the arrangement of the pubescence, it is
clear that the surfaces of the legs which are naturally adjacent are constructed as
posterior surfaces, and the forms of the two are complementary to each other, the
hindmost of the extra legs being formed as a left leg, while the foremost is a right
leg. As the}' stand, however, the two tibia? are not in the same position relatively to
the body, for the foremost is placed normally, having its plantar surface turned
downwards, but the hindmost is rotated so that its plantar surface is partially
turned forwards. The relative positions are nearly those marked DP in the Scheme,
but the most posterior tarsus is more rotated than it should be according to that
diagram. This condition may be to some degree connected with the presence of the
amorphous growth at the base of the extra tibia?. This specimen was kindly lent
for description by Dr Mason.

762. Fimelia interstitialis (Tenebrion.) : left posterior femur bears two super-
numerary tibia? arising from the postero-dorsal surface of its apex. These two are
a pair, for the tibia nearest to the normal tibia is a right tibia, the remoter being a
left. The adjacent surfaces are chiefly anterior surfaces in structure, but the
ventral surfaces are inclined to each other at an obtuse angle. The position of the
extra legs is almost that marked DP in the Scheme, but the inclination of the
ventral surfaces of the extra legs is rather more acute than it would be in the
Position DP. The tarsi are all broken off. Specimen originally described by
Mocqvekys, Col. anorm., p. 44, fig.

7Q3 Acinopus lepelletieri (Carab.): two extra legs arising from posterior surface

of base of femur of /. middle leg. From position it seems that the most anterior is
the normal, but this is doubtful. The arrangement is nearly that of Position DP,
but as one of the femora is constricted and bent, the relations are rather irregular.
Specimen first described by Mocquerys, Col. anorm., p. 41, Jig.

(7) Position P.

*764. Silis ruficollis^ (Malacoderm) : right anterior femur bearing
a supernumerary limb (Fig. 165). The coxa and trochanter normal.
The femur is of about twice the antero-posterior thickness of a
normal femur and at its apex presents two articulations in the
same horizontal plane. Of these the anterior bears a normal
tibia and tarsus, but the posterior bears an extra tibia which
appears at first sight to be a single structure. This tibia is more
slender than the normal one and is provided with four tarsal
joints, the terminal one being withered and without claws. Upon
closer examination it is found that this extra tibia is in reality
made of the posterior surf aces of a paii; of tibice not separated from
each other. In this case the morphological duplicity of the extra
tibia is capable of proof. For, as shewn in Fig. 165, II, the
normal tibia is not bilaterally symmetrical about its middle line.
On the contrary the anterior surface is differentiated from the

CHAP. XX.]

EXTRA LEGS : POSITION P.

499

posterior by several points. This may be seen in the spurs at
the apex of the tibia, for the anterior spur (a) is long, but the

a-

II

II

III

Fig. 165. Silts ruficollis, No. 764. I. The right anterior leg seen from ventral
surface, a, anterior, p, posterior. This figure was drawn with the microscope
and is reversed. II. Detail of apex of tibia of the anterior or normal tibia,
shewing a, the anterior, and p, the posterior sjjurs. III. Similar detail of apex of
the tibia of the extra limb, shewing p' and p", two structurally posterior spurs.

posterior (p) is short (as is usual in the front leg of many beetles).
The hairs on the surface of the tibia are also directed asymmetri-
cally and the parting or division between them is not median,
but is nearer to the anterior border (see figure).

But in the extra part there is no such differentiation, and botli
surfaces are structurally posterior surfaces. The hairs part in the
middle, and both spurs (p, p") are formed as posterior spurs. This
extra structure is therefore made up of the two posterior borders
of a right and a left tibia compounded together in Position P.
(See diagram, Fig. 165, II.)

This specimen was found by Dr Sharp amongst a number
of insects collected by myself in his company at Wicken Fen on
Sunday1, July 26, 1891.

Such a case taken in connexion with others {e.g. Xo. 801 )
makes it certain that many cases of supposed " single ': extra
appendages are really examples of double extra parts.

1 A day or two before, the manuscript of this part of the subject had been put
by with the remark that no good opportunity of thoroughly investigating a case
of " single" extra leg had occurred, but that it could scarcely lie doubted that traces
of duplicity would be found in them. Considering the great rarity of extra ap-
pendages in Insects, and remembering that even of the whole number very few are of
the supposed " single " order, I have thought the occurrence of this capture a
coincidence of sufficient interest to be worthy of mention. Dr Sharp tells me thai
amongst all the beetles that have gone through his hands only one case of extra
appendage (No. 755) was seen.

32—2

500 MERISTIC VARIATION. [part I.

765. Scarites pyracmon (Carab.). At base of posterior face of the
trochanter of left normal front leg, immediately above the cotyloid
articulation was implanted an elongated lanciform joint. This joint
was directed backwards and represented a pair of trochanters com-
pounded by their anterior surfaces. With each of the two apices of
this double trochanter was articulated a complete leg, in all respects
formed as an anterior leg. The two moved as a complementary pair.
[Details given. This is one of the earliest and best described cases.
AsMUSS1 in quoting it points out that the description and figure plainly
shew that the two extra legs were a pair, a right and a left, respect-
ively. They were in fact a pair, arising from the posterior surfaces of
the normal leg, and presenting their anterior surfaces to each other.]
Lefebvkk, A., Gu&rin's Mag. de ZooJ., 1831, Tab. 40.

766. Geotrupes mutator (Lainellicorn) : two supernumerary limbs arising from
femur of right anterior leg. Femur greatly widened, upon posterior border giving
off a large prominence which divides into two processes at right angles to each
other. Each of these processes bears a normal tibia and tarsus, but the foremost of
these tibiae is shaped as a left tibia, having its serrated border placed anteriorly,
while the other extra tibia is formed as a right tibia, having its serrated border
placed 'posteriorly. [The pair of limbs arise from the posterior surface of the normal
limb and have their anterior surfaces adjaceut, as in Position P.] FRiVALDsm:, J.,
Term. Fuzetek., 1886, x. p. 79, PI.

76/. Pterostichus lucublandus ? (Carabidre): third tarsal joint of left middle leg
at apex presents wide articular surface. On this stands a triple 4th joint, made up
of a single anterior portion, bearing the rest of the normal tarsus and a posterior
portion, double in structure, the two parts being completely united. The single
anterior part of this 4th joint bears a normal 5th joint with claws. The double
posterior part of the 4th joint bears a pair of separate 5th joints, each having a pair
of claws. Of these the anterior is perfect, but the peripheral part of the posterior
5th joint is crumpled, so that its claws are twisted out of position, but at its base it
stands exactly as the normal 5th joint, and as the 5th joint of the anterior extra
tarsus, all three being in the same horizontal plane. These extra parts, therefore,
are in the Position marked P in the Scheme and have the relations there indicated
for that position. This specimen was kindly lent to me by Mr Harrington, who
first described it Can. Ent., 1890, xxn. p. 124.

(8) Positions VPP to VVP.

*768. Ceroglossus valdiviae, Chili (Carabidse): left anterior tibia
bearing a pair of supernumerary legs. The tibia widens, and in
its middle part gives off posteriorly and ventrally a wide branch
having the form of a pair of tibial apices compounded together.
The double tibia bears two tarsi (Fig. 166, B! , L') having a common
proximal joint, but these have unfortunately been broken, two
joints being missing from the one and three from the other. The
legs are a right and left as usual, and they stand in the relative
positions marked VPP in the Scheme. This is a very simple
and striking case, for the animal is of good size and the parts
are well formed. The two tibial spurs which are adjacent in
the two extra tibiae are compounded so as to form a double spur
with two points as shewn in the figure. As shewn for the Position

1 Monstrositates Goleopterorum, 1835, p. 44, PI.

chap, xx.] EXTRA LEGS : POSITION VPP. 501

VPP in the Scheme, the compounded parts of the extra ap-
pendages, viz., the double tibia and the double first tarsal joint
have two complete ventral surfaces inclined to each other at an
obtuse angle, while there are only two halves of dorsal surfaces.

Fig. 166. Ceroglossw valdivia, No. 768. Left
anterior tibia with extra parts seen from the
ventral surface. L, the normal left tarsus. R' and
L', the extra tarsi, compounded in their proximal
joint. A, anterior. P, posterior.

Xote that the anterior spur of the normal is
curved and that the double spur representing the two
anterior spurs of the extra tibial apices has thus a
bifid point. (Specimen the property of Mr E. W.
Janson.)

Similarly there are two structurally posterior surfaces, but no
structurally anterior surfaces, for these are adjacent and un-
developed. This specimen was kindly lent by Mr E. \V. Janson.

769. Silpha nigrita (Heteromera): from right middle femur arises a

pair of legs which are completely united as far as the apex of the last
tarsal joint. The point of origin of the supernumerary limbs is on the
anterior and ventral border of the femur. The form of the extra limbs
is shewn in Fig. 167. The surfaces V and V are structurally ventral
surfaces. They are turned chiefly forwards, but are inclined to each
other at an acute angle. The surfaces, therefore, which arc adjacent
in this pair of legs, and which are consequently obliterated, arc chiefly
the morphologically anterior surfaces and to some extent the dorsal
surfaces. The plantar or ventral surfaces of the last tarsal joints are
inclined to each other rather more obtusely than those of the tibiae, 80
that the curvatures of the two pairs of claws are very nearly turned
forwards as well as away from each other. This is not fully brought
out in the figure. The position of origin is about VP, but the claws are
in Position VPP. Specimen first described and figured by MoCQUERYS,
Col. anorm., p. 43, fig.

502

MERISTIC VARIATION.

[part I.

Fig. 167. Silpha nigrita, No. 769. Right middle femur bearing a compounded
pair of extra legs. V, ventral surface of nearer extra leg. V, ventral surface of
the remoter extra leg. (In Rouen Mus.)

770. Tenthredo solitaria (Sawfly): tibia of right middle leg divides
in peripheral third to form two branches, of which the anterior bears
the normal tarsus. The posterior branch arises from the postero-ven-
tral surface of the normal and bears a double tarsus consisting of the
posterior parts of a pair compounded in Position VP, almost exactly.
Tibial spurs as in Fig. 166. The compound tarsus has only 4 joints, the
5th being apparently broken off. In Cambridge Univ. Mus., history
unknown.

771. Telephorus rusticus (Malacoderm) : tibia of left middle leg dilated
and somewhat deformed in its peripheral portion. It presents two
apical processes, the one anterior and the other posterior. The anterior
of these bears a normal, backwardly directed tarsus, but the posterior
process bears two tarsi by separate articulations. The anterior of these
two tarsi is directed forwards to face the tarsus of the other apex, but
the posterior tarsus is backwardly directed. [From its attitude it is
clear that the middle of these tarsi is a structure complementary to one
of the others, but there is no evidence to shew whether it is a pair to
the anterior or to the posterior. Position either VPP, or DAA, pro-
bably the former.] Kraatz, Deut. ent. Zt., 1880, p. 344, fig. 33.

772. Anthia sp. (Carabidae) : left posterior tibia bearing two supernumerary tarsi.
The postero-ventral side of the apex of the tibia is dilated so as to form a triangular
projection, causing the point of articulation of the normal tarsus to be raised
upwards. The projection bears two tarsi of which the posterior curves downwards
and backwards, being fashioned as a left tarsus while the anterior curves forwards
and slightly upwards being a right tarsus. These two tarsi have unfortunately been
broken but were presumably complete. The whole apex of the tibia bears five spurs
instead of two, but the relation of the spurs to the separate tarsi was not clear. The

chap, xx.] EXTRA LEGS : UNCONFORMABLE CASES. 503

tarsi are very nearly in the Position VPP. Specimen very kindly lent by Mr E. W.
Janson.
773. Julodis aequinoctialis (Buprestida?) : the extra legs arise from the posterior and
ventral side of the base of the tibia of left middle leg. They are a pair, and are
compounded together by their lateral and dorsal surfaces in such a way that the
morphologically ventral surfaces of the two are almost in contact along the anterior
border of the compound limb. The ventral surfaces here converge at an acute
angle. The two extra legs are compounded together throughout the tibiae and first
4 tarsal joints. The 5th tarsal joints are free, but only one of them remains. The
former presence of the other is only shewn by a socket. The normal tibia is con-
stricted and bent at one point so that it does not stand in its normal position. The
femoro-tibial articulation is rigid.

This is a case of a pair of legs compounded as in the position marked VVP in
the Scheme but the point of origin is more nearly that of VPP. Specimen originally
described by Mocquerys, Col. anorm., p. 47 Jig.

774 Metrius contractus (Carab.) Esch.: specimen in which the middle left femur
' bears an incomplete pair of legs in addition to the normal one. The femur is of

normal length. The tibia of the normal leg is articulated with the end of the femur
as usual, but is somewhat shorter, stouter and more curved than the tibia of the
corresponding leg of the other side. A supernumerary tibia arises from the posterior
[and ventral ?] side of the femur a short distance within the apex, and is articulated
with it by a separate cotyloid cavity ; the two articular cavities for the two tibia?
are confluent, being connected by a groove. The end of this tibia is dilated at its
outer end, and bears two articular surfaces, one on each side ; with each of these
surfaces, a complete tarsus is articulated, nearly normal in form but somewhat
stouter than a normal tarsus. There are four terminal spurs to this tibia, two being
below the outer tarsus and two being below the inner tarsus. [It therefore seems
that this tibia is made up of parts corresponding with the ventral side of a right
tibia and the ventral side of a left tibia, and it is hence probable that if the dis-
position of the claws of the tarsi had been examined, it would have been found that
they too were a pair, one being a right foot and the other a left. Position probably
VVP.] Jayne, H. V., Trans. Amer. Ent. Soc, 1880, vin. p. 156, PL iv. figs. 3
and 3 a .

775 Aromia moschata ? (Longicorn) : right anterior coxa bearing a pair of super-
numerary legs having trochanter and the proximal half of the femur in common.
The normal leg and the extra ones were all somewhat reduced in size but were
complete. The extra leg adjacent to the normal is a left leg. [From the figure it
appears that the legs arose in the Position P, or VPP, and their relative positions
seem to have been those indicated in the Scheme. Of course it is not possible to
state this definitely without examination, but it is clear that there was at least no
great departure from the position shewn in the Scheme.] It is remarked that in
this specimen the right mandible was abnormally small. Kolbe, H. J., Naturw.
Wochens., 1889, iv. p. 169, Jigs.

(9) Two cases not conforming to the Scheme.

Two cases of double supernumerary tarsi require separate con-
sideration. The arrangement in both of these cases departs from
chat which is usually followed, but it will be seen that there is
considerable though imperfect agreement between the two ex-
ceptions. Both of these occur in the anterior legs of males of
the genus Galathus, and it happens that in the normal form the
apex of the tibia presents a considerable modification from the
simple structure of other beetles. This modification affects the
anterior legs only, and is found in several genera of Carabidae,
being especially pronounced in Calathus.

504 MERISTIC VARIATION. [part i.

In order to appreciate the nature of these cases it is necessary
that the anatomy of the parts should be understood.

The apex of the tibia in the simple form, e.g. the second or
third leg in Carabus, bears two large articulated spurs. The two
spurs are ventral to the articulation of the tarsus, and one of
them is placed at the anterior border of the tibial apex while
the other is posterior. In these unmodified legs both spurs are
placed at the same level in the limb, so that the bases of both
are in the same transverse section (cp. Fig. 166). In the forms
presenting the sexual modification, the anterior spur is of some-
what small size but occupies the same position relatively to the
other parts that it does in a simple leg.

The posterior spur however, which is large, does not stand
at the same level on the tibial apex, but has, as it were, travelled
up the tibia so that it stands at a considerable distance central
to the apex, and instead of marking the posterior border of the
limb it is placed nearly in the middle of the actual ventral surface.
A long channel runs from the posterior spur to the anterior one,
and the appearances suggest that the modified form is reached
by a deformation of the original apical surface, which is twisted
so that the posterior spur is thus drawn up into the secondary
position. In the fore leg of a male Carabus the beginning of
such a change can be seen, but in Pterostichus and especially in
Calathus it reaches a maximum. The change may be briefly
described by saying that a section to include the two spurs must
be taken in a plane which is oblique to the long axis of the limb
instead of transverse to it.

As a result of this modification the morphological surfaces
of the anterior tarsus of Calathus &c. have a peculiar disposition
relatively to the same surfaces of the tibia when compared with
other forms. Commonly the ventral surface of the tarsus is
parallel to a line taken through the bases of the spurs, but owing
to the rotation of the posterior spur into its secondary position
this plane is here oblique to the ventral surface of the tarsus.
These points will be at once evident if the front leg of a male
Calathus is examined.

It was laid down as a principle generally followed in cases of
double extra appendages, that the three terminations, when ex-
tended, stand in the same plane, and the chief feature which
distinguishes the two following cases is that the three termina-
tions are not in one plane.

Moreover, though the two supernumerary tarsi are a com-
plementary pair, and together with the normal tarsus are arranged
as a series of images, yet in order to produce the arrangement of
the present cases the planes of reflexion would not be parallel to
each other (as in Fig. 154) but inclined in the manner to be
described.

CHAP. XX.]

EXTRA LEGS : CALATHUS.

505

g a

*77G. Calathus graecus g (Carabiclre) : left anterior tibia bearin

pair of supernumerary tarsi compounded together. The diagram,
Fig. 169, I, shews, in projection, the relations of the parts round the
tibial apex. As lias been explained, the posterior spurs P1, P2 and P3
are really much central to the apex, but they are here represented as it*
they were projected upon the apex. The head of the tibia is produced
posteriorly into a long and narrow process which is formed of the united
parts of the two extra limbs and bears the articulation common to the
two extra tarsi. The two tarsi stand with their ventral surfaces almost
at right angles to each other, but the united dorsal surfaces are almost
in a continuous plane. The fifth joints alone are separate, that of RT
being small (Fig. 168).

RT,

Fig. 168. Calathus gracus, No. 776. Left anterior tibia bearing a double extra
tarsus. L2\ normal tarsus. RT, L'T, extra pair of tarsi. LAS, LPS, normal
anterior and posterior spurs. L'A'S', L'P'S', anterior and posterior spurs belonging
to L'T. RAS, RPS, anterior and posterior spurs belonging to RT. x, .v, dotted
line indicating plane of morphological division between extra tarsi, .r.v, .vx, plane
of division between the normal and RT. (Specimen the property of Dr Kraatz.)

In studying this case one source of confusion should be specially
referred to. It is seen that though the origin of the extra tarsi is
posterior to the normal tarsus, the extra tarsi are as a fact united along
their morphologically posterior borders. Nevertheless the position of the
spurs shews that it is the anterior surfaces which are morphologically
adjacent to each other, for the spurs are arranged in the series A'P',
PA2, A3P3, and the union of the posterior borders of the tarsi is a
result of the modification in the form of the tibia consequent on the
rotation of the posterior spur.

To produce the arrangement here seen, the planes of reflexion would
be M1 and M2 respectively, and these are almost at right angles to each

506

MEBJSTIC VARIATION.

[part t.

other. The present case therefore is very different from those hither-
to described, for in them the planes of reflexion were nearly or quite
parallel. Whether this difference in the Symmetry of the extra parts
may be connected with the departure of the normal tibia from its own
customary symmetry cannot be affirmed, but such a possibility should
be borne in mind.

This specimen was kindly lent to me by Dr G. Kraatz, who first
described it in Deut. ent. Zt., 1877, xxi. p. 62, fig. 23.

Dorsal

t3 Posterior

A/2 I

II

Posterior

Anterior

Fig. 169. I. Ground-plan of tibial apex of Calathus grams, No. 776.
II. Similar ground-plan of the tibial apex of Calathus cisteloides, No. 777.

In each case the spurs are conceived as projected upon one plane, t1, the
normal tarsus. A1, P1, its anterior and posterior spurs, t2, A2, P2, similar parts
of nearer extra tarsus, t3, A9, Ps, similar parts of remoter extra tarsus. M1,
plane of reflexion between t1 and t2. M2, plane of reflexion between i2 and t3.

Calathus cisteloides ^ (Carabidae): right anterior tibia bearing
a pair of supernumerary tarsi compounded together. In this case the
extra parts were anterior to the normal tarsus. The parts were
arranged as in the diagram, Fig. 169, II, which is a projection of the
tibial apex. The apex is produced anteriorly so as to form a wide
expansion which bears the common articulation for the double tarsus.
This produced portion is of course formed by the composition of parts
of a pair of tibiae. It is noticeable that the three tibial apices which
enter into the formation of the general apex are in one respect not
actually images of each other. For the angular distances between A1
and P1, and between A2 and P2, are exceedingly small, being far less than
in a normal tibia of the species, and in fact the grooves running from
each anterior spur to the corresponding posterior one are almost paral-

chap, xx.] EXTRA LEGS I UNCONFORMABLE CASES. 507

lei to each other and to the long axis of the tibia. The tarsi f and f'
separate in the first joint.

The relative positions are shewn in the diagram, and it is thus seen
that the planes of reflexion Mx and M2 are inclined to each other at an
acute angle.

This specimen was kindly lent to me by Dr L. von He yd ex and
was first described and figured by Mocquerys, Col. anorm., 1880, p.
65, Jig.

It is difficult to observe the two foregoing cases without sus-
pecting that the fact that they deviate from the normal symmetry
of extra parts may be connected with the normal modification
of the anterior tibia in these Carabidw. It should be remembered
that the tibia and tarsus of the unmodified leg of a beetle are
very nearly bilaterally symmetrical about the longitudinal median
plane of the limb, but in this leg of these forms the symmetry
is lost. Possibly then the upsetting of the ordinary rules for
the Symmetry of extra parts may follow on this modification.
The difference between the two cases moreover is possibly due
to the fact that in one the extra parts are on the posterior surface
of the leg, while in the other they are on the anterior. Since the
normal limb is not bilaterally symmetrical it is reasonable to expect
that the results would differ in the two cases. One other case
of a pair of extra tarsi in the fore leg of a male Calathus is re-
corded (No. 777 a), but insufficiently described. It is to be hoped
that a few cases of extra tarsi in the fore leg of male Calathus
or Pterostichus may be found, and it is very possible that such
a case even in Carabus would help to clear up these points.

777 a. Calathus fulvipes 3 (Carabidre) : tibia of right fore leg bears pair of extra tarsi.
[Fig. and description inadequate.] Perty, Mitth. not. Ges. Bern, 1866, p. 307, Jig. 5.

(10) Nine other cases departing from the Schematic Positions.

Each of these needs separate consideration.

*778. Platycerus caraboides (Lucan.) : left hind tarsus has form
shewn in Fig. 170. The terminal joint had only one
claw. R and L' are presumably the extra pair, but it
will be seen that they arise at separate places from the
3rd tarsal joint. Otherwise, they stand approximately
in Position V. Described originally by Mocquerys,
Col. anorm., p. 67, Jig.
779. Philonthus ventralis (Staphylinidse): third joint
of right posterior tarsus bearing supernumerary termi-
nation of double structure. The apex of the third joint
is enlarged, and at a point anterior and slightly dorsal
to the articulation of the normal fourth joint the super-

raboides, No. 778. Left bind tarsus from posterior surface.
L, the presumably normal apex, has only one median claw. R
and L', arise separately from the 3rd joint. (In Houen Mus.)

508 MEMSTIC VARIATION. [part i.

numerary parts arise. The fourth and fifth joints of the supernumerary
tarsi are of double structure, but are not separated from each other.
The double fifth joint bears two pairs of claws, of which the two adja-
cent members are compounded together at their bases. The plane in
which one pair of claws stands is about at right angles to the plane in
which the other pair is placed, the opposed surfaces being ventral
surfaces. Stated in terms of the Scheme on p. 481, the supernumerary
tarsi are placed as in the position DDA, whereas their position of
origin is DA A. It is noticeable that the normal fifth joint does not
stand quite in its usual jDosition, but is a little twisted so that it par-
tially turns its ventral surface in an anterior direction. This specimen
was described and figured by Fauvel, Rev. d'Fnt., 1883, n. p. 93, PI.
ii. No. l'. It was kindly lent to me by M. Bleuse, to whom it belongs.

780. Alaus sordidus (Elateridae) : Ceylon, femur of right middle leg
bears two supernumerary legs arising from its postero-dorsal surface.
All three legs are somewhat abnormal in form and the principal femur
is partly shrivelled at its base. At a point on the postero-dorsal sur-
face about halfway from the apex there is a large, irregular boss from
which the two extra femora diverge. Of these that wdiich is nearest
to the normal leg may be distinguished as a left leg by the planes of
movement of its tibia and tarsus, while the remoter leg is a right leg.
The tarsus of the latter is broken but was probably complete. The
surfaces which the extra legs present to each other are structurally
anterior surfaces, but the relative positions of the three legs do not
correspond with any of the positions shewn in the Scheme. It should
however be noticed that this fact may be connected with the presence
of the amorphous thickening at the point of origin of the extra femora.
Specimen in Hope Collection first described and figured by AVestwood,
Oriental Entomology, PL XXV. fig. 9, and mentioned Proc. Linn. Soc.
1847, p. 346.

781. Clythra quadripunctata (Phyt,): left anterior trochanter bears
two supernumerary legs. Both the normal leg and the two extra ones
are complete. The position of the latter is very peculiar ; for, arising
from the anterior surface of the trochanter, they turn their structurally
dorsal surfaces towards the anterior surface of the normal leg, which
thus stands between them, one of them being above it and the other
ventral to it. Of these that which is placed dorsally is structurally a
right leg, while the lower one is a left, like the normal one. Both the
extra legs are also partly rotated so that their ventral surfaces are
partially directed upwards. From these facts it appears that the
position of these extra legs relatively to the normal one does not
correspond with any of the positions indicated in the Scheme, and it
did not seem to be possible to refer this deviation from the usual
arrangement to any special malformation of any of the parts. Speci-
men originally described by Mocquerys, Col. anorm., p. 42, fig.

782. Clytus liciatus (Long.) : right tibia reduced and thickened, being-
shapeless and bent. Its apex presents two articulations, the one anterior
and the other posterior, the latter bearing a normal, 4-jointed tarsus.
The anterior articulation bears a slender double tarsus, the two parts
of which are compounded in the 1st, 2nd, and 3rd joints but separate
in the 4th or terminal joints. The supernumerary tarsi are very

chap, xx.] EXTRA LEGS : UNCONFORMABLE CASES.

509

slender and the whole thickness of their common proximal joint is
even less than that of the proximal joint of the normal tarsus. The

ac

Fig. 171. Clytus liciatus, No. 782. I. View of right tibia. II. Detail of the
extra parts, from plantar surface, ac, ac, claws supposed to be morphologically
anterior, pc, rudiments supposed to represent posterior claws. III. Enlarged
view of the end of the normal tarsus. (The property of Dr Kraatz.)

terminal joints of the extra tarsi are well formed, but they each bear
only one fully developed claw, the claw of the adjacent side of each
being only represented by a rudimentary knob. It appears at first
sight that these extra tarsi are at their origin from the tibia only a
single appendage and that their double nature only begins from the
third joint. This however is not the case, for there are five spurs on
the tibia, together with a small brown knob which perhaps represents
the sixth spur. The tibia is greatly misshapen and the arrangement of
the spurs is so amorphous that I did not succeed in determining their
morphological relations. This specimen was kindly lent by Dr Kraatz,
having being first described by him in Berl. ent. Zt., 1873, xvrn. p. 433,
figs. 1 7 and 17 a.

783. Cryptohypnus riparius (Elater.). The tibia of the right anterior le<j is
enlarged at its apex and bears one very large tarsal joint: this joint has two apical
articulations, of which the posterior bears the remaining 4 joints of what is pre-
sumably the normal tarsus. The other articulation bears a large tarsal joint, connn< in
to a pair of complete extra tarsi. This pair of tarsi stand with their lateral parts
closely adjacent and their plantar surfaces downwards, but the other tarsus which
is posterior to them, and is presumably the normal, stands with its plantar surface
turned backwards. This disposition differs considerably from that indicated in the
Scheme. For the place of origin of the extra tarsi and their position relatively to
each other is A; but the normal tarsus is twisted so that it turns its dorsal surface
forwards, towards the posterior surface of the nearer extra tarsus. For this specimen
I am obliged to Dr Mason.

784. Taurhina nireus (Lamell.) : right middle tibia bearing two extra tarsi. [In
the normal leg of this beetle the tibia is like that of many other Lamellicorns,
presenting at its apex two sharp processes, the one anterior and the other dorsal :
and ventrally two articulated spines, one anterior and the other posterior to the
tarsus. The abnormal tibia of this specimen is considerably widened at its apex,
and bears in addition to the normal two processes two other processes of a similar
kind separated from each other by a pair of articulated spines. Instead of a single

-

5 1 0 MEMSTIC VARIATION. [part l

pair of articulated spines, this tibia bears five such spines, of which a pairstand
between the two extra processes. The disposition of these spines could not be made
clear without several figures. There are two complete tarsi and both have their ventral
surfaces turned downwards. The anterior tarsus is somewhat the smaller. I did
not succeed in definitely determining the homologies of the parts in this specimen.
It should be specially observed that while the tarsi are only two in number, suggesting
that the supernumerary part is sinr/le, the spines indicate that there are here at
least some elements of further repetition.] Specimen figured by Kkaatz, Deut. ent.
Zt., 1889, xxxiii, p. 221, fig. 18, and kindly lent by him.
7g5 Ranzania bertolonii (Lamellicorn) : in the right posterior foot the last joint of

the tarsus is curved outwards and bears six claws instead of two, and three onychia
instead of one. The arrangement of the parts is somewhat complex and could not
well be made clear without elaborate figures. Speaking generally, the last (fifth)
tarsal joint presents at its apex a large articular surface of irregular shape. This
surface bears four large claws disposed in the same direction as the normal pair of
claws. Of the four claws the two adjacent ones are in solid continuity for a part of
their length, being joined together by chitin much as the extra dactylopodites are in
l''i^r. 184, in. It is clearly shewn that the conjoined claws are respectively the fellows
of the two free claws, for the two extra onychia stand one upon either side of and
opposite to the curvature of the conjoined claws. Terminally the fifth tarsal joint
bears also a small pair of somewhat deformed claws with which an enlarged and
misshapen onychium corresponds. This specimen was kindly lent to me by M.
Henri Ctadeau de Kerville and was mentioned by him in Bull. Soc. Ent. France,
Ser. 6, vi. 1886, p. clxxx.

786. Rhizotrogus aestivalis $ (Lamellicorn), bearing supernumer-
ary parts of double structure upon the right posterior 5th tarsal
joint (Fig. 172). The structure found in this case is very re-
markable and is, I believe, in some respects unique. The tarsus
is normal as far as the extremity of the terminal joint, and the
abnormality consists entirely in repetition of claws and pulvillus.
The normal formation is shewn from the ventral surface in
Fig. 172, A. There is an anterior claw, a posterior clawT and a
small pulvillus, placed ventrally to the claws, bearing two hairs.
Fig. 172, B, shews the abnormal foot from the ventral side. Each
claw gives off from its base a ventrally-directed supernumerary
claw, and each supernumerary claw is bifid at its point. Ex-
amined from below each of these extra claws is seen to bear
two grooves separated by a ridge, and is therefore morphologically
a double structure. The next structure of importance is the
pulvillus. The normal pulvillus (pid) is in place and of the usual
form, but dorsally to it there is a supernumerary pulvillus (pid-)
of cylindrical form and rather longer than the normal pulvillus.
At its apex this extra pulvillus bears a median bifid hair with
another hair on each side of it ; these hairs thus prove that the
extra pulvillus is morphologically double.

In this foot, therefore, a supernumerary pair of claws and a
supernumerary double pulvillus are intercalated between the
normal claws and the normal pulvillus. Hence though the repet-
ition affects both claws and pulvilli, and the structures found
are sufficient for an incomplete pair of extra feet, yet the extra
parts are disposed in the system of symmetry of the normal foot,
forming, all taken together, one foot only. Specimen very kindly
lent by Dr G. Kraatz.

chap, xx.] EXTRA LEGS : MISCELLANEOUS CASES.

511

A

B.

A

a'and

p'andp'

D.

K ,.P

pul -/

Fig. 172. Ehizotrogus cestivalis, No. 786. A, normal hind foot from ventral
surface. B, right hind foot of No. 786 from ventral surface. C, enlarged view of
pulvilli. D, inside view of the claws at the anterior border of the apex. E, inside
view of the claws of the posterior border of the apex. A, anterior. P, posterior.
a, normal anterior claw of abnormal foot, p, normal posterior of the same.
a', a", the two points of extra claw of anterior side. p's p", the two corresponding
posterior points. In D the posterior group of claws is supposed to be cut off at P.
pul, normal pulvillus. pul2, extra double pulvillus.

(11) Cases in which the legs were either mutilated, or in part
amorphous, or insufficiently described.

'87. Want of space prevents me from giving more than a list of refer-
ences to these cases. Most of them besides are imperfectly known. Of
those seen by myself the case of Ulster would, I think, be interest
ing, but I regret that my notes of this case are imperfect. In the
following list the letters R and L shew the leg affected ; the " means
that the case probably did not agree with the Scheme, the , that it
probably did agree ; the J means that the parts were either mutilated,
or imperfect, or deformed. Of those unmarked, the accounts are
inadequate.

E3 Tischbeix, Stet.ent. Ztg., 1861, xxn. p. 128.
Kraatz, Deut. eut. Zt.. 1889, xxxni. p. 222,
fig. 17.
Lj Gkkdlkh, Korresp. zool.-min. Ver. Regetuo.,

1877, xxxi. p. 139.
Ro LANDOis, Zool. dart., 1**1. xxv. p. 2SS[q.v.J
L." Kraatz, Berl. ent. Zt., 1873, xvn. p. 432.

Ichneumon luctatorius
Carabus auratus

C. auronitens

C. cancellatus

ditto <?

512

MEBISTIC VARIATION.

[part I.

B„
B"

1

C. catenulatus
C. italicus
Dyschirius globulosus

(Car.)

Calopus cisteloides (Het.)
Pterostichus prevostii L3

(Car.)
Chl.-rnius nigricornis (Car.) L.{
Agra catenulata (Car.) L3

Prionus coriarius (Long.) B3

Prionus sp. ? 3

Aromia moscliata (Lam.) Lx

Dorcadion rufipes (Long. ) L3

Blaps sp. (Het.)

B,

Ptinus latro (Plin.) Lx

Dytiscus marginalis (Dyt.) Bx

Colymbetes sturmii (Dyt.) Lx
Strategus antaeus (Lam.) L2
Rutela fasciata (Lam.) B3

Hister cadaverinus (Clav.) Bx
Cetonia morio- (Lam.) Lx

ivielolontha vulgaris (Lam.) L3
ditto Bx

ditto L,

ditto

*3

La

Ri

Li

and

B3
Oryctes nasicornis (Lam.) P^

Enema pan. (Lam.) L3

+ % ditto

|| Rhizotrogus castaneus
(Lam.)

t H- aestivalis

Brit. Mm.

Baudi, Nat. Sicil., vni. No. 9, p. 199.
Jaynk, Trans. Amer. Ent. Soc., 1880, vm.

p. 157, PI. ix. jigs. 6, 6a.
vox Heyden, Isis, 1836, ix. p. 761.
Muller, A., Proc. Ent. Soc, 1869, p. xxviii.

Mocquerys, Col. anorm., 1880, p. 62, Jig.
Stannius, Miill. Arch. f. Anat. Phys., 1835,

p. 306, fig. 13.
Perty, Mitth. not. Ges. Bern, 1866, p. 308,

fig- 11.

Ann. and Mag. N. H., 1841, p. 483.
Kraatz, Dent. ent. Zt., 1877, xxi. p. 56, PI.

i,2,^.ll.
Perty, I.e.
Laroulrene, Bull. Soc. Ent. Fr., S. 4, v.

1865, p. xlix.
von Fricken, Ent. Nachr., 1883, ix. p. 44.
Bitzema Bos, J., Tijds. v. Ent., 1879, xxn.

p. 206, PI.
Stannius, I.e., p. 307, fig. 9.
Jayne, I.e., p. 159, fig. 10.
Spinola, A nn.Soc. ent.Fr. 1835,iv.p.587,P7.
Mocquerys, I.e. , p. 59, fig.
Sartorius, Wien. ent. Monats., 1858, 11. p. 50.
Treuge, Ent. Nachr., vin. 1882, p. 177.
Doumerc, Ann. Soc. cut. Fr., 1834, in. p. 171,

PI. 1 a, fig. 1.
Boulard, Bull. Soc. ent. Fr., 1846, S. 2, iv.

p. xwin.fig.
Tiedemann3, MeckeV s Arch. f. Phys., 1819,

v. p. 125, PI. 11. fie. 1.
Mocquerys, I.e., p. ii8, fig.
Bassi, Ann. Soc. ent. Fr., 1834, in. p. 373,

PI. VII A.

/Perroud, Ann. Soc. Linn. Lyon, 1854, n.
( p. 325.

Audouin, Bull. Soc. ent. Fr., 1834, in. p. iv.
Taschenrerg, Zts. f. ges. Naturiv., 1861,
xviii. p. 321.

1 As Kraatz suggests, this is presumably the case given by Sartorius, /. c.

2 Probably same specimen as that of Gredler, Korresp. zool.-min. Ver. Begensb.,
1869, xxiii. p. 35.

3 Tiedemann's grave comment is of interest as recalling past phases of thought.
He says: " Was die Entstehung der oben beschriebenen Missbildung betrijf't, so lasst
sich wohl annehmen, dass die Phantasie der Mutter des Maikdfers durch ein voraus-
gegangenes Versehen aufgeregt, hier nicht als Ursache beschuldigt werden kann, theils
weilwir iiberhaupt keine Beiveise filr eine lebhafte Phantasie der Maikdfer haben,und
theih weil die Bildung des Embryo ausserhalb des Leibes der Mutter nur sehr langsam
geschieht, und die Mutter ohnehin gleich nach Legung der Eier stirbt " I. c, p. 126.

chap, xx.] EXTRA ANTENX.E : PRELIMINARY. 513

Paired Supernumerary Antenna

In dealing with extra antennae there is more difficulty in de-
termining the true nature of the parts than there is in the case
of extra legs. We have seen that the real duplicity of com-
pounded extra parts often appears only in the fact that they
have a bilateral symmetry, while in the normal appendage one
side is differentiated from the other. Now in very many species
of Insects the antenna seems to be a bilaterally symmetrical fila-
ment, having joints cylindrical or elliptical in section. When from
such an antenna there proceeds an extra filament, itself bilaterally
symmetrical, it is almost impossible to determine whether the
extra filament is really a single repetition of the normal or
whether it is made up of two homologous borders of a pair.
(Cp. Nos. 801 and 764.) In speaking of actual cases of
duplicity in Arthropodan appendages we shall have to return
to this subject.

Meanwhile evidence will be given as to examples of obvious
duplicity in extra antennae. It will be seen that in species having
normally a marked differentiation between the anterior1 and
posterior borders of the antennae (Lainellicorns, Lucanidae, &c. ).
and the case has been really studied, there is often clear proof
not only of the duplicity of the extra parts but also that they
are arranged as images, almost as described for legs.

We shall moreover meet cases where of the paired extra
parts one springs free from the normal at a point proximal bo
the point of origin of its fellow. Among extra legs there is scarcely
any certain example of this phenomenon, Platycerus caraboides No.
778 being perhaps the clearest case. But among antennae there
are several where no other interpretation seems possible. These
cases I have set in a separate section.

Of the remainder, little can be said with confidence. Probablv
if they were carefully examined microscopically it would be found
that differentiation between the two sides exists in respect of
the distribution of sense-organs or hairs, and that thus the du-
plicity and symmetry might be traced.

After giving the clear cases I have thought it enough bo give
a list of those of this doubtful order. As has been said, there is
little doubt that with careful study of the specimens many
of the cases now included in the list of supposed single extra
appendages might be shewn to be cases of extra parts in
Secondary Symmetry.

1 This term is used, as in the case of legs, to denote the border which ia anterior
when the appendage is extended horizontally at right angles to the body. The
upper surface will then be dorsal, the lower ventral. These terms are thus applied
without any intention of affirming that they are morphologically correct.

b. 33

5 1 4 MERISTIC VARIATION. [part i.

(1) Clear cases of Supernumerary Antennce in Secondary

Symmetry.

(a) The extra ixirts arising together.

f788. Phyllopertha horticola (Lamellicorn) : specimen in which
the right antenna bears a supernumerary pair of clubs. This
specimen may conveniently be described in detail as it furnishes
a good example of the mode in which repetition of the antenna^
occurs in the Lamellicorns. The left antenna is normal and
possesses nine joints (Fig. 173, L). The first is a large pear-
shaped joint, articulating with the head by its narrow end. The

L R

Fig. 173. Phyllopertha horticola, No. 788. L, the normal left antenna. E,
the normal right antenna. /, r, extra left and right clubs.

second joint is also a pear-shaped joint, of about half the size
of the first. The third, fourth and fifth joints are elongated and
cylindrical. The sixth is short and wide. The seventh, eighth
and ninth are each expanded into a lamella. These three la-
mellae are generally kept firmly closed together and form the
sensory organ, or " club." In Melolontha (v. infra) and several
other genera of Lamellicorns, there are ten joints, of which seven
are developed as lamellae, forming the club.

In the right antenna (Fig. 173, It), which bears the extra
pair of clubs, the basal joint is rather thick. The second joint
is longer than it normally is, and curves slightly backwards and
downwards. At its apex it bears the rest of the normal antenna,
which is in all respects well formed. In addition to the normal
antenna, the second joint upon its anterior surface gives attach-
ment to a large joint which is imperfectly constricted into two
parts in a vertical plane at right angles to the general direc-
tion of the normal antenna. Each of these half-joints bears a
structure containing in itself all the parts proper to an antenna
peripherally to the third joint, the clubs being well-formed and
normal. In absolute size they are equal, but are a little smaller
than the normal antenna.

CHAP, xx.] EXTRA ANTENNAE ARISING TOGETHER. 515

These two antennae curve in opposite directions and arc in
all respects complementary to each other, forming a true pair.
The most anterior of them, r, is disposed as a rir/ht antenna,
while the posterior, I, is disposed as a left. This specimen
was taken by M. Albert Mocquerys, and was kindly lent to me
by M. Henri Gadeau de Kerville.

789. Melolontha vulgaris $ (Lamellicorn) : left antenna bearing a
pair of supernumerary clubs. The extra pair arises from the second
joint of the normal antenna, and they have their third joints united at
the base. The relative positions of the extra clubs and the normal one
are those marked VP in the Scheme. All these three clubs are perfect
and of the same size, but each is a little smaller than a normal club.
At the thoughtful suggestion of Prof. Howes this specimen was
very kindly lent to me by Mr E. E. Green, and has been placed in the
Museum of the Royal College of Surgeons.

790. Melolontha vulgaris : [right antenna bearing a supernumerary
pair of clubs in Position P. For details see original, where a different
and I think untenable view is taken] Lereboullet, Rev. et Mag. de
Zool., S. 2, in., 1851, Jig.

791. Melolontha vulgaris £ , with a pair of supernumerary antenna?
arising from the left antenna. [The figure shews that the proximal joint
or scape was of abnormal thickness and had two peripheral articulations
in the same horizontal plane. The anterior articulation bore a normal
antenna. The posterior articulation bore a single large first funicular
(2nd) joint which in its turn bore a pair of clubs in the same horizontal
plane, the anterior being a right club and the posterior a left, having
their anterior surfaces adjacent : they are therefore a complementary
pair in Position P.] Kraatz, G., Ueut. ent. Zt., 1880, XXIV. p. 341,
figs. 7 and 7 a.

792. Amphimallus solstitialis (Lamellicorn): left antenna bearing a
supernumerary pair of imperfect antenna? articulating by a common
stalk on the anterior surface of the second joint. The two extra clubs
are an imperfect pair, complementary to each other, being set on bark
to back, in Position A. The most anterior of the clubs has only two
lamellar joints, one small and one large. The posterior has three
lamella?. The normal club has three lamella? as usual. Originally
described by Mocquerys, /. c, p. 15, Jig.

793. Anomala junii (Lamellicorn) : left antenna bears 3 clubs, each having 3-jointed
stem articulating with elongated 2nd joint of antenna. [Symmetry not clear:
possibly Position DPP.] Kraatz, Ueut. cut. /A., 1881, xxv. p. Ill, PI. in. fig. 4.

*794. Geotrupes typhaeus ^ (Lamellicorn): left antenna bearing
a pair of supernumerary clubs compounded together. The an-
tenna is normal up to the 7th joint which is dilated. The 8th is
still more dilated and bears posteriorly the normal club com-
posed of three lamellae; and anteriorly by a separate articulation
a supernumerary structure (Fig. 174, mr,ml) consisting of three
joints, each of which has the form of a complementary pan oi
lamellae joined by their morphologically posterior (so. external)
edges. The whole supernumerary structure is thus morphologic-

33—2

516

MERISTIC VARIATION.

[part I.

ally a pair of clubs, a right and a left, compounded together.
The histology of the supernumerary lamellae is just the same as

Fig. 174. Geotrupes typhous, No. 794. Left antenna bearing a compounded
pair of clubs, ml, mr, morphological left and right of the extra parts. (The
property of Dr Kraatz.)

that of the normal lamellae, all being covered with pubescence.
The form of the compound eleventh joint is somewhat irregular.
The extra parts are in the Position A of the Scheme. Specimen
kindly lent by Dr Kraatz, and first described and figured by
him in Dent, ent Zt, 1889, xxxni. p. 221, fig. 13.
795. Melolontha hippocastani <£ having supernumerary parts of
double structure upon both the right and the left antenna.

Right Antenna. Third joint elongated, thickened and pre-
senting two articular surfaces ; of these one is terminal and bears
a normal autennary club, while the other is dorsal and bears a
supernumerary double club. This structure has the form shewn
in the drawings. Fig. 175, A, shews its appearance when looked
at from above, B shews the structure when seen from below and
externally. It consists of seven pieces shaped like half-funnels,
fitted into each other.

Fig. 175. Melolontha hippocastani, No. 795. D, view of the whole head and
antennae after von Heyden. C, view of right antenna. B, detail of right antenna
from below. A, detail of the same from above.

chap, xx.] EXTRA ANTENNAE ARISING TOGETHER. 517

The morphological nature of this supernumerary organ may
be determined thus. The upturned edges of the folds bear
hairs as shewn in the figure A; since in the normal antenna
the dorsal edges of the lamellae alone bear hairs, these edges
are in this case dorsal morphologically as well as by position.

Since the outermost lamella (marked 4) is articulated into
the third joint of the funiculus, it is therefore the 4th joint, or
proximal lamella, and the remaining lamellae are therefore 5th,
6th, 7th, 8th, 9th and 10th respectively. Next, the surface ////•
is structurally like that of the internal (sc. anterior) surface of
the proximal lamella of a normal club, and the surface ml is a
similar surface : but ml, being an internal surface, faces towards
the right and is therefore morphologically a left; while mr, being
an internal surface and facing towards the left, is a right ; hence
this club consists of two clubs compounded together by their
external or posterior borders, and the two are a right and a left,
the left being next the normal right club.

Lastly, since the upper free edges of the lamella* are structur-
ally dorsal, it follows that their lower edges are structurally
ventral: but these lower edges do not exist as free edges, f'« >r
the lamellae are continuous upon their ventral aspect : therefore
the surfaces which are adjacent in the extra right and left clubs,
and by which they are compounded together, are partly ventral
surfaces. This is approximately Position DP of the Scheme.

Left Antenna. Second joint thickened and presenting three
articulations as follows. 1. a peripheral articulation bearing the
normal club ; 2. a ventral articulation bearing a 4th joint and
club composed of 3 formless lamellae ; 3. a dorsal articulation
bearing a small cylindrical joint only. The shape and formation
of these extra parts is so indefinite that their morphology could
not be determined.

For the loan of this specimen I am indebted to Dr L. v< »x
Heyden, who first described it in Deut ent. Zt.y 1881, XXV, p. 10"),
fig. 1.

796. Rhizotrogus aequinoctialis (Lain.) : 4-th joint of right antenna
bears a supernumerary structure projecting forwards and lying in the
same horizontal plane as the normal club. This structure is lanceolate
in form and its outer surface is in texture similar to the external surfaces
of a normal club. On the ventral aspect it presents a simple ridge, but
on the dorsal side its outer coating is divided by a spindle-shaped slit
through which part of the internal structure protruded. The edges of
this opening and the protruding portion of the interior bear a few
hairs. There can be little doubt that this supernumerary body repre-
sents an imperfectly formed pair of cluhs, and that it is in fact a more
rudimentary condition of the parts found in No. 795. Specimen origi-
nally described and tigured by Mocquerys, Col. anorm., p. 1 •>,./?'#.

797. Llchnanthe vulpina (Lam.) : right antenna bears in addition to normal club a
small spherical club made up of three joints, arising from posterior border of a l<>n^

518 MERISTIC VARIATION. [part i.

joint apparently representing the normal 4th, 5 th, and 6th joints not segmented from
each other. [As this supernumerary part is in itself symmetrical it probably con-
tains within itself parts of a pair of clubs compounded in Position P. Cp. No.
795.] Jayne, H. F., Trans. Amer. Ent. Soc, 1880, vm. p. 158, PI. iv. fig. 8.
798. Polypbylla decemlineata (Lamellicorn). A specimen in which the right
antenua bears a partially double supernumerary branch in addition to the normal
antenna. This additional structure articulates with the second joint of the antenna
by means of a single large joint. This joint carries a double club consisting of two
sets of lamellae, seven being in each set. The two sets of lamellae are united at
their bases at an angle of forty-five degrees. The plane of the normal club is per-
pendicular to that of the abnormal ones. The normal club itself is Ath shorter than
that of the other side. [The details of the structure of this specimen are difficult
to follow and the reader is referred for further particulars to the description and
figures given in the original.] Jayne, H. F., Trans. Amer. Ent. Soc, 1880, vm.
p. 158, Ji(]s.

(b) The extra parts arising from the normal at separate points.

99. Odontolabis stevensiij (Lucanidae). As the repetition in
this specimen is almost complete and the relations of the parts
fairly clear though in some respects peculiar, a detailed account
will be useful.

The body, legs, &c. are normal, save that the back of the
head and thorax have been crushed by some accident. The
antennae are both abnormal in the way shewn in Fig. 176. The
condition will be better understood if the normal antenna is first
described.

*7

ri

Fig. 176. Odontolabis stevensii, No. 799. The liead seen from below, and

enlarged views of the two antennae. R, right. L, left. There is some doubt as

to which of the branches is the normal and which the supernumeraries. See
description in text.

The normal antenna of Odontolabis is much like that of its
ally Lit can us cervus, the Stag-beetle. It is made up of 10 joints
composing three parts differentiated from each other.

The first, or " scape, ': is a single joint as long as the rest
of the antenna. It widens a little from its central end or base
towards the apex, and is slightly flattened from above downwards.
The second part, or " funiculus," has six simple joints. The last
three joints form the club. They are flattened from above down-
wards and lie in a horizontal plane. The anterior (" inner ")
border of each of these three joints is produced into flat ex-
pansions, covered with sensory pores, which together form a series
of serrations along the anterior border. When in its natural

chap, xx.] EXTRA ANTENNAE ARISING TOGETHER. 519

position the serrated border of the right antenna faces towards
the left side, and that of the left is turned towards the right.
The structure of the abnormal specimen is as follows.

Left Antenna. Scape normal. Its plane however is not quite
horizontal as usual, but is a little oblique, the anterior border being
slightly higher than the posterior. In the funiculus the 1st and
2nd joints (2nd and 3rd of the whole antenna) are a little thicker
than usual but otherwise normal. The 3rd joint of the scape
is enlarged and presents at its apex two sockets, each bearing
a continuation as shewn in the figure. The two sockets are not
in a horizontal plane, but their plane is oblique and nearly at
right angles to the plane of the scape, the socket bearing the
branch ll being the higher. It is important that the precise re-
lations of these parts should be clearly understood.

This outer socket of the 3rd funicular joint bears the branch l\
made up of three more funicular and three club-joints, turning
their serrated border in the direction of the rigid antenna : I1 is
therefore structurally a left antenna. Its surface is of the same
nature as that of a normal antenna, but its size is a little smaller.
It is in an oblique plane inclined to the horizontal at about 45 .
the posterior (outer) border being the higher.

The inner socket of the 3rd funicular joint bears a cylindrical
joint not quite fully segmented off from the next joint peripheral
to it. These two are 4th and 5th funiculars. The 5th again
presents two sockets, bearing respectively the branches I2 and
I3. The branch I2 has one small joint (6th funicular) and three
club-joints, turning their serrated border towards I1. This branch
is therefore structurally a right antenna. It stands in the same
oblique plane as I1, the serrated border being the higher. In
size it also agrees with l\ being rather smaller than the normal.
The branch I3 is a normal left in size and shape, and it lies in
a horizontal plane.

Here therefore there is a left antenna and a pair, one a right
and the other a left. Which then is the normal, I1 or I3 ? Inas-
much as I3 and P arise by a common stalk it may seem that
they are the extra pair and that I1 is the normal. We have
now seen in many cases that extra parts in Secondary Symmetry
are compounded together as P and I2 are here. But considering
the fact that Is is of normal size and in the normal horizontal
plane, whereas I1 and I- are both smaller and are in an oblique
plane complementary to each other, I incline to the view thai
if one branch is the normal, it is I3, and that /l and I- are the
extra pair in Secondary Symmetry, though tlieij do not arise to-
gether. They are then nearly in Position DPP, but depart from
that position in the fact that I1 is not horizontal (cp. No. 757).

If I1 and I2 are really the extra parts, in the fact that they
do not arise together, but spring separately from different points
on the normal, wre meet with a condition rarely seen, but that

520 MERISTIC VARIATION. [part t.

this is a possible condition is proved beyond doubt by the
succeeding case.

Right Ante)i int. Scape precisely as in left antenna. The
1st funicular (2nd antennary) has two sockets at its apex, placed
like those on the 3rd funicular of the left side, the anterior socket
being the lower and the posterior socket being the higher. The
anterior socket bears a normal right antenna, ?-3. The posterior
bears the structure shewn in the figure. This appendage has
unfortunately been broken, but enough remains to suggest the
original structure. It consists of five funicular and a 1st club-
joint. The 5th joint of the whole funiculus bears a large socket
looking downwards and forwards, its other socket looking back-
wards and upwards. From the former the original continuation
has been lost. The latter bears the 6th funicular and its 1st
club-joint, this again having an empty socket.

The plane of the two sockets of the 5th funicular is oblique
to the horizon, like that of I1 and I'2. Though it is clearly im-
possible to shew how this antenna was in its unbroken state,
we may note that if it were continued in the way suggested
by the dotted lines it would have borne a complementary pair
of clubs, r1 and r2, like I1 and I'2 of the other side, placed like
them in an oblique plane nearly corresponding with DPP of the
Scheme.

This specimen was kindly entrusted to me by M. Henri
Gadeau de Kerville. He tells me that he believes a description
of it has already appeared, but this I have failed to find. I
have therefore ventured to describe it again, with apologies to
the original describer. The specimen bears a label in the hand-
writing of the late Major Parry and was no doubt in his cele-
brated collection of Lucanidse.

800. Melolontha vulgaris : right antenna bearing a pair of incomplete
supernumerary antennae (Fig. 177). The first joint is normal ; it bears a
second joint of singular form, consisting of a long anterior branch, and
a short posterior branch i the length of the anterior. The anterior
bears two clubs in the manner shewn in the figure (Fig. 177). Of these

Fig. 177. Melolontha vulgaris, No. 800. Lettered according to the view that R
is the normal right club. L, the supernumerary left, and R' the supernumerary
right. (From Wesmael.)

*

801,

chap, xx.] EXTRA ANTENNA ARISING SEPARATELY. 521

one (E) is inwardly directed and is as wide as, but only | the length of
a normal club. The posterior of the two clubs (L) is directed back-
wards and has only four lamellae which are apparently united together.
The other small club (R') is also composed of only four lamella? which
are similarly united together. In both L and R the middle lamellae shew
traces of further subdivision. The figure represents the three clubs as
being all in one plane, but the club R' is really below /,, which stand-
up from the normal antenna. It is mentioned that some of the tarsi
were mutilated or defective. [Here L and R' are clearly a complement-
ary pair, though separately arising from the normal. It will be
observed that as in Lereboullet's case (No. 790) the second joint, which
is common to two clubs, is greatly elongated.] Wesmael, Bull. Ac.
Belg., 1850, xvi. 2, p. 382, fig.

Navosoma sp. (Longic.) Left antenna abnormal. The joints of
the normal are a little flattened from above downwards and are nearly
elliptical in section. But the anterior border is differentiated from the
posterior by the presence of two elongated patches of tissue covered
with sensory pores. The two patches are both on the anterior border,
one being* on the dorsal surface and one on the ventral, separated from
each other by a chitinous ridge. Upon the general surface of the
peripheral joints of the antennae are several other such patches, but
none are so distinct as those of the anterior border. The abnormal left
antenna has the form shewn in Fig. 1 78. So far as the 8th joint it does

L'*R

L'+R'

Fig. 178. Navosoma, No. 801. Left antenna seen from below. Lettered on
the view that R and L' are the extra parts. S, sensory patch. (In Hope
Collection.)

not differ from the normal. The 9th and 10th joints have besides their
chief patches of sensory pores (S) on the anterior border, an additional
patch (L' + R') posterior to the chief patch. But up to the 10th joint
there is no vertical division. The 10th joint however has two articular
surfaces, anterior and posterior, in the same horizontal plane. The posterior
bears an apical (11th) joint of normal form, having anteriorly a sensory
patch. But the apical joint borne by the anterior articular surface has
two such sensory patches, an anterior and a posterior. This joint
therefore contains in itself parts of a pair of joints. It is not quite
fully segmented off from the 10th joint.

Nevertheless it is difficult to suppose that the anterior joint is the
extra pair in Secondary Symmetry, for its anterior patch, Ls, seems to
continue the normal series of patches, S, S, etc. Therefore the patches
R and L' seem to be the patches of the extra pair, though one of them
is on a separate joint and the other is applied to the normal. Taken
with the case of Odontolabis No. 799 and Mehlontha No. 800, this

522 MERISTIC VARIATION. [part i.

must, I think, be judged to be a possible account, and in this case R
and L' are, as regards symmetry, in Position P. It is of course possible
that Ls and R are really the extra pair in Position A, but the presump-
tion is rather the other way1. Specimen in Hope Collection at Oxford.

(2) Cases of double extra antennce, Symmetry unknown.

802. In none of the following can any confident statement be made
as to the symmetrical relations of the parts, Several of the
cases I have myself seen, but I noticed no clear indications as
to their symmetry. A good many of them however were ex-
amined before I was fully alive to the importance of these matters
in the case of filamentous antennae, and perhaps if they were
studied with proper regard to the question of symmetry more
might be made of them. Many cases that followr are mutilated
or partly amorphous, and of almost all the descriptions are very
imperfect. For our purpose some value attaches to these records
as evidence of the distribution of such abnormalities, and to
any person who may hereafter pursue the subject a fairly com-
plete list of the references may be of use. To this therefore I
shall confine myself; for on reviewing the abstracts that I have
made of these examples it is clear that they only give the results
of superficial examination.

Speaking generally, in these cases, from some one joint of an
antenna there arises either a pair of extra antennae compounded
for a greater or less extent of their proximal parts, or two extra
antennae distinct from their point of origin.

The letters R and L indicate the side affected, and the number
following is approximately that of the joint from wrhich the extra
parts spring. In the greater number of sound cases the three
branches lie in or nearly in a horizontal plane and are, I anticipate,
in Positions A or P.

Cases which seem from the indications to conform to the
Scheme are marked ||. Mutilated or partially amorphous cases are

marked J.

Blaps attenuata (Het.)

R3

Mocquerys, Coleopteres anormaux, 1880,
p. 5, Jig.

' || Malachius marginellus

L2

ibid., p. 7, fig.

(Mai.)

Timarcha tenebricosa

R9

ibid., p. 13, fig.

(Phyt.)

Clytus tricolor (Long.)

L7

ibid.'2, p. 19, fig.

* X C. arcuatus

LI

ibid., p. 20, fig.

Calopteron reticulatum

LI

ibid., p. 25, fig.

(Mai.)

Carabus monilis (Car.)

L3

ibid., p. 3, fig.

' C. auronitens

L7

ibid., p. 9, fig.

■ Ftinus latro (Ptin.)

L5

ibid., p. 8, Jig.

Elater murinus (Elat.)

L2

Ann. and Mag. of N. H., 1831, iv. p. 476.

Zonites praeusta (Het.)

E3

Stannius, Mull. Arch. f. Anat. Phys., 1835,

p. 303.

1 This is perhaps too strongly put.

2 Description and figure incorrect. Apical joint of extra branch is bifid.

chap, xx.] EXTRA ANTENNA : OBSCURE CASES.

523

Helops cacruleus (Het.) R5

Dendarus hybridus (Het.) L 4

: Scraptia fusca (Het.) L 5

: Carabus sacheri (Car.) R7

Fimelia scabrosa (Het.) R 2
Anchomenus sex punctatus L 6

(Car.)

Calosoma investigator R 5

(Car.)

Dromrcolus barnabita L 5

(Eucn.)

Carabus arvensis L 4

Shringe, Ann. Soc. Linn, de Lyon, 1836, PI.
Romano, Atti Ac. sci. Palermo, 1845, N. S.,

i. fig.
Rouget, Ann. soc. ent. France, 1849, S. •_'.

vii. p. 437.
Letzner, Jahresb. schles. Ges. f. vaterl.

Kultur, 1854, p. 86.
Blackmore, Proc. Ent. Soc, 1870, p. xxix.
Kraatz, Dent. ent. Zt., 1877, xxi. p. 56,

fig. 19.
ibid., 1889, xxxm. p. 221, fig.

von Heyden, ibid., 1881, xxv. p. 108, jig. 16.

Specimen kindly lent by M. A. Fauvel.

803. Meloe violaceus ? : between rigbt eye and tbe base of the right antenna arise
two supernumerary antenna from the head. Of these one has 3 joints and the other
has one. Kraatz, Bent. ent. Zt., 1877, xxi. p. 57, PI. i.fig. 22.

804.

The following example is mentioned here, though its nature
is quite obscure. In it there is a suggestion that parts of two
extra antennae are present, but the extra parts seem to be peri-
pheral to the parts which they repeat.

As my stay in Rouen was short I was not able to give as much
time to this specimen as I should have wished \

Melolontha vulgaris ^ : left antenna abnormal. This case
differs wholly from any other that I know of. I can only describe
it in a most tentative way. The appearance when the lamella'
were cleaned and separated was as shewn in Fig. 179. Joints
1 — 8 are fairly normal, but peripheral to this place there were

Fig. 179. Left antenna of Melolontha vulgaris, No. 804. The numbers air
set in tentative suggestion of the possible nature of the parts. (In Rouen Mas.)

1 This antenna was when I saw it covered with mould and dirt. In washing it
I accidentally detached it from the head, but I mounted it again carefully with the
specimen.

524 MERISTIC VARIATION. [part i.

a number of lamellae, some like normal lamellae, others quite
irregular. As far as I could make out, the divisions were as
shewn in the figure, and I have affixed numbers to the several
parts in illustration of their possible nature. The appearance
suggests that there is an irregular repetition of a pair of clubs
peripheral to the normal antenna, but I can form no opinion
as to the morphology of the parts. Originally described by
MoCQUERYS, Col. an arm., 1880, p. 12, fig. [Description and
figure altogether misleading.]

Paired extra Palpi.

805. Bembidium striatum (Carabidae) : left maxillary palp arises by a
first joint enlarged towards its apex, bearing three separate terminal joints
instead of one. Of these joints one stands apart on a small process of
the first joint, but the other two are placed close together, on either
side of the apex of the first joint, and diverge from each other at about
a right angle. Jacquelix-Duval, Ann. Soc. Ent. France, 1850, Ser. 2,
viii. p. 533, Plate xvi.

806. Helops sulcipennis (Het. ): supernumerary, partially double
apical joint arises from the 2nd joint of right maxillary palp. It is
set on at right angles to the plane of the normal palpus. Jayxe, H. F.,
Trans. Amer. Ent. Soc., 1880, viii. p. 1QI, jig. 14.

807. Euprepia purpurea (Arctiidse): a specimen in which the right wings and
antenna were male and the left wings and antenna female, is declared to have
possessed an extra pair of palpi. [No sufficient description of this extraordinary
occurrence is given; and as the repetition of the palpi is only incidentally mentioned,
it may be doubted whether a full examination was made.] Freyer, C. F., Beitr.
zur Schmetterlingshunde, 1845, Vol. v, p. 127, Tab. 458, Jig. 4.

CHAPTER XXL

Appendages in Secondary Symmetry — continued.

The Evidence as to Crustacea1.

The facts as to Secondary Symmetries in Crustacea are so
similar to those already detailed in Insects that, were it not for
their value as confirmation of the principles indicated, it would
be scarcely necessary to describe them at large. Some few of
the cases have besides a special interest, as in them may be seen
rudimentary or bud-like structures apparently presenting the
lowest condition of paired parts in Secondary Symmetry.

Precisely as in Insects there are a number of cases (including
those last mentioned) where it would at first sight be supposed
that the extra parts are single, but on inspection most of them
prove double. Nevertheless there remain some few where this
cannot be shewn, and strange as it may seem, these must be
admitted to be genuine examples of duplicity of limbs. Of them
a special account will be given in another chapter.

There are besides, as in Insects, a considerable number of
cases in which the nature of the parts is not clear, though the
majority of such cases are not examples of extra parts, but are
normal appendages mutilated or deformed.

One specimen (No. 821) is the only case known to me in
which tivo pairs of supernumerary parts arise from one append-

ase-

Another (No. 827) is unique in the fact that according to the
description three separate appendages are repeated upon a single
appendage. It is not clear that this is in any strict sense an
instance of Secondary Symmetry, but for convenience it is taken
in this chapter.

1 Useful bibliography given by Faxon, Harv. Bull., 1880—1, vm. p. 271.

526 MERISTIC VARIATION. [part i.

Of the whole number, two affect antennas, four are in non-
ehelate ambulatory legs, one is in a chelate ambulatory leg and
the rest, being the great majority, are all in chelae.

With reference to these extra parts several false views have
from time to time been held. For example, in some of the
commonest cases there is an extra pair of dactylopodites, or of
indices, curving towards each other. The extra parts may then
greatly resemble the dactylopodite (or " pollex ") and index of
a normal chela, and many authors have not unnaturally supposed
that the extra parts were actually an extra pair of forceps re-
peating those of the normal chela. This may easily be shewn
to be an error, from the fact that it is often possible by some
slight structural difference between the pollex and the index to
detect that both extra parts are either both pollices or both
indices.

But the fullest disproof of this supposition is found in the
fact that the great majority of the phenomena will be readily
seen to conform to the principles enuntiated for Secondary Sym-
metries in Insects (p. 479).

A good many authors from the time of Rosel vox Rosexhof1
onwards have said that these cases are a result of injury, or of
regeneration after injury. For this belief I know no ground.
It should be remembered as an additional difficulty in the way
of this belief, that when the limb of a Crab or Lobster is injured
it is usually thrown off bodily, while the extra parts most often
spring from the periphery of the chela. But since, according to
Heixekex2, such mutilated parts are sometimes retained, this
must not be insisted on.

In the case of an ambulatory leg the surfaces may be named
as in an insect (without any suggestion that these names denote
true homologies between the surfaces so named). In describing
chelae I propose to use the following arbitrary terms. The border
upon which the dactylopodite articulates is the pollex-border, the
opposite border being the index-border. It should be noted that
in the Crab the pollex-border is superior, but in a Lobster3 it
is internal.

(1) Clear cases of Extra Parts in Secondary Symmetry.

A. Legs.

*808. Palinurus vulgaris : left penultimate ambulatory leg bore
two supernumerary legs (Fig. 180). Coxopodite of great width.
The basipodite had three articular surfaces as shewn in Figure 180,

1 Eosel von Rosenhof, Insekten-Belustigung ', 1755, in. p. 344.

2 Heineken, Zool. Jour. 1828—29, iv. p. 284.

3 It is worth noticing that in the chela of a Scorpion though a close copy
of that of a Decapod, the arrangement is reversed, the articulated pincer being
external.

chap, xxl] SECONDARY SYMMETRY : CRUSTACEA.

527

each bearing a complete leg. When seen by me the leg marked L'
was lost.

Normal tytl

Fig. 180. Palinurus vulgaris, No. 808. Left penultim ate walking leg. (After

Leger.)

*

I could not quite satisfy myself as to which of the three was
the normal, but it was clear that R' was in form a right leg and
that the other two were lefts. If the leg L' is the normal, it
has been pushed out of place by a pair of extra legs in Posi-
tion DAA, but if R' and U be the extra legs, then the most
anterior leg is the normal and has been pushed out of place by a
pair in Position VPP. For an opportunity of examining this
specimen, I am obliged to the courtesy of Prof. A. MlLNE EDWARDS.
Originally described and figured by Leger, M., Ann. Sci. Nut.,
ZooL, 1886, S. vii. I, p. Ill, PI. 6.

809. Lithodes arctica : 2nd leg on right side has terminal joint as
shewn in Fig. 181, II. If E be the normal then K and L are a pair in
Position Y, but if B! be the normal then R and L' are a pair in Position
D. Attention called to the sreat diminution in size of all three termi-
nations as compared with the normal (Fig. 181, I). Original description,
Herklots, J. A., Bijdr. tot J. h. Genootsch. Sat. Art is Mag., 1852, iv.
p. 37, PI. ; repeated Arch, neerl., 1870, v. p. 410, PI. xi.

810. Cancer pagurus : last left leg closely like last case [in Position
D]. Richard, Arch. Zool. exp., 1893, p. 102, fy.

811. Carcinus maenas : 2nd amb. leg as in Fig. 181, III. A pair of

528

MERISTIC VARIATION.

[part I.

compounded extra points in Position J). Duns, Proc. jR. PJiys. Soc.
Edin., ix. p. 75, PL

Fig. 181. I. Lithodes arctica, normal terminal joint of ambulatory leg.
II. Second right leg of No. 809. (Both after Herklots.) III. Carcinus mcenas,
No. 811, second ambulatory leg. (After Duns.) P, normal terminal point. P',
P", extra terminal points in Position D.

B. Chelate Appendages.

(a) Two extra dactylopodites and double extra index.

812. Eriphia spinifrons $ : specimen of unusually large size,
normal but for left chela shewn in Fig. 182, I and II1. The
chela bore normal left dactylopodite, LD, and index, LI ; also,
upon pollex-border the structures shewn. These consisted of two
dactylopodites, R'D, L'D, working opposite each other on a com-
pounded double index, R'l\ L'l, which had two toothed borders,
one for each of them. This is therefore a pair of chelae repeated
in Position D [if indeed the dactylopodite mark the dorsal surface].
Taken from Herklots, Arch, neerl., 1870., v. p. 412, PL XI.

1 In connexion with this case Herklots states that the rt. chela in the normal
is the larger and otherwise differs from the left (1 in 8 being reversed in this
respect). It does not seem from the figure that there was such differentiation
between the extra pair, but in future cases this point should be looked for.

chap, xxi.] SECONDARY SYMMETRY : CRUSTACEA.

529

813. Astacus fluviatilis : about 3 years old according to Sou-
beiran's (Camp. Rend. 1865, lx. p. 1249) account. Right chela ap-
parently deformed by injury or disease. Left chela had all normal

Fig. 182. I and II. Eriphia spinifrons, No. 812. I. A view of the left chela.
II. An enlarged view of the extra parts from the other side. LD, LI, normal lift
dactylopodite and index. R'D, L'D, right and left extra dactylopodites. R'l, LI,
right and left extra indices not separated from each other. (After Herklots.)

III. Cheliped of Homarus americanus, No. 811. (After Faxon.) I), I. normal
dactylopodite and index. D', D", extra dactylopodites. I', I", perhaps an
indication of double extra indices.

IV. Astacus fluviatilis, No. 813, left chela. L, normal left dactylopodite.
R'D, L'D, right and left extra dactylopodites. L'l + R'I, left and right extra
indices not separated from each other. (After Maggi.)

parts and in addition the structure shewn in Fig. 182, IV upon the
pollex-border of propodite. Here was a boss, separated by a
groove. It was observed that the structure was that of a rt.
and 1. dactylopodite working upon a double index [as in last
case]. Structure of muscles, fully described, was also in agree-
ment with the view that the extra parts were a complementary

B.

3-1

530

MERISTIC VARIATION.

[part I.

814

815.

pair [similarly in Position D]. Maggi, L., Rend. R. 1st. Lomb.,
1881, xiv. p. 333,^5.

Homarus americanus : small cheliped as shewn in Fig. 182,
III. It bears normal dactylopodite (D) and index (7), but this
part is bent almost at rt. angles. From the outer angle arise
the parts shewn. Apparently U and D" are a complementary
pair of extra dactylopodites in Position D. The piece I' + I'
is not described ; from the figure it seems possible that it may
represent parts of the indices proper to D' and D". Case given by
Faxon, Harv. Bull, 1880—1, vm. p. 261, PI. II. fig. 2.

Cancer pagurus : right chela as shewn in Fig. 183. This is a case
of some complexity. The figure will best make it clear. The dactylo-
podite D' is single and so also is the index P. D is a double dactylo-
podite, and F having teeth on two sides may be judged to be a double
index. But if D' and P are the normal chela they each stand opposite

Fig. 183. Cancer pagurus, No. 815. Eight chela seen from the apex, and
from the outside. The lettering is arranged on the hypothesis that 1)' is the
normal dactylopodite, P the normal index. D, the double extra dactylopodite,
P', small double extra index. (From Proc. Zool. Soc.)

the pincers to which they do not belong. Nevertheless I see no other
interpretation possible. (This case is curiously like that of the tarsal
claws in Rhizotrogus No. 786.) Specimen incorrectly described by
myself, P. Z. S., 1890, p. 581, fig. 2. C.

816. Cancer pagurus : right chela in a condition not far removed from r
that of the last case, le S£n£chal, Bull. Soc. Zool. France, 1888, p. 123,

figs-

817. Uca una: a chela having complex repetition of parts somewhat

as in No. 815. Jaeger, G., Jahresh. d. Ver. vaterl. JVaturk, 1851, xvn.

p. 35, PL i. figs. 12 and 13.

Perhaps of this nature is the case in Astacus fiuviatilis, Eoesel v. Kosenhof,
Ins.-Belust., in. Tab. L.x.fig. 28.

(b) Two extra dactylopodites arising from normal dactylo-
podite.
*818. To this and the next division belong the great majority of

chap, xxi.] SECONDARY SYMMETRY : CRUSTACEA.

531

cases of repetition of parts in Crustacea. Including examples
recorded by various authors and specimens in different Museums
there are nearly fifty cases of this class known to me.

Indjpx

Fig. 184. Three cases of two extra dactylopodites arising from a normal
dactylopodite. I. Left chela of Carcinus mamas in Brit. Mus. II. Left chela of
C. mcenas after Lucas, Ann. Soc. ent. France, S. 2, n. p. 42, PL I. Jig. 2. III. Right
chela of Homarus, after van Beneden, Bull. Ac. Belg., S. 2, xvn. p. 371.

Fig. 185. Cancer pagurus. Two chela? of the kind specified in No. 818,
described by myself in Proc. Zool. Soc, 1890, p. 581, whence figs, are taken.

34—2

532

MERISTIC VARIATION.

[part I.

The various simple forms taken are illustrated by the eight
cases shewn in Figs. 184, 185 and 186. It will be seen that when
such extra processes arise on the toothed border of the dactylo-
podite they turn their smooth borders to each other, but when

819

Fig. 186. Homarus americanus. Three chela whose dactylopodites bear double
extra dactylopodites. I. A left. II. A left. III. A right. R, normal right.
L, normal left. R', extra right. L\ extra left. (From Faxon.)

they arise on the smooth border they turn their toothed borders
to each other, thus fulfilling the conditions of the Scheme given
at p. 481. Though from the close agreement between the three
prongs in some of the specimens it is not always possible to
tell the normal dactylopodite with certainty, it will be seen that
in these the rules hold whichever of the two possible prongs be
supposed to be the normal.

Astacus leptodactylus : left chela has dactylopodite as
shewn in Fig 187, II. Presumably D is the normal pushed out
of place, and D' and D" are the two extra dactylopodites. They
are so placed that none meets the index. Karoli, J., Term.
Filzetek, 1877, i. p. 53, PI. II.

chap, xxi.] SECONDARY SYMMETRY : CRUSTACEA,

533

7?

I Jl

Fig. 187. I. Cancer pagurus, No. 820, right chela. Specimen in Coll. Surg.
Mus. II. Astacus leptodactylus, left chela, after Karoli.

820. Cancer pagurus : somewhat similar case in rt. chela (Fig. 187,
I) ; but here the normal, R, stands in its normal place. In Coll.
Surg. Mus.
•821. Homarus americanus : dactylopodite only of right chela
preserved. It is bent sharply downwards, out of the plane of
the " hand," and bears upon its upper surface two pairs of blunt,
toothed processes [probably being rudiments of two pairs of extra
dactylopodites]. Faxon, I.e., p. 261, PL II. fig. 1.

822. Homarus americanus : dactylopodite {a) bent upwards and
outwards, crossing index without meeting it (Fig. 188). From
the smooth border of dactylopodite arise two toothed processes

Fig. 188. Homarus americanus, No. 822, left chela, a, normal point of
dactylopodite. b, c, extra points. (After Faxon.)

(b and c) curving towards index. [I take it that this is some-
thing like the cases of Position A in Insects (p. 4M) but from
the original figure the relations cannot be quite decided.] Faxon.
I.e., p. 260, PI. I. fig. 15.

534

MERISTIC VARIATION.

[part I.

(c) Two extra indices arising from a normal index.
*823. This again is a fairly common form, though much less frequent

pi

Fig. 189. I. Right chela of Homarus americanas. R', L', right and left extra
indices not separated from each other. (After Faxon.) II. Homarus vulgaris,
right chela in Brit. Mus. III. H. vulgaris, right chela bearing extra double index.
R' and L', not separated. (After Lucas, I. c.)

R' V

i. n

Fig. 190. I. Left chela of Carcinus mcsnas, indices only shewn, d, place of
articulation of dactylopodite. In Coll. Surg. Mus. II. A similar case in
Homarus americanus, after Faxon. L, normal left index. R', L'y extra right and
left indices.

chap, xxi.] SECONDARY SYMMETRY [ CRUSTACEA.

535

than the last. The cases known to me amount to about ten
or fifteen. Seven cases are illustrated in Figs. 189, 190, and 191.

Fig. 191. Two cases of extra indices in Cancer pagurus. I. In Coll. Surg.
Mus. II. After le Senechal. R, normal right index. L, normal left. R', L',
extra rights and lefts.

(d) Simple processes, probably being rudimentary extra pairs

of indices or of dactylopodites.

*824. Many such are described, but of
few can anything be said with confid-
ence. A comparatively simple case
is shewn in Fig. 19:2, where there is
a decided suggestion that the process L'
+ R' is morphologically a pair of indices
that have not separated from each other
but stand compounded by their toothed
borders. On comparing this case with
for instance, Fig. 191, II, it will be seen
that the two conditions might readily
pass into each other in the way so often
seen in Insects.

Other cases of a more doubtful cha-
racter are shewn in Fig. 193. Though
in each the nature of the extra part is
obscure, it is probable that they are all
rudimentary states of the repetitions
described. The alternative view that

they are single repetitions certainly can-

,i i- j . n £ • ' ji„ mu puber from le Senechal. Bull.

not be applied to all, for m many the Soc/XlluL ,,,.„„,,, l888, m... p. 125.

extra process, though in the plane ot the L, normal index. L' + ll\ ?pair

index and dactylopodite, is similar on of extra indices in Position V.

Fig. 192. Left chela of Porta-

536

MEKISTIC VARIATION.

[part I.

m

Fig. 193. I. Eight chela of C. pagurus in Coll. Surg. Mus. E, right index.
II. Similar specimen whose dactylopodite bears x, a supernumerary process. In
Coll. Surg. Mus. III. Astacus fluviatilis, left chela bearing ,r, a supernumerary
process. EI, ED, right index and dactylopodite. (After Lucas.)

both its faces in this plane. There is however no doubt that the
distinction between these cases and true duplicity is hard to trace
and possibly enough it is not really absolute.

825. -A-s each case differs from the others I give a list of those not in private col-
lections1. The ? indicates that the case perhaps approaches the condition of
true duplicity.

D, dactylopodite. I, index.

Tiedemann, Meckel's Arch., 1819, v. p. 127,
PL u. Jig. 2.

Jaegek, G., Jahresh. Ver. vaterl. Naturk.,
1851, xvn. p. 35, PL i. fig. 7.

id., Meckel's Arch., 1826, p. 95, PL n. fig. 3.

Eosel v. Eosenhof, Ins.-Belust., in. p. 314,
fig. 31.

ibid., fig. 30.

Lucas, Ann. soc. ent. Fr., 1814, Ser. 2, n.
p. 45, PL i. fig. 6.

Faxon, Harv. Bull., vm. p. 259, PL i. fig. 11.

ibid., PL i. fig. 6.

Eichard, Ann. sci. nat., 1893, p. 106.

Coll. Surg. Mus.

Coll. Surg. Mus.

E, right. L,

left. .

Astacus fluviatilis

EI

? A. fluviatilis

EI

A. fluviatilis
A. fluviatilis

LD
EI

'.' A. fluviatilis
A. fluviatilis (Fig. 193, in.)

LI
LI

Homarus americanus
H. americanus
'? Cancer pagurus
C. pagurus (Fig. 193, i.)
C. pagurus (Fig. 193, n.)

LI

ED
LD
LI
LD

(e) Exceptional Gases.

*826. Homarus americanus : Right chela. Meropodite sub-
cvlindrieal instead of flattened ; peripherally divides into two
parts each bearing an articulated appendage as shewn in Fig. 194.
[The appendage R is a normal chela. What is B! + 1/ ? Faxon,
carefully describing the case, thinks that R! + U is a rudimentary
and reversed copy of R, and that the case is one of duplicity.
But from the particulars given, and especially from the circum-
stance that the carpopodite was " much more spiny ,; than the
normal, I think it likely that R' + U is morphologically a double
structure formed of a pair of carpopodites compounded together.

1 With these may perhaps be mentioned the following : Apus cancriformis,
having upon the 40th foot a second small flabellum shaped like the normal flabellum.
The bract was greatly reduced in size. Lankestek, E. E., Q.J. M.S., 1881, xxi. p.
350, PL xx. fig. 12. [In explanation of Plate the abnormal foot is called the 30th.]

chap, xxi.] CRUSTACEA : EXCEPTIONAL CASES.

537

Without having seen the specimen it is impossible to say much,
but the parts should be examined with a view to this possibility.
I conceive that the large spine marked by Faxon &p' stands on

1B' + L'

Fig. 194. Homarus americanus, No. 826. A right chela. (After Faxon.)

the morphologically middle line between the two extra half-

meropodites.] Faxon, Harv. Bull VIII. p. 262, PI. II. fig. G.

*827. Astacus fluviatilis $ : large adult. /.

Abdomen wide in comparison with

slender chelae: otherwise normal except

left chela. This was formed as in Fig.

195. All normal except carpopodite,

from which arose a fixed piece seeming

to be an extra misshapen carpopodite,

bearing three extra chelce, L', R and x.

[R! and L' are a clear pair of images L'

being right and left respectively. But

between R' and the normal L there is

the third extra chela x. As to the

nature of this nothing can be said.

Whether it is a left or a right cannot

be told from fig. So far as I know, Fk;. 195. A$tacu» fluviatilis $Ho.

this case is unique. Full description 82?, 1(,ft chela. /.. the normal. 7/ .
onj w,^nm,^,.^v,4.„ • • • • i L>', presumaMv extra right and lelt

and measurements given in original, oh^ *, exta-a chela of uncertain

q. V.] CANTONI, Rend. R. 1st, Lomb., nature. (After Cantoui.)

1883, xvi. p. 771,^.

538

MERISTIC VARIATION.

[part I.

C. Antenna}.

*82S. Palinurus vulgaris : right antenna bore three complete
filaments. So far as last spiny joint (merocerite) normal. Of
this joint the peripheral portion
much enlarged, presenting two
articulations. The most posterior
bore a normal carpocerite and fila-
ment (Fig. 196, 1). The anterior
articulation bore a double carpo-
cerite with two filaments (II and
III). As author points out, II is
structurally a left antenna. [By
the kindness of M. Alphonse Milne
Edwards I have been allowed to
examine this specimen. I am not
sure that I succeeded in correctly
determining the surfaces of the
extra antennae, for the basal parts
were not veiy fully formed ; but
according to my determination

their relations differed markedly „,«„„., . ,

r ,1 r f»j_i o l- j.* Fig. 196. Proximal parts of the right

from those of any of the Schematic antenna of PaUnurm vulgaris, No. 828.

positions, for while the position I, the normal. II, extra left. Ill, extra
of origin is VVA the two extra right- (After Leger0
antennae stand very nearly in the Position DA.]
sci. nat, ZooL, 1886, S. 7, i. p. 109, PI. 6.
*829. Astacus fluviatilis : exopodite of left
antenna (Fig. 197) bears two supernumerary
points, R' and L', which seem to have been
inserted upon the internal border of the
normal exopodite. Stamatt, G., Ball. Soc.
Zool. France, 1888, xm. p. 199,^.

Amorphous Cases.

As has been stated, there are many cases,
recorded or preserved, in which the nature of
the parts cannot be made out. The majority
of these are, I believe, injured or deformed
limbs, and not cases of repetition of parts.

Nevertheless of the latter class there are un- tiUs paving extra points to

, exopodite of left antenna. R,

doubtedly some amorphous cases, though they normal right. L, normal left.

are far less common than regular ones, even R', L', extra right and left.

as normal structures are more common in their (After Stamati.)

regular shapes than in a deformed state. I mention the following as

being, I think, the earliest record of abnormalities of this class.

830. Homarus : left chela having irregular process on inner border of

dactyl opodite, and two irregular processes on inner border of index.

[No description.] Bernhardus a Berniz, Miscell. Curios., Jena, n.

1671, p. 175, Obs. ci. PI.

L£ger, A

nn.

Fig. 197. Astacus fiuvia-

CHAPTER XXII.
Duplicity of appendages in Arthropoda.

That there should be such a thing as a limb double in the
sense in which the following are double, has always seemed to
me most strange. We know that a segment of an Annelid, or
a vertebra, may be on one side of the body divided to form
two segments or two vertebrae (as in No. 88 or No. 7) while
on the other side of the middle line the segment is single. This
is in keeping with all that we know of Division of parts in Linear
Series. So might we suppose that a parapodium, or a rib, or
perhaps a limb-bud might divide into two ; but the two half-
segments or half- vertebrae are in Succession to each other, and
are not complementary images of each other as these double-
limbs are.

That a parapodium may divide into two Successive para-
podia is possible enough, though, apart from division of the
segment bearing it, I know no clear case. But it may be stated
at once that in Arthropods and Vertebrates such a phenomenon
as the representation of one of the appendages by two identical
appendages standing in Succession is unknown. No right arm
is ever succeeded on the same side of the body by another arm
properly formed as a right, and no Crustacean has two right
legs in Succession, wThere one should be. The only cases at all
approaching this state are those of Macacus No. 504 (q. r.), a case
that must be interpreted with great hesitation ; and of the Frogs
described by Cavanna and by Kingslev, also doubtful cases
(see Chapter xxm).

But though such repetition is probably unknown and is perhaps
against Nature, there are still these strange double-limbs: fcwo
limbs, always I believe imperfect, placed not in Succession, but as
complementary images of each other, more or less exact. These
we have seen in the hand of Man and in the feet of Artiodactvles;
we have now to study them in Insects and in Crustacea1.

1 With mistrust I name cases in Amphibia and Fishes, perhaps of tin's nature.
Lissotrjton punctatus (Newt): left pes having 10 digits in two groups, ('» and 4.
Coll. Surg. Mas., Ter. Sei\. 293, a [not dissected]. Protopterus annectens : rt.

540 MERISTIC VARIATION. [part i.

On the morphology or significance of duplicity in limbs I can
make no comment beyond the few remarks given on p. 406.
It is just possible that in Nos. 832 to 834 the duplicity of the
chela or of the index is a division in the middle line of a Bilateral
Minor Symmetry ; for some chelae are peripherally very nearly
symmetrical about the plane of the dactylopodite and index.

In Arthropods double-limbs are no less rare than in Vert-
ebrates, for though in various works there are some scores of
cases to be found, the great majority may be safely rejected as
being almost certainly cases of double extra parts in Secondary
Symmetry having their duplicity disguised as we saw it in
Nos. 750, 764, or 801. By most of those who have dealt with
these things the possibility of disguised duplicity in the extra
part has been unheeded ; and ignorant of the special difficulties
of these cases they have thus set down specimens as examples
of duplicity of appendages at a casual glance. For this reason
therefore I shall only give particulars of those few cases which
are better established or otherwise of special interest, letting the
rest follow as a list of references.

It will not be forgotten that whenever an extra part is in
itself symmetrical it always may be a double structure, and the
special application of this fact to cases of extra filamentous an-
tennas must in particular be borne in mind.

Crustacea.

*831. Hyas araneus : a left chela having the form shewn in
Fig. 198, II and III. Fig. 198, I shews a normal left chela of
this species from the outside in the same position as II. In
the abnormal specimen the dactylopodite D is normal save that

pectoral fin double, the division being in a horizontal plane, so that the two filaments

were dorsal and ventral to each other [cp. No. 503]. Albrecht, Sitzb. Ak. Wiss.

Bed., 1886, p. 545, PL vi. Silurus glanis : extra fin attached to pelvic girdle and

partly to rt. pelvic fin. Warpachowski, Anat. Anz., 1888, in. p. 379, fig. Rana

esculenta : left hind foot double ; rt. not seen [a very clear case]. Ercolani,

Mem. Ace. Bologna, 1881, S. 4, in. p. 812, PI. iv.fig. 11. '

In Kaiidae a group of cases of extra fin are known. They are upward projections

from the dorsal surface near the middle line. They are often spoken of as " dorsal ':

7902
fins, but in the only case I have seen (Paris Mus. N. H., —^ , kindly shewn me by

Prof. L. Vaillant) the attachment is not really median but is slightly oblique, and
seems, from external examination, to spriug from some part of the pectoral girdle
('? left scapula). See Lacepede (who named such a fish "Raja cuvieri"), Hist. not.
des Poiss., 1798, i. p. 141, PL vn.; Neill, Mem. Wern. Soc., 1808, i. p. 554;
Moreau, Poiss. de la France, 1881, i. p. 206. In these fishes the real dorsal fins
were in the proper place (though in some species they may be far forward, Forskal,
Descr. Anim. in itin. Orient., 1775, i. p. 18). This repetition is of course quite
distinct from that other curious and also Discontinuous variation in which the
pectorals are partly divided into two lobes (R. clavata, Yarrell, Brit. Fish., eel.
Richardson, 1859, ii. p. 585) ; or are separated from the head so as to project like
horns on either side, as in last case ; and also in R. clavata, Yarrell, ibid. ; p. 384 ;
Day, Brit. Fish., n. p. 345, PL clxxi. fig. 2; in R. batis, Day, l. c., p. 337; in
R. asterias, Bureau, Bull. soc. zool. France, 1889, xiv. p. 313, fig.

chap, xxn.] DOUBLE APPENDAGES : ARTHROPODA.

541

its point is rather worn. Where the index should be, there is
a great eminence, bearing apically a second articulated dactylo-
podite D\ complementary to D. Between the two dactylopodites

Fig. 198. Hyas araneus. I. A normal left chela. II. The left chela of
No. 831 from the outside. III. The same from the inside. D, normal dactylo-
podite. D', extra dactylopodite. j, normal index, f, a small index toothed on
both sides. (In Brit. Mus.)

at the inner side of the eminence there is a fixed short process,
j', which is toothed upon both the edges which it presents to
the two dactylopodites. Round the articulation of 1)' are setae
like those round the place of articulation of D. Specimen in
Brit. Mus., kindly shewn to me by Mr R. I. Pocock.

832. Cancer pagurus : right chela.
Dactylopodite and index each double
in the way shewn in Fig. 199. Each is
toothed on the side presented to the
other half-pincer. Note that there is
no proof that one or other of these
points is not a pair compounded in
Position A or P, but since both seemed
equally to diverge from the normal plane
of the propodite this is most unlikely.
Specimen in Museum of Newcastle-
upon-Tyne.

833. Homarus americanus : right chela
shewn in Fig. 200, I. Two dactylo-
podites separately articulating. Index
bifid at apex and bearing two rows of
teeth, one on each edge. Dactylopod-
ites did not meet index. Faxon, Harv.
Bull, vin. p. 260, PL I. fig. 13.

834. ? Hyas sp. Right chela. Dactylopodite single and in normal
plane. Two separate and similar indices, each toothed as usual,

Fig. l'J'.l. Ki-ht i-h. hi of
Cancer pagurus, No. 832. I>\
D2, two partially Beparate
dactylopodites. I1, 1-, two
partially separate indices. (In
Newcastle Mus.)

542

MERISTIC VARIATION.

[part I.

Fig. 200, I. Homarus americanus, right chela, No. 833. (After Faxon.)
II. Lupa dicantha, left chela, No. 836. LI), LI, left dactylopodite and index.
x, supernumerary index. (After Lucas.)

making angle of about 45° with each other. This angle almost
exactly bisected by the plane in which dactylopodite moves.
Bell Collection, Oxford.

835. Maia squinado : from inner side of base of
index of right chela arises a second index as
shewn in Fig. 201. It is about half as large as
the supposed normal index. The latter is dis-
placed outwards. Dactylopodite moves in ap-
proximately normal plane, missing both indices
and falling between them. Specimen kindly lent
by Prof. C. Stewart.

Fig. 201. Right chela of Maia squinado, No. 835.
The following are cases very similar to Nos. 834 and 835.

836. Lupa dicantha, left chela (Fig. 200, II). Lucas, Ann. Soc. eat.
' France, 1844, S. 2, II. p. 43, PI. i. fig. 1.

837. C. pagurus, right chela, 2 cases, le Sknechal, Bull. Soc. Zool.
France, 1888, xm. p. 125, Jig. 2.

838. Xantho punctulatus, left chela (Fig/ 202) in which the index
divided at about its middle to form two similar and equally diverging
blunt processes. Herklots, Arch, neerl, 1870, v. p. 410, PI. x.

839. Homarus americanus : right chela bearing an extra index.
Dactylopodite does not meet the normal index. [Very doubtful if of
same nature as foregoing cases.] Faxon, I.e., PL I. fig. 14.

The following cases are exceptional.

840. Homarus vulgaris : right chela has coxopodite single ; but basi-

chap, xxil] DOUBLE APPENDAGES : ARTHROPODA.

543

Fig. 202. Xantlw punctulatw. Two views of left chela of No. 838, shewing the
division of the index. (After Herklots.)

podite is wrinkled and has two apical articulations, each bearing a small
chela ; both are soft and not calcined, having articulations indicated
by furrows only. [No information as to planes.] Richard, Ann. Sci
Nat., 1893, p. 106.

841. Homarus americanus : right chela having a short articulated
process below the dactylopodite moving in plane at right angles to it.
[?a double structure]. Faxox, Haw. Bull., viii. PI. i. fig. 12.

842. H. americanus : toothless process articulating beloiv dactylopo-
dite, moving in plane at right angles to its plane of motion. It articu-
lates upon a separate process given by the propodite. [It is difficult
to suppose that this extra process can be double.] Faxon, I. c , PI i
fig. 16.

Mr G. Dimmock of Canobie Lake, N. H. has kindly sent rue word of a Gelasimus
having a chela of very anomalous form. Both index and dactylopodite are said to
have been bifid, but the plane of division was at right angle* to the plane of the
dactylopodite and index, so that all four points were in one plane. This specimen
has unfortunately been destroyed ; but Mr Dimmock tells me that the arrangement
was certainly thus, and that the unusual difficulty of bringing this case into agree-
ment with others was recognized in examining it.

INSECTS.

Among the following 110 cases which all either have been
or might be called cases of " duplicity ,J of legs, antenna-, or
palpi, there is, I think, not one clear case of unmistakeable
duplicity, such as for instance those of the chela? in Nos. 831
or 832. They should thus be considered as cases in which bhe
extra parts have not been or cannot be shewn to be double,
rather than as examples of proved duplicity of normal appendag 3.
In every case that I have myself properly examined, it is either
possible to prove the duplicity of the extra parts; or else essential
features {e.g. spurs &c.) by which a right appendage may be
told from a left are wanting. Nevertheless the few straight-
forward cases of double-limbs in Crustacea k«-i-j» one alive to the
possibility that some of these also may be the same. The most
probable cases of true duplicity of limbs are Nos. 844, JS40 and 85 I .

544

MERISTIC VARIATION.

[part I.

*843. 1. Legs.

Prionus californicus (Longic.) : each femur bore two tibiae
and tarsi : both maxillary palps and also the left labial palp were
partially double (Fig. 203). [No statement as to right labial
palp. This shewn in fig. much thicker than left, but on com-

S44.

Fig. 203.
Jayne.)

Prionus californicus, No. 843, having extra legs and palpi. (After

paring with a specimen it seems to be of normal thickness.]
In some of the legs the two tibise are compounded at their bases,
in others they articulate separately. [Several details given ; and
in particular, enlarged views of the palpi and of the bases of
the tibiae. But as no details are given regarding the apices and
apical spurs of the tibia3 nothing can be said as to symmetry.

It will be remembered that we have already had a case of
a Prionus, No. 750, which similarly was supposed to have two
of its legs double ; but there by means of the tibial spurs it was
shewn that the extra part was in Secondary Symmetry. Possibly
enough the same could here be shewn. It is much to be hoped
that this specimen can be traced.] Jayne, H. F., Trans. Anier.
Ent. Soc.y 1880, viii. p. 159, fig. 12.

Allantus sp. (Tenthred., Sawfly) : extra leg borne by coxa
of right middle leg. This coxa is imperfectly double, bearing
two separate trochanters. Of these the anterior bears a small
leg which, though ill formed, is complete in all its parts, but
has the tarsal joints of abnormally small size. The posterior
trochanter bears a leo; of full size. Its femur curves forwards

and then backwards. The femur of the smaller

curves

for-

chap, xxil] DOUBLE APPENDAGES : INSECTS.

545

wards, but its tibia curves backwards. The femora are so twisted
that I failed to determine the symmetry of these 1<-l;s ; and while
it was clear that neither was a normal left it was equally doubtful
whether either was shaped as a right. Of all cases in Insects
this is one of the nearest to the condition of true duplicity. Hope
Collection, Oxford.

845. Carabus intricatus : middle right femur is partially bifid, pre-
senting two apices in the same horizontal plane. The anterior apex
bears a tibia and tarsus of nearly normal form. The other apex bears
a tibia and tarsus of full length but much more slender than a normal
one. This leg was ill-formed. The tibia bore no spurs, and there
was no indication as to its symmetry, and nothing shewed that it was
a right or a left leg. It is stated in the original description that the two
legs could be separately moved and that both assisted in locomotion.
Originally described by Mocquerys, Col. anorm., p. 45, ^y.

f846. Melolontha vulgaris : right anterior leg divided to form two
legs. The femur dilates in peripheral third to form two apices, each
bearing a tibia. These two tibiae are at right angles to the femur and
are together in the same straight line, the one pointing forwards and
the other backwards, each tibia turning its ventral or flexor surface
towards the femur. The anterior tibia carries a tarsus of 4 joints
with claws, while the posterior tibia lias a normal tarsus of live joints.
For a figure of this specimen and particulars concerning it I am in-
debted to Professor Alfred Giard.

847. Leptura testacea (Longic.): in tarsus
of left middle leg the 2nd joint presents two
apices (Fig. 204). The posterior bears normal
3rd and 4th (terminal) joints with a proper
pair of claws. The anterior apex bears a
narrow7 3rd and 4th joint, the latter having
only a single median claw [cf. No. 848].
Kraatz, Deut. ent. Zt., 1876, xx. p. 378,
fig. 14.

848. Tetrops praeusta (Longic.) : right
anterior femur widened towards apex, which
presents two articulations in same horizontal
plane. Each of these bears a tibia. The post-
erior tibia and tarsus are complete in all
respects, but they flex downwards and back-
wards. The anterior tibia has a normally
4-jointed tarsus, but the apical joint bears
only one claw, and there is no sign of muti-
lation [cp. No. 847]. Were it not for the
closely similar case of Silis No. 764 there
would be no reason to doubt that this is
a true case of duplicity, but that example

shews how masked may be the doubleness of extra parts ; and though
I could not prove either of these legs to be double I feel no certainty
that one of them is not double. Specimen very kindly lent for descrip-
tion by Mr F. H. YVateruouse.

b. 35

Fig. 204. Leptura tes-
tacea, No. SIT. Tarsus of
left middle Leg from the
plantar surface. (The pro-
perty of Dr Kraatz.)

546 MERISTIC VARIATION. [part i.

849. Chlaenius holosericus (Carab.): left anterior tibia enlarged and
dividing close to base into two branches of similar form and length
[curving towards each other], botli equally furnished with hairs and
bearing spines characteristic of the species. Anterior branch bears a
complete tarsus like that of a leg of the other side, but posterior branch
bears only one tarsal joint. Camerano, Atti Ac. Sci. Torino, 1878,
xiv. fig.

850. Brachinus crepitans (Carab.): 3rd joint of right posterior tarsus
enlarged ; 4th joint divides to form two apices (Fig. 205), each bearing-
separate 5th joint in same horizontal plane. Each of these has a pair

*.Q^

Fig. 205. Eight hind foot of Brachinus crepitans, No. 850. A, anterior.
P, posterior. E, the supposed normal right apex. (In Rouen Mus.)

of claws curving ventralwards. The two apical joints are not identical,
the anterior being the shorter and continuing the general direction of
the tarsus. I could not determine the symmetry. When examined by
me the specimen was intact, but in cleaning it I broke this abnormal
leg. First described by Mocquerys, Col. anorm., 1880, p. 63, fig.

The two following cases differ from the rest in that the extra
leg arose from the body separately from the normal leg. Among
the cases of extra limbs in Secondary Symmetry were a few in
which the coxa of the extra limbs was in the same socket as
the coxa of a normal leg, though not united to it ; but in the
first, and perhaps in both of the two cases that follow, the extra
leg was wholly separate. The first case, No. 851, is the only one of
the kind that I have seen.

*»^

851. Tenthredo ignobilis (Tenthred., Sawfly) : extra leg arising from
2?rothorax, on the left side of the body, at some distance behind the
proper left anterior leg. Behind the anterior legs the prothorax of a
normal specimen presents ventrally an elevation on each side of the
middle line ; the point of origin of the extra leg is about halfway
between this elevation and the socket of the coxa of the normal left
anterior leg. The specimen had been a good deal injured by being-
pinned very nearly through the point of origin of the extra leg, and on
relaxing the specimen and attempting to restore the parts to their
former positions I unfortunately broke off the extra leg from the
body1. The leg is fairly well formed, but is a little shorter and a good

1 The specimen has been mended as nearly as possible in the position originally
occupied by the leg. As it may pass hereafter into other hands, it may be well to

chap, xxii.] SUPPOSED CASES OF DOUBLE LEG.

54'

deal more slender than the normal anterior leg. Owing to the slighl
degree to which the anterior legs of this insect are structurally differen-
tiated from the middle legs, it cannot be positively stated that the
extra leg is in form an anterior or a middle leg, but in size and general
conformation it approaches very nearly to that of an anterior leg. It
is complete in all its joints, having normal ciliation and claws, but the
spurs are entirely absent from the apex of the tibia and probably have
never been formed. This is an unfortunate circumstance; for, ina
much as the anterior spur of a normal anterior tibia in this specie- is
markedly differentiated from the posterior spur, it would have been
easy to determine the surfaces of this leg had the spins been present.
As it is, the matter cannot be positively decided, and it must sutlice to
say that the general form of the leg and the shape and curvat are of its
joints are such as to make it appear to be fashioned as an anterior leg
and as a leg of the side upon which it occurs, namely, the left. This
specimen was most kindly lent for description by Mr C. W. Dale, of
Glanville's Wootton, Dorsetshire. It is the specimen mentioned in
Ann. and Mag., 1831, iv. p. 21.
352. Elater variabilis (Elat.): complete extra leg articulating by
separate coxa close to right anterior leg. Germar, E. F., May. cU r
Ent., II. p. 335, PI. i. fig. 12. [This case has been copied by many
authors. The figures represent the right fore leg and the extra one as
normal right legs, but they are not sufficiently detailed to give con-
fidence that this was so. If the specimen still exists it is to be hoped
that it may be properly described.]

o ko This is a list of all remaining cases in which it is in any way possible that there

is duplicity of a leg. The point of origin is shewn approximately.

* , seen by myself. J, partly amorphous or mutilated. 0, no description.

R, right. L, left, tr., trochanter, f, femur, tb, tibia, ts, tarsus.

* % Osmoderma eremita1 (Lamell.) L 1. c.

Mallodon sp. (Longic.) R 3. c.

Pasimachus punctulatus (Carab.) L 2. tr.

Broscus vulgaris (Carab.) R 1. tr.

Agonuxn sexpunctatum (Carab.) R 3. f.

% Carabus septemcarinatus £ R3. f.

J Carabus nemoralis L 3. f.

Carabus creutzeri ? L 1. f.

Procrustes coriaceus'2 (Carab.) R3. f.

IVIeloe coriaceus (Het.) L 1. f.

0 Carabus helluo R 1. f.

0 Trichodes syriacus (Cleriche) R 1. f.

X Chrysomela haemoptera (Phyt.) ? 3. f.

1— ii.

Mocquerys, Col. anorm.,

p. 40, fig.
ibid., p. 50, fig.
Jayne, Trans. Amer. Ent. Soc.,

1880, yiii. p. 150, PI. iv. fig. I.
Imhoff, Ber. Vale nut. Get.

Basel, 1838, in. p. 3.
Schneider. Jahresb. scJdes. (?< -.

vaterl. Kultur, I860, p. L29.
Kraatz, Dent. cut. Zt., 1*77. xxi.

p. 57, PI. i.fig. 32.
Otto, Herm., Term.fuzetek, 1*77,

i. p. 52, PI. ii.
Kk.vatx, /. c, fig. 31.
MOCQUEBYS, /. «'., )'. ">■">. fig.
Staxnius, Mail. A n-li. . I wit.I'h >/■<..

1835, i>. 3( >!'>,. //'.</. 11.
Rey, Ann. Soc. Linn. <l, Lyon,

1882, xxx. p. 123.
ibid.
Curtis, Brit. Ent., PI. 111,.//'//. 5*.

state explicitly that there was no conceivable doubt as to the genuineness of the
abnormality. When received by me it was absolutely natural an. I had not been in
any way mended.

1 Probably this is the specimen mentioned byBELLiER DB LA Ohavionebie, lUill.
Soc. ent. France, 1851, S. 2, ix. p. lxxxii.

2 See also Klingelhofer, Stet. cut. At., 1844, v. p. 330.

35—2

548

MERISTIC VARIATION.

[part I.

Jayne, I.e., p. 157, PI. vr.fig. 7.
Krause, Stet. ent. Zt., 1871,

xxxn. p. 136.
Perty, Mitth. not. Ges. Bern,

1866, p. 307, fig. 6.

MOCQUERYS, I.C., p. iS,jig.

Kraatz, Dent. ent. Zt., 1877, xxi.

p. 56, PI. i. Jig. 11.
Otto, Herm., I. c., 1877, i. p. 52,

PI. ii.
Kraatz, Dent. ent. Zt., 1880, xxiv.

p. 344.
Mocquerys, I.e., p. 49, Jig.
Lent by M. H. Gadeau de Ker-

ville1.
Ragusa, Nat. Sicil., i. p. '281,

fig.

Lent by Dr Mason.
Mocquerys, I.e. , p. 60, Jig.
Ann. and Mag. N. H.,'l829, n.

p. 302, fig.
Bassi, Ann. Soc. ent. France, 1834,

S. 1, m. p. 375.
von Heyden, Isis, 1836, ix.

P. 761.
ibid.

X CMaenius diffinis (Carab.) L 2. tb.

Rhagium mordax (Longic.) R 2. tb.

Agabus uliginosus (Dytisc.) R 3. tb.

* J Acanthoderes nigricans (Longic.) L 2. tb.

Colymbetes adspersus (Dytisc.) <? L3. tb.

$ Procrustes coriaceus (Carab.) R3. tb.

J Carabus melancholicus <? R3. tb.

* £ Tenebrio granarius (Het.) L 3. tb.

* j Calosoma auropunctatum (Carab.) Rl. tb.

0 Silpba granulata (Clav.) R3. tb.

* Philonthus succicola (Staph.) R 3. ts.

* J Telephorus excavatus (Mai.) R 2. ts.

Chlacnius vestitus (Carab.) L2. ts.

0 Telephorus fuscus (Mai.) ? 2 ?

0 Prionus coriaceus (Longic.) ?

0 Prionus sp. (Longic.) ? ? f.

2. Antennae.

The remarks made in preface to the last section apply here
also, and with additional force from the consideration pointed out
(p. 513), that many antennae are without obvious differentiation
between their anterior and posterior surfaces. As Kraatz has
pointed out, it is especially in such forms as Lamellicorns or
Lucanidae that extra antennas are found double, and I think there
is an obvious inference that this greater frequency in them is due
to the fact that the two borders are so markedly differentiated
that the duplicity cannot easily be disguised. I have sometimes
fancied too that perhaps the existence of this great differentiation
between the two borders may actually contribute to the physical
separation of the two extra parts in the Positions A and P and
thus prevent that masking of the duplicity which is seen for
instance in Navosoma No. 801.

However this may be, special importance must be attached to
the few cases in Lamellicorns, Lucanidas and the like, where there
seems to be a single extra part, making that is to say a duplicity
of the antenna. Cases of this kind that I have myself seen I
therefore treat more fully, and it may be stated that in none of
them is there anything that can be called clear duplicity. In
many on the contrary the extra part is nearly cylindrical, and
thus symmetrical in itself. Hence it may possibly be morpho-
logically double. Of the remainder I can give no confident
account. For as has been said, though many, e.g., Zonabris
^-punctata (in No. 858), do look very like cases of true duplicity

1 Originally described by Fleutiaux, Rev. d'Ent., 1883, p. 228.

chap, xxii.] SUPPOSED CASES OF DOUBLE ANTENNA. 54'.)

I feel no certainty that they are so. Nothing but careful micro-
scopical examination can shew this, and it would in every case
be necessary to begin by fixing upon some definite character
differentiating the anterior from the posterior border in the

normal antenna.

In the majority of cases one of the branches has Less than the
normal number of joints.

Special attention is called to No. 854, for in it is seen not only
an extra branch, but an extra joint in the course of the chief
antenna.

N.B. At the end of this list I have set three cases of extra
antenna arising from the head.

*854. Lucanus cervus g (Lucanidae) : left antenna normal, practi-
cally same as that described for Odontoiatria No. 799. I light
antenna shews a rare condition. Scape and 2nd joint normal.
Then follows a piece as long as the 3rd, 4th and 5th joints of a
normal, together. This joint has a complex form. It has no trans-
verse division and is clearly one segment from base to apex, but
the posterior border is divided from the anterior by an irregular,
crescentic suture, giving it the look of two joints spliced together.
The posterior portion gives origin to a small, backwardly directed
branch made up of two nearly spherical joints, the apical having
a minute depression whence a fragment may have been broken.

The long third joint just described bears at its apex the rest
of the antenna, which is abnormal in structure and diverges a
little forward of the normal direction. In the normal there are
only 7 joints peripheral to the 3rd, making 10 in all: here
there are 8, making 11 in all. The four apical flattened joints
are normal, but the joint preceding them (7th in this antenna)
is more produced on the anterior border than in the normal,
and it is thus in form almost intermediate between a funicular <ni</
a lamellar joint. The other three are simple funicular joints.
For this singular specimen I am indebted to the kindness of
M. Henri Gadeatj de Kerville.

855. Nigidius sp. (Lucanidae) New Guinea: the second joint of
the right antenna bears a small supernumerary three-jointed
branch directed forwards and upwards. The terminal joint of the
branch, which morphologically stands fifth from the body, bears
a long hair of the kind which is borne in the normal antenna only
by the seventh and subsequent joints.

There appears to be no deformation in the normal antenna in
correspondence with the presence of this extra branch. The (tui-
tion of the antenna with reference to the second joint is a little
altered, but it is not in any other way changed. This specimen
was kindly lent to me by M. Henri Gadeau de Kerville.

856. Lucanus cervus J* : the second (1st funicular) joint of the
left antenna bears a four-jointed, pointed filament. The lower

550

MERISTIC VARIATION.

[part I.

parts of the head on the left side are also greatly deformed.
Vox Heydex, Deut. ent. Zt, 1881, xxv., p. 110, fig. 24.

857. Melolontha vulgaris (Lamell.) : from ventral surface of
2nd joint of left antenna a separate joint projects vertically down-
wards. This joint bears a forward ly-directed process which is
about as long as a normal club and is imperfectly divided into
lamellae. Nothing could be definitely determined as to the
symmetry of this structure. Originally described by MoCQUERYS,
Col. anorm., p. 22, Jig.

858. In this list * means that 1 have seen the specimen, $ that it is partly amorphous
or mutilated, 0 that there is no description. The number is a rough indication of
the joint from which the extra part arose.

113.

* J Cicindela sylvatica (Cicind. )

Cararid^e

Carabus sylvestris <?

C. auratus

ditto

ditto

C. italicus

C. exaratus

C. intricatus

C. emarginatus ?

C. cancellatus

C. catenulatus <?
Pterostichus planipennis ?
Procrustes coriaceus J

ditto ?

Harpalus calceatus ?
Calosoma sycophanta
C. triste

Anchomenus albipes

Mus. H. Gadeau de Keryille.

+

* A. angusticollis
0 Nebria sp.
Agonum viduum

J Ditomus tricuspidatus

Colymbetes coriaceus (Dytisc.)

Thylacites pilosus (Rhyn.)

* Rhynchitcs germanicus (Rhyn.)

Cryptophagus scanicus ? (Clav.)
C. dentatus

0 Monotonia quadricollis (Clav.)

Chrysomela cacalicc «J (Phyt.)

Adimonia tanaceti (Phyt.)

R8.

L8.

8.

L5.

9.

L2.

Kraatz, Dent. ent. Zt., 1877, xxi.
p. 55, fig. 9, and Sartorius, Wien.
ent. Monats., 1861, v. p. 31.
R2. ibid., fig. 8.

R5. Doumerc, Ann. Soc. ent. Fr., 1834,
S. 1, in. p. 174, PI. i.
Perty, Mitth. nat. Ges. Bern, 1866,

p. 307, fig. 4.
Gredler, Corr.-Bl. zool.-min. Ver.

Regensb., 1877, xxxi. p. 139.
ibid.

Ann. and Mag. N. H., 1841, p. 483.
von Heyden, Deut. ent. Zt., 1881,
xxv. p. 109,^.
R 10. 1 Sartorius, Wien. ent. Monats. , 1858,
LlO.j ii. p. 49.
L 8. Brit. Mus.

Kraatz, I.e., p. 56, fig. 17.
ibid., fig. 10.
ibid., 1881, xxv. p. 112.
ibid., 1877, xxi. p. 57, fig. 24.
Gredler, /. e. , 1858, xn. p. 195.
R 6. Jayne, Trans. Amer. Ent. Soc., 1880,

viii. j3. 155, PI. rv. fig. 1.
L 10. Mocquerys, Col. anorm., 1880, p. 17,

fig.

ibid., p. 10, fig.

Gredler, 1. c., 1869, xxiii. p. 35.

von Heyden, Deut. ent. Zt., 1881,

xxv. p. 109, fig. 19.
ibid., fig. 18.

R9.
L7.
5.
R9.
L9.

R8.

?

R6.

R8.
R5.

L.
R10.
L 9.

R9.

L3.

R.

L7.

L5.

Lucas, Ann. Soc. ent. Fr., 1843,

S. 2, i. p. 55, PL
Kraatz, I. c, 1876, xx. p. 378, fig.

Lent by Dr Mason.

Kraatz, /. c. , 1877, xxi. p. 57, fig. 25.
Sartorius, Wien. ent. Monats.,

1861, v. p. 31.
Rey, C., Ann. Soc. Linn, de Lyon,

1882, xxx. p. 424.
liKrz~SER,Jahresb.schles. Ges. vaterl.

Kultur, 1855, p. 106.
Schneider, ibid., 1860, p. 129.

chap, xxii.] SUPPOSED CASES OF DOUBLE ANTENNA, 551

Heteromera

X Sepidium tuberculatum
Zonabris quadripunctata

Eleodes pilosa
* Blaps chevrolati
B. cylindrica
B. similis
Akis punctata

LONGICORNIA

0 Prionus1 sp.
Aromia moschata

ditto

* ditto

X Cerambyx cerdo ?
X C. scopolii '
X Lamia textor

* X Strangalia atra

S. calcarata

* X Solenophorus strepens-

Clytus arcuatus
Hammaticherus heros

Callidium variabile

L5. Pebty, /. e., jig. 10.

LG. Kbaatz, l.c, L889, xxxm. p. 221,

fig. 14.

B 9. Jayne, /. <■., p. 161, fig. 13.

L 7. Miimh i.k, s, /. <•., p. 11, jig.

L 3. i6fd., p. 6, fig.

II H. von HeYDEN, /. c, p. lO'.t. fig, 22.

L3. Baudi, /.'////. Sioc. ent. //<//., 1877,
ix. p. 221, fig.

10. J/o/. and Man. N. II., 1841, S. 1,

p. 483.
6. Kbaatz, /. c, 1889, xxxm. p. 221,

fig. 15.

R2. Mocquebys, /. c, p. 18,.//'//.

L 5. Lent by Mr Janson.

L6. von Heydkn, /. c, p. 10!), .//'</. 23.

R3. Kraatz, /. c, 1877, xxi. p. 56, fig.

L 1. Smith, P., Zuol., vi. p. 2245.

LI. Mocquerys, /. c, p. 14, fig.

? Gredler, /. c, 1858, xii. p. 195.

K2. Mocquerys, /. c, p. I'd, jig.

R5. von Heydkn, ////. 21.

L 7. Klingelhofi.i;, Stef. ent. Zt., 1844,

v. p. 330.

L3. Mocquerys, I. c, p. 24, j'uj.

Lycus sp. (Mai.)
* Telephorus lividus (Mai.)

T. rotundicollis
0 E later hirtus (Elat.)

LI. von Heyden, I. c, p. 109,.////. 17.
L2. Lent by Mr F. H. Watebhouse.
R2. Jayne, I. c, p. 159, fig. 11.
9. Eassi, Ann. Sue. cut. Er., 1*34,
S. 1, in. p. 375.
R6. Kawall, Stet. ent. Zt., 1858, xix.

p. 65.
L6. Westwood, Proc. Linn. Soc., 1847,
i. p. 34(3.
IVIacrognatlius nepalensis (Lucan.) R3. Kraatz, /. c, 1880, xxv. p. 342.

fig. 10.
Julodis clouei (Bupr.) R5. Buquet, Ann. Soc. ent. Fr., 1843,

S. 2, i. p. 97, PI. iv.

Extra antenna arising from the head.

Ampedus ephippium (Elat.)
Chiasognathus grantii (Lucan.)

*

859. Callidium violaceum ? (Longic.) li.

Saperda carcharias (Longic.) L.

* Cerambyx cerdo (Longic. ) L.

von Roder, /•.'///. Sarlir., 1888, xiv.

p. 219.
Bitzema Bos. Tijds. r. Ent., 1879,

xxii. p. 208, PL
Kbaatz, Pent. ent. Zt., lss«», xxxm.

p. 222,.////. 23.

3. Palpi.

Subject to the reservations made in regard to instances of
duplicity in antennae, &c, the following examples of supposed
duplicity in palpi are given.
*860. Nebria gyllenhalli £ (Carab.) : maxillary palps abnormal.

1 I suspect that this is Navosoma No. 801.

2 Doubtless the specimen mentioned by Ltcas. Hull. Soc. ent. France, 1848,
S. 2, vi. p. xix.

552 MERISTIC VARIATION. [part i.

Fig. 206, I, shews the normal form of a right maxillary palp.
Fig. 206, II, represents the right palp of this specimen. The 1st
and 2nd joints are much thickened and the latter has 8 hairs
(instead of 4) and two apical articulations, the anterior bearing

Fig. 206. Nebria gyllenhalli, No. 860. I. Normal right maxillary palp.
II. Right palp of this specimen. III. Left palp of the same, m, terminal
membrane. (The property of Dr Kraatz.)

an apparently normal terminal joint, the posterior bearing a
symmetrical piece ending in a sharp point with no membrane like
that at the apex of the normal. The left palp of this specimen is
shewn in Fig. 206, III. In it the 2nd joint has 8 hairs instead of
4, and the terminal joint though very much enlarged is not
divided at all. For the loan of this specimen I am indebted
to Dr G. Kraatz who first described it in Bed. ent, Zt, 1873,
xvii. p. 4s33,fig. 12.

861 . Carabus splendens : penult, jt. of 1. labial palp enlarged, and bearing two nearly
similar jts. [broken before seen by me]. Mocquerys, /. c, p. 29, fig.

862. C. auratus : 1st. jt. of 1. maxillary palp bears two similar branches at rt. angles
to each other, each with two jts. [Specimen not seen.] Mocquerys, /. c, p. 30, Jig.

863. C. purpurascens : extra labial palp on 1. side. [Specimen not seen.] Moc-
querys, I.e., p. '62, fig.

4. Mandibles.

864. Lucanus. Three cases are recorded in which one of the
mandibles bore an extra process of considerable size. Whether
any of these are examples of duplicity, or whether the jaw, mor-
phologically single, has in them varied towards a state of greater
complexity, cannot well be said. The cases are L. cervus ^ ,
Mocquerys, I. c, p. 106 [figure fairly true]: L. cervus J,
Kraatz, Beat. ent. Zt,, 1881, xxv. p. Ill, fig. ; L. capreolus J y
id., I. c, 1876, xx. p. 378, fig.

CHAPTER XXIII.
Secondary Symmetry in Vertebrates.

Remarks on the Significance of Repetitions in Secondary

Symmetry: Units of Repetition.

The evidence as to repetition of appendages in vertebrates
is of great extent and has been studied by many, but in tin-
morphology of these repetitions there is still much that is ob-
scure. Speaking generally, the phenomena are similar to those
seen in Arthropods, but there is no approach to the same regu-
larity. Nevertheless when two extra limbs are present, it is
usually possible to recognize that they are together a comple-
mentary pair; and if the extra part is apparently a single limb
it is, I believe, never a normal limb and may very often be
shewn to contain parts of a pair of limbs. The fact that the
geometrical relations of the parts are less regular than they are
in Arthropods may probably be ascribed in some measure to the
circumstance that the surfaces of the vertebrate limbs do not
maintain their original relations but are more or less rotated in
the course of their development.

In Insects it appeared that repetition of the peripheral parts in
Secondary Symmetry was not much more common than repetitions
of whole limbs, but apparently this is not the case in vertebrates.
Perhaps it would be more true to say that in vertebrates it i^
only in those extensive repetitions which include the greater
part of the limbs beginning from the girdles, that the parts
are clearly in Secondary Symmetry. From this circumstance
doubt suggests itself whether some of the phenomena of poly-
dactylism, at present regarded as repetitions »»i' digits in Series,
may not really be of the nature of Repetitions in Secondary
Symmetry (see p. 378). But however this may be, there are,
with the exception of some Artiodactyle cases, no examples of
paired repetitions of digits or phalanges at all suggesting a
comparison with the double extra tarsi &c. of Insects, or the
double extra dactylopodites of Crustacea.

554 MERISTIC VARIATION. [part i.

In the most usual forms of extra limbs in vertebrates a more
or less amorphous pair of limbs, compounded together for a great
part of their length, are attached to a supernumerary piece fitted
into some part of the shoulder-girdle, or more often into the
pelvic girdle.

It is important to notice that though, as many (especially
Ercolaxi) have shewn, a complete series can be constructed,
ranging for instance from the ordinary pygomelian up to com-
plete posterior duplicity, yet repetition of limbs may be and often
is wholly independent of any axial duplicity, being truly a repe-
tition of appendicular parts only.

The question naturally arises whether there is ever an extra
limb placed as a single copy of a normal limb of the same side
as that on which it is attached. As to this the evidence is not
wholly clear, but I incline to think that no case known to me
can properly be so expressed. Perhaps the condition which comes
nearest to this is exemplified by a case of a Frog fully described
by Kingsley1, where a single extra left hind leg is said to have
been attached to the left side of the pelvis. It is difficult to
question that this was actually the fact, for the figure clearly
represents the extra limb as a left leg; but though the muscles
are fully described, the bones are not; and it still seems possible
that there was in reality some duplicity in the limb. The leg
was admittedly abnormal in its anatomy and the naming of the
muscles must in part have been approximate.

But though perhaps it should not be positively stated that
no single extra limb is ever formed in a vertebrate in Succession
to the normal limb of the same side of the body, it is certainlv
true that in the enormous majority of polymelians the extra
repetition consists of parts of a complementary pair. These phe-
nomena are thus of interest as bearing upon the morphology of
repetitions in Secondary Symmetry, but in all probability are
not of the nature of variations in the constitution of the Pri-
mary Symmetry.

A just view of the details of these phenomena can only be gained
from the specimens or from numerous drawings. The cases of extra
limbs in Batrachia may be conveniently studied as exhibiting most of the
different kinds of Secondary Symmetries both in the fore and hind
limbs. In all, some fifty cases are recorded. These may be found
from the following references. The evidence up to 1865 was put
together by Dum^ril, and an abstract of it is given also by Lunel,
and by Kingsley. A fuller bibliography is given by Ercolaxi. The
best papers on the subject are marked with an asterisk. I have added
a few references of less importance not included in the other biblio-
graphies.

* Dumeril, Nouv. Arch. Mus. Paris, 1865, i. p. 309, PI. xx.

* Lunel, Mem. soc. phys. d'hist. not. de Geneve, 1868, xix. p. 305, PL

1 Proc. Bost. N.H.S., 1881—2, xxi. p. 169, PI. n.

chap, xxiil] SIGNIFICANCE OF SECONDABT? SYMMETRY. 55

* Kingsley, Proc. Boston N.H.S., 1881—2, xxi. p. 169, PL n.

* Cavanna, G., Pubbl. del J!. 1st. di Studi super, in , 1879, p. 8, Tav. i.
Four important cases; one, jig. 2, apparently resembling Km in somen -p-

* Mazza, Atti Soc. ital. sci. nat., 1888, xxxi. p. I 15, PI. i.

TUCKERMAN, JOW. Alldt. I'ln/s., 1886, p. 517, PI. X\ I.

Cat. Terat. Ser. Coll. Surg. Mus., 1872, No. 23.
Heron-Koyer, Bull. soc. Zool. France, 1884, ix. p. 165.
Bergendal, Bihang k. svensk. vet. Ah., 1889, xiv. Aid. iv. PI. i.

* Ercolaxi, Mem. Ace. Bologna, 1881, iv. p. 810, PI. iv. Four important ca
and very good bibliography.

Sutton, Trans. Path. Soc., 1889, xe. p. 161, fig.

[Three cases in Newts: Triton cristatus, Jackei,, /.<»,!. Cart., lssl. xxn. p. l.'.f,.
Triton tceniatus, Landois, H., ibid., 1884, xxv. p. (J4; Cabiebano, Atti Soc. ital.
nat., 1882, xxv].

From these Batrachian cases most of the chief features of the
phenomena may be learnt. To those wishing to get a general view of
the subject of repetition of Vertebrate limbs in a comparatively small
compass the valuable memoir of Ercolaxi quoted above is especially
recommended.

Before proceeding to a consideration of the significance of the
phenomenon of Repetition in Secondary Symmetry it must be
expressly stated that there are in vertebrates a certain number
of cases, perhaps even classes of cases, which it is likely differ
widely from the rest ; but as was said above, the chief difference
between the Vertebrate and Arthropod cases lies in the com-
parative simplicity of the latter. It may be stated further that
this greater simplicity of the Arthropod cases consists especially
in the maintenance of the relation between the extra pair and
some normal limb.

Remembering always the existence of unconformable cases we
may, I think, safely gather up from the simple cases several
points relating to the problems of Natural History at large. I
only propose here to make allusion to those considerations which
are not developed in the ordinary teratological treatise-.

Of the fact that any regularity can be discerned in thes<
strange departures from normal structure, and of the bearings
of this fact on current conceptions of the causes determining the
forms of animals it is now hardly necessary to speak further.
Other points not before noticed remain.

In the Arthropod cases that were spoken of as 'regular' it
was seen that the polarity of the Secondary Symmetries has a
definite relation to that of the body which bears them. This
is quite in harmony with the supposition that they are related
to the normal body somewhat as buds are related to a colony,
for in most colonial forms the morphological axes and planes
of the buds are definitely related to those of the stock.

But in the Vertebrate cases though there is generally a re-
lation of images between the extra pair, a definite geometrical
relation between them and a normal limb is seen more rarely.

556 MERISTIC VARIATION. [part I.

That this is so may, I think, be in part at least attributed to
the normal twisting of the vertebrate limb, especially of the hind
limb, from its original position (see Note on p. 459).

A question brought into prominence by facts of this kind
is that of the nature of the control which determines how mucli
of a body shall be repeated, or be capable of repetition, in a
Secondary Symmetry.

What is a unit of repetition ?

With repetition of a whole body we are familiar. Apart from
the processes of sexual reproduction, we know this total repetition
in the many forms of asexual reproduction, whether occurring
by budding, or by division either of adult bodies or of embryos1,
and we thus commonly look on the whole body of any organism
as in a sense a unit, capable of repetition or of differentiation — the
latter especially in gregarious and colonial forms. Again, we
familiarly use the conception of cells as units of repetition or of
differentiation. Besides these we have come to recognize that
members of series of segments are, in their degree, similar units.
And generally, the same attribute of separateness may in un-
defined senses be properly attached to all organs that are re-
peated in Series, and to appendicular parts especially.

The attribution of some of the undefined properties of "unity2"
to some at least of these various groups is very ancient, and there
can be no doubt that it is in the main a right and useful in-
duction.

The chief interest of repetitions in Secondary Symmetry lies
in the fact that they give a glimpse of new light upon the nature
of this unity, shewing a new form in which it may appear.

For in Secondary Symmetry there is not a simple repetition
of a part in Series, taking its place as a member of that series,
but an addition of paired parts, whose intrinsic relation to each
other is the same as that of any pair of parts occurring in the
Primary Symmetry.

The addition is thus a unit, is in form complete in itself, and
seems to have no place in the Primary Symmetry of the whole
body any more than a late side-chapel — also a unit with its own
focus and polarity — had a place in the design of t lie original archi-
tect of the Cathedral.

From analogy, and from general knowledge of vital processes
it would I think have been impossible to foresee the very curious
indeflniteness of the quantity of the parts repeated in systems
of Secondary Symmetry. It seems, especially in Arthropod cases,

1 As a normal occurrence notably in the case of Cyclostomatous Polyzoa of the
genus Grisia described by Harmer, S. F., Q. J. M. S., 1891, p. 127, Plates.

2 This somewhat incorrect term is used here to express some of the meanings
commonly still more incorrectly rendered by the word "individuality" — a word
etymologically most unhappy in this application to things endowed with divisibility
as a conspicuous attribute.

chap, xxiii.] UNITS OF REPETITION. 557

that the repetition may begin from any point in an appends
and include all the parts peripheral to the poinl of origin. Seeing
that the repeated parts are, in their degree, comparable with a
whole organism, this indefmiteness is remarkable. We have thus
to recognize that the property of morphological "unity" may
attach not only to a pair of appendages beginning from the
body, or from some definite surface of articular segmentation, bu1
also to a pair of parts having no semblance of morphological dis-
tinctness.

Strangest of all is the repetition of the index of Crabs and
Lobsters in Secondary Symmetry. The dactylopodite is of course
a separate joint. Double extra dactylopod it es in Secondary Sym-
metry present no feature different from double extra tarsi, &c.
But the index we think of as merely a large spine or tubercle.
It is in no sense a joint or segment. Yet a pair of indices may
be added to a normal body. The interest of this fact is in it-- value
as a comment on the principle given on p. 476 that extra parts
in Secondary Symmetry contain the structures peripheral to their
point of origin. The case of extra indices shews that tin- term
peripheral, if it is to include the case of indices, must be inter-
preted as meaning not morphologically but geometrically peri-
pheral \

We have spoken of parts in Secondary Symmetry as having
no place in the Primary Symmetry of the body. This is on
the whole a true statement, but there are a few cases which
make it uncertain whether it is absolutely true. These e.-^es
are those few where repetitions in Secondary Symmetry were
present on appendages of both sides of the body.

Cases of this class were Odontolabis stevensii, No. 7!>l), and
Melolontha hippocastani, No. 795, where such extra parts were
present on both antennae, suggesting that the similarity of the
repetition of the two sides is due to the relation of Symmetry
between the right side and the left. But against this view may
be mentioned the cases Prionus coriarius, No. 750, and Carabus
irregularis, No. 760, where two legs of the same side each bore
extra parts, and the Lobster, No. 821, having two pairs of extra
points on one dactylopodite. These cases suggest that bilateral
simultaneity in such repetition may perhaps represent merely
a general capacity for this form of repetition. The case of
Prionus calif orm'c us, No. 843, would no doubt bear on this
question, but unfortunately the facts in that case are scarcely well
enough known to justify comment.

1 A case is given by Faxon {llarv. Bull., vin. PI. n. fig. 8) of Callinectes has-
tatus in which the left lateral horn of the carapace, instead of being simple as in
normal specimens, had three spines. It is just possible that two of these may have
been in Secondary Symmetry. All other cases known to me arc in appendicular
parts.

558 MERISTIC VARIATION. [part i.

One further point remains to be spoken of. We have said
that a system of parts in Secondary Symmetry is in a sense
analogous with a bud, but in one respect the condition of these
parts differs remarkably from all phenomena of budding or
reproduction that are seen elsewhere. In a bud the various
organs always present the same surfaces to each other, or in
other words, the planes of division always pass between similar
surfaces. In Secondary Symmetries this is not the case. As
illustrated by the diagram on p. 481, the extra parts may present
to each other, or remain compounded by any of their surfaces,
whether anterior, posterior, or otherwise. This seems to be
altogether unlike anything ever met with in animals and plants.
It is as if in a bud on a plant two leaves on opposite sides of the
axis could in their origin indifferently present any of their surfaces
to each other.

It will be remembered that the symmetry cannot be the result
of subsequent shiftings, but must represent the original manner of
cleavage of the two extra limbs from each other. We must there-
fore conceive that in the developing rudiment of the two extra
limbs either surface may indifferently be external, the polarity
being ultimately determined by the relation of the bud or
rudiment to the limb which bears it.

CHAPTER XXIV.
Double Monsters.

Of the evidence as to double and triple " monstrosity ' and

of the classification of the various forms no account can be given
here. This may be found in any work on general teratology. In
this chapter are put together a few notes on points respecting
these formations of interest to the naturalist, and having relation
to what has gone before.

It is now a matter of common knowledge that in animals [and
plants] division may occur in such a way that two or more bodies
may be formed from what is ostensibly one fertilized ovum (cp.
multipolar cells). But by a similar division, imperfectly effected,
the resulting bodies instead of being complete twins or triplets
may remain united together, frequently having a greater or less
extent of body in common. In other words, speaking of simple
cases in bilateral animals, the whole body, resulting from the
development, may contain more than one bilaterally complete
group of those parts which normally constitute the Primary Sym-
metry of an " individual."

If well developed, the component groups are most often united
by homologous parts, so that there is a geometrical relation <>t'
images between the groups together, forming the compound struc-
ture, the whole being one system of Symmetry. Concerning the
relations of the several parts of such a system to each other
numerous questions of interest arise, but with these it is not now
proposed to deal.

To those unacquainted with facts of this class it may be of use to point out in
the fewest words the direction in which this importance lies. It arises, briefly, from
the fact that in the resemblance between a pair of homologous twins, win fcher wholly
or partially divided, there is once again an illustration of the phenomenon of Sym-
metry, and of the simultaneous Variation of structures related to each other as sym-
metrical counterparts.

The frequency of close resemblance between twins is a matter of common know-
ledge. If it be true that such twins may result from the development of one ovum—
a fact that cannot be doubted in face of the complete series of stages intermediate
between total and partial duplicity — the resemblance between these twins is then of
the same nature as that subsisting between the two halves of any other bilaterally
symmetrical system. A wide field of inquiry is thus opened up. for, as suggested
in the Introduction (p. 30) if the very close resemblance of twins to each other is a
phenomenon dependent on Symmetry of Division, the less close resemblance betw een
members of families may be a phenomenon similar in kind.

560 MERISTIC VARIATION. [part i.

It will be remembered that the resemblance between twins is a true case of
similar and simultaneous Variation of counterparts. This is clearly proved by the
fact that when distinct Meristic Variations are exhibited by one twin they are not
rarely present in the other also. Cases of this simultaneous Variation are familiar
to all who have studied this subject. A useful list of examples in completely separate
twins is given by Windlk1. One of the best known cases in twins incompletely
separated, is that of the Siamese Twins-, who had each only eleven pairs of ribs
(instead of twelve).

Reference must lastly be made to a particular corollary which may naturally be
deduced from the fact that the bodies of incompletely separated twins are grouped
as a single system of Symmetry. If the whole common body were bilaterally sym-
metrical, one twin must be the optical image of the other. But if the organs of one
twin be normally disposed, the organs of the other must be transposed in completion
of the Symmetry. This theoretical expectation is in part borne out by the facts.
With a view to this question Eichwald3 examined the evidence as to thoracopagous
double monsters (including xiphopagi, &c), and found that in almost every case one
of the bodies shewed some transposition of viscera, though to a varying extent4.

There are nevertheless a few cases even of thoracopagi where neither body ex-
hibits any transposition5. Moreover, contrary to natural expectation, it does not
appear that in ordinary cases of completely separate twins either twin has its
viscera transposed; and conversely, of 152 cases of transposition collected by
Kuchenmeister only one could be shewn to have been a twin6. It seems therefore
that the frequency of transposition in double monstrosity depends in some way upon
the maintenance of the connexion between the twins; and that if the separation be
completed early, as it must be supposed to be in cases of homologous twins born
separate, then both bodies as a rule develop upon the normal plan, like the bodies
of multiple births of other animals. But as the evidence now stands there is no
reason to suppose that individuals with transposition of viscera, born as single births,
have ever had a counterpart any more than individuals whose viscera are normally
placed, tempting as it is to imagine that both may have had some counterpart which
in the ordinary course does not develop.

For the present we need not go beyond the fact that between
complete duplicity resulting in " homologous twins," and the
least forms of axial duplicity, consisting in a doubling of either
extremity of the longitudinal axis almost all possible degrees
have been seen7. By persons unfamiliar with abnormalities it

1 Windle, B. C, Jour. Anat. Phys., xxvi. p. 295.

2 For full abstracts of all evidence relating to this case, see Kuchenmeister,
Die angeb. Verlagerung d. Eingeweide d. Menschen, Leipzig, 1883, p. 201.

3 Eichwald, Pet. med. Ztsch., 1870, No. 2, quoted from abstr. Virch. u. Hirsch,
Jahresb., 1871, p. 167.

4 Eichwald supports the view that in these cases it is the right twin which shews
the transposition. As Kuchenmeister (I. c.) points out, this cannot by the nature
of the case be a universal rule ; for the relative position of xiphopagous twins may
result singly from the way in which they happen to be laid by the mother or the
midwife. Of the Siamese Twins, besides, it was Chang, the left twin, in whose body
there were indications of transposition. The twins may also remain face to face.
The expression " right twin " must always need further definition, and it should be
qualified as the right when the livers are adjacent, or when the hearts are adjacent,
as the case may be. Whether the rule is wholly or partially true for either of these
positions seems to be very doubtful.

5 For example, Bottchee, Dorpater med. Ztschr., n. p. 105, quoted from V. u.
II., Jahresb., I. c. In the specimen Terat. Cat. Coll. Surg. Mus., 1872, No. 114, there
is no transposition, but here the hearts were not separate.

6 1. c., p. 268. One, however, was a child of a mother who had before borne
twins, I. c, p. 313.

7 The fact that some of the degrees are much more common than others has an
obvious bearing on the question of Discontinuity, which might with profit be pur-
sued. A statistical examination as to the angles at which the bodies are most
frequently inclined to each other would also probably lead to an interesting result.

chap, xxiv.] AXIAL DUPLICITY: BEPTILES. 561

is sometimes supposed that axial duplicity is a phenomenon more
or less peculiar to Man and to domesticated animals [and plants],
and the occurrence is looked on as a part of thai Meristic in-
stability which is ascribed to absence of the control of a Btrict
and Natural Selection. This view is far from Bound Such
phenomena have on the contrary been found in many classes of
animals, vertebrate and invertebrate, and the unquestionable
frequency in domesticated animals may in great measure be
fairly attributed to the comparative ease with which the births
of these creatures can be observed. As considerations of tin-
kind have weight with many it has seemed worth while to give
references to examples taken from a variety of different groups,
shewing not only that such compound bodies may be produced
in wild animals, but also that they may sometimes be able to carry
on the business of life without artificial help.

In Mammals and Birds I do not know an authentic case of a double
monster that had grown up in the wild state.
*865. In Reptiles many such cases are known and are referred to by
most of the older writers. Of Snakes having complete or partial
duplicity, nearly always of the head, some twenty cases are recorded.
Several of these were animals of good size, and must have had aD
independent existence for some considerable time.

Some of the cases have special points of interest, but into these it
is not now proposed to enter. As bearing on the question of the
frequency of Meristic Variation in families and strains attention is
called to the circumstance that Mitchill's three specimens were all
found in one brood of 120 which were taken with the mother. The
following is a list of records of snakes having the head whollv or
partially double.

Coluber constrictor. Wyman, J., Proc. Bost. X. II. S., 1862,
ix. p. 193, fg.

Coluber constrictor. Mitchill, S. L., Amer. Jour, of Sri., x.
1826, p. 48, PI. (3 specimens).

Ophibolus getulus. Yarrow, Amer. Xat., 1878, xn. p. 470.

Pityophis. ibid., p. 264.

Pelamis bicolor. [Remarkable case1 : the duplicity appearing
only in the fact that there were 4 nasal plates instead of 2, each with a
nostril] Boettger, 0., Per. iib. d. Seuck. nat. Ges. in Frank/, a. J/.,
1890, p. lxxiii.

In the remainder the species is not clear. Redi, Osserv, int. agli
anim. viventi, &c, 1778, p. 2, Tav. i. [very good account]; LaceVkde,
Hist. nat. des Serpens, n. 1789, p. 482; Bancroft, Nat Hist, of
Guiana, 1769, p. 214, PL; Laxzoxi, Miscell. curios., 1690, Obs. « i.wi.
p. 318, Fig. 36; Boston Soc. Med. Imp., Catal. of Mas.. No. 856,
quoted from Wyman, /. c. ; Edwards, Nat. Hist, of Birds, dfcc, Pt. iv.
1751, p. 207, PI. ; Dorxer, Zoo!. Gart., 1873, xiv. p. 407 : Coll. Surg.
Mus., Terat. Cat, 1872, Nos. 24—27.

1 Compare with Mitchill's two last cases, and also with a case ill Alytes ob-
stetricans. Herox-Royer, Bull. Soc. Zool. France, 1884, ix. p, 164,

B.

36

562

MERIST1C VARIATION.

[part I.

EC

TV

Fig. 207. Chrysemys picta, 2 or 3 days old. I, II, normal. Ill and IV, two-
headed specimen. In the latter the nuchal and two pygal plates are normal. Be-
tween them are 12 plates on each side, 11 being the most usual number. Among
the costals an extra plate is wedged in on the rt. First vertebral divided by suture ;
fifth is made up of 4 irregular plates. In the plastron there is a doubling of the
gular plate. The rt. femoral has a suture. (From Barbour.)

chap, xxiv.] AXIAL DUPLICITY: IX VERTKIiKATKS. 563

See also, Geoffroy St. Hilaire, Hist, des a num., ed 1838, 11. p.
197; Dumeril et Bibron, Erpdt generate, 1884, vi. p, 209.

866. Duplicity of the head is less common in Lizards, but several
examples are known. See Geoffkoy St. HlLAlBB, I c, p. 195: Con
Paris, 1869, S. 3, v. p. 136, etc.
*867. In Chelonia also are several such instances. See Edwards, N<U.

Hist, of Birds, d/c, Pt. IV. 17">1, p. lMm1, ; .Mnniii.i, /. ,-. ; BaBBOUB,
E. H., Amer. Jour, of $ci., 1888, S. 3, xxxvi. p. 227, PL v. The lasi i
particularly interesting case from the circumstance that the behaviour
during life was observed to some extent, though only a popular account
is given. The two heads seemed to act independently, and it is said
that there was no concerted action between the feet of the two sides.
Barbour's figures are reproduced in Fig. 207.

In fish-hatching establishments double monstrosity is of frequent
occurrence among young Salmon and Trout. A two-headed embryo of
a Shark is preserved in Coll. Surg. Mus. {Terat. Cat. 1s7l', No. 22

The following cases relate to invertebrates.

Chaetopoda. Duplicity in this Class has been often seen, but
that any of the cases are truly congenital cannot be stated. There is
evidence that in many Annelids regeneration1 both of head or tail may
freely occur, and it is quite possible that the second head or second tail
may have grown out from an injured place, though of this there is no
actual proof. In cases of posterior bifurcation each tail generally
contains all the parts proper to the normal, but in Xo. S71 one of the
tails was without the terminal cirri usual in the species. So far as can
be gathered from the evidence it does not appear that the two con-
tinuations of the body have always the same number of segments,
which might perhaps be expected were both the result of a natural
division of the developing body. On the other hand, they do seem
generally to have a nearly equal development, and are almost always
(in cases of double tails, at least) fairly equal in length, which would
not be anticipated if one only were a new growth. Moreover, if the
double tail is in some way due to regeneration one would expect to
find such duplicity in its minor conditions much more commonly.

Into the details of the structure it is not now proposed to enter,
and indeed of most of the cases there is little to be told. The evidence
is mentioned here simply in further proof of the power of these indiv-
iduals, thus greatly departing from the normal of their species, to
maintain themselves with no apparent difficulty. It will be noticed that
the species concerned are most various, and include not only Errant ia,
but two cases also in Serpulida?.

The literature of the subject was collected by Collin ', and a list of
the references was independently collected and published with abstracts
by Andrews3. This list, with a few additions, was republished by
Friend4. Though many of the accounts are imperfect they are referred

1 The evidence on this point does not come within the scope of this work.
References to it may be obtained from Akdbbws, Zeppelin, <ic (r. infra).
3 Collin, A., Naturw. Wochens., 1891, No. 12, p. 113.

3 Andrews, E. A., Amer. Nat., 1892, xxvi. p. 729.

4 Friend, H., Nature, 1893 (1), p. 397.

36—2

564

MERISTIC VARIATION.

[part l

*S6S.

to below, in evidence that the total number of cases is considerable.
There are only two certain cases of double head (see Typosyllis, No. 868,
and Allolobophora, No. 873).

POLYCH.ETA.

Typosyllis variegata : individual having two small heads, as
shewn in Fig. 208. Heads of unequal size, that od the left having 4
segments behind the eyes, while that on the right had two. The

869.
870.

871.
872.

Fig. 208. Typosyllis variegata, No. 868, having two small heads.

(After Langerhans.)

appearance suggested that the original head had been broken off and
that two new ones had grown in its place. Langerhans, P., Nova
Acta Ac. C. L. C, xlii. p. 102, PL

Nereis pelagica : bifid posteriorly. Bell, F. Jeffrey, Proc. Zool. Soc., 1886, p. 3.

Salmacina incrustans (Serpulida?) : posterior end double. [Two tails shewn in
figure as of equal length and in the same straight line, at right angles to the body.
The arrangement of the segmentation at the junction is not clearly shewn.]
Claparede, Mem. soc.phys. et dltist. nat. Geneve, xx. 1869 — 70, p. 177, PI. xxx. fig. 5 f.

Proceraea tardigrada (Syllid*) : tail double; two specimens. In one of these
the tails were nearly equal, but one had no anal cirri. Andrews, E. A., Proc. U. S.
Nat. Mus., 1891; xiv. p. 283, and Amer. Nat., 1892, xxvi. p. 729, PI. xxi.

Branchiomma sp. (Sabellidre) : two posterior ends, one being rudimentary.
Brunette, Trav. Stat. Zool. de Cette, 1888, p. 8 [quoted from Andrews, I. c]

[With these conditions compare Syllis ramosa, a form found by the Challenger
in two localities, inhabiting a HexactineUid Sponge. The body of this creature con-
sisted of vast numbers of branches, about as thick as thread, passing off at right angles,
coiling upon each other and forming inextricable masses. In some specimens no
head was found, but a single head was afterwards discovered. It seemed likely that
large tracts of the body have no head, but there was no evidence to shew how many
heads occur in the colony. Many female buds were found, and a single complete
male. McIntosh, Chall. Rej)., xn. p. 198, PI. xxxi.]

chap, xxiv.] AXIAL DUPLICITY : INVBRTEBBATES. oG5

Oligoch^ta,

*873. Allolobophora longa : specimen represented as bearing a Becond
head on the right side of the first segment behind the peristomium.
The second head is represented with prostomium, peristomium and one
more segment which rests on the peristomium of the normal body.
Friend, H., Science-Gossip, 1892, July, p. 161, fig,

874. Ctenodrilus monostylos : double tail; in many hundreds
examined, three cases seen, Zeppelin, Z.f, //•. Z., 1883, xxxix. ]». 621.
PI. 36, figs. 18 and 19.

875. Lumbriculus variegatus : similar cases, von Bulow, A rch, f
Naturg., 1883, xlix. p. 94.

876. Acanthodrilus sp. : case of two tails arising from a much thicker
anterior portion. Such worms were believed or alleged to be common
in a particular district in New Zealand. Kirk, T. ^Y., Trans. N. Zeal.
Inst., xix. p. 64, PL

877. Earthworms generally, belonging to genera Lumbricus, or
Allolobophora : cases of double tail recorded, as follows : Robertson,
C, Q. J. M. S.} 1867, p. 157, fig.; Horst, Notes Legd. Mu8.t vn. p. 42 :
Thompson, W., Zool, xi. p. 4001 ; Bell, F. Jeffrey (2 cases), Ann. <v
Mag. N. H., 1885 (2), p. 475, fig.; Friend, H., Sci.-Gossip, 1892, p.
108, figs.; Marsh, C. D., Amer. Nat, xxiv. 1890, p. 373; Fitch, A.,
Eighth Rep. upon Insects of State of X. Y., Append., 1865, p. 204 [from
Andrews, I.e.]; Terat. Cat. Mus. Coll. Surg., 1872, No. 20. Breese,
West Kent N. H. S., 1871; Broome, Trans. N. II. S. Glasgow, 1888, p.
203 ; Foster, Hull. Sci. Club, 1891; [the last three quoted from Friend,
Nature, 1893 (1), p. 397]; Collin, A., Naturw. Wochens., 1891, No. 12,
figs. I have also a specimen with two nearly symmetrical tails kindly
sent by Mr W. B. Beniiam.

Arthropoda.

Three cases.
*878. Chironomus (Gnat): larva with two heads, duplicity beginni 2
from the 5th segment behind the head [important details given, g. v.].
Weyenbergh, H., Stet. ent. Ztg., 1873, xxxiv. p. 452, fig.

879. Euscorpius germanicus (Scorpion): tail double from 4th prse-
abdominal segment [figure represents each abdomen with one segment
too few, presumably an error]. Pavesi, P., Rend. R. 1st. Lmib., S. II.,
xiv. 1881, p. 329, fig.

880. [Scorpio africanus :] specimen with two tails. Skba, Rerum
Naturalium Thesaurus, 1734, i. p. 112, PI. lxx. fig. 3. This example
was kindly sent me by Mr R. I. Pocock, who tells me that the figure
shews the animal to be of the species named.

Cestoda.

Conditions, perhaps akin to duplicity, have been seen to occur
under three forms.

881. > Taenia ccenurus : specimen whose head had 6 suckers instead of
4, and 32 hooks instead of 28. Proglottides were 3-sided prisms, in
section triangular. Longitudinal vessels 6 instead of 4, two being in
each angle. Absolute size of head greater than normal. This abnormal

566 MERISTIC VARIATION. [part i.

form is known to occur in many kinds of Tapeworms, and especially in
Cysticerci. Leuckart, Parasiten d. Menschen, pp. 501 — 2, cp. p. 577.
[Case withfii'e suckers mentioned, ibid., p. 578.]

In another form of abnormality the chain of segments has three
longitudinal flanges, formed, as it were, by the union of two chains of
proglottides having one edge in common. Head not found, but several
cases known. Genital openings in one case all upon the common edge.
Leuckart, ibid., p. 574. Cp. Cobbold, Trans. Path. Soc, xvn. p. 438;
Levacher, Comptes Yendus, 1841, xm. p. 661.
882 Bifurcated chains of proglottides have also been seen, e.g. specimen

of TaBnia (cysticerci) tenuicollis, which bifurcated several times in
terminal portion, though normal in front of this. Momez, Bull. >Sci. du
No rd, x. p. 201. See also Taenia saginata ? Leuckart, I. c, p. 573.

Brachiopoda.
883. Acanthothyris spinosa (Rhynchonellida^): case of duplicity

I u

Fig. 209. Acanthothyris spinosa, No. 883. Case of duplicity. (From P. Fischer.)
I. Seen from ventral valve. II. Looking between the valves.

as shewn in Fig. 209. Fischer, P., Jour, de Conchyl. S. 3, xix. p.
343, PL xm. figs 4—7.

HOLOTHURIOIDEA.

884. Cucumaria acicula : specimen made up of two individuals
cohering laterally at posterior ends. Schmeltz, Verh. d. Ver. f.
naturw. Unterhaltung, Hamb., 1877, iv. p. XV.

885. Cucumaria planci : case of second mouth and ring of tenta-
cles borne on a lateral bud-like projection. Ludwig, H., Z.f. w.
Z., liii. Supp. p. 21, PI. v.

886. Ccelenterata. Forms which are commonly simple, such as Actinia or Sagartia,
are rarely found with two discs seemingly due to incomplete division, which in
these forms may take place longitudinally [?] as well as by ordinary budding.
Gosse, P. H., Sea-Anemones, p. xxi., &c. See also Guyon, Zoologist, p. 7026, fig.

Similar occurrences, not distinguishable from budding, have been seen in
Medusas, e.g., Phialidium variabile, Davidoff, Zool. Anz., iv. p. 620, fig.; Gastro-
blasta raffaeli, Lang, A., Jen. Ztseiir., xix. p. 735. An interesting case of this kind
* was seen in Cordylophora lacustris. Several polystomatous specimens were found
on a particular mass of Cordylophora, but were not found on all colonies gathered
with this mass and had not been seen previously in specimens from the same
locality. [Further particulars.] Price, H., Q. J. M. S„ 1876, p. 23, figs.

Protozoa. Double and triple monstrosity has been seen in several
Foraminifera, see e.g., Dawsox, Canad. Nat., 1^70, p. 177, figs.; Balkwit>l
and Wright, Trans. B. Irish Ac, 1885, xxviii. p. 317, PL xiv., &c.
[As to cases in Stentor, see Balbiani, J. de Vanat., 1891, No. 3, but these
are doubtless examples of regeneration and duplicity following injury.]

CHAPTER XXV.

Concluding Reflexions.

To attempt at this stage any summary of conclusions would be
misleading. The first object of this work is not to set forth in
the present a doctrine, or to advertise a solution of the problem of
Species, but rather to bring together materials that may help
others hereafter to proceed with the solution of that problem. A
general enumeration of particular conclusions is therefore to be
avoided. Indeed, from the scantiness of the evidence, its present
value is chiefly in suggestion, and the facts must therefore be
themselves still studied in detail. The reader must interpret as
he will.

But, as often happens, that which may not shew the right road
is enough to shew that the way taken has been wrong, and so is it
with this evidence. Upon the accepted view it is held that the
Discontinuity of Species has been brought about by a Natural
Selection of particular terms in a continuous series of variations.
Of the difficulties besetting this doctrine enough was said in the
introductory pages. These difficulties have oppressed all who have
thought upon these matters for themselves, and they have caused
some anxiety even to the faithful. And if in nice of the difficulties
reasonable men have still held on, it has not been that the obstacles
were unseen, but rather that they have hoped a way through them
would be found.

Now the evidence, of which a sample has been here presented,
gives hope that though there be no way through the difficulties, there
is still perhaps a way round them. For since all the difficulties grew
out of the assumption that the course of Variation is continuous,
with evidence that Variation maybe discontinuous, for the present
at least the course is clear again.

Such evidence as to certain selected forms of variations has
I submit, been given in these chapters, and so tar a presumption
is created that the Discontinuity of which Species is an expression
has its origin not in the environment, nor in any phenomenon of
Adaptation, but in the intrinsic nature of organisms themselves,
manifested in the original Discontinuity of Variation.

But this evidence serves a double purpose. Though some may

568 MERISTIC VARIATION. [part I.

doubt whether the variations here detailed are such as go to the
building of Specific Differences (a doubt which, it must be granted,
does fairly attach to some part of the evidence), yet the existence
of sudden and discontinuous Variation, the existence, that is to
say, of new forms having from their first beginning more or less of
the kind of perfection that we associate with normality, is a fact
that disposes, once and for all, of the attempt to interpret all per-
fection and definiteness of form as the work of Selection. The
study of Variation leads us into the presence of whole classes of
phenomena that are plainly incapable of such interpretation.

The existence of Discontinuity in Variation is therefore a final
proof that the accepted hypothesis is inadequate. If the evidence
went no further than this the result would be of use, though its
use would be rather to destroy than to build up. But besides this
negative result there is a positive result too, and the same Discon-
tinuity which in the old structure had no place, may be made the
framework round which a new structure may be built.

For if distinct and "perfect" varieties may come into existence
discontinuous!)', may not the Discontinuity of Species have had a
similar origin ? If we accept the postulate of Common Descent
this expectation is hard to resist. In accepting that postulate it
was admitted that the definiteness and Discontinuity of Species
depends upon the greater permanence or stability of certain terms
in the series of Descent. The evidence of Variation suggests that
this greater stability depends primarily not on a relation between
organism and environment, not, that is to say, on Adaptation, but
on the Discontinuity of Variation. It suggests in brief that the
Discontinuity of Species results from the Discontinuity of Variation.

This suggestion is in a word the one clear and positive indica-
tion borne on the face of the facts. Though as yet it is but an
indication, there is scarcely a problem in the comparison of
structures where it may not be applied with profit.

The magnitude and Discontinuity of Variation depends on
many elements. So far as Meristic Variation is concerned, this
Discontinuity is primarily associated with and results from the fact
that the bodies of living things are mostly made up of repeated
parts — of organs or groups of organs, that is to say, which exhibit
the property of "unity," or, as it is generally called, "individuality."
Upon this phenomenon depends the fact that Meristic Variation in
number of parts is often integral, and thus discontinuous.

The second factor that most contributes to the Discontinuity of
Variation is Symmetry, manifesting its control in the first place
directly, leading often to a result that we recognize as definite and
perfect because it is symmetrical.

But besides this direct control that we associate with Symmetry,
other erfects greatly contributing to the magnitude of Variation

chap, xxv.] CONCLUDING REFLEXIONS. 569

can be traced to a factor not clearly to be distinguished from
Symmetry itself. For, as has been explained, Symmetry, whether
Bilateral or Radial, is only a particular case of that phenomenou of

Repetition of Parts so universally characteristic of living bodies ;
and that resemblance between two counterparts, which we call
Bilateral Symmetry, is akin to the resemblance between parts
repeated in Series, though, as is shewn by their geometrical re-
lations, the processes of division by which the parts were originally
set off, must be in some respects distinct. Bilateral Symmetry <>t
Variation is thus only a special case of the similar and simul-
taneous Variation of repeated parts.

The greatness of the observed change from the normal is often
largely due to this possibility of simultaneity in Variation, the
change thus manifesting itself not in one part only, but in many
or all of the members of a series of repeated parts. Instances of
such similar and simultaneous Variation of serial parts in animal-
have now been given. Examples still more marked may be seen
abundantly among plants. A variation, for example, in the form or
degree of fission of the leaf, slight perhaps by itself, when taken up
and repeated in every leaf in its degree, constitutes a definite and
conspicuous distinction. Everyone has observed this common fact.
Few illustrations of it are more evident than that of the common
Hawthorn. In a quickset hedge soon after the leaves begin to
unfold almost each separate plant can be recognized even at a
distance, and its branches can be traced by their special character-,
by the shapes and tints of the leaves, by the angles that they make
with the stem, by the manner of unfolding of the buds, and -
forth. These variations, sometimes slight in themselves, by their
similarity and simultaneity build up a conspicuous result.

The phenomenon of serial resemblance is in fact an expression
of the capacity of repeated parts to vary similarly and simul-
taneously. In proportion as in their variations such parts retain
this capacity the relationship is preserved, and in proportion as it
is lost, and the parts begin to vary independently, exhibiting
differentiation, the relationship is set aside. It will be noticed
that to render the converse true we must extend the conception of
Serial Homology in special cases to organs not commonly regarded
as serially homologous with each other, but which having assumed
some common character thereafter may vary together (cp. p. :*()!»).

In the power of independent Variation, members of series once
more exhibit the property of "unity" that we have already noticed
as appearing in the manner in which the number of the members
is changed. ' The fact that members of series should hi' capable of
varying as "individuals" is paradoxical. Such members, teeth,
digits, segments of Arthropods, and the like, are each made up of
various tissues endowed with miscellaneous functions and dissimilar
in their morphological nature. Nevertheless each group is capable

570 MERISTIO VARIATION. [part I.

of independent division and of separate Variation. Single digits for
instance may thus be independently hypertrophied as a whole, single
segments or single appendages or pairs of appendages may be differ-
entiated in some special way, and so forth.

At this point reference may again be made to that extraordinary
Discontinuity of Variation appearing in what I have called Ho-
mceosis, so strikingly seen in the few Arthropod cases given (p. 146),
and so common in flowering plants. In these changes a limb,
a floral segment, or some other member, though itself a group of
miscellaneous tissues, may suddenly appear in the likeness of some
other member of the series, assuming at one step the condition to
which the member copied attained presumably by a long course of
Evolution.

Many times in the course of this work we have had occasion to
consider the modifications in the conception of Homology demanded
by the facts of Variation. It is needless to speak further of this
matter here, and the reader is referred to pp. 125, 191, 269, 394
and 417, where the subject is discussed in relation to Linear Series
of several kinds, and to the facts given in Chapter XVI and at
p. 433 bearing on the same questions in their application to Radial
Series. The outcome of these considerations shews, as I think,
that the attribution of strict individuality to each member of a
series of repeated parts leads to absurdity, and that in Variation
such individuality may be set aside even in a series of differentiated
members. It appears that the number of the series may be in-
creased in several ways not absolutely distinct, that a single
member of the series may be represented by two members, that
a terminal member may be added to the series, and also that the
number of the members may change, no member precisely corre-
sponding in the new total to any one member of the old series : in
short, that with numerical change resulting from Meristic Variation
there may be a redistribution of differentiation.

But though this is, in my judgment, a fact of great consequence,
its relation to the Study of Variation is merely incidental. It is
not so much that to enlarge the conception of Homology so as to
include the phenomena of Meristic Variation is a direct help, as
that to maintain the old view is a hindrance and keeps up an
obstacle in the way of any attempt to apprehend the real nature
of the phenomena of Division, and hence of Meristic Variation.
So long as it is supposed that each member of a series of repeated
parts is literally individual, it is impossible to form any conception
of Division that shall include the facts of Meristic Variation, for in
Variation it is found that the members are divisible.

It is an unfortunate thing that the study of Homology has been
raised from its proper place. The study of Homologies was at first
undertaken as a means of analyzing the structural evidences of
relationship, and hence of Evolution. This is its proper work and

chap, xxv.] CONCLUDING REFLEXIONS. 571

use ; but the pursuit of this search as an aim in itself has led to
confusion, and has tended to conceal the fact that there are pheno-
mena, to which the strict conception of individual Homology is not
applicable.

This exaggerated estimate of the fixity of the relationship of
Homology has delayed recognition of the Discontinuity of Meristic
Variation, and has fostered the view that numerical Variation
must be a gradual process.

This view the evidence shews to be wrong, as it was also im-
probable.

Brief allusion may be made to three separate points of minor un-
importance.

It is perhaps true that, on the whole, series containing large num-
bers of undifferentiated parts more often shew Meristic Variation than
series made up of a few parts much differentiated, but throughout the
evidence a good many of the latter class are nevertheless to be seen.

Reference may be made to a point that might with advantage be
examined at length. The fact that Meristic Variation may take place
suddenly leads to a deduction of some importance bearing on the expect-
ation that the history of development is a representation of the course of
Descent. In so far as Descent may occur discontinuously it will, I
think, hardly be expected that an indication of the previous term will
appear in the ontogeny. For example, if the four-rayed Tetracrinus
may suddenly vary to both a five-rayed and also to a three-rayed form
(see p. 437) it is scarcely likely that either of these should go through
a definitely four-rayed stage; and if the origin of the four-rayed form
itself from the five-rayed form came similarly as a sudden change, it
would not be expected that a five-rayed stage would be found in its
ontogeny. Similarly, if a flower with rive regular segments arise as a
sport from a flower with four, it would not, I suppose, be expected that
the fifth segment would arise in the bud later than the other four. I
suggest these examples from Radial Series, as in them the question is
simpler, but similar reasoning may be applied to many cases of Linear
Series also.

It will be noted that the attempt to apply to numerical variations
the conception of Variation as an oscillation about <>n> mean is not
easy, difficulty arising especially in regard to the choice of a unit for
the estimation of divergence. In few cases can facts be collected in
quantity sufficient even to sketch the outline of such an investigation :
but, to judge from the scanty indications available, it seems that in
cases of numerical change variations to numbers greater than the
normal number, and to numbers less than it are not generally of equal
frequency. Probably no one would expect that they should be so.

As was stated in the Introduction, wo arc concerned here with
the manner of origin of variations, not with tin- manner of their
perpetuation. The latter forms properly a (list ind subject. We
may note however, in passing, how little do the lew known facta
bearing on this part of the problem accord with those ready-made

572 MERISTIC VARIATION. [part i.

principles with which we are all familiar. Upon the special
fallacy of the belief that great Variation is much rarer in wild than
in domesticated animals we have often had occasion to dwell. As
was pointed out in the discussion of the evidence on Teeth (p. 266)
this belief arises from the fact that domesticated animals are for
the most part variable, and that wre have every opportunity of ob-
serving and preserving their variations. To compare rightly their
variability with that of wild animals choice should be made of
animals that are also variable though wild. Taken in this way the
comparison is fair, and as I have already said, if we examine the
variation in the vertebrae of the Sloths, in the teeth of the Anthro-
poid Apes, in the colour of the Dog-whelks {Purpura lapillus), &c,
we find a frequency and a range of Variation matched only by
the most variable of domesticated animals.

It is needless to call attention to the fact that in hardly any
cases even of extreme variations in wild creatures is there evidence
that the animal was unhealthy, or ill nourished, or that its economy
was in any visible way upset ; but in almost every example, save
for the variation, the body had the ajDpearance of normal health.

After all that has been said few perhaps will still ask us to
believe that the fixity of a character is a measure of its importance
to the organism. To try to apply such a doctrine in the open air
of Nature leads to absurdity. Let one more case be enough. I go
into the fields of the North of Kent in early August and I sweep
the Ladybirds off the thistles and nettles of waste places. Hun-
dreds, sometimes thousands, may be taken in a few hours. They
are mostly of two species, the small Coccinella decempunctata .or
variabilis and the larger C. septempunctata. Both are exceedingly
common, feeding on Aphides on the same plants in the same places
at the same time. The former (G. decempunctata) shews an ex-
cessive variation both in colours and in pattern of colours, red-
brown, yellow-brown, orange, red, yellowish-white and black, in
countless shades, mottled or dotted upon each other in various
ways. The colours of pigeons or of cattle are scarcely more variable.
Vet the colour of the larger G. septempunctata is almost absolutely
constant, having the same black spots on the same red ground.
The slightest difference in the size of the black spots is all the
variation to be seen. (It has not even that dark form in which
the black spreads over the elytra until only two red spots remain,
which is to be seen in C. bipunctata.) To be asked to believe that
the colour of G. septempunctata is constant because it matters to
the species, and that the colour of C. decempunctata is variable
because it does not matter, is to be asked to abrogate reason.

But the significance of the facts does not stop here. When,
looking further into the variations of 0. decempunctata it is found
that most of its innumerable shades of variation are capable of
being grouped round some eight or ten fairly distinct types, surely

chap, xxv.] CONCLUDING REFLEXIONS. 57 3

an expectation is created in the mind that the distinctness of these
forms of varieties, all living [and probably breeding] together, may
be of the same nature as the distinctness of Species : and since it
is clear that the distinctness of the varieties is not the work of
separate Selection we cannot avoid the suspicion that the same
may be true of the specific differences too.

An error more far-reaching and mischievous is the doctrine
that a new variation must immediately be swamped, if I may use
the term that authors have thought fit to employ. This doctrine
would come with more force were it the fact that as a matter of
experience the offspring of two varieties, or of variety and normal,
does usually present a mean between the characters of its parents.
Such a simple result is, I believe, rarely found among the facts of
inheritance. It is true that with regard to this part of the problem
there is as yet little solid evidence to which we may appeal, but in
so far as common knowledge is a guide, the balance of experience
is, I believe, the other way. Though it is obvious that there are
certain classes of characters that are often evenly blended in the
offspring, it is equally certain that there are others that are not.

In all this we are still able only to quote case against case.
No one has found general expressions differentiating the two
classes of characters, nor is it easy to point to any one character
that uniformly follows either rule. Perhaps we are justified in the
impression that among characters which blend or may blend evenly,
are especially certain quantitative characters, such as stature : while
characters depending upon differences of number, or upon quali-
tative differences, as for example colour, are more often alternative
in their inheritance. But even this is very imperfectly true, and
as appeared in the case of Earwigs (p. 40) there may be a definite
dimorphism in respect of a character which to our eye is simply
quantitative. Nevertheless it may be remembered that it is
especially by differences of number and by qualitative differences
that species are commonly distinguished. Specific differences are
less often quantitative only.

But however this may be, whatever may be the meaning of
alternative inheritance and the physical facts from which it results,
and though it may not be possible to find general expressions to dis-
tinguish characters so inherited from characters that may blend, it
is quite certain that the distinctness and Discontinuity of many
characters is in some unknown way a part of their nature, and is
not directly dependent upon Natural Selection at all.

The belief that all distinctness is due to Natural Selection, and
the expectation that apart from Natural Selection there would be
a general level of confusion, agrees ill with the facts of Variation.
We may doubt indeed whether the ideas associated with that
flower of speech, "Panmixia," are not as false to the laws of Hie as
the word to the laws of language.

574 MERISTIC VARIATION. [part I.

But beyond general impression, in this, the most fascinating
part of the whole problem, there is still no guide. The only way
in which we may hope to get at the truth is by the organization of
systematic experiments in breeding, a class of research that calls
perhaps for more patience and more resources than any other form
of biological inquiry. Sooner or later such investigation will be
undertaken and then we shall begin to know.

Meanwhile, much may be done to further the Study of Varia-
tion even by those who have none of the paraphernalia of modern
science at command. Many of the problems of Variation are pre-
eminently suited for investigation by simple means. If we are to
get further with these problems it will be done, I take it, chiefly
by study of the common forms of life. There is no common shell
or butterfly of whose variations something would not be learnt were
some hundreds of the same species collected from a few places and
statistically examined in respect of some varying character. Any-
one can take part in this class of work, though few do.

At the present time those who are in contact with the facts and
material necessary for this study care little for the problem, or at
least rarely make it the first of their aims, and on the other hand
those who care most for the problem have hoped to solve it in
another way.

These things attract men of two classes, in tastes and tempera
ment distinct, each having little sympathy or even acquaintance
with the work of the other. Those of the one class have felt the
attraction of the problem. It is the challenge of Nature that
calls them to work. But disgusted with the superficiality of
"naturalists" they sit down in the laboratory to the solution of
the problem, hoping that the closer they look the more truly will
they see. For the living things out of doors, they care little. Such
work to them is all vague. With the other class it is the living
thing that attracts, not the problem. To them the methods of
the first school are frigid and narrow. Ignorant of the skill and of
the accurate, final knowledge that the other school has bit by bit
achieved, achievements that are the real glory of the method, the
"naturalists" hear onlv those theoretical conclusions which the
laboratories from time to time ask them to accept. With senses
quickened by the range and fresh air of their own work they feel
keenly how crude and inadequate are these poor generalities, and
for what a small and conventional world they are devised. Dis-
appointed with the results they condemn the methods of the
others, knowing nothing of their real strength. So it happens
that for them the study of the problems of life and of Species
becomes associated with crudity and meanness of scope. Beginning
as naturalists they end as collectors, despairing of the problem,
Turning for relief to the tangible business of classification, account-
ing themselves happy if they can keep their species apart, caring

chap, xxv.] CONCLUDING REFLEXIONS. 575

little huw they became so, and rarely telling ns how they may be
brought together. Thus each class misses that which in the
other is good.

But when once it is seen that, whatever be the truth as to the
modes of Evolution, it is by the Study of Variation alone that the
problem can be attacked, and that to this study both classes of
observation must equally contribute, there is mice more a place
for both crafts side by side: for though many things spoken ..f in
the course of this work are matters of doubt or of controversy, of
this one thing there is no doubt, that if the problem of Species i^
to be solved at all it must be by the Study of Variation.

INDEX OF SUBJECTS.

Acanthoderes nigricans, double (?) leg,

548
Acanthodrilus, double tail, 565
Acanthothyris, double monster, 566
Accessory hoofs of Ox, connected with

supernumerary digits, 285
Acherontia atropos, colours of larva?, 304,

305
Acinopus lepelletieri, extra legs, 498
Actinometra, variation in number of

radial joints, 421; 4-rayed specimen,

437 ; 6-rayed, 437
Adaptation, Study of, as a method of

solving problems of species, 10;

logical objection to the method, 12 ;

speculations as to, avoided, 79; of

species, approximate only, 11
Adimonia tanaceti, double (?) antenna,

550
Agabus uliginosus, double (?) leg, 548
Agestrata dehaanii, extra legs, 491
Agonum sexpunctatum, double (?) leg,

547; riduum, double (?) antenna, 550
Agra catenulata, extra legs, 512
Akis punctata, double (?) antenna, 551
Alans sordidus, extra legs, 508
Aleochara mcesta, extra legs, 488
Allantus, extra appendage, 544
Allolobophora, generative organs of, 160,

162, 165 ; duplicity of head and tail,

565 ; lissaensis, spermathecae, 165
Allurus, generative organs of, 164, 165;

putris, 165; hercynius, tetraedrus, 164
Alytes, vertebras, 127; axial duplicity,

561
Amblypneustes, 4-rayed, 443; 6-rayed,

446; partial reduction of a ray, 443;

partial duplicity of a ray, 446
Ammoccetes, alleged case of eight pairs

of gill-openings, 174
Ampedus ephippium, double (?) antenna,

551
Amphicyclus (Holothurian), tentacles

not in multiples of five, 435
Amphimallus solstitialis, extra antenna?,

515
Amphioxus, number of gill- slits, 174.
Anagallis arvensis, colour- variation, 44
Anas querquedula, division of digits, 392
Anchomenm sexpunctatus, extra antenna?,

523; double (?) antenna, albipes, an-

gusticollis, 550
Angora breeds, 55
Anisoplia floricola division of epistome,

454
Annelids, segmentation compared with

that of Chordata, 86; imperfect seg-
mentation, 156; spiral segmentation,

157 ; variation in generative organs,
159 ; axial duplicity, 563
Anomala junii, extra antenna?, 515
A user, spinal nerves, 130, 133
Antedon, variation in number of radial
joints, 421; 4-rayed specimen, 436;
6-rayed specimen, 437; abnormal
branching, 438
Antenna developed as foot, 146, 147
Anteuna?, variation in number of joints,
Prionida?, 411; Polyarthron,
412; Lyriphlebus, 412;
Donatio,, 413; Forficuhi,
413
extra, in Secondary Symmetry,
513-522 ; symmetry un-
known, 522; arising from
head, 551
supposed double, 548
Anthia, extra legs, 502
Antkocharis cardamines, colour-varia-
tion, 45
eupheno, 45 ; ione, 72
Anthropoid Apes, Variation in Verte-
bra?, 116; teeth, 199; digits, 349
Aphodius, extra legs, 494
Apis mellifica, union of compound eyes,

461
Appendages, joints of, 410

supernumerary, arrange-
ment of evidence, 474
in Secondary Symmetry,
475 ; mechanical model
illustrating relations,
480; duplicity of, 406, 539
Apteryx, brachial plexus, 130
Apus, extra fiabellum, 536
Aquila chrysaetos, extra digits, 393
Archibuteo lagopus, extra digit, 392
Arctia, colour-variation, 46
Arctocephalus australis molars, 243
Arge pherusa, eye-spots, 295
Avion, sinistral, 54

Aromia moschata, extra legs, 485, 503,
512 ; double (?) antenna, 3 cases, 551
Artemia, salina and milhausenii, 96;
gracilis, 100; relation to Branchipus,
96 ; segmentation of abdomen, 100
Arteries, renal, 277; in a case of double-
hand, 333
Arthronomalus, number of segments, 94
Arthropoda, variation in number of
segments, 87; Homoeosis in append-
ages, 146; axial duplicity, 565
Articular processes, change from dorsal
to lumbar type, 109 ; variations in
position of change, 110, 112, 114, 117,
122

INDEX OF SUBJECTS.

577

Artiodactyla, polydactylism, 373; syn-
dactylism, 383 ; teeth, 245, 246
Ascidia plebeia, specimens having every
fourth vessel of branchial sac dilated,
172
Ascidians, variation in branchial struct-
ures, 171, 172; extra atriopore, 456
Ass, canines, 245 ; molars, 246 ; absence

of digital variation in, 360
Astaeus fluvidtilis, colour-variation, 44

variation in number
of oviducal open-
ings, 84, 152
absence of male open-
ing, 154
absence of oviducal

opening, 152, 153

absence of opening

from green gland,

154

extra chela?, 529, 537

extra processes from

chela?, 536
repetition of exopod-
ite of antenna, 538
A. leptodactylus, extra dactylopodites,

532
A. pilimanus and braziliensis, apparent
presence of female opening in males,
155
Aster ias, variation of pedicellariae, 429;
arms, 439
with 8 rays and 3 madreporites,

440; extra water-pore, 466
polaris, normally 6-rayed, 433
problema, tenuispina, undergo
fission, 433
Asterina, 4-raved and 6-rayed specimens,

440
Asteroidea, arms, 439-441
Ateles, teeth, 205, 206, 207
Atriopore, extra, in Ascidians, 456
Attelabus, division of pronotum, 455
Aulastoma gulo, asymmetrical variation

in generative organs, 167
Aurelia aurita, Meristic Variation of,

426 ; statistics as to, 428
Auricles, cervical, in Man, 177; in Pig,
179; in Sheep and Goats, 180; are
repetitions of ears, 180

Baer, von, Law of, 8; its proper scope,
9; probably not applicable to cases
of Discontinuous Meristic Variation,
571

Balance between mamma?, 189 ; between
teeth, 213

Balanocrinus, 4-rayed specimens, 436

Balanoglossus, two methods of develop-
ment, 9 ; number of gill-slits, 174 ;
extra proboscis-pore, 466 ; supposed
relation to Chordata, 86

Batrachia, extra limbs, 554; spinal
nerves, 141; vertebra?, 124; extra

B.

atrial opening, 465; axial duplicitv,
561
Bdell08tQmat individual and specific
variations in number of
gill-sacs, 173, 174
cirrhatum, heptatrema,
heterotrema, hexatrema,
173; btichoffi,polytrema,
174
Beech, fern -leaved, 25
Bees, hermaphrodite, 68 ; union of
eyes, 461 ; antenna modified as foot,
147
Beetles, variation of horns, 38; an-
tenna?, 411, 413; extra ap-
pendages in Secondary Sym-
metry, 475; legs, 483; an-
tenna?, 513; palpi. 524; di-
vision of pronotum. 455
supposed double leg.-,, 544 ; sup-
posed double antennas, 51s ;
supposed double palpi, 551
Benibidium striatum, extra palpi, 524
Bettontjia, variation in molars, 258;

cuniculus, lesueri, penicillata, 258
Bilateral asymmetry, Homceosis in cases

of, 465
Bilateral Series, nature of. 88; Bieristic

Variation of, 448
Bilateral Symmetry. 19 ; in variation of
vertebra?, 128; in variation
of Annelids, 167 ; in varia-
tion of mamma, 183; in
variation of teeth, 267; in
cervical fistula. 175; in
variation of ocelli, 292; in
variation of digits, 402; in
variation in antennae <>f /•'<</•-
fieula, 414; in variation of
Radial Series, 427; in ab-
normal branching of Ante-
don, 438; in distribution of
triasters in segmenting egg,
464 ; in abnormal union of
blastomeres, 164
as found in manna and p< -.

369, 403
influence on Secondary Sym-
metries doubtful, 5 7
Bipinnaria, extra water-pore, (66
Birds, spinal nerves, 129; digital Varia-
tion, 390, 396
Blaniulus, mod.' of increase in uum

of segments, 93
Blaps, extra legs, 512; extra antennae,
attenuate, 522; double antenna, ehev-
rolati} cylindrica, similis, •">•"> 1
Blatta, variation in number ><( tarsal
joints, discussion of, 63; facts, 1 1 5 :
regeneration of tarsus with 4 joint-.

116

Blue, as variation of i. .1. 1 1
Boar, Wild, extra digits, 38
Bombinator, vertebra . 127

37

578

INDEX OF SUBJECTS.

Bomlms variabilis, antenna developed as

foot, 147
Borribyx, extra wing, quercus, 284, rubi,

282
Box-turtle, digital variation, 396
Brachial plexus, birds, 129; Man, 113,

135 ; Bradypodidae, 141
Brachinus crepitans, double (?) leg, 546
Brachiopod, double monster, 566
Bradypodidae, vertebrae, 118; brachial

plexus, 141
Brachy teles, teeth, 205
Branchiae, variations in number, 172
Branchiomma, double tail, 564
Branchipus, segmentation of abdomen,
97; relation to Artemia,
96 — 101 ; species dis-
tinguished by sexual
characters of male, 100
ferox, xpinosus, 97, 100;
stagnalis, 100
Brill, pigmentation of blind side, 468,

470
Brimstone butterfly, variation in colour,

45 ; nature of pigment, 48
Broseus vulgaris, double (?) leg, 547
Buccinum, teeth, 262 ; double operculum,

457
Bucorvus, brachial plexus, 131, 132
Bulldog, teeth, 210, 221
Bulldog-headed races of Dogs, 57: of

Fishes, 57
Buteo latissimus, extra digit, 393 ; vul-
garis brachial plexus, 131
Buzzard, extra digit, 392, 393

Calathus fuscus, extra eye, 280; extra
legs, cisteloides, 506, fulvipes, 507,
grceeus, 505

Callidium variabile, double (?) antenna,

551; ciolaceum, extra antenna arising

from head, 551
Call into rpha, colour-variation of species

of this genus, 46
Callinectes hastatus, extra spines on

lateral horn of carapace, 557
Callithrix, teeth, 208
Callorhinus ursinus, teeth, 343
Caloptenus «]>retus, colour-variation, 44
Calopteron reticulatum, extra antennae,

522
Calopus cisteloides, extra legs, 512
Calosoma investigator, extra antennae,

523; auropunctatum, double (?) leg,

548; double (?) antenna, sycophanta,

triste, 550
Cancer pagurus, maxillipede developed

as chela, 149, 150 ; extra parts of

limbs, 527 ; variations in chelae, 530 —

536
Canidje, digits, 401; mammae, 189

teeth, 209—222; incisors, 210;
canines, 210; premolars, 211;
molars, 217

CaxidjE, teeth,

Canis antarcticus, 215; azarce,
217; cancrivorus, 218; corsac,
214; dingo, 212, 215; javan-
icns, 209; lacjopus, 220; later-
alis, 212; lupus, 212,213,217,
220; magellanicus, 218; me-
somelas, 212, 217 ; occidentalis,
214,219 ipennsylvanicus, 210 ;
prinuevus, 209; procyonoides,
215,220; vetulus, 217 ; viver-
rinus, 212; vulpes, 210, 212,
213, 214, 219, 220 ; zerda, 220
vertebras, 122; cervical rib, 122
Canines, supernumerary, Tiger, 225 ;

Ass, 245; divided in Dor. 211
Capreolus, horns, 286; union of horns,

460; polydactylism, 371, 379
Caprimulgus, brachial plexus, 131
Carabus, antenna, supposed cases of
double, auratus, cancellatus,
catenulatus, emarginatus, ex-
aratus, intricatus, italicus,
sylvestris, 550
antennae, paired extra, arv en-
sis, 523; auronitens, 522;
monilis, 522; sacheri, 523
leg, supposed cases of double,
creutzeri, 547; helluo, 547;
intricatus, 545; melanckoli-
cus, 548; nemoralis, 547;
septemcarinatus, 547
legs, extra in Secondaiy Sym-
metry, auratus, 511; auro-
nitens, 511 ; cancellatus, 511;
catenulatus, 512; grcecus,
486; granulatus,48£; irregu-
laris, 497; italicus, 512;
marginalis, 484; perforatus,
484; sche idler i, 4V3
palpi, supposed cases of double,
auratus, purpurascens, splen-
dens, 552
pronotum, division of, lothar-
ingus, 456; scheidleri, 455
Carcinomata, multipolar cells in, 431
Garcinus nucnas, external segmentation
of abdomen changed by parasites, 95 ;
extra parts in limbs, 527, 531, 534
Carnivora, teeth, 209; vertebrae, 122
Carp, bulldog-headed, 57
Cassowary, feathers partially without

barbules, 55
Castration, parasitic, of crabs, 95
Cat, variation in colours of, 48

digits, 312, 313; porydact3*lism in-
herited, 323
spinal nerves, 138
teeth, 222
vertebrae, 122
Caterpillars, segmental Repetition of

pattern in, 25
Catocala nupta, colour-variation in hind
wings, 44, 46

INDEX OF SUBJECTS.

579

Caudal fin, division of, in Gold-fishes,

451
Cebida), teeth, 205
Cebus, teeth, 205
Cell-division, variations in, 430
Centrosomes, variations in number of,

480
Cephalotia, 458
Cerambyx, extra legs, 491; double (?)

antenna, cerdo, scopolii, 551; extra

antenna arising from head, cerdo, 551
Cercocebus, teeth, 204
Cercopithecus, teeth, 204; abnormality

in, 204
Ceroglossus valdivice, extra legs, 500
Cervical vertebrae, assumption of dorsal

characters, Man, 107
Cervus axis, molar, 246

rufus, premolar, 246
darna, extra digits, 379
Cestoda, variation in segmentation of,

168; bifurcation and other conditions

allied to duplicity, 565
Cestracion, teeth, 261
Cetonia, extra legs, opaca, 488, morio,

512
Chalcides, digital variation in the genus,

395
Chamois, extra horns, 286
Charadrius, brachial plexus, 130, 132
Chela?, extra parts in Secondary Sym-
metry, 528 ; amorphous cases,
538; duplicity of, 540
developed from third maxillipede
in Cancer, 149
Chelonia, axial duplicity, 563
Gheraps preissii, apparent presence of

female openings in males, 155
Chiasognathus grantil, double (?) anten-
na, 551
•Chilognatha and Chilopoda, variation in

segmentation of, 93
Chirocephalus, sujaernumerary horn to

generative sac, 457
Chimpanzee, vertebrae, 116

spinal nerves, 139
teeth, 202
'Chionobas, eye-spots, 295
Chironomw, double head, 565
Chiropotes, 208

Chitons, repetition of eyes in, 26; vari-
ation in colours of scutes, 307
ChUenius nigricornis, extra legs, 512;

double (?) leg, holosericus, 546, dijli-

nis, 548, vestitus, 548
Cheerocampa, colours of larva3, 304
Cholapus, vertebrae, 118, 120; brachial

plexus, 141
Cholornis, hallux absent, 397
Chordata, segmentation of, 86
Chroicocephalus, brachial plexus, 130
dhrysemys, axial duplicity, 563
Chrysomela, division of pronotum,/HCt7f(i,
455

Chry8omela, extra legs, banksii, 194;
graminis, 198
double (?) leg, hcemoptera,

517
double (?) antenna, eacalia ,
550

Chub, bulldog-headed, 58

Cicindela sylvatica, double (?) antenna,

550
Cidarite8, 4-rayed specimen, 411
Clmbex axillaris", antenna developed as

foot, 146
Cimoliasaurus, imperfect division of ver-
tebra?, 103
Ciona intestinal is, variation in number

of stigmata, 172
Cistudo, digital variation in, 396
Cladocera of salt lakes, 101
Clausilia bidens, extra eye, 280
Clavatella, variation in number of s< g
ments, 425 ; in number of eyes in each
segment, 425
Clupea pilchardus, scales, 274
Glythra quadripunctata, extra legs. 5os
Clytus liciatus, extra legs, 508; extra
antenna?, arcuatus, 522, tricolor, 522;
double (?) antenna, arcuatus, 551
Coccinclla decempunctata, bipunctata
and septeiupunctata, colour-variation,
49, 572
Cochin fowls, "silky" variety, 55
Cockroach, variation in number of tarsal

joints, 63, 415
Coelenterata, imperfect division, 566
Colias, colour-variation, 44 ; interme-
diates between ediua and helice, 14;
varieties of hyale, 45
Colobns, teeth, 204
Colour and Colour-patterns, variations

in, 42, 288, 572
Colour-variation, discontinuity of, per-
haps chemical, 72; simultaneous, in
segments, <\c, 303
Coluber, double monster, 561
Columba, brachial plexus, 131, 134
Colymbetes sturmii, extra legs, 512; ad-
spersus, double (?) leg, 548; coriaceut,
double (?) antenna, 550
Col y tubus, brachial plexus, 130
Conepatus chilensti and mapurito, teeth,

232
Continuity, use of term as applied to
Variation. 15; of differences in En-
vironment, 5

Copepoda, Of salt lakes, 101

Cordylophora lactutris, porystomatous

specimens, 566
Correlation, between variations of nerves

and vertebra, 145; between Keristic

and Substantive Variation, L96

CorvtU, brachial plexus, 131
Corymbitet cupretu, colour-variation. 18
Counterparts, simultaneous variation of,
500

M7— 2

580

INDEX OF SUBJECTS.

Cow, variation in number of teats, 188

Crab, extra parts of appendages, 527 —
536 ; variation in segmentation of ab-
domen, 95

Crateronyx, extra wing, 285

Crayfish, variation in number of gene-
rative openings, 152 ; repetition of
parts of chelae, 529, 532, 537; extra
parts in antennas, 538

Cribrella, abnormal branching of an arm,
440

Crinoids, radial joints, 421; variation in
number of rays, 435 ; 4-rayed varieties,
436 ; 6-rayed varieties, 437 ; 3-rayed
and 5-rayed varieties of a 4-rayed
form, 437; variation in number of
canals in stems, 438; abnormal
branching, 438

Crista, division of embryos, 556

Crossarchus, teeth, 227—231 ; zebra, 230,
231

Crustacea, theory of descent of Yerte-
brata from, 29 ; of salt lakes, 100 ;
Secondary Symmetry in, 525; Homce-
osis in, 149

Cryptohypnus riparivx, extra legs, 509

Cryptophagus scanicus, dentatus, double
(?) antenna, 550

Ctenodrilus, double tail, 565

Cucumaria planei, with six radii, 433;
double monster, 566
aciculi, double monster, 566

Cnon, one lower molar absent, 209

Cupressocrinus, imperfect variation to
4-rayed state, 437 ; variation in num-
ber of canals in stalk, 438

Curve of Frequency of Variations, 37, 64

Cuvierian organs, variation in number of,
435

Cj'clopia, 458

Cygnus olor, cervical vertebras, 33 ; colour-
variation of young, 44 ; atratus,
brachial plexus, 130

Cyllo leda, variability of ocelli, 289

Cyncelurus, teeth, 222, 224

Cynocephalus jyorcarius, extra molar, 204

Cyprinus carpio, bulldog-headed varie-
ties^?; hungaricus, ditto, 58; auratus,
division of fins, 451

Cyprus, 4-horned sheep, 285

Cypselus, brachial plexus, 131

Cystophora cristata, premolars, 238;
molars, 243

Dachshund, hallux in, 401 ; duplicity of

hallux and pollex, 401
Dactylopodites. extra, 528
Dactylopsila, premolars, 255
Darwin's solution of problem of Species,

5; views on Reversion, 77; on sudden

Variation in eye-spots, 289
Dasyuridas, incisors, 247
Daayurua, incisors, 247 ; premolars, 255 ;
molars, 256

Dasyurus, viverrinus, variation in molars,.
256
maculatus, molars, 256
Deilephila euphorbia*, colours of larvae,

305; hippophaes, 305
Dendarus hybridus, extra antennas, 523
Descent, Doctrine of, assumed to be

true, 4
Diaptomus, colour-variation of eggs,

44
Dicotyles torqaatus, incisors, 245
Didolphyidae, incisors, 246
Didelphys, teeth, 246, 258
Digits, Variation of

Mammals. Capreolus, 374 ; Cat,

313; Cervus, 379; Dogs, 401;

Erinaceus, 397; Elephas, 397;

Goat, 377; Herpestidas, 346;

Horse, 360; Hylobates, 346;

Macacus, 340; Man, 324; Mule,

360, 370; Ox, 374, 383; Pig,

381, 387; Sheep, 373, 380

Birds. Anas, 392; Aquila, 393;

Archibuteo, 392; Buteo, 393;

Fowl,390;La/'us,393; Pheasant,

393; Rissa, 396; Turkey, 393

Reptiles. Chalcides, 395 ; Cis-

tudo, 396

Reduction in number, Man, 355,

358 ; Artiodactyla, 383
Union of, Ox, 383; Pig, 387 ; Man, 355
Variation in, associated with other

variations, 399
Inheritance of Variation in, 398
Recapitulation of evidence, 400
Dimorphic condition, its relation to the

monomorphic condition, 37
Dimorphism in Spinal nerves, 138; in
position of generative openings in
Pachydrilus, 165, 168 ; in secondary
sexual characters, 38
Diopatra, abnormal repetition, 159
Discoidea (Echinid), 4-rayed specimen,

442
Discontinuity of Species, 5

in Variation, a possibility,
17 ; suggestion as to its
nature, 68, 568
in chemical processes, ] 6,

48, 72
in colour-variation, 43, 48,
72; in colour-patterns,
48
in states of matter, 16
of Meristic Variation per-
haps mechanical, 70
of Substantive Variation
perhaps in part chemi-
cal, 71
in the Variation of spinal

nerves, 145
in the Variation of the
generative organs of
Annelids, 168

INDEX OF SUBJECTS.

581

Discontinuity in the Variation of digits,
•407
in Meristic Variation of

Radial Series, 423
partly dependent upon
Symmetry, 568
Discontinuous Variation, use of the term,

15
Disease, analogy with Variation, 74
Ditomus tricuspidatux, double (?) an-
tenna, 550
Division of organs, a process of repro-
duction, 193
of teeth, 268; of mamma?, 193;
of digits, 349, 369; of ten-
tacles, 280 ; of radius of
Echinid, 446; median, 454
Dog, cervical rib, 122; hairless, 57; bull-
dog, 210, 221; digits, 401; nipples,
189
teeth, 209—222; incisors, 210;
canines, 211 ; premolars, 213,
215; molars, 220; deficiencies in
Esquimaux, 215; in Inca, 216
Dog-whelk, colour-variation, 48
Domestication, variability falsely ascrib-
ed to, 266, 401
Dunacia bidens, Variation in antennre,

413
Dorcadion rufipes, extra legs, 512
Dorking Fowl, digital variations, 390 —

395
Dorocidaris papillata, variation in pedi-

cellaria?, 429
Double-foot, Artiodactyles, 378; Frog,

540; Macacus, 340; Man, 337, 338
Double-hand, 325, 331
Double Monsters, 559
Double-thumb, 349
Dromceolus barnabita, extra antennae,

523
Duck, no variation in number of digits
recorded, 401 ; cases of absence of
webs between toes, 401
Duplicity of single members of series not
distinct from other modes
of addition, 193, 407
of appendages, 406 ; in Arthro-
poda, 539; in Vertebrata,
539
axial, 559
Dutch pug, 57

DyscJiirim globuloxus, extra legs, 512
Dytiscus marginalis, extra legs, 512

Eagle, extra digits, 393

Ears, repetitions of, known as cervical
auricles, 180

Earthworms, variation of generative
organs, 159 ; of segmentation, 157 ;
asymmetrical arrangement of genera-
tive organs, 160, 161 ; table of arrange-
ment of ovaries, 162; duplicity of
head, 565, of tail, 565

Earwig, variation of forceps, 40 ; of
antennary joints, 413

Echinocomu, 4-rayed specimen, 441 ;
alleged case of 3 rays, 411

Echinodermata, Meristic Variation in,
432; variations of pedicellaria-, 429;
duplicity,

Echinoidea, Meristic Variation of, 411 ;
4-rayed specimens, 441; partial dis-
appearance of a ray, 413; partial
duplicity of a ray, 446; 6-rayed speci-
men, 445; pedicellariae, 429; variation
in number of genital pores, 446 ; sym-
metrical reduction of two rays, 4 13

Echinus melo, partial reduction of an
ambulacrum, 443

EcJtinus sphcera, partial reduction of an
interambulacrum, 445

Ectrodactylism, Man, 355, 358

Elater murinus, extra antennas, 522 ;
variabilis^ extra leg, 547 ; hirtus,
double (?) antenna, 551

Elcdone, supernumerary hectocotylus.
473

Eleodex pilosa, double (?) antenna, 551

Elephas, tusks, 244; hoofs, 397

Elytra, said to have been replaced by
legs in Prionus, 148

Embryology, as a method of investigating
problems of Descent, 7

Emperor moth, ocelli absent, 289, 301;
colour- variations of larva, 306

Emu fowls, 55

Enchytr&'idae, generative openings, 165

Encrinus, variation in number of radial
joints, 421 ; 4-rayed calyces. 436 ;
radius bearing only one arm, 438

Enema pan, extra legs, 512

Entoniscians, alter segmentation of
some crabs but not of all, !'">

Enhydris, incisors, 211

Epiglottis, division of, 451

Epipodites, variation of in Hippolyte,
151

Epistome (of Beetle), division of, 1">1

Erebia bland inn, ocelli, 289

Erinaceus, variation in hallux, 3'.i7

Eriphia spinifrom, extra chela . 528

Eros minutus, extra Legs, 487

Enox Indus, bulldog-headed, 58

Esquimaux Dog, absi ace of first pre-
molars, 214, 215, •-'•-'}_

Euchloe, pigments of, 72

Eugeniacrinus, 4-rayed specimens, i

Euprepia puipurea, extra palpi (alleged),
524

Eurycephahu maxillosus^ extra legs, 1^7

Euscnrpius, double tail, 565

Eve of Palinurtu developed as antenna,
160

Eye-colour of Man. 43

Eye-spots, 288; Variation as a whole.

291; outer /.one- first to appear, 291;

analogy with chemical phenomena.

582

INDEX OF SUBJECTS.

292; in Linear Series, 288, 293;
simultaneous Variation of, 293 ; corre-
lated with variation of neuration, 293,

301

Arge, 295; Chionobas, 295; Hip-
parchia, 294; Satyrus, 295;
Morpho, 296 ; Vanessa, 299 ;
Junonia, 299, 300; Pararge, 300;
Saturnia, 301, 302; Raiidae, 302;
Polyplectron, 450
Eyes of Clavatella, variation in number,

425
Eyes of Molluscs, 279; of Insects, 280;
union of, 458, 461

Feathers, of "hairy" Moorhen, without

barbules, 55
Felid.e, digits, 313

teeth, 223—226

Felis brachyurus, 224; cali-
gata, 223 ; caracal, 224
catus, 224; chaus, 224; chi
nensis, 224 ; concolor, 223
domestica, 223, 224, 225, 226
eyra, 223; fontanieri, 225
226 ; inconspicua, 223 ; ja
guarondi, 224 ; javanensis
224; jubata, 224; leo, 226
/;//(.r, 226; manicirfata, 223
manul, 224; minuta, 223
nebulosa, 224; cwca, 224
pajeros, 224; pardalis, 226
pardus, 223, 226; tetraodon
223; tigrina, 22G; tigris, 224,
225
vertebrae, 122
Feronia muhlfeldii, extra legs, 485
Fins, division of, in Gold-fish, 451
Fishes, undifferentiated teeth in certain,
32 ; bulldog-headed, 57

division of caudal fins, 451 ;
scales, 274 ; flat-fishes, 466
Fistulae, cervical, 174; morphology of,
176 ; aural, 177

in Man, 175; in Pig, 179; in
Horse, 180; unknown in Sheep,
Goats and Oxen, 180
Flat-fishes, reversed varieties, 54, 466 ;

"double" varieties, 466
Fcenius tarsatorius, extra legs, 491
Foot, double, Artiodactyla, 378 ; Frog,

540; Macacus, 340; Man, 337, 338
Foraminifera, duplicity, 566
Forfieula auricularia, variation of for-
ceps, 40; of antennary joints, 413
Fowls, silky variety of, 55

digital variation in, 390; ovary
and oviduct, 465
Frog, vertebrae, 124; extra legs, 554;
double foot, 540 ; Secondary Sym-
metry, 554
Fusus antiquus, sinistral, 54

Galerita africana, extra legs, 495

Galerites albogalerus, 6-raved specimen,
445

subrotiuidus, 4-rayed specimen,
441
Galictis, teeth, barbara, vittata, 232

vertebrae, 123
GaUinula chloropus, hairy variety, 55 ;

extra digits, 392
Gallus, brachial plexus, 130; digits,

390; oviduct, 465
Garganey Teal, division of digits, 392
Garrulus, brachial plexus and ribs, 135
Gasteroxteu*, scales, 276
Gavialis, change in number of vertebrae,

123
Gecinus, brachial plexus, 131
Generative openings, repetition of, in
Astacus, 152; absence of, in Astacus,
152, 154; of Earthworms, 159; of
Hirudo, 166
Generative organs of Earthworms, varia-
tions in, 159; of Leeches, 165
Genital pores, variation in number in

Echini, 446
Geophilus, variation in number of seg-
ments, 94
Geotrupes mutator, extra legs, 500 :

typhcvus, extra antennae, 515
Gill-slits, of Ascidians, 171; of Hyxine,
172; of Bdellostoma, 173; of Ammo-
coctes, 174 ; of Notidanidae, 174 ; of
Balanoglossus and Amphioxus, 174
Glaucium luteum, colour-variation, 47
Gmelin's test for bile-salts, 292
Goat, incisor, 245 ; horns, 286 ; digits,

377 ; cervical auricles, 180
Gold-fish, simultaneous variation in
length of tail and fins, 309; division
of anal and caudal fins, 451; "Tele-
scope," 453
Gonepteryx rJiamni, similarity of fore

and hind wings,
25
colour - variation,
45 ; nature of
the yellow pig-
ment, 48
extra wing, 283
Goose, brachial plexus, 133; pygomelian.

401
Gorilla, vertebrae, 117; spinal nerves,

139; teeth, 202
Goura, brachial plexus, 130
Grits, brachial plexus, 130
Guinea-hen, double-hallux, 392
Guinea-pig, inversion of layers in, 9
Gido, teeth, 231

Haemal spines, division of, in Gold-
fishes, 453
Hair, absence of, in Mouse, Horse,

Shrew, 56 ; silky in Mouse, 55 ;

excessive length in mane and

tail of a horse, 309

INDEX OF SUBJECTS.

583

"Hairy" Moorhen, 55
Halichoerus, vertebras, 123; molars, 242,
243

Haliotis, extra row of perforations, 287;
perforations occluded, 287; perfora-
tions confluent, 287
Halla, imperfect segmentation in, 156
Hallux, duplicity in Man, 349; Fowl,
390; variations in Kittiwake (Rissa),
396; Erinaceus, 397; Herpestidae, 397,
normally absent in certain birds, 396
Hammaticherus hews, double (?) an-
tenna, 551
Hand, digital variations in, 324; double,
325, 331
progressive series of Conditions,
324
Hapalida?, teeth, 208
Harpalus, rubripes, extra legs, 493; cal-

ceatus, double (?) antenna, 550
Hawthorn, variation of, 569
Hectocotylus, supernumerary, in Ele-

done, 473
Helictis orientalis, teeth, 233, 234
Helix kermovani, extra e3'e, 280

hispida, union of tentacles, 461
Heloderma, vertebrae, 123
Ilelops ceeruleus, extra antennae, 523

sulcipennis, extra palpi, 524
Hemiaster ; cases in which one ambula-
crum wanting, 445 ; two ambulacra
reduced, 443 ; duplicity of ambulacra,
446
Hepialus humuli, males like females in

Shetland, 254
Heptanchus, seven gills, 174
Heredity, objection to use of term, 75 ;

in digital variation, 398
Hermaphroditism, 67 ; in bees, 68
Hermodice carunculata , abnormal seg-
mentation, 158
Herpestid.e, hallux, 397
teeth, 227-231

Herpestes galera, 229; gracilis, 227,
228, 229; griseus, 229; ichneu-
mon, 229, 230, 231 ; microcephalus,
229; nipalcnsis, 227; nyula, 228;
persicus, 227; pulverulentus, 228,
229; smithii, 228, 229
Herring, supposed hybrid with Pilchard,

275
Heterocephalus, a naked Eodent, 56
Heterogeneity, universal presence of in
living things, 18
symmetrically distributed
around centres or axes,
19
Heterorhina nigritarsis, division of pro-

notum, 455
Hexanchus, six gills, 174
Hipparchia tithonus, eye-spots, 293, 294
Hippocampus compared with Pliyllo-

pteryx, 309
Hippoglossus pinguis, 471

Hippolyte fabricii, variation in epipo-

dites of legs, 151
Hirudinea, variation in generative
organs, 165
in colours, 304
Hirudo medicinalis, variation in numbei

of testes, 165, L66
officinalis, supernumerary penis,
166
HUter cadari rinus, extra legs, 512
Holopus rangi, 4-rayed specimen, 436
Holothurioidea, variation in number of
radii, 433; variations in numbers of
organs, 435; double monsters, 5C6
Homarus, repetition of parts in cheliped,
530; in chela , 531-538 ; colour varia-
tion, 44; hermaphrodite, 155
"Homodynamy," 133
Hornceosis, use of the term, 85

between vertebra;, 106-127 :
backward and forward, use
of terms, 111; forward in
vertebra?, 112; backward in
vertebra, 111 ; in spinal
nerves, 144 ; of appendages
in Arthropoda, 146; in Beg-
ments of Annelids with re-
spect to genital organs, 162,
163, 167, eve; in teeth, 272;
in bilateral asymmetry, 465;
in parts of flowers, 111
Homology between members of Series
of Repetitions, 30
individual, not attributed if
series is undifferentiated,
32; attempt to trace in
mammas, 191 ; discuss* J
in the case of teeth, 269;
in the case of digits, 351,
391, 371, 377; in the case
of joints of tarsus of Blatta ,
418 ; in the case of radii of
Holothurioidea, 433
Horns, Sheep, 285 ; Goat, 286; Boebuok,
286, 460 ; Chamois, 286 ; of EU A ■
buck united in middle line, 4»ii»
Horse, similarity of fore and hind L<
25, 26
naked variety, 56 ; teeth, 244, 2 !•">
cervical fistula?, 180
simultaneous variation of mane

and tail, 309
extra digits, 360; by development

of digit ii.
;stil 367
by development
ofdigit iv,367
by development
of digits n
and iv, 368
by division of
digit in, 369
by intermediate
process, 371

584

INDEX OF SUBJECTS.

Hyas, double chela, 540; double index,

541
Hybrids, supposed, between Herring and

Pilchard, 274 ; supposed, between Tur-

bot and Brill, 468 ; supposed, in genus

Terias, 52, 53
Hydrobius fuscijjes, pronotum having

three lobes, 454
Ilylobates, vertebrae, 118; teeth, 204;

leuciscus, extra digit, 346
Hylotrupes bajulus, extra legs, 494
Hypsiprymnus, teeth, 258

Iceland, 4-horned sheep, 285
Ichneumon luctato^•ius, extra legs, 511
Ichueumonidae, extra legs, 491, 511
Icticyon venations, teeth, 220
Ictonyx, teeth, 233

Images, relation of, the basis of Symme-
try, 19
between upper and lower jaws,
196, 267; between right and
left sides, 88; in the case of
the manus and pes, 404
division and union of parts re-
lated as, 449
principles of, followed in the
structure and position of parts
in Minor Symmetry, 479
Inca Dogs, a bulldog found amongst,
57 ; variation of premolars and molars,
216, 222
Incisors, supernumerary, Gorilla, 203 ;
Ateles, 207; Canidae, 210;
Felidae,222; Herpestidas,227;
Pecora, 245; Licotyles, 245;
Horse, 244
division of, Canidse, 210; Ele-

phas, 244
absence of, Canidse, 211 ; Feli-
dae, 222; Herpestidae, 227;
Phocida?, 235 ; Horse, 244
Index of crabs and lobsters, peculiarity

in repetition of, 557
Individuality, attributed to members of
Meristic Series, 31 ; such individuality
not respected in Variation, 32; cases
illustrating the absence of supposed
individuality in Members of Meristic
Series, 104, 115, 124, 191, 269, 407,
433; an unfortunate term, 556

Jacamaralcyon tridactyla, distinguished

by absence of hallux, 396
Jackal, vertebrae, 122; teeth, 217
Japanese pug, probable independent

origin of, 57
Jaws, relation of upper to lower, 196
Julodis cequinoctialis, extra legs, 503;

clouei, double (?) antenna, 551
Julus tevrestris, mode of increase in

number of segments, 93

Kallima inachys, colour- variation, 53

Karvokinesis, symmetry in, 20; varia-
tions in, 430; bilaterally symmetrical
variation of, in the segmentation of
an egg, 464

Kidney, supernumerary, 277 ; horse-
shoe, 278, 459

Kittiwake, variations in hallux, 396

Laciniation, simultaneous, of petals, 310

Lady-birds, colour-variation, 49

Lagorchestes, teeth, 258

Lagothrix, teeth, 208

Lamarck's solution of problem of Species,

4
Lamellibranchs, sinistral, 54
Lamia textor, double (?) antenna, 551
Larus leucopterus, digits, 393
Larvae of Lepidoptera, variations in

colours of, 304
Leaf-butterfly, colour-variation, 53
Leeches, variation in generative organs

of, 165 ; in colours, 304
Legs, extra, in Secondary Symmetry,
general account, 475, cases in
Insects, 483; in Position V,
483 ; in Position VAA, 485 ; in
Position A, 487; in Position DA,
491; in Position D, 494; in
Position DP, 496; Position P,
498 ; Position VP, 500. Uncon-
formable cases, 503; miscel-
laneous cases, 511 ; in Crus-
tacea, 526 ; in vertebrates, 554
supposed double in Insects, 544
Leopard, two cases of dental variation

in a Chinese, 225, 226
Lepidoptera, colour-variation of larvae,

304; ocellar markings, 288; nature of

yellow pigments, 73
Leptura testacea, double (?) leg, 545
Leuciscus dobula, bulldog-headed variety,

58
Lichnanthe vulpina, extra antennae, 517
Ligula, absence of segmentation in, 168
Limax, union of tentacles, 460
Limenitis populi, extra wing, 283
Limulus, division of caudal spine, 450,

456
Linaria, many symmetrical variations

of, 76
Linckia multijiora, fission, 433
Linear Series, Meristic Variation in, 63 ;

simultaneity in colour-variations of, 303
Lissotriton, supposed double limb, 539
Lithobius, number of segments, 93
Lithodes arctica, extra legs, 527
Littorina rudis, colour- variation, 49
Littorina, sp. , extra eye, 280
Lixus angustatus, division of pronotum,

456
Lizards, digital variation in, 395, 396
Lobster, colour-variation, 44 ; herma-
phrodite, 155; variations in chelae,

530—538

INDEX OF SUBJECTS.

585

Local Races, evidence as to, not a direct
contribution to Study of Variation, 17
Locusts, variation in colour of tibia?, 44
Loligo, variations in segmentation of

egg, 4(i3
Lucanus cervus, extra antennary branch,
2 cases, 549 ; extra branch on man-
dible, 2 cases, 552 ; capreolus, ditto, 552
Luidia ciliaris, variation of pedicellariae,

429
Lumbo-sacral plexus, 138
Lumbriconercis, imperfect segmentation,

156
Lumbriculus, double tail, 565
Lumbricus, undifferentiated segments in,
82 ; imperfect segmenta-
tion, 156 ; spiral segmen-
tation, 157 ; repetition of
ovaries, 160; asymmetrical
arrangement of organs, 160,
161 ; variation of genital
openings, 162 ; duplicity,
565
agricola, 162; herculeus, 160;
pvrpurens, 160; terrestris,
156, 157 ; turgidus, 160
Lupa dicantha, extra index, 542
Lurcher, teeth, 221
Lutra, teeth, 228, 233, 234, 235

constancy of pl in L. vulgaris,
228
Lyccena icarus, extra wing, 284
Lycalopex group of Foxes, frecpuency of

extra molars in, 217
Lychnis, repetition of fimbriation in

petals, 26
Lycus, double (?) antenna, 551
Lynx, teeth, 224
Lysimaehia, Meristic variation in flower

of, 61
Lysiphlebus, variation in number of an-
tennary joints, 412

Macacus cynomologus, syndactylism, 356
inuus, spinal nerves, 137, 139
teeth, 204
radiatus, doubtful extra molars,

204
rhesus, extra molar, 204
Macroglossa, colours of larvae, 304, 305
Macrognathus nepalensis, double (?) an-
tenna, 551
Macropodidae, teeth, 259
Macrorhinus leoninus, teeth, 243
Madreporites, repetition of, 440
Maia squinado, extra index, 542
Major Symmetry, 21, 87
Malachius marginellus, extra antenna,

522
Males, high and low, 39
Mallodon, double (?) leg, 547
Mammae, numerical Variation in, 181 ;
along mammary lines, 181 ;
in other positions, 186 ; in

axilla, 185 ; below and inter-
nal to normal mamma, 186;
above and external, 185
Mammae, variation in Cow, 101 ; Dog.
189; Pig, 190; Man, 181;
A]h -. L88
comment on facts, 191
development of, 191
Mammary extensions to axilla, 185
lines, 181
tumours. 185, 187
Man, cervical fistula;, 174; cervical auri-
cles, 177
digits, increase in number, 324 :
reduction in number, 355; poly-
dactyliam in general, 344; double-
hand, 331 ; symmetry of manna
and pes, 403
kidneys, union of, 459; renal arte-
ries, 277 ; ureter-. 27>
mammae, 181

nerves, spinal, 135; brachial plexus.
135 ; notable variation in, 137,
113 ; lumbo-sacral plexus com-
pared with that of Chimpanzee,
etc., 138
teeth, 198

transposition of viscera, 559
uterus, double, Darwin's comment

on, 77
vertebrae, Meristic and Homceotic
variation in, 103, 106 — 116, 458
Mandibles, supposed duplicity of, in

Lucanus, 552
Manns, variations in, compared with
those of pes, 405 ; as a system of
Minor Symmetry. 4(>:-i
Marsupialia, teeth. 2 16 — 258
Mastiff, teeth, 210, 221 ; hallux per-
mitted in, 401
Maternal impressions and extra Legs in

a beetle, 512
Maxillipede developed as a chela, 149,

150
Median nerve, variations in composition

of, 136
Medicago, repetition of brown Bpol in

leaflets, 26
Medusas, Meristic Variation i>i\ [23 ;

duplicity in, 666
Melanopliu packardit, colour-variation,

44
Meles, teeth, 2:52, 233, 236
Mellivora, teeth, 233, 235
Meloe coriaceus, double (?) I , 547 j
pro8carabau8i extra 1. 188; viola-
a us, extra antenna
HJelolonthavulgarii, division ol pronotum

i .". . . i ."> \

division of pygi-
dium, :

tra legs, 184, 512
extra antennas, 515,
520, 533, 550

586

INDEX OF SUBJECTS.

Melolontha vulgaris, double (?) leg, 545
hippocastani, extra antennae,
510, 557
Mephitis, teeth, 232

Merism, 20; importance of, to Study of
Variation, 23
indirect bearing of, on the
magnitude of Variations,
25
Meristic Repetition, 20 ; kinship of parts
so repeated, 26 ; similar Variation of
parts in, 27, 310, 46-4; compared with
asexual reproduction, 34
Meristic Variation, distinguished from
Substantive Variation, 22 ; compared
with Hoinceotic Variation, 84
Metacarpals, development of lateral, in
Artiodactyla in correlation with syn-
dactylism of metacarpals III and IV,
383
Metameric Segmentation, not distin-
guishable from other forms of Repe-
tition, 28 ; errors derived from such
distinction, 30
Metasternal plates, division of, 456
Metazoa, comparison with Protozoa, 35
Metritis contractus, extra legs, 503
Middle Line, division by images in, 404,

450 ; union of images in, 383, 458
Minnow, bulldog-headed specimen, 58
Minor Symmetry, 21, 88 ; Meristic Varia-
tion in, 311, 410 ; in manus and pes,
403
Molars, supernumerary, Simla, 200 ;
Troglodytes, 202; Gorilla,
203; Cynocephalus, 204; Ma-
cacus, 204 ; Cebus, 205 ; Ateles,
205 ; Mycetes, 207 ; Canidae,
217, 220 ; Felidae, 226 ; Her-
pestidae, 230; Mustelidae, 234;
Phocidse, 242; Ungulata, 245,
246; Dasyurus, 256; Bet-
tongia, 258

special frequency in Anthro-
poid Apes, 200; in Lycalopex
group of Foxes, 217
absent, Sirnia, 200; Ateles, 207 ;
Pithecia, 208; Canidae, 219,
221; Felidae, 226; Herpes-
tidae, 231; Mustelidae, 235;
Phocidse, 243; Bettongia, 258
division of, Canis cancrivorns,

219 ; Crossarchus, 230
Variation in form, Crossarchus,

231 ; Dasyurus, 256
in Icticyon and Otocyon, 220
Monkevs, Old World, teeth, 204; New

World, 205
Monodon, development of right tusk, 465
Monomorphism, 33

Monotonia quadricollis, double (?) an-
tenna, 550
Moorhen, hairy varietv, 55; extra digits,
392

Morpho, eye-spots, 296—299

achillcs, 297; menelaus, 298;
montezuma, 297; psyche, 299 ;
sulkoicskii, 299

Mouse, colour-variation, 44 ; with silky
hair, 55 ; black variety, 55 ; naked,
56

Mugil capito, bulldog-headed, 58

Mule, rarity of digital variation in, 360 ;
case of, 370

Mullet, bulldog-headed varietj-, 58

Multipolar cells, 430

Mustelidae, teeth, 231, 235; premolars in
M. foina, martes, melanojnis, zibellina,
231

Mycetes, teeth, 207, 208

Mycomelic acid, relation to yellow
colouring matters, 73

Mydaus, teeth, 232

Myriapoda, variation in number of seg-
ments, 91, 93

Myrmecobius, incisors, 247, 248

Myxine, variations in number of gill-
sacs, 172

Ncenia typica, extra wing, 284
Narcissus, Substantive and Meristic
Variation in, 23 ; colour- variation, 40
Narwhal, development of tusks, 465
Nasalis, teeth, 204

Natural Selection, chief objection to

theory of, 5 ; misrepresentations of

the theory, 80 ; difficulty in connexion

with regeneration, 420

Navosoma, extra antennae, 521

Nebria, double (?) antenna, 550; gyllen-

halli, double (?) maxillary palp, 551
Nectarine, discontinuous variation in,

59
Nereis, double tail, 564
Nerves, spinal, Birds, 129 — 135; Man,

135; Apes, 138; Cat,
138; Dog, 140; Brady -
podidae, 141; Pipa,
141
attempt to homologize,

32
variations, 129-145
correlation with verte-
brae, 145
relation to limbs, 143
Neural canal, division of, 451
Neuration of wings varying with eye-

spots, 293
Nigidius, extra branch on antenna, 549
Nipples, supernumerary, on normal
breast, 184; on normal areola bifid,
184; on mammary lines, 186; in Pig,
190; in Dog, 189
Notidanidae, number of gills, 174
Nuclei, multipolar division, 430, 464;

precocious division, 464
Nyctcreates procyonoides, teeth, 215
Nyctipithecus, teeth, 208

INDEX <)F sriUKcTs.

.W

Ocellar markings, 288, 449

Lepidoptera, 288 ; Raiida ,
302 ; Birds, 449
Odontolabis stevensii, extra antennae, ">18,

557
Oligochseta, axial duplicity, 503 ; ge-
nerative organs, 159; segmentation,
156
Ommatophoca rossii, premolars, 237
Onitis bison, division of pronotum, 455
Operculum, double in Buccinum, 457
Ophiacantha anomala, normally 0 arms,

not known to divide, 433
Opkiactis, fission, 433
Ophibolus, double monster, 561
Ophidia, vertebra, 103, 123
Ophidiaster cribrarius, fission, 433
(Jphiocoma pumila, young with 6 arms,

adults witb 5 arms, 433
Ophiothela isidicola, fission, 433
Ophiuroidea, variation in number of arms,

447; fission, 433
Opisthocomus, brachial plexus, 130
Orang, vertebrae, 118; spinal nerves, 13'J ;
teeth, 200 ; extra digit, 349 ; extra
mamma, 188
Organic Stability, 36
OrtUosia Icevis, extra wing, 284
Oryctes nasicornis, division of pronotum,

455; extra legs, 512
Osmoderma eremita, double (?) leg, 547
Otaria cinerea, molars, 240

jubata, premolars, 240, 243
ursina, premolars, 239, 241
Otocyon, teeth, 220, 221
Ouaharia, teeth, 208
Ovaries, variations in number and posi-
tion in Earthworms, 160, 162
not always correlated with
variations in oviducts, 167
Ovary, right, developing in Fowl, 466
Oviduct, right, case of, in Fowl, 466
Oviducts of Astacu*, variation in number,

152; in Earthworms, 167
Ox, incisors, 245; molar, 246; poly-
dactylism, 374-381 ; syndactylism,
384-387; syndactylism together with
development of digits II or V, 385 ;
with duplicity of II and V, 386; cer-
vical auricles and fistula? unknown,
180

Pachydrilus sphagnetprum, dimorphic in
respect of position of generative open-
ings, 165, 168
Painted Lady butterflv, colour-variation,

49
Palaornis torquatus, colour-variation, li-i
Palamnaus borneensis, division of poison-
spine, 457
Palinurus penicillatus, eye developed as

antenna, 150
vulgaris, extra legs, 527 ; extra
antennae, 538

Palloptera ustulata, abnormal growth

from thorax, 285
Palpi, paired extra, in Insects, 524

supposed doable, 551
Pangenesis, 75
" Panmixia," 573
Papaver nudicaule, colour-variation, 16;

pigment of, 17, 72
Parakeet, colour- variation, 13
Pararge megara, eye-spots, 289, 800
" Parhomology," 133
Pariah dog. teeth, 221
Parnassius, ocelli. 292
Parra, feathers, 55
Pasimachus punctulatus, double (?) .

547
Patella, extra tentacle and eye, 279
Pattern, universal presence of, in organ-
isms, 19-21; difficulties arising from,
21
Peach, discontinuous variation in. 59
Peacock, ocelli, 449
Peacock butterfly, repetition of i

spots in, 26; variation of, 299
Pecora, polydactylism, 'M'>
Pecten, double eye-, 280
Pedicellariae, Meristio Vaiiatiou of, 4 J '. *
Pelamis bicolor, imperfect division of

vertebrae, 105; axial duplicity, 561
Pelecanus, brachial plexus, I'M
Pelobates fuscus, extra spiracle, 165
Penis, supernumerary, in Hirudo, 166;

in Aulastoma, 167
Pentacrinus miilleri, increase in nun:

of radial join
4-rayed >p< cim<
dubius, dumorti-
i r/, jurensis, tub-
tulcatus, 436
6-rayed specimens,
jurensis, I
Penthina salicella, extra wing, 285
Peramelidee, digits of pes, 313
Perichata, variation in number of -i

mathecse, 165 \forbesi, hilgendorfi, 165
PeHcrocotus Hammeus, oolour-vanati

16
Perionyx, generative organ watus,

163, 167, L68
griim waldi, 164
l\ ripatus, variation in nnmbei i

ments, 84, 91, 94
l\ taurus, premolars, 26*5
Puai.ani.i Kin.v.. incisors, 248; premo

Lars, 248 256
Phalanger maculatus, incisors, 248; |

molars, 258; females Bpot-
t. i in Waigiu, 2
orientalis, incisors, 248, 250;

premolars, 250
ornatus, first pn molar two

root* d as \;n tation, 25 i
ursinus, first premolar nor-
mallv two-root* d. 254

588

INDEX OF SUBJECTS.

Phalanges, reduction in number, 355

Phascologale dorsal is, teeth, 257

Pheasant, digits, 393

Philonthus succicola, double (?) leg, 548
ventralis, extra legs, 507

Phoca barbata, incisors, 235, 236
cristata, premolars, 238
groenlandica, premolars, 238, 2-40,

242; molars, 243
vitulina, premolars, 238, 241,
242; molars, 242

PJuvnicopterus, brachial plexus, 130

Phoxinus Icevis, bulldog-headed, 58

Phratora vitellines, colour-variation, 43

Phreoryctes, generative organs, 162

Phyllopertha horticola, extra antenna?,
514

Phyllophorus, tentacles not in multiples
of live, 435

Phyllopteryx, compared with Hippo-
campus, 309

Physa acuta, tentacle bifid, 280

Picua uiridis, colour-variation, 43; me-
dius, brachial plexus, 131

Pieridae, colours of, 73; eye-spots in,
292

Pig, digits, 381; syndactylism. 387;
syndactylism with division of digit V,
389 ; cervical auricles, 179 ; cervical
fistulas, 180

Pigeon, cervical vertebras, 33 ; brachial
plexus, 134

Pigments, definite variations proper to
certain, 43; nature of yellow, in Pie-
ridae, 48.

Pike, bulldog-headed, 58

Pilchard, variation in scales, 274 ; sup-
posed hybrid with Herring, 275

Pilumnus, not altered by Entoniscians,
95

Pimelia inter stitialis, extra legs, 498
scabrosa, extra antennae, 523

Pinnipedia, Teeth, 235—243

Pipa, spinal nerves, 141

Pithecia, absent molar, 208

sa tanas, syndactylism in, 356

Pityophis, axial duplicity, 561

Plaice, symmetrical spotting of blind
side, 467

Plant, compared to the body of Man, 29

Platycerus caraboides, extra legs, 507

Platyonychus, not altered by Entonis-
cians, 95

Platysomatichthys, 471

Pleuronectes, pigmentation of blind side,
467, 471

Plume moths, repetition of pattern in
wings, 26

Pluteus, double, 35

Podargus, brachial plexus, 131

Pcecilogale, 232

Pointer, teeth, 221

Polian vesicles, variation in number of,
434, 435

Pollex, duplicity in, Man, 349 ; Bogs,

401
Polyarthron, variation in number of an-

tennary joints, 412
Polychaeta, axial duplicity in, 564
Polydactylism, Cat, 312; Man, 324;
Macacus, 340; Hylobatcs, 346; Simia,
349; irregularcasesinMan,353 ; Horse,
360—371 ; Artiodactyla, 373
Polydesmus, mode of increase in number

of segments, 93
Pohjodontophis, vertebrae, 123
Polyphylla decemlineata, extra antennae,

518 '
Polyplectron, eye-spots, 449, 450
Polyzoa, division of embryos, 556
Poppy, Iceland, colour- variation, 46;

Horned, colour- variation, 47
Porania, 4-rayed specimen, 440; irregu-
lar division of an arm, 440
Portunion, change in Carcinus produced

by, 95
Portunus puber, extra parts on chela,

535; not altered by Entoniscians, 95
Potorous, teeth, 358
Premolars, nomenclature, 199

supernumerary, Brachy teles,
205; Ateles, 206; Mycetes,
208; Canidae, 212—214;
Felidae, 225 ; Herpestidae,
229; Mustelidae, 231—234;
Phocidae, 237—242; Cer-
vus, 246; Phalangeridae,
248; Phascologale, 257
absence of, Canidae, 214 —
216 ; Felidae, 224 ; Herpes-
tidae, 229; Mustelidae, 231
—234 ; Phocidae, 237—242
apparent division, Brachy-
teles, 205; Canidae, 213;
Dasyurus, 255; Phocidae,
237
displacement and other va-
riations, Simia, 201
Pbionus, supposed development of elytra
as legs, coriarius, 148
variation in number of anten-
nary joints, imbricomis, 411,
Jissicornis, 412
extra legs, coriarius, 488, 512,
califomicus, 544, 557, cori-
aceus, 548
double (?) antenna, 551
double (?) legs, califomicus, 544
Procercea, double tail, 564
Protozoa, sujjposed relation to Metazoa,

35 ; duplicity, 566
Pseudochirus, premolars, 250, 255; in-
cisors, 248
Pterostichus, extra legs, lucublandus, 512;
miihlfeldii, 485; prevostii, 512; dou-
ble (?) antenna, planipennis, 550
Ptinus latro, extra legs, 512; extra an-
tennae, 522

INDEX OF SUBJECTS.

.>:>

Pujinus, brachial plexus, 130

Pug, breeds of, 57; teeth, 221

Purpura lapillus, colour-variation, 48

Putorius, teeth, 231, 234

Pygara anastomosis, extra wing, 284

Pygidium, division of, in Melolontho, 456

Pygoinelian geese, 401

Pyrameis cardui, aberrations of, 49, 52 ;

var. kershawi, 49, 52; var. <'l>/>ui, 50, -51
Pyrodes speeiosus, extra legs, 490
Python, imperfect division of vertebra?,

103, 105

Radial joints of Crinoids, 421
Radial Series, Meristic Variation in, 60 ;
evidence, 422; in Echinodermata, 432
Radii, variations in number, Holo-
thurioidea, 433 ; Crinoidea, 435 ; As-
teroidea, 439; Echinoidea, 441; Ophi-
uroidea, 433, 447
Radius, absence of, 360
Radula? of Buccinum, 262
Raiidre, eye-spots, 302: extra fin, 540;
division of fin into lobes, 540; separa-
tion of fin from head, 540
Rana, vertebrae, 124, 126; double foot,
540 ; spinal nerves, 142 ; extra limbs, 554
Ranzania bertolonii, extra legs, 510
Raspberry, yellow variet}', 47
Red, variations of, 44 — 48 ; as variation

from blue, 44
Renal arteries, 277
Repetition of Parts, association of these

phenomena, 21
Repetition, Linear, Bilateral or Radial,
distinctions between, 88
Units of, 556
Reptilia, vertebra?, 103, 123
Reversion, hypothesis made in order to
escape recognition of Discontinuity in
Variation, 76
Rhagium mordax, double (?) leg, 548
Rhea, brachial plexus, 130
Rhinoptera, teeth, 259 — 261, javanica,

261, jussieui, 259
Rhizocrinus, 6-rayed specimen, 437
Rhizotrogus, extra legs, aestivalis, 510;
castanius, 512
extra antennae, aquinoc-

tialis, 517
division of metasternal
plates, 456
Rhombus, pigmentation of blind side,
467—471 ; Usvis, 467, 468,
470; maximus, 467, 470
variations in scales, 468
RJupichites permanicus, double (?) an-
tenna, 550
Rhyttirhinus, supposed case of extra

eye, 281
Ribs, division of, in Man, 105

cervical, in Man, 108, 112, 115; in
Dog, 122; Bradypodids, 119: on
6th vertebra in Man, 108

Ribs, variations in dorso-lumbar region,
Man, 109—116; Anthropoid Ap< s,
116— lis; Bradypodide, Vi\ ;
Felis, 122; Canis, 122; Galietis,
123; Halichams, 123; eleven in

Siamese Twins. ."> t , « i

Rissa, variations of hallux in the genus

396, 397
Roebuck, horns, 286 ; polydactylism,

374,379; union of horns, 160
Rubus idaus, colour-variation, 17
Rupicapra tni<itt.<, horns, 286
Rutela fasciata, extra Legs, 512

Sacculina, effect of, on segmentation of
Carciniu and other Crabs, 93

St Bernard dog, duplicity of hallux in.
401

Salinity, doubtful relation of variations
of Crustacea to changes in, 100

Salmo fario, salar, trutta, 58

Salmon, bulldog-headed variety, 58; axial

duplicity, :>f>:i

Salmacina, double tail. 564
Salt lakes, Crustacea of. 96, LOO
Samia cecropia, extra wing, 28
Sand-canals, repetition of, in Aster

440
Saperda carcharias, extra antenna ariai

from head, 551
SarcophiluS) teeth, 255
Sarsia, Meristic Variation in. 424; with

six segments, 424 ; with five Begments,

425
Saturnia carpini, repetition ofeye-8]

in wings, 26; extra wing. 282; varia-
tion of eye-spots, 289, 301, 302;

colours of Larva, 306
Satyrus hyperanthus, eye-spots, 294
Sawfiy, extra legs, 502, 546
Scales of Pilchard, 271; of GasUi

276; of Snakes, 276
Scarites pyraemon, extra legs, 500
« Scheme, shewing the relations ^i parts in

Secondary Symmetry, 1M
Scolopendra, numlx r of w jm< nts. 94
Scorpion, double poison-spine, r~

double tail, 565
Saraptia fusca, extra antenna?, 523
Is, variations in dentition. 235
Segmentation, metameric, not in 1.
distinol from other foi i
of Repetition, 28; two
way- by which a full s.

mentation mayhavi l>< . □
achieved in phyiogeny,

of Axthropoda, variation

in. 91 ; impi if. ct in An-
nelids. L56 : spiral in
Annelids, L57 : variation
of in Cestoda, L68, 17"

of mamma . I'M

of ovum, variations in. ,

590

IXDEX OF SUBJECTS.

Selachians, teeth in, 259

Semnopithecus, teeth, 204

Sepidium tuberculatum, double (?) an-
tenna, 551

Sex, analogy with Discontinuous Varia-
tion, 66

Sexual characters, statistics as to, in
Beetles, 38; Earwigs, 40
of Hepialus in Shetland, 254
of Phalanger in Waigiu, 254

Sheep, cervical auricles, 180; incisors,
245 ; change in form of canines, 245 ;
molar, 246; extra horns, 285; poly-
dactylism, 373, 380

Sheep-dog, teeth, 221

Shetland, variety of Hepialus in, 254

Shrew, naked variety, 56

Siamese Twins, 560

Siberia, Crustacea of salt lakes, 97, 100

Silis rvficollis, extra"legs, 498

Silky fowls, 56

Silpha nigrita, extra legs, 501 ; granu-
lata, double (?) leg, 548

Silurus, extra fin, 540

Simia, vertebrae, 118; teeth, 200; extra
digit, 349 ; extra mamma, 188

Simultaneity of Variation, possibilities
of, 25, 26, 308 ; in fore and hind
wings of Lepidoptera, 293; in counter-
parts, 569; in colours of segments of
Lepidopterous larvae, 303 ; in Chiton
idffi, 307; in limbs, 402; in homo-
logous twins, 559 ; in radial segments,
423; not clearly distinguishable from
Symmetry, 569

Sinistral varieties, 54

Situs transversus, 465, 560

Sledge-dog, absence of first premolar,
215; division of premolar, 214

Smerinthus, colours of larvae, ocellatus,
pojnili, tilice, 306, 307

Snakes, vertebrae, 103, 123; axial du-
plicity, 561

Solea, pigmentation of blind side, 471

Solenophorus strepens, double (?) an-
tenna, 551

Sore.r, naked variety, 56

Spaniel, teeth, 221

Species, the problem of, 2. Methods of
attacking, 6
Discontinuity of, a fact, 2

Specific Differences, indefinite, 2

Spermathecae of Earthworms, variation
in number, &c. of, 160, 165

Spharocrinus, imperfect variation to 6-
rayed state, 437

Sphingida?, repetition of markings in
larvae of, 26 ; variation in, 304

Sphinx Ugustri, division of proboscis, 456

Spinal nerves, 129; Birds, 130; Man,

135; Primates, 138; Bra-

dypodidre, 141 ; Pipa,

141; Rana, 142

dimorphism in respect of,

138 ; distribution to

limbs, 143 ; Homeeosis,

144; recapitulation, 144

Spinal nerves, principles of distribution,

143
Spiracle, extra in tadpole of Pelobate*,

465
Stability, Organic, 36
Starfishes, theory of origin of repetition
in, 29; variations in number of rays,
439 ; multiplication by fission, 433
Stentor, duplicity, 566
Sticlioj)us, arrangement of tube-feet

changes with age, 435
Stickleback, variation in number of

bony plates, 276
Stomobrachium octocostatum, variety
having tentacles in double series,
425
S trau galia, double (?) antenna, atra,

551, calcarata, 551
Strategns antceus, extra legs, 512
Struthio, brachial plexus, 130
Styela, variations in branchial sac, 172
Subemarg inula, extra eye, 279
Substantive Variation, distinguished
from Meristic, 23; cor-
related with Meristic in
vertebra?, 125
in size, 38, 40; in colour,
43 — 48; in colour-pat-
terns, 48 — 54 ; miscel-
laneous, 54 — 60
Swan, cervical vertebrae, 33; colour-
variation of young, 44 ; brachial
plexus, 130
Symmelian "monster," 459
Symmetry, the conception of, 19, 569

a relation between optic-
al images, 19
almost universal pre-
sence of in living or-
ganisms, 21
of mammae, 191
in dental Variation, 267
in digital Variation, Man,
324,402; Cat, 314; in
manus and pes, 4U3
in nuclear division, 430;
in variations in seg-
mentation of ovum,
463
in variations of homo-
logous twins, 559, 560
in double monstrosity,

559
Bilateral, characters of,
88; as appearing in
variations of flat-
fishes, 467
Major and Minor, 21, 86
Primary and Secondary,

90
Kadial, characters of, 89

INDEX OF SUBJECTS.

591

Symmetry, Secondary, preliminary ac-
count, 475; principles,
479
Scheme of relations of
parts in, 481; parts
repeated in, geometri-
cally peripheral to
points of origin, 557;
relation to Primary,
556, 557
in Insects, 475; Crus-
tacea, 525 ; Verte-
brates, 553 ; Batra-
chia, 554; Triton, 555
Syndactylism, Man, 355, 356; Pithecia,
356; Macacus, 356; Ox, 384—387;
Pig, 387—390

Tadpole, extra Bpiracle in, 465
Tcenia coznurus, transposition of genera-
tive organs, 170 ; case of six
suckers and segments pris-
matic, 565
elliptica, asymmetrical arrange-
ment of genital pores, 170

saginata, "intercalated

seg-

ments, 169; repetition of gene-
rative organs in proglottides,
169 ; two genital pores at the
same level, 170; consecutive
genital pores on same side,
170; bifurcation of chain, 566
solium, changes in position and
alternate arrangement of geni-
tal pores, 170
tenuicollis, bifurcation of chain,
566
Tail-fin, division of, in Gold-fish, 451
Tail-spine, division of, Limulus, 456;

Scorpion, 457
Tapeworms, variations, 168 — 170; du-
plicity in, 565
Tarsus, in some beetles with only four
joints appearing, 25 ; variation in
number of joints, Blatta, 63, 415;
various numbers of joints in families
of Orthoptera, 415
Taurhina nireus, extra legs, 509
Taxidea, teeth, 233
Ta.vus baccata, colour-variation, 47
Teal, Garganey, division of digits, 392
Teeth, in undifferentiated series not
credited with individuality, 32
numerical Variation, 195 ; di-
vision of, 268 ; duplicate, 268 ;
statistics of Variation, 200,
209, 222, 235
relation of upper to lower, 196
of Primates, 199—208; Canidae,
209—222; Felidae, 223—226;
Viverridee, 227—231; Mus-
telidae, 231—235 : Pinnipedia,
235—243 ; Ungulata, 243—
246; Marsupialia, 246—258;

Selachians, 259—262; 7.v

a a in, 262
Teeth, terminal, least size of, 270; pn -
sence and absence of, 269;
Homteotic Variation in, 272
Recapitulation, 265
Telephorus, colour-variation, lividus, 43
division of pronotum, nigri-
cans, 455
double (?) antenna, lividus,
rotundicollis, 551

double (?) leg, <.ff,ir,itii-.

fuscus, 5 18
extra Legs, rusticus, 502
" Telescope " Gold-fish, 453
Tellina, sinistral variety. 54
Tenebrio granarius, double (?) leg, 548
Tentacles of Molluscs united, Helix
hispida, 461 ; Limazagn -•
tie, 460
repeated, Patella vulgata, 27$
bifid, Phy8a acuta, 280
of Holothurians, 4.;~<
Tenthredo solitaria, extra legs, 502
ignobilis, extra leg, 546
Terias, colour-variation, 52, "»:5 ; am -
mone, hecabe, mandarina, mariesii, 52 ;
betheseba, constantia, jaegeri, 53
Terminal members of Series, variation
of, 79, 269, 271. 272. 407
teeth, 269, 272; digits, 107
Terrier, absence of premolar, 21"<
Testes, variation in number in Hirudo,

165, 166
Tetraceros, horns not as in 4-horned

Sheep, 285
Tetracrintu, normally 4-rayed, 5-r;r

and 3 -rayed varieties, 137
Tetrops prceusta, double (?) It-}.'. ">1">
Thoracopagous twins, transposition in.

560
Thumb, variation in number of phalan-
ges, 324
double, 349
Thylacinus, teeth, 255
Thylacites pilosus, double (?) antenna,

550
Thyonidium, variation in number of 01

gans, 435
Tiaraps polydiademata, specific charad

of, 426
Timarcha tenebricosa, extra anteni

522
Tomato, colour-variation. 47
Tonicia, variation in colour of BOUfc

308
Tongue, division ^i. L51
ToxotUS, extra « \. . 280
Transposition of viscera. 560
Triasters, symmetry of. ISO; found in
bilaterally symmetrica] areas "t" a
menting ovum, 164
Trichodet syriacus, double i?.1 leg, 547
Trichosurus vulpecula, premolars, 254

592

INDEX OF SUBJECTS.

TricenopJwrus, segmentation of, 168
Triopa clavigera, rhiuophore trifid, 280
Triton, legs repeated, 555
Troglodytes, vertebra?, 116; teeth, 202
Trupidonutus, vertebrae, 123 ; scales, 276
Trout, bulklog-headed, 58, 59; axial du-
plicity, 563
Tulip, Meristic Variation in, 60
Turbot, pigmentation of lower side, 467,

470
Turdus, brachial plexus, 131
Turkey, digits, 31)3

Twins, homologous, 559 ; Simultaneous
Variation of, as a case of Bi-
lateral Symmetry, 559
Siamese, peculiarities of, 560 ;
thoracopagous, 560
in Echinoderms and in Amphi-
oxus, 35
Typosxjllis, double head, 564

Uca una, extra parts in chela, 530

Ulna, a second, 331

Ulnar nerve, variations in composition
of, 136; a second, 333

Ungulata, teeth, 243 ; digits, 360—390, 397

Union, mediau, 458; of horns of Roe-
buck, 460; of eyes of Bee, 461; of
kidneys, 459; of tentacles of Umax,
460; of tentacles of Helix, 461; of
posterior limbs of Vertebrates, 459 ; of
digits in Ox, 383, 386; of digits in
Pig, 387—390

Units, of Repetition, 556

I'metos, brachial plexus, 131

Ureters, supernumerary, 278

"Useless'' parts, supposed variability of,
78

Uterus, double, Darwin's comment on,
77; is a case of median division, 451

Utility, fallacies of reasoning from, 12

Uvula, division of, 451

Vanessa atalanta, colour-variation, 46
urticce, extra wing, 283
io, eye-spots, 299, 300
Variation, defined, 3

the Study of, as a method

of attacking the problem of

Species, 6
Continuous and Discontinu-
ous, 15
Meristic and Substantive,

distinguished, 23, 24
magnitude of integral steps

affected by Merisrn, 25
about a Mean form, 37
perfection in, 60, 64
causes of, 78
Homoeotic, 85, in vertebras,

106; in Arthropoda, 146;

in teeth, 272
Simultaneity of, in repeated

parts, 303, 402, 425, 464

Variations, minimal, questionable uti-
lity of, 16
Vertebras, Meristic Variation in, 102
imperfect division, 103, 458
Homceotic Variation, 106
reduction in numbers, Man,

111
numerical variation, 102
Man, 103, 106—116; Anthro-
poid Apes, 116; Bradypodi-
dae, 118; Carnivora, 122;
Reptilia, 123 ; Batrachia,
124; features of Variation
recapitulated, 127; correla-
tion with spinal nerves, 113,
115. 139, 145
Vesper us luridus, extra eye, 280
Veronica buxbaumii, numerous symme-
trical variations in, 76 ; illus-
trating variations of Bila-
teral Series, 448
Viverridae, teeth, 227 — 231

Waigiu, female Phalanger maculatus
coloured like male in island
of, 254
Wall butterfl}', variation in ocelli and

neuration, 300
Water-pore, extra, in Bipinnaria, 466
Webs, between toes of Duck, absent, 401
Weevils, four visible joints in tarsus, 25
Wing, supposed to replace a leg in Zy-

gcena, 148
Wings, supernumerary in Insects, 281
fore and hind, varying simul-
taneously in Lepidoptera, 293
quills of, varying with quills of
tail in Pigeons, 309
Woodpecker, Green, colour-variation, 43

Xantho punctulatus, duplicity of index,
542

Xiphopagous twins, transposition of

viscera in, 560
Xylotrupes gideon, variation of horns in,

38

Yellow, variations of, 43-48, 73
Yew, yellow-berried, 47

Zalophus calif or nianus, molars, 243

lobatus, premolars, 238, 242;
molars, 243
Zebra, repetition of stripes in, 26
Zeugopterus, white varieties, 467; varia-
tion in dorsal fin, 471
Zonabris quadripunctata, double (?) an-
tenna, 551
Zonites prausta, extra antenna?, 522
Zyyana filipenduUc, colour variation, 46

supernumerary wing,
148
minos, colours, 46; extra wing,
284

IXDKX OF PERSONS.

Acton, 286

Adolphi, 124, 127, 142

Agassiz, A., 469

Agassiz, L., 396, 424

Ahlfeld, 840, 354, 451, 458

Albrecht, 105, 540

Aldrovandi, 344

Allen, J. A., 243

Alston, 286

Ammon, 348, 349

Anderson, 399

Andrews, 563, 564

Annandale, 327, 345, 346, 350-352, 355-

358
Appellor", 473
Arloing, 363, 370
Ascherson, 174
Ashmead, 413
Asmuss, 484, 500
Asper, 167
Assheton, 152
Audouin, 512
Auld, 390
Austin, 436
Auvard, 349
Auzoux, 203

Babington, 47

Bacon, 29, 146

Baird, 223, 232

Balbiani, 566

Balding, 305

Balk will, 566

Ballantyne, 334

Bancroft, 561

Barbour, 563

Bardeleben, 183

Barr, P., 46

Barrier, 384, 388

Bartels, 187

Barth, 187

Bartlett, 216

Bassi, 512, 548, 551

Baster, 453

Bateson, Miss A., 77, 468

Bather, 436

Baudi, 456, 512, 551

Baudon, 54

Baum, 401

Baumuller, 374

Baur, 103, 105, 123, 124

Beddard, 159, 162, 163, 165

B.

Bedria^a, 127

Bell, P. J., 443, 564, 565

Bellamy, 113

Belt, 56, 57

Beneden, van, 531

Benham, 152, 15i>, 161, 565

Beranger, 347

Bergendal, 555

Bergh, 160

Bernhardus a Berniz. 5j -

Betta, de, 43

Bibron, 563

Bicknell, 45

Billardon de Sauvigny, 454

Billott, 399

Birkett, 178

Birnbaum, 350

Blackinore, 523

Blainville, de, 118, 119, 205, 224

Blanchard, 187

Blanford, W. T., 398

Blasius, 354

Bles, 440

Bleuse, 482, 508

Boas. 369, 383, 385

Boettger, 5<il

Boisduval, 45

Bolau, 349

Bond, 301

Bonnier, 95

Bottcher, 560

Boulard, 512

Boulenger, 123, 276, 277. 16, 165

Boulian, 351

Bourne, A. G. 12">. 127

Boyd-Cainpbell, 399

Bramson, 52

Brandt, 466

Bredin, 31M

Breese, 565

Brenner, 3ti0

Brindley, 38, 39, 63, 280, 416

Brisout de Barneville, 116

Brooks, 466

Broonir. 565

Bruce, 181, 185

Brulerie, de la, 280

Brum r, I *

Brunette, 56 l

Brunner von Wattenwyl, 11, 113, 116

Buchanan, Mi^s P., 156, 1 57

Buckler, 304, 305, 307

38

594

INDEX OF PERSONS.

Buffon, 286, 398
Bull, 340
Biilow, von, 565
Buquet, 551
Bureau, 540
Burmeister, 123, 232
Busch, 198, 345
Butler, A. G., 52, 53

Cauierano, 127, 546, 555

Cameron. 1S5

Canestrini, 58

Cantoni, 537

Carlet 59

Carpenter, P. H., 421, 422, 436-438

Carre, 339

Cassebohm, 178

Cauroi, du, 344, 354

Cavanna, 539, 555

Cazeaux, 185

Champneys, 139, 185

Chapman, J., 244

Charcot, lsl

Chavignerie, de la, 455, 547

Chworostansky, 165

Claparede, 425, 564

Clark, J. A., 51

Clark, J. W., 465

Clarke, E., 397

Claus, 80, 100

Cleland, 401

Coale, 393

Cobbold, 566

Cockerell, 44

Cocks, 55

Colin, 169

Collin, 563, 565

Cooke, A. H., 262, 263

Coquillet, 413

Cori, 156, 157, 158

Cornevin, 363

Cornish, 150

Cotteau, 446

Couch, 440, 470, 471

Coues, 232, 390

Cowper, 391, 393

Cramer, 346

Cuenot, 429, 433, 441

Cunningham, 320, 467

Curtis, 547

Cusset, 176

Daintree, 376

Dale, 482, 547

Dareste, 458

Darwin, C, 1, 5, 13, 56, 57, 59, 77, 121,

288, 449
DavidofT, 566
Dawson, 566

Day, 275, 276, 302, 467, 540
Delplanque, 354, 370, 377, 379
Demidoff, 468
Dendy, 438
Desmarest, 152

Devay, 399

Dimmock, 543

Dobson, 397

Dohrn, 86

Donceel, de, 51

Donitz, 212, 217, 220, 246, 445

Donovan, 302, 471

Dorner, 561

Doue, 456

Doumerc, 512, 550

Drechsel, 455

Drew, 381

Driesch, 35

Dubois, 330

Duhamel du Monceau, 470, 471

Dumeril, 554, 563

Dunn, 374

Duns, 528

Duponchel, 456

Dusseau, 352, 355

Duval, 184

Dwight, 325, 334

Ebrard, 166, 304

Eck, 437

Edward, T., 43, 174, 563

Ehrenberg, 425, 426, 428

Eichwald, 560

Ekstein, 339

Ek strom, 471

Elwes, 45

Engramelle, 46

Ercolani, 369, 377, 380, 381, 392, 393,

540, 554, 555
Eudes-Deslongchamps, 180

Fackenheim, 345, 351, 352, 399

Failla-Tedaldi, 295

Fairmaire, 454

Farge, 327, 399

Fauvel, 44, 494, 508, 523

Faxon, 152, 530, 532, 533, 536, 537,

541, 542, 557
Field, 466
Filippi, 425
Fischer, 41
Fischer, Or., 174
Fischer, P., 54, 279, 566
Fischer de Waldheim, 97
Fisher, W. K., 392
Fitch, 565

Fitch, E. A.,'44

Fitzinger, 200

Flemming, 430

Flemyng, 307

Fleutiaux, 548

Flower, W. H., 106, 119, 217, 220, 233

Forbes, E., 54, 425, 460

Forbes, W. A., 356

Forgue, 143

Forskal, 540

Forsyth, 398

Fort, 344, 356, 358

Foster, 565

INDEX OF PER80N8.

Fotherby, 360, 399

Franck, 368

French, 451

Freund, 459

Freyer, 524

Fricken, von, 512

Friedlowsky, 244, 356

Friele. 262, 264

Friend, 563, 565

Fries, 471

Frivaldsky, 500

Froriep, 35 1

Fumagalli, 336

Fiirbringer, 131, 133, 135, 142

Fiirst, 399

Gadeau de Kerville, 415, 455, 4s2, 510,

548, 549
Gaillard, 346, 350
Galton, F., 36, 40. 43, 418, 419
Garrod, 390
Gaskell, 86
Gaskoin, 56

Gautbier, 443, 445—447
Gebhard, 459
Gegenbaur, 77
Geissendbrfer, 360
Gene, J., 127
Geoffroy St Hilaire, I., 57, 205, 330,

368, 377, 379, 383, 392, 451, 459, 563
Gercke, 285
Gervais, 203
Gherini, 337

Giard, 95, 440, 468, 482, 545
Gibbons, Sir J., 44
Gibson, 166
Giebel, 234
Gifford, 44
Giraldes, 336
Girard, 305
Godman, 53, 297
Godwin-Austen, 286
Goldfuss, 436, 437
Goodman, 376
Goossens, 300
Gordon, 56
Gorre, 187
Gosse, 566
Gosselin, Mrs, 44
Gotte, 127
Gottsche, 466, 471
Goubaux, 180, 244, 245
Grandelement, 355
Grandin, 340

Gray, J. E., 56, 242, 287, 396
Gredler, 286, 511, 512, 550, 551
Green, 515
Grobben, 169
Gruber, W., 108, 111, 119, 122, 330, 345,

346, 350, 352, 354, 359, 360
Guerdan, 45H
Guermonprez, 327
Giinther, 173, 174, 260, 309, 468
Gurlt, 368

Gurney, .1. H.. 1

( in\. i| 1 1 in .•-, B60

Baacke, 1 13, L46
Bagen, I L8
Bagenbaoh, B52
Hammond, 805

I I;, 111. v. 160

Bannams, 1 84

Bark( r, A., 119
Barker, .1., 354, B
Barmer, i M), 556
Harrington, 182, 191, "00

Harrison, 211

Bartung, 1-7

Harvey, 178

Haworth, L5

Heincki n. 526

Hell.i-, 1*7

Heller, 170

Henne^ny, 430

Hennig, 349

Hensel, 203, 20n. 212 216, 220, 223,

226, ->w>. 244, 246, 269
Herdman, 171, 172, 139, 156
Herkluts. 527, 528, 529, 542
Heron, Sir R., 453
Heron-Rover, 465, 55.1. 56]
HerrichSchiilY.]', 51
Herrin^hain, 137, 138
Hertwig, O., 431
Heuglin, von. 234. 235
Heusinger, 174, 179
Hewett. 55

Hevden, H. von. 4s*. 512. 5 1*
Heyden, L. von. 484, 187—490, 194,

517, 523, 550, 551
Heynold, 355
Higgins, 471
Hill, 391
Hincks. 425
His, 177

Hodgson, 209, 398
Hoeven. van der, 21s
Hoffmeister, 162
Honratli. 284
Hopkins. 48, 73
Horn, 411
Horst. 565

Howes, 126, 153, 210, 891, 121, 515
Hubner,&05
Hudson, 56

Hiigel, Huron A. von, 89
Humphreys, 221
Humphreys, 11. N.. 801
Humphry, 200
Huxley, 217, 218, 219

Imhoff, -")47

.Tiiekrl. 393

Jackson, '-531
Jaequelin-Duval, 524

596

INDEX OF PERSONS.

Jaeger, G., 536

Janson, 482, 491

Jayne, 503, 512, 518, 524, 544, 547, 548,

550, 551
Jeffreys, G., 54, 457
Jekyll, Miss, 46
Jentink, 248, 252, 253
Jhering, von, 140, 142, 300
Johnson, Atbol, 354
Jollv, 337
Joly, 370, 372
Joseph, 350

Karoli, 532

Kawall, 551

Kerckring, 344

Kiesen wetter, von, 281

Kingsley, 539, 554

Kirk, 565

Kitt, 363, 383, 384, 386, 390

Kleyn, 453

Klingelhofer, 547, 551

Klob, 187

Koenen, von, 436

Kolbe, 484, 503

Kolliker, 142

Kostanecki, von, 175

Kraatz, 146, 454, 456, 484, 485, 494,
498, 502, 506, 509—511, 515, 516,
523, 545, 547, 548, 550, 551, 552

Krause, 455, 548

Kriechbaumer, 147

Krohn, 425

Kroyer, 151

Kuchenmeister, 560

Kuhnt, 339

Laboulbene, 512

Lacaze-Dutbiers, 171

Lacepede, 540, 561

Lafosse, 244

Lamarck, 4

Lambert, 446

Lampert, 435

Landois, 58, 383, 387, 511, 555

Lane, 113

Lang, 566

Langalli, 336

Langerhans, 564

Lankester, 536

Lannegrace, 143

Lanzoni, 561

Lataste, 127

Laurent, 184

Lavocat, 354, 372

Le Clerc, 357

Leech, J. H., 46

Lefebvre, 500

Le Gendre, 184

Leger, 527, 538

Legge, 46

Leichtenstern, 181 — 185

Lereboullet, 515

Le Senechal, 530, 535, 542

Letzner, 280, 523, 550

Leuckart, 168—170, 566

Levacher, 566

Leveling, 458

Lidth de Jeude, van, 58

Linnams, 453

Lisfranc, 355

Lister, 218, 457

Loriol, P. de, 436, 437, 438

Loudon, 47

Lucas, 399

Lucas, H., 462, 536, 542, 550, 551

Ludwig, H., 433, 566

Lunel, 58, 554

Liitken, 433

Lydekker, 105, 217, 233

Macalister, A., 112, 278

MacAndrew, 54

MacBride, 440

McCoy, 52

Mcintosh, 470, 564

Maggi, 530

Magitot, 198, 203, 205, 210, 221, 244,

245, 270
Malm, 469
Manifold, 451
Mantell, 436
Marjolin, 355
Marsh, 349
Marsh, C. D., 565
Marsh, O. C, 364, 366, 368
Marshall, 86
Martens, von, 155
Martin, 430

Mason, 282, 488, 498, 509, 548, 550
Mason, F. , 355
Masters, 60, 84, 310
Mayer, 200
Mazza, 555

Meckel, 278, 346, 458, 459
Melde, 355
Meldola, 284
Meyer, A. B., 441, 445
Michaelsen, 162, 164, 165
Mielecki, von, 175
Milne-Edwards, 151, 202, 527
Mitchill, 561, 563
Mivart, 212, 217, 219
Mobius, 401
Mocquerys, 455, 487, 488, 494, 496, 498,

501, 503, 507, 508, 512, 515, 517, 522,

545—548, 550—552
Mojsisovics, 367
Moniez, 169, 566
Moquin-Tandon, 280, 304
Morand, 346, 348, 354, 399
Moreau, 540

Morgan, T. H., 157, 466
Morot, 245, 384
Morris, F. O., 44, 401
Mortillet, de, 186
Mosley, S. L., 45, 300
Muir, 352, 399

INDEX OF PERSONS.

597

Miiller, A., 512

Miiller, J., 17.5
Murray, 330

Nathusius, H. von, 285, 373, 374
Nehring, 57, 123, 210, 212, 216, 221, 2

242
Neill, 540

Neugebauer, 183, 186
Neubofer, 170
Newman, 51, 205, 300
Newport, 04
Newton, A., 44, 55
Nicbolls, 155
Nilsson, 471
Norman, 100, 457
Notta, 185

Oberteufer, 330

Oberthiif , 44

Ocbsenbeimer, 40, 284, 302

Odin, 450

Olliff, 51, 52

Otto, 58, 278, 340, 348, 350, 354, 350,

458
Otto, H., 547, 548
Owen, 119, 188, 211, 261

Packard, 100, 457

Paget, Sir J., 175, 177

Pallas, 180

Parry, 520

Partsch, 451

Paullinus, 184, 187

Pavesi, 565

Pelseneer, 280

Pennetier, 482

Percy, 184, 187

Perroud, 512

Perty, 512, 548, 550, 551

Peters, 200, 277

Pbilippi, 443

Pichancourt, 400

Pocock, 93, 457, 565

Pooley, 451

Popham, 355

Porritt, 295

Pott, 399

Potton, 399

Pouchet, 451

Poulton, 304—307, 320, 321, 323

Prackel, 184

Prevost, 457

Price, 500

Puecb, 181

Pusch, 436

Putnam, 174, 396

Piitz, 366

Quenstedt, 430
(juinquaud, 185

Rabl, 176
Ragusa, 548

Rambur, 50

Ramsay, l;. <i. \\\. L6

R;m-. . d( . 899

Rapp, L20

Rathke, '.i7. K

I;, di, 561

!;• ichenan, iron, 392

Reid, i 9

Ri itter, 281

Rey, "'IT. 550

Richard, L50, 586, 543

Richardson, 1 1^

Richmond, 279

Ridgway, 393

Rijkebusch, 329

Ritzema Bos, 512, 55]

Rivers, 17

Rober, 283

Roberts, (r., 401

Roberts, 1.. t (•_'

Robinson. II.. O'J

Roder, von, 551

Rogenhofer, 284, 286

Romanes, 125 128

Romano, 523

Rorberg, 355

Rose! von Rosenhof, 526, 530, 536

Rosenberg, 116—118, 138, 373, 383

Rosinus, 136

Rouget, 523

Rousseau, 152

Roux, 35

Riidinger, 330

Rudolphi, 2(>7. 244

RuefE, 344

Riitimeyer, 246

Saage, 1 L8

Salvia, 53, 2:17

Sanderson, 398

Sandifort, 458

Sarasin, 433

Sartorius, 512, 550

Saunders, Howard, 897

Sauvage, 276

Schaff, 210

Scbleep. 470

Schlegel, 220

Schmankewitsch, 96

Bchmeltz, 566

Schmitz, 177

Schneider, "'17. 550

Schneider, A.. 17 1

Schultze, L., 138

Schnltze, 0., 194

Sdater, P. L., 396

Sclater, W. L., 37 1

Scndder, "»0

Seba, 566

Sedgwick, 84, 92, 93, 173. 197

Seerig, 3 18

Seidel, L76

Seringe, 523

Serville, 412, 413

598

INDEX OF PERSONS.

Shannon, 185

Sharp, D., 43, 53, 149, 411, 482, 494, 499

Shaw, E., 413

Shaw, V., 401

Sherrington, 137, 138, 144, 168

Siebold, von, 148

Sinety, 184

Smit, 471

Smith, E. A., 287

Smith, F., 551

Smith, S. J., 151

Solger, 141

Soubeiran, 529

South, 300

Spengel, 466

Speyer, 283

Spinola. 512

Spronok, 329

Stamati, 538

Stannius, 142, 455, 461, 512, 522, 547

Staudinger, 44

Steenstrup, 466, 469

Steindachner, 58, 468

Steinthal, 359

Stevens, 41

Stewart, C, 180, 429, 440, 446

Storer, 471

Strahl, 154

Strauch, 123

Strecker, 51, 283, 295

Streng, 352

Strombeck, von, 436, 438

Struthers, 103, 105—119, 122, 140, 327,

329, 334, 346, 351, 356, 370, 389
Studer, 277
Sundevall, 471
Sutton, 105, 176, 179, 180, 188, 555

Tachard, 398

Tarnier, 185, 345

Taschenberg, 512

Tegetmeier, 57, 393

Testut, 187

Thielmann, 277

Thomas, O., 56, 120, 199, 228, 230, 246

—249, 254, 257, 258, 313, 322, 397
Thompson, W., 565
Thomson, 412
Thomson, Wyville, 466
Tiedemann, 184, 512, 536, 540
Tischbein, 511
Traquair, 469
Treitschke, 284
Trelat, 451

Treuge, 512
Trimen, 51, 300
Trinchese, 118
Tuckerman, 170, 555
Turner, Sir W., 465

Urbantschitsch, 177

Vaillant, 309, 471

Viborg, 180

Virchow, 74, 177, 178, 17

Voigt, 58

Vrolik, 58

Wagner, 421

Wagner, J., 451

Walsingham, Lord, 300

Ward, E., 379

Warpachowski, 540

Watase, 451, 463

Waterhouse, F. H., 45, 545

Webb, S., 301

Wehenkel, 366, 368

Weir, J. Jenner, 45, 51, 52, 254

Weismann, 76, 304—307

Welcker, 118, 120

Weldon, 172

Werner, 170

Wesmael, 521

Westwood, 283, 284, 508, 551

Weyenbergh, 565

White, 44

Wilde, 178

Wilder, 465

Williams, 181, 185, 191

Wilson, 304, 305, 307

Wilson, E. B., 35

Windle, 221, 326, 328, 392, 560

Wiskott, 285

Wolf, 399

Woodgate, 284

Wood-Mason, 367

Woodward, M. F., 160, 162

Woodward, Smith, 259

Wright, 566

Wright, L., 55, 393

Wyman, 57, 203, 226, 401, 465, 561

Yarrell, 59, 469, 471, 540
Yarrow, 561
Youatt, 285, 286

Zeppelin, 565
Zundel, 180

FWPCT7T UBtAItT

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BOOKS BY DR. A. R. WALLACE, F.R.S.

DARWINISM : An Exposition of the Theory of Natural Selection,
with some of its Applications. Illustrated. Extra Crown 8vo. 9s.

SATURDAY REVIEW.— u Mr Wallace's volume maybe taken as a faithful
exposition of what Darwin meant. It is written with perfect clearness, with a
simple beauty and attractiveness of style not common to scientific works, with a
dignity and freedom from anything like personal bitterness worthy of Darwin him-
self, and with an orderliness and completeness that must render misconception
impossible."

ATIIENJEUM. — "Mr 'Wallace adds so much that is new, and he writes in so
charming and simple a style, that his readers more than he are to be congratulated
on the latest service he has rendered to the science he has served so well."

Prof. Ray Lankester in NATURE. — "No one has so strong a claim as Mr
Wallace to be heard as the exponent of the theory of the origiu of species, of which
he is— with Darwin — the joint author. . . . The book is one which has interest
not only for the general reader, to whom it is primarily addressed, but also for the
more special students of natural history. The latter will find in its pages an
abundance of new facts and arguments which, whether they prove convincing or
not, are of extreme value and full of interest."

THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS:

with a study of the relations of living and extinct faunas as elucidating
the past changes of the earth's surface. With Maps and Illustrations.
In two Vols. Medium 8vo. 42s.

NATURAL SELECTION AND TROPICAL NATURE:

Essays on Descriptive and Theoretical Biology. New Edition with
corrections and additions. Extra Crown 8vo. 6s.

ISLAND LIFE: OR, THE PHENOMENA AND CAUSES

OF INSULAR FAUNAS AND FLORAS. Including a revision and
attempted solution of the problem of Geological climates. With Illustra-
tions and Maps. Second Edition. Crown 8vo. 6s.

THE MALAY ARCHIPELAGO: THE LAND OF THE
ORANG-UTAN AND THE BIRD OF PARADISE. A Narrative of
Travel. With Studies of Man and Nature. With Maps and Illustrations.
Fourth Edition. Extra Crown 8vo. 6s.

GLASGOW HERALD. — "There is probably no more interesting book of

travel in the language For one-and-twenty years it has held its place as a

monograph in a region of the East which is full of fascination, not only for the
naturalist and ethnographer, but for the ordinary reader of travels."

MACMILLAN AND CO., LONDON.