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EX LIBRIS
BERTRAM.C.A
WINDLE
D.Sc.M.D
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7*£?
STUDIES IN THE THEORY
OF DESCENT
BY
DR. AUGUST WEISMANN
PROFESSOR IN THE UNIVERSITY OF FREIBURG
WITH NOTES AND ADDITIONS BY THE AUTHOR
TRANSLATED AND EDITED, WITH NOTES, BY
RAPHAEL MELDOLA, F.C.S.
LATE VICE-PRESIDENT OF THE ENTOMOLOGICAL SOCIETY OF LONDON
WITH A PREFATORY NOTICE BY
CHARLES DARWIN, LL.D., F.RS.
Author of " The Origin of Species," &°<r.
IN TWO VOLUMES
VOL. I.
WITH EIGHT COLOURED PLATES
lontiott;
SAMPSON LOW, MARSTON, SEARLE, & RIVINGTON
CROWN BUILDINGS, 188, FLEET STREET
1882
rights reserved. ]
PREFATORY NOTICE.
THE present work by Professor Weismann, well
known for his profound embryological investiga-
tions on the Diptera, will appear, I believe, to every
naturalist extremely interesting and well deserving
of careful study. Any one looking at the longi-
tudinal and oblique stripes, often of various and
bright colours, on the caterpillars of Sphinx-
moths, would naturally be inclined to doubt
whether these could be of the least use to the
insect ; in the olden time they would have been
called freaks of Nature. But the present book
shows that in most cases the colouring can hardly
fail to be of high importance as a protection.
This indeed was proved experimentally in one of
the most curious instances described, in which
the thickened anterior end of the caterpillar bears
two large ocelli or eye- like spots, which give to
the creature so formidable an appearance that
birds were frightened away. But the mere ex-
planation of the colouring of these caterpillars is
but a very small part of the merit of the work.
This mainly consists in the light thrown on the
a
vi Prefatory Notice.
laws of variation and of inheritance by the facts
given and discussed. There is also a valuable dis-
cussion on classification, as founded on characters
displayed at different ages by animals belonging
to the same group. Several distinguished natural-
ists maintain with much confidence that organic
beings tend to vary and to rise in the scale, inde-
pendently of the conditions to which they and
their progenitors have been exposed ; whilst
others maintain that all variation is due to such
exposure, though the manner in which the envi-
ronment acts is as yet quite unknown. At the
present time there is hardly any question in
biology of more importance than this of the
nature and causes of variability, and the reader
will find in the present work an able discussion
on the whole subject, which will probably lead
him to pause before he admits the existence of an
innate tendency to perfectibility. Finally, who-
ever compares the discussions in this volume with
those published twenty years ago on any branch
of Natural History, will see how wide and rich a
field for study has been opened up through the
principle of Evolution ; and such fields, without the
light shed on them by this principle, would for
long or for ever have remained barren.
CHARLES DARWIN.
TRANSLATOR'S PREFACE.
IN offering to English readers this translation of
Professor Weismann's well-known u Studies in the
Theory of Descent," the main part of which is
devoted to entomological subjects, I . have been
actuated by the desire of placing in the hands of
English naturalists one of the most complete of
recent contributions to the theory of Evolution as
applied to the elucidation of certain interesting
groups of facts offered by the insect world.
Although many, if not most, working naturalists
are already familiar with the results of Dr. Weis-
mann's researches, of which abstracts have from
time to time appeared in English and American
scientific journals, I nevertheless believe that a
study of the complete work, by enabling the
reader to follow closely the detailed lines of
reasoning 'and methods of experiment employed
by the author, will be found to be of considerable
value to those biologists who have not been able
to follow the somewhat difficult phraseology of
the original. It is not my intention, nor would it
be becoming in me to discuss here the merits of
a 2
viii Translator s Preface*
the results arrived at by the minute and laborious
investigations with which Dr. Weismann has for
many years occupied himself. I may however
point out that before the appearance of the
present work the author, in addition to his well-
known papers on the embryology and develop-
ment of insects, had published two valuable con-
tributions to the theory of descent, viz. one
entitled "Uber die Berechtigung der Darwin'schen
Theorie" (1868), and another " Uber den Einfluss
der Isolirung auf die Artbildung " (1872). These
works, which are perhaps not so well known in
this country as could be desired, might be advan-
tageously studied in connection with the present
volume wherein they are frequently referred to.
Since every new contribution to science is a
fresh starting-point for future work, I may venture
without any great breach of propriety to dwell
briefly upon one or two of the main points which
appear to me to be suggested by Prof. Weis-
mann's investigations.
Although the causes of Glacial Epochs is a
subject which has much occupied the attention of
geologists and physiographers, the question is one
of such great complexity that it cannot yet be
regarded as finally settled. But apart from the
question of causes — a most able discussion of
which is -given by the author of " Island Life "
there is not the least doubt that at no very
distant geological period there occurred such an
Translator s Preface. ix
epoch, which, although intermittent, was of con-
siderable duration. The last great geological
event which our globe experienced was in fact
this Ice Age, and the pure naturalist has not
hitherto attributed in my opinion sufficient im-
portance to the direct modifying effects of this
prolonged period of cold. It is scarcely possible
that such a vast climatic change as that which
came on at the close of the Pliocene Period
should have left no permanent effect upon our
present fauna and flora, all the species of which
have survived from the glacial age. The great
principle of Natural Selection leads us to see
how pre -glacial forms may have become adapted
to the new climatic conditions (which came on
gradually) by the " survival of the fittest " or
" indirect equilibration.1' The influence of the
last Glacial Epoch as a factor in determining the
present geographical distribution of animals and
plants has already been amply treated of by many
writers since the broad paths were traced out by
Darwin, Lyell, and Wallace. The last named
author has indeed quite recently discussed this
branch of the subject most exhaustively in his
work on " Island Life" above mentioned. The
reference of a particular group of phenomena—
the seasonal dimorphism of butterflies — to the
direct action of the Glacial Period and the subse-
quent influence of the ameliorating climate, was
however the first step taken in this neglected
x Translator s Preface.
field by the author of the present work in 1875.
It is possible, and indeed probable, that future
researches will show that other characters among
existing species can be traced to the same causes.
The great generalizations of embryology, which
science owes so largely to the researches of Karl
Ernst von Baer, bear to the theory of descent
the same relations that Kepler's laws bear to the
theory of gravitation. These last-named laws are
nothing more than generalized statements of the
motions of the planets, which were devoid of
meaning till the enunciation of the theory of
gravitation. Similarly the generalized facts of
embryology are meaningless except in the light
of the theory of descent. It has now become a
recognized principle in biology that animals in
the course of their development from the ovum
recapitulate more or less completely the phases
through which their ancestors have passed. The
practical application of this principle to the
determination of the line of descent of any
species or group of species is surrounded by
difficulties, but attempts have been made of late
years — as by Haeckel in his Gastrula theory — to
push the law to its legitimate consequences. In
this country Sir John Lubbock, in 1874, appealed
to the embryonic characters of larvae in support
of his views on the origin of insects. To the
author of this work (1876) is due the first appli-
cation of the principle of Ontogeny as revealing
Translator's Preface. xi
the origin of the markings of caterpillars. A
most valuable method of research is thus opened
up, and entomologists should not be long in
availing themselves of it. Our knowledge of the
subject of larval development in Lepidoptera
is still most imperfect, and it cannot as yet be
foreseen to what extent the existing notions of
classification in this much-studied order may have
to be modified when a minute study of the Com-
parative Ontogeny of larval characters, worked out
as completely as possible for each family, has
enabled a true genealogical system to be drawn
up. The extent to which such a larval genealogy
would coincide with .our present classification
cannot now be decided, but he who approaches this
fruitful line of inquiry in the true spirit of an investi-
gator, will derive much instruction from Prof.
Weismann's remarks on " Phyletic Parallelism in
Metamorphic Species." The affinities of the
larger groups among Lepidoptera would most
probably be made out once and .for ever if
systematists would devote more time to observa-
tion in this field, and to the co-ordination and
working up of the numerous data scattered
throughout the vast number of entomological
publications.
The doctrine of development by no means
implies, as has sometimes been maintained, a
continuous advancement in organization. Al-
though the scale of organic nature has continued
xii Translator s Preface.
to rise as a whole, cases may occasionally occur
where a lower grade of organization is better
adapted to certain conditions of life. This
principle of <( degeneration " was recognized by
Darwin as early as in the first edition of the
" Origin of Species ;" it was soon perceived to be
applicable to the phenomenon of parasitism, and
was first definitely formulated by Dr. Anton
Dohrn in 1875. In a lecture delivered before the
British Association at Sheffield in 1879, Prof.
E. Ray Lankester ascribed to " degeneration " a
distinct and well-defined function in the theory of
descent. Dr. Weismann's explanation of the
transformation of Axolotl given in the fourth
essay of this work, may be regarded as a special
contribution! to this phase of Darwinism. Whilst
refuting the idea held by certain naturalists, that
such cases are arguments against the origin of
species by the accumulation of minute variations,
and prove the possibility of development per
saltum, the theory here advanced (that Siredon
at a former period existed at a higher stage of
development as Amblystoma, and that the observed
cases of metamorphosis are but reversions to this
lost higher stage) suggests the question whether
there may not still be in existence many other
degenerated forms quite unsuspected by natural-
ists.
Many of the opponents of Evolution have from
time to time denounced this doctrine as leading
Translator s Preface. xiii
to (< pure materialism," a denunciation which may
appear somewhat alarming to the uninitiated, but
which may not seem fraught with any serious
consequences to those who have followed the
course of philosophical speculation during the last
few years. Those who attack the doctrine on
this ground will however do well to consider Prof.
Weismann's views set forth in the last essay
in this volume, before hastily assuming that the
much dreaded " materialism " is incompatible with
any other conception of Nature.
The small amount of leisure time which I have
been able to devote to the translation of this
volume has delayed its completion considerably
beyond the anticipated time, and it was with a
view to meeting this difficulty that I departed
from the original form of the German edition and
issued it in parts. Owing to the extremely
idiomatic character of the German text, I have
throughout endeavoured to preserve only the
author's meaning, regardless of literal translation
or of the construction of the original. In some
few cases, however, I have intentionally adopted
literal translations of certain technical expressions
which might, I think, be advantageously intro-
duced into our biological vocabularies. Some
alterations have been made in the original text
by the author for the present edition, and many
new notes have been added. For those bearing
my initials I am alone responsible.
xiv l^ranslators Preface.
It gives me much pleasure in conclusion to
express my thanks to Dr. Weismann, not only for
the readily given permission to publish an English
translation of his work, but also for much valuable
assistance during the execution of the task. The
author has been good enough to superintend the
drawing of the plates for this edition, and he has
also read through the greater part of the manu-
script. From Mr. Darwin also I have received
much kindly encouragement, and among ento-
mologists I am especially indebted to Mr. W. H.
Edwards of West Virginia, for his valuable ad-
ditions to the first part. To my friends Mr. A.
G. Butler, Mr. Roland Trimen, and Mr. F. Moore,
I owe acknowledgments for much useful in-
formation concerning the caterpillars of exotic
Sphingid&} which I have incorporated in the
notes and appendices, and Mr. W. S. Simpson
has given me occasional advice in the translation
of some of the more difficult passages.
R. M.
London, November ; 1881.
PREFACE TO THE ENGLISH EDITION.
WITH the appearance of Charles Darwin's work
"On the Origin of Species," in the year 1858,
there commenced a new era in biology. Weary
of the philosophical speculations which, at the
beginning of this century, had at first been started
with moderation but had afterwards been pushed
to excess, biologists had entirely let drop all
general questions and confined themselves to
special investigations. The consideration even of
general questions had quite fallen into disuse,
and the investigation of mere details had led to a
state of intellectual shortsightedness, interest
being shown only for that which was immediately
in view. Immense numbers of detailed facts were
thus accumulated, but they could not possibly be
mastered; the intellectual bond which should
have bound them together was wanting.
But all this was changed in a short time. At
first only single and mostly the younger naturalists
fell in with the new theory of development pro-
claimed by Darwin, but the conviction soon
became general that this was the only scientifi-
xv i Preface to the English Edition.
cally justifiable hypothesis of the origin of the
organic world.
The materials accumulated in all the provinces
of biology now for the first time acquired a deeper
meaning and significance ; unexpected inter-rela-
tions revealed themselves as though spontaneously,
and what formerly appeared as unanswerable
enigmas now became clear and comprehensible.
Since that time what a vast modification has the
subject of animal embryology undergone ; how
full of meaning appear the youngest develop-
mental stages, how important the larvae ; how
significant are rudimentary organs ; what depart-
ment of biology has not in some measure become
affected by the modifying influence of the new
ideas !
But the doctrine of development not only
enabled us to understand the facts already
existing ; it gave at the same time an impetus to
the acquisition of unforeseen new ones. If at the
present day we glance back at the development
of the biological sciences within the last twenty
years, we must be astonished both at the enormous
array of new facts which have been evoked by the
theory of development, and by the immense series
of special investigations which have been called
forth by this doctrine.
But while the development theory for by far the
greater majority of these investigations served as
a light which more and more illuminated the
Preface to the English Edition. xvii
darkness of ignorance, there appeared at the same
time some other researches in which this doctrine
itself became the object of investigation, and
which were undertaken with a view to establish it
more securely.
To this latter class of work belong the
" Studies " in the present volume.
It will perhaps be objected that the theory of
descent has already been sufficiently established
by Darwin and Wallace. It is true that their
newly-discovered principle of selection is of the
very greatest importance, since it solves the riddle
as to how that which is useful can arise in a purely
mechanical way. Nor can the transforming in-
fluence of direct action, as upheld by Lamarck, be
called in question, although its extent cannot as yet
be estimated with any certainty. The secondary
modifications which Darwin regards as the conse-
quence of a change in some other organ must
also be conceded. But are these three factors
actually competent to explain the complete trans-
formation of one species into another ? Can they
transform more than mere single characters or
groups of characters ? Can we consider them as
the sole causes of the regular phenomena of the
development of the races of animals and plants ?
Is there not perhaps an unknown force underlying
these numberless developmental series as the true
motor power — a "developmental force" urging
species to vary in certain directions and thus
xviii Preface to the English Edition.
calling into existence the chief types and sub-
types of the animal and vegetable kingdoms ?
At the time these " Studies " first appeared
(1875) they had been preceded by a whole series
of attempts to introduce into science such an un-
known power. The botanists, Nageli and Askenasy,
had designated it the " perfecting principle " or the
" fixed direction of variation;" Kolliker as the "law
of creation;" the philosophers, Von Hartmann and
Huber, as the " law of organic development," and
also " the universal principle of organic nature."
It was thus not entirely superfluous to test the
capabilities of the known factors of transformation.
We had here before us a question of the highest
importance — a question which entered deeply into
all our general notions, not only of the organic
world, but of the universe as a whole.
This question — does there exist a special
11 developmental force " ? — obviously cannot be
decided by mere speculation ; it must also be
attempted to approach it by the inductive
method.
The five essays in this volume are attempts to
arrive, from various sides, somewhat nearer at a
solution of the problem indicated.
The first essay on the " Seasonal Dimorphism
of Butterflies " is certainly but indirectly connected
with the question ; it is therein attempted to dis-
cover the causes of this remarkable dimorphism,
and by this means to indicate at the same time
Preface to the English Edition. xix
the extent of one of the transforming factors with
reference to a definite case. The experiments
upon which I base my views are not as numerous
as I could desire, and if I were now able to repeat
them they would be carried out more exactly than
was possible at that time, when an experimental
basis had first to be established. In spite of this,
the conclusions to which I was led appear to be
on the whole correct. That admirable and most
conscientious observer of the North American
butterflies, Mr. W. H. Edwards, has for many
years experimented with American species in a
manner similar to that which I employed for
European species, and his results, which are pub-
lished here in Appendix II. to the first essay,
contain nothing as far as I can see which is not
in harmony with my views. Many new questions
suggest themselves, however, and it would be a
grateful task if some entomologist would go
further into these investigations.
The second essay directly attacks the main
problem above indicated. It treats of the "Origin
of the Markings of Caterpillars," and is to some
extent a test of the correctness and capabilities of
the Darwinian principles ; it attempts to trace the
differences in form in a definite although small
group entirely to known factors.
Why the markings of caterpillars have particu-
larly been chosen for this purpose will appear for
two reasons.
xx Preface to the English Edition.
The action of Natural Selection, on account of
the nature of this agency, can only be exerted on
those characters which are of biological im-
portance. As it was to be tested whether, besides
Natural Selection and the direct action of external
conditions, together with the correlative results of
these two factors, there might not lie concealed
in the organism some other unknown transforming
power, it was desirable to select for the investi-
gation a group of forms which, if not absolutely
excluding, nevertheless appeared possibly to re-
strict, the action of one of the two known factors
of transformation, that of Natural Selection ; a
group of forms consisting essentially of so-called
" purely morphological " characters, and not of
those the utility of which was obvious, and of
which the origin by means of Natural Selection
was both possible and probable ab initio. Now,
although the colouring can readily be se°n to be
of value to the life of its possessors, this is not
the case with the quite independent markings of
caterpillars ; excepting perhaps those occasional
forms of marking which have been regarded as
special cases of protective resemblance. The
markings of caterpillars must in general be con-
sidered as " purely morphological " characters,
i. e. as characters which we do not know to be of
any importance to the life of the species, and
which cannot therefore be referred to Natural
Selection. The most plausible explanation of
Preface to the English Edition. xxi
these markings might have been that they were
to be regarded as ornaments, but this view pre-
cludes the possibility of referring them either to
Natural Selection or to the influence of direct
changes in the environment.
The markings of caterpillars offered also
another advantage which cannot be lightly
estimated ; they precluded from the first any
attempt at an explanation by means of Sexual
Selection. Although I am strongly convinced of
the activity and great importance of this last
process of selection, its effects cannot be esti-
mated in any particular case, and the origin of a
cycle of forms could never be clearly traced to its
various factors, if Sexual Selection had also to be
taken into consideration. Thus, we may fairly
suppose that many features in the markings of
butterflies owe their origin to Sexual Selection,
but we are, at least at present, quite in the dark
as to how many and which of these characters
can be traced to this factor.
An investigation such as that which has been
kept in view in this second essay would have been
impracticable in the case of butterflies, as well as
in the analogous case of the colouring and marking
of birds, because it would have always been
doubtful whether a character which did not
appear to be attributable to any of the other
transforming factors, should not be referred to
Sexual Selection. It would have been impossible
b
xxii Preface to the English Edition.
either to exclude or to infer an unknown de-
velopmental force, since we should have had to
deal with two unknowns which could in no way be
kept separate.
We escape this dilemma in the markings of
caterpillars, because the latter do not propagate
in this state. If the phenomena are not here en-
tirely referable to Natural Selection and the direct
action of the environment — if there remains an
inexplicable residue, this cannot be referred to
Sexual Selection, but to some as yet unknown
power.
But it is not only in this respect that cater-
pillars offer especial advantages. If it is to be
attempted to trace transformations in form to the
action of the environment, an exact knowledge of
this environment is in the first place necessary,
i. e. a precise acquaintance with the conditions of
life under the influence of which the species con-
cerned exist. With respect to caterpillars, our
knowledge of the life conditions is certainly by no
means as complete as might be supposed, when
we consider that hundreds of Lepidopterists have
constantly bred and observed them during a most
extended period. Much may have been observed,
but it has not been thought worthy of publication;
much has also been published, but so scattered
and disconnected and at the same time of such
unequal credibility, that a lifetime would be required
to sift and collect it. A comprehensive biology of
Preface to the English Edition. xxiii
caterpillars, based on a broad ground, is as yet
wanting, although such a labour would be both most
interesting and valuable. Nevertheless, we know
considerably more of the life of caterpillars than
of any other larvae, and as we are also acquainted
with an immense number of species and are able
to compare their life and the phenomena of their
development, the subject of the markings of
caterpillars must from this side also appear as the
most favourable for the problem set before us.
To this must be added as a last, though not as
the least, valuable circumstance, that we have
here preserved to us in the development of the
individual a fragment of the history of the species,
so that we thus have at hand a means of following
the course which the characters to be traced to
their causes — the forms of marking — have taken
during the lapse of thousands of years.
If with reference to the question as to the
precise conditions of life in caterpillars I was
frequently driven to my own observations, it was
because I found as good as no previous work
bearing upon this subject. It was well known
generally that many caterpillars were differently
marked and coloured when young to what they
were when old ; in some very striking cases brief
notices of this fact are to be found in the works,1
1 A most minute and exact description of the newly hatched
larva of Chionobas Aello is given by the American entomologist,
Samuel H. Scudder. Ann, Soc. Ent de Belgique, xvi., 1873.
b 2
xx iv Preface to the English Edition.
more especially, of the older writers, and principally
in that of the excellent observer Rosel von
Rosenhof, the Nuremberg naturalist and miniature
painter. In no single case, however, do the
available materials suffice when we have to draw
conclusions respecting the phyletic development.
We distinctly see here how doubtful is the value
of those observations which are made, so to
speak, at random, i. e. without some definite
object in view. Many of these observations may
be both good and correct, but they are frequently
wanting precisely in that which would make them
available for scientific purposes. Thus every-
thing had to be established de novo} and for this
reason the investigations were extended over a
considerable number of years, and had to be
restricted to a small and as sharply defined a
group as possible — a group which was easily
surveyed, viz. that of the Hawk-moths or
Sphinges.
Since the appearance of the German edition of
this work many new observations respecting the
markings of caterpillars have been published,
such, for example, as those of W. H. Edwards
and Fritz Mliller. I have, however, made but
little use of them here, as I had no intention of
giving anything like a complete ontogeny of the
markings in all caterpillars : larval markings were
with me but means to an end, and I wished
only to bring together such a number of facts as
Preface to the English Edition. xxv
were necessary for drawing certain general con-
clusions. It would indeed be most interesting to
extend such observations to other groups of
Lepidoptera.
The third essay also, for similar reasons, is
based essentially upon the same materials, viz.
the Lepidoptera. It is therein attempted to
approach the general problem — does there or
does theje not exist an internal transforming
force ? — from a quite different and, I may say,
opposite point of view. The form-relationships
of Lepidoptera in their two chief stages of de-
velopment, imago and larva, are therein analysed,
and by an examination of the respective forms it
has been attempted to discover the nature of the
causes which have led thereto.
I may be permitted to say that the fact here
disclosed of a different morphological \ with the
same genealogical relationship, appears to me to
be of decided importance. The agreement of the
conclusions following therefrom with the results
of the former investigation has, at least in my own
mind, removed the last doubts as to the correct-
ness of the latter.
The fourth and shortest essay on the " Trans-
formation of the Axolotl into Amblystoma," starts
primarily with the intention of showing that cases
of sudden transformation are no proof of per
saltum development. When this essay first ap-
peared the view was still widely entertained that
xxvi Preface to the English Edition.
we had here a case proving per saltum develop-
ment. That this explanation was erroneous is now
generally admitted, but I believe that those who
suppose that we have here to deal with some quite
ordinary phenomenon which requires no explana-
tion, now go too far towards the other extreme. The
term " larval reproduction " is an expression, but
no explanation / we have therefore to attempt to
find out the true interpretation, but whether the
one which I have given is correct must be judged
of by others.
These four essays lead up to a fifth and con-
cluding one " On the Mechanical Conception of
Nature." Whilst the results obtained are here
summed up, it is attempted to form them into a
philosophical conception of Nature and of the
Universe. It will be thought by many that this
should have been left to professed philosophers,
and I readily admit that I made this attempt with
some misgiving. Two considerations, however,
induced me to express here my own views. The
first was that the facts of science are frequently
misunderstood, or at any rate not estimated at
their true value, by philosophers ;2 the second
consideration was, that even certain naturalists
and certainly very many non-naturalists, turn dis-
trustfully from the results of science, because
* I am aware that this certainly cannot be said of philo-
sophers like Lotze or Herbert Spencer ; but these are at the
same time both naturalists and philosophers.
Preface to the English Edition. xxvii
they fear that these would infallibly lead to a view
of the Universe which is to them unacceptable,
viz. the materialistic view. With regard to the
former I wished to show that the views of the
development of organic Nature inaugurated by
Darwin and defended in this work are certainly
correctly designated mechanical ; with reference
to the latter I wished to prove that such a me-
chanical conception of the organic world and of
Nature in general, by no means leads merely to
one single philosophical conception of Nature, viz.
to Materialism, but that on the contrary it rather
admits of legitimate development in a quite
different manner.
Thus in these last four essays much that
appears heterogeneous will be found in close
association, viz. scientific details and general
philosophical ideas. In truth, however, these are
most intimately connected, and the one cannot
dispense with the other. As the detailed investi-
gations of the three essays find their highest
value in the general considerations of the fourth,
and were indeed only possible by constantly
keeping this end in view, so the general con-
clusions could only grow out of the results of the
special investigations as out of a solid foundation.
Had the new materials here brought together
been already known, the reader would certainly
have been spared the trouble of going into the
details of special scientific research. But as
xxviii Preface to the English Edition.
matters stood it was indispensable that the facts
should be examined into and established even
down to the most trifling details. The essay
"On the Origin of the Markings of Caterpillars"
especially, had obviously to commence with the
sifting and compilation of extensive morphological
materials.
AUGUST WEISMANN.
Freiburg in Baden,
November ', 1881.
CONTENTS.
lact I.
ON THE SEASONAL DIMORPHISM OF
BUTTERFLIES.
I.
The Origin and Significance of Seasonal Dimorphism, p. i.
Historical preliminaries, i. Does not occur in other orders of
insects, 4. Beginning of experimental investigation, 5. Lepidop-
terous foes, 7. First experiments with Araschnia Levana, 10.
Experiments with Pieris Napi, 13. Discussion of results, 17.
Origination of Prorsa from Levana, 19. Theoretical considerations,
23. The case of Papilio Ajax, 30. Experiments with Pieris Napi
var. Bryonice, 39. The summer generations of seasonally dimorphic
butterflies the more variable, 42.
II.
Seasonal Dimorphism and Climatic Variation, p. 45.
Distinction between climatic and local varieties, 45. The case
of Euchloe Belia and its varieties, 47. The case of Polyommatus
Phlaas, 49. The case of Plebeius Agestis, 50.
III.
Nature of the Causes producing Climatic Varieties, p. 52.
Seasonal dimorphism of the same nature as climatic variation,
52. How does climatic change influence the markings of a
butterfly? 52. The cause of this to be found in temperature, 54.
Part played by the organism itself, 58. Analogous seasonal dimor-
phism in Pierina, 60. The part played by sexual selection, 62.
xxx Contents.
IV.
Why all Polygoneutic Species are not Seasonally Dimorphic, p. 63.
Homochronic heredity, 63. Caterpillars, pupae and eggs of
summer and winter generations of seasonally dimorphic butterflies
alike, 64. The law of cyclical heredity, 65. Climatic variation of
Pararga sEgeria, 68. Continuous as distinguished from alternating
heredity, 68. Return from dimorphism to monomorphism, 70.
Seasonally dimorphic species hibernate as pupae, 71. Retrogressive
disturbance of winter generations, 72. The case of Plebeius
Amyntas, 75.
V.
On Alternation of Generations, p. 80.
Haeckel's classification of the phenomena, 80. Proposed modifi-
cation, 81. Derivation of metagenesis from metamorphosis, 82.
Primary and secondary metagenesis, 84. Seasonal dimorphism
related to heterogenesis, 86. Heterogenesis and adaptation, 89.
Differences between seasonal dimorphism and other cases of hetero-
genesis, 89. The case of Leptodora Hyalina, 93.
VI.
General Conclusions, p. 100.
Species produced by direct action of environment, 100. The
transforming influences of climate, 103. The origin of variability,
107. The influence of isolation, 109. Cyclically acting causes of
change produce cyclically recurring changes, in. Specific constitu-
tion an important factor, 112. A "fixed direction of variation,"
114.
Appendix /., p. 117.
Experiments with Araschnia Levana, 117. Experiments with
Picrintz, 122.
Appendix II., p. 126.
Experiments with Papilio Ajax, 126. Additional experiments
with Pap. Ajax, 131. Experiments with Phyciodes Tharos, 140:
with Grapta Interrogations , 149. Remarks on the latter, 152.
Explanation of the Plates, p. 159.
Contents. xxxi
ON THE FINAL CAUSES OF TRANSFORMATION.
I.
THE ORIGIN OF THE MARKINGS OF CATERPILLARS.
Introduction^ p. 161.
I.
Ontogeny and Morphology of Sphinx Markings, p. 177.
The genus Chcerocampa, 177; C. Elpenor, 177; C. Porcellus, 184.
Results of the development of these species and comparison with
other species of the genus, 188. The genus Deilephila, 199; D.
Euphorbia, 201 ; D. Nicoza, 207 ; D. Dahlii, 208 ; D. Vespertilio,
209; D. Galii, 211; D. Livornica, 215; D. Zygophylli, 217; D.
Hippophaes, 218. Summary of facts and conclusions from this
genus, 223. The genus Smerinthus, 232 ; S. Tilicz, 233 ; S.
Populi, 236 ; S. Ocellatus, 240. Results of the development of
these species, 242. The genus Macroglossa, 245 ; M. Stellatarum,
245 ; comparison of this with other species, 253. The genus
Pterogon, 255; P. (Enotherce, 256; comparison with other species,
256. The genus Sphinx, 259 ; S. Ligustri, 259; comparison with
other species, 261. The genus Anceryx> 264; A. Pinastri, 265;
comparison with other species, 268.
II.
Conclusions from Phylogeny, p. 270.
The Ontogeny of Caterpillars is a much abbreviated but slightly
falsified repetition of the Phylogeny, 270. Three laws of de-
velopment, 274. The backward transference of new characters to
younger stages is the result of an innate law of growth, 278. Proof
that new characters always originate at the end of the development ;
the red spots of S. Tilia, 282.
III.
Biological Value of Marking in general, p. 285.
Markings of Caterpillars most favourable to inquiry, 285. Are
the Sphinx- markings purely morphological, or have they a biological
value ? 287.
xxxii Contents.
IV.
Biological Value of Colour, p. 289.
General prevalence of protective colouring among caterpillars, 289.
Polymorphic adaptive colouring in C. Elpenor, C. Porcellus, P.
QLnothera, D. Vespertilio, D. Galii, £>. Livornica, D. Hippophaes,
295. Habit of concealment primary; its causes, 298. Polymor-
phism does not here depend upon contemporaneous but upon
successive double adaptation; displacement of the old by a new
adaptation; proof in the cases of D. Hippophaes, D. Galii, D.
Vespertilio, M. Stellatarum, C. Elpenor, and S. Convolvuli, 300.
V.
Biological Value of special Markings, p 308.
Four chief forms of marking among Sphingidcz, 309. Complete
absence of marking among small caterpillars and among those living
in obscurity, 310. Longitudinal stripes among grass caterpillars,
312. Oblique striping. Coloured edges are the shadows of leaf
ribs, 317. Eye-spots and ring-spots. Definition, 326 : Eye-spots not
originally signs of distastefulness, 328; they are means of alarm,
329; experiments with birds, 330; possibility of a later change of
function in eye-spots, 334. Ring-spots. Are they signs of dis-
tastefulness? Are there caterpillars which are edible and which
possess bright colours ? 335; experiments with lizards, 336. In D.
Galii, D. Euphorbia, D. Dahlii and D. Mauritania the ring-spots
are probably signs of distastefulness, 341. In D. Niccza they are
perhaps also means of exciting terror, 342. The primary ring-spot
in D. Hippophaes is a means of protection, 344. Subordinate
markings. Reticulation, 347. The dorsal spots of C. Elpenor and
C. Porcellus, 348. The lateral dots of S. Convolvuli, 348. Origi-
nation of subordinate markings by the blending of inherited but
useless markings with new ones, 349.
VI.
Objections to a Phyletic Vital Force, p. 352.
Independent origination of ring-spots in species of the genus
Deilephila, 352. Possible genealogy of this genus, 358. Inde-
pendent origination of red spots in several species of Smerinthus,
360. Functional change in the elements of marking, 365. Colour
change in the course of the ontogeny, 367.
Contents. xxxiii
VII.
Phyktic Development of the Markings of the Sphingida. Summary
and Conclusion, p. 370.
The oldest Sphingida were devoid of marking, 370. Longi-
tudinal stripes the oldest form of marking, 371. Oblique striping,
373. Spot markings, 375. The first and second elements of
marking are mutually exclusive, but not the first and third, or the
second and third, 377. Results with reference to the origin of
markings; picture of their origin and gradual complication, 380.
General results; rejection of a phyletic vital force, 389.
II.
ON PHYLETIC PARALLELISM IN METAMORPHIC
SPECIES.
Introduction, p. 390.
I.
Larva and Imago vary in Structure independently of each other, p. 401.
Dimorphism of one stage only, 402. Independent variability of
the stages (heterochronic variability), 403. Constancy and varia-
bility are not inherent properties of certain forms of marking, 407.
Heterochronic variability is not explained by assuming a phyletic
vital force, 410. Rarity of greater variability in pupae. Greater
variability more common among caterpillars than among the
imagines. Causes of this phenomenon, 412. Apparent independent
variability of the single larval stages. Waves of variability, 416.
Saturnia Carpini an instance of secondary variability, 419. Causes
of the exact correlation between the larval stages and its absence
between the larva and imago, 429.
II.
Does the Form-relationship of the Larva coincide with that of the
Imago? p. 432.
Family groups, 432. Families frequently completely congruent
435. Exception offered by the NymphalidcB, 435. In transitional
families the larvae also show intermediate forms, 441. Genera ;
almost completely congruent ; the Nymphalideous genera can be
based on the structure of the larvae, 444. So also can certain sub-
genera, as Vanessa, 445. Incongruence in Pterogon, 450. Species;
in congruence very common ; ,5". Ocellatus and Populi, 451. Species
xxxiv Contents.
of Deilephila show a nearer form-relationship as imagines than as
larvae, 454. Systemy not only the expression of morphological
relationship, 455. Varieties; incongruence the rule; seasonal dimor-
phism ; climatic varieties; dimorphism of caterpillars ; local varieties
of caterpillars, 456. Result of the investigation, 458. Causes of
incongruence, 460. A phyletic vital force does not explain the
phenomena, 461. This force is superfluous, 464.
III.
Incongruences in other Orders of Insects, p. 481.
Hymenoptera. The imagines only possess ordinal characters, 481.
Double incongruence : different distance and different group-forma-
tion, 483. Diptera, 488. The larvae form two types depending on
different modes of life, 489. The similarity of the grub-like larvae
of Diptera and Hymenoptera depends upon convergence, 494.
These data again furnish strong arguments against a phyletic vital
force, 496. The tribe Aphaniptera, 498. Results furnished by the
form-relationship of Diptera and Hymenoptera, 499. Difference
between typical and non-typical parts transient, 501.
IV.
Summary and Conclusion, p. 502.
First form of incongruence, 503. Second form of incongruence,
506. General conclusion as to the elimination of a phyletic vital
force, 511. Parallelism with the transformation of systems of
organs, 513.
Appendix I., p. 520.
Additional notes on the Ontogeny, Phylogeny, <fcc., of Caterpillars.
Ontogeny of Noctua larvae, 520. Additional descriptions of Sphinx-
larvae, 521. Retention of the subdorsal line by ocellated larvae, 529.
Phytophagic variability, 531. Sexual variation in larvae, 534.
Appendix II., /. 536.
Acr<za and the Maracuja butterflies as larvae, pupae, and imagines,
536.
Explanation of the Plates, p. 546.
Contents. xxxv
ON THE FINAL CAUSES OF TRANSFORMATION
(continued).
III.
THE TRANSFORMATION OF THE MEXICAN AXOLOTL
INTO AMBLYSTOMA.
Introduction, p. 555.
Experiments, 558. Significance of the facts, 563. The Axolotl
rarely or never undergoes metamorphosis in its native country, 565.
North American Amblystomas, 570. Does the exceptional transfor-
mation depend upon a phyletic advancement of the species? 571.
Theoretical bearing of the case, 574. Differences between Axolotl
and Amblystoma, 575. These are not correlative results of the sup-
pression of the gills, 578. Explanation by reversion, 581. Cases of
degeneration to a lower phyletic stage : Filippi's sexually mature
" Triton larvae," 583. Analogous observations on Triton by Jullien
and Schreibers, 591. The sterility of the artificially produced Am-
blystomas tells against the former importance of the transformation,
594. It is not opposed to the hypothesis of reversion, 596.
Attempted explanation of the sterility from this point of view, 597.
Causes which may have induced reversion in the hypothetical Mexican
Amblystomas, 600. Saltness of the water combined with the drying
up of the shores by winds, 604. Consequences of the reversion
hypothesis, 609; Systematic, 609; an addendum to the "funda-
mental biogenetic law," 611 ; General importance of reversion, 612.
Postscript ; dryness of the air the probable cause of the assumed re-
version of the Amblystoma to the Axolotl, 613. Addendum, 622.
IV.
ON THE MECHANICAL CONCEPTION OF NATURE.
Introduction, p. 634.
Results of the three foregoing essays : denial of a phyletic vital
force, 634. Application of these results to inductive conclusions with
reference to the organic world in general, 636. The assumption of
such a force is opposed to the fundamental laws of natural science,
637. The "vital force" of the older natural philosopher, 640.
Why was the latter abandoned? Commencement of a mechanical
theory of life, 642.
xxxvi Contents.
I.
Are the Principles of the Selection Theory Mechanical ? 645.
Refutation of Von Hartmann's views, 645. Variability, 646. The
assumption of unlimited variability no postulate of the selection theory,
647. The acknowledgment of a fixed and directed variability does not
necessitate the assumption of a phyletic vital force, 647. Heredity,
657. Useful modifications do not occur only singly, 657. New charac-
ters appearing singly may also acquire predominance, 659. A mecha-
nical theory of heredity is as yet wanting, 665. HaeckePs " Perigenesis
of the Plastidule," 667. Correlation, 670. The "specific type"
depends upon the physiological equilibrium of the parts of the
organism, 671. The theoretical principles of the doctrine of selec-
tion are thus mechanical, 675. Importance of the physical constitu-
tion of the organism in determining the quality of variations, 676.
All individual variability depends upon unequal external influences,
677. Deduction of the limitability of variation, 682. Deduction of
local forms, 686. Parallelism between the ontogenetic and the phy-
letic vital force, 687. The two are inseparable, 690.
II.
Mechanism and Teleology ', p. 694.
Von Baer's exaction from the theory of selection, 694. Justifica-
tion of his claim, but the impossibility of the co-operation of a
metaphysical principle with the mechanism of Nature, 695. Per
saltum development (heterogeneous generation). 698. Weakness of
the positive basis of this hypothesis, 699. The latter refuted by the
impossibility of the co-operation of "heterogeneous generation " with
natural selection, 702. The interruption by a metaphysical principle
cannot be reconciled with gradual transformation, 705. The meta-
physical (teleological) principle can only be conceived of as the
ultimate ground of the mechanism of Nature, 709. Value of this
knowledge for the harmonious conception of the Universe, 711.
Explanation of the spiritual by the assumption of conscious matter,
714. The theory of selection does not necessarily lead to Mate-
rialism, 716.
INDEX p. 719.
STUDIES IN THE THEORY OF DESCENT.
part fc
ON THE SEASONAL DIMORPHISM OF
BUTTERFLIES.
I.
THE ORIGIN AND SIGNIFICANCE OF SEASONAL
DIMORPHISM.
THE phenomena here about to be subjected to a
closer investigation have been known for a long
period of time. About the year 1 830 it was shown
that the two forms of a butterfly (Araschnia) which
had till that time been regarded as distinct, in spite
of their different colouring and marking really be-
longed to the same species, the two forms of this
dimorphic species not appearing simultaneously
but at different seasons of the year, the one in
early spring, the other in summer. To this phe-
nomenon the term " seasonal dimorphism" was
subsequently applied by Mr. A. R. Wallace, an
expression of which the heterogeneous composition
B
.2 . Studies in the Theory of Descent.
may arouse the horror of the philologist, but, as it
is as concise and intelligible as possible, I propose
to retain it in the present work.
The species of Arascknia through which the
discovery of seasonal dimorphism was made,
formerly bore the two specific names A. Levana
and A. Prorsa. The latter is the summer and the
former the winter form, the difference between the
two being, to the uninitiated, so great that it is diffi-
cult to believe in their relationship. A. Levana
(Figs, i and 2, Plate I.) is of a golden brown
colour with black spots and dashes, while A.
Prorsa (Figs. 5 and 6, Plate I.) is deep black
with a broad white interrupted band across both
wings. Notwithstanding this difference, it is
an undoubted fact that both forms are merely the
winter and summer generations of the same species.
I have myself frequently bred the variety Prorsa
from the eggs of Levana, and vice versd.
Since the discovery of this last fact a consider-
able number of similar cases have been established.
Thus P. C. Zeller1 showed, by experiments made
under confinement, that two butterflies belonging to
the family of the * Blues/ differing greatly in colour
and marking, and especially in size, which had
1 " Uber die Artrechte des Polyommatus Amyntas und Poly-
sperchon" Stett. ent. Zeit. 1849. Vol. x. p. 177 — 182. [In
Kirb/s " Synonymic Catalogue of Diurnal Lepidoptera "
Plebeius Amyntas is given as a synonym and P. Polysperchon as
a var. of P. Argiades Pall. R.M.]
On the Seasonal Dimorphism of Butterflies. 3
formerly been distinguished as Plebeius (Lycczna)
Polysperchon and P. Amyntas, were merely winter
and summer generations of the same species ; and
that excellent Lepidopterist, Dr. Staudinger, proved
the same2 with species belonging to the family of
the ' Whites/ Euchloe Belia Esp. and E. Ausonia
Hlib., which are found in the Mediterranean
countries.
The instances are not numerous, however, in
which the difference between the winter and sum-
mer forms of a species is so great as to cause them
to be treated of in systematic work as distinct
species. I know of only five of these cases.
Lesser differences, having the systematic value of
varieties, occur much more frequently. Thus, for
instance, seasonal dimorphism has been proved to
exist among many of our commonest butterflies
belonging to the family of the ' Whites,' but the
difference in their colour and marking can only be
detected after some attention ; while with other
species, as for instance with the commonest of our
small 'Blues/ Plebeius Alexis (j=. Icarus, Rott.),
the difference is so slight that even the initiated
must examine closely in order to recognize it.
Indeed whole series of species might easily be
grouped so as to show the transition from complete
similarity of both generations, through scarcely
2 " Die Arten der Lepidopteren-feattung Ino Leach, nebst
einigen Vorbemerkungen iiber Local varietaten." Stett. ent.
Zeit. 1862. Vol. xxiii. p. 342.
B 2
4 Studies in the Theory of Descent.
perceptible differences, to divergence to the extent
of varieties, and finally to that of species.
Nor are the instances of lesser differences be-
tween the two generations very numerous. Among
the European diurnal Lepidoptera I know of
about twelve cases, although closer observation in
this direction may possibly lead to further dis-
coveries.3 Seasonal dimorphism occurs also in
moths, although I am not in a position to make a
more precise statement on this subject,4 as my own
observations refer only to butterflies.
That other orders of insects do not present the
same phenomenon depends essentially upon the
fact that most of them produce only one genera-
tion in the year ; but amongst the remaining orders
there occur indeed changes of form which, although
8 [Eng. ed. W. H. Edwards has since pointed out several
beautiful cases of seasonal dimorphism in America. Thus
Plebeius Pseudargiolus is the summer form of P. Violacea, and
Phyciodes Tharos the summer form of P. Marcia. See
Edwards' " Butterflies of North America," 1868-79.]
4 [Eng. ed. I learn by a written communication from Dr.
Speyer that two Geometrae, Selenia Tetralunaria and S. Illu-
naria Hub., are seasonally dimorphic. In both species the
winter form is much larger and darker.] [Selenia Lunaria,
S. Illustraria, and some species of Ephyra (E. Pundaria and
E. Omicronarid] are likewise seasonally dimorphic. For
remarks on the case of »S. Illustraria see Dr. Knaggs in Ent.
Mo. Mag., vol. hi. p. 238, and p. 256. Some observations
on E. Punctaria were communicated to the Entomological
Society of London by Professor Westwood in 1877, on the
authority of Mr. B. G. Cole. See Proc. Ent. Soc. 1877,
pp. vi, vii. R.M.]
On the Seasonal Dimorphism of Butterflies. 5
not capable of being regarded as pure seasonal
dimorphism, may well have been produced in part
by the same causes, as the subsequent investiga-
tion on the relation of seasonal dimorphism to
alternation of generation and heterogenesis will
more fully prove.
Now what are these causes ?
Some years ago, when I imparted to a lepidop-
terist my intention of investigating the origin of
this enigmatical dimorphism, in the hope of pro-
fiting for my inquiry from his large experience, I
received the half-provoking reply : " But there is
nothing to investigate : it is simply the specific
character of this insect to appear in two forms ;
these two forms alternate with each other in regular
succession according to a fixed law of Nature, and
with this we must be satisfied." From his point
of view the position was right ; according to the
old doctrine of species no question ought to be
asked as to the causes of such phenomena in par-
ticular. I would not, however, allow myself to be
thus discouraged, but undertook a series of investi-
gations, the results of which I here submit to the
reader.
The first conjecture was, that the differences in
the imago might perhaps be of a secondary nature,
and have their origin in the differences of the cater-
pillar, especially with those species which grow
up during the spring or autumn and feed on dif-
ferent plants, thus assimilating different chemical
6 Studies in the Theory of Descent.
substances, which might induce different deposits
of colour in the wings of the perfect insect. This
latter hypothesis was readily confuted by the fact,
that the most strongly marked of the dimorphic
species, A. Levana, fed exclusively on Urtica major.
The caterpillar of this species certainly exhibits a
well defined dimorphism, but it is not seasonal
dimorphism : the two forms do not alternate with
each other, but appear mixed in every brood.
I have repeatedly reared the rarer golden-brown
variety of the caterpillar separately, but precisely
the same forms of butterfly were developed as
from black caterpillars bred at the same time under
similar external conditions. The same experiment
was performed, with a similar result, in the
last century by Rb'sel, the celebrated miniature
painter and observer of nature, and author of the
well-known " Insect Diversions" — a work in use
up to the present day.
The question next arises, as to whether the
causes originating the phenomena are not the same
as those to which we ascribe the change of winter
and summer covering in so many mammalia and
birds— whether the change of colour and marking
\ does not depend, in this as in the other cases, upon
! the indirect action of external conditions of life,
i. e., on adaptation through natural selection. We
are certainly correct in ascribing white coloration
to adaptation 5 — as with the ptarmigan, which is
6 [In 1860 Andrew Murray directed attention to the dis-
On the Seasonal Dimorphism of Butterflies. 7
white in winter and of a grey-brown in summer,
both colours of the species being evidently of
important use.
It might be imagined that analogous phenomena
occur in butterflies, with the difference that the
change of colour, instead of taking place in the
same brood, alternates in different broods.6 The
nature of the difference which occurs in seasonal
dimorphism, however, decidedly excludes this view ;
and moreover, the environment of butterflies
presents such similar features, whether they emerge
in spring or in summer, that all notions that we
may be dealing with adaptational colours must be
entirely abandoned.
I have elsewhere7 endeavoured to show that
butterflies in general are not coloured protectively
during flight, for the double reason that the colour
guising colours of species which, like the Alpine hare, stoat,
and ptarmigan, undergo seasonal variation of colour. See a
paper " On the Disguises of Nature, being an inquiry into the
laws which regulate external form and colour in plants and
animals." Edinb. New Phil. Journ., Jan. 1860. In 1873 I
attempted to show that these and other cases of " variable
protective colouring " could be fairly attributed to natural selec-
tion. See Proc. Zoo. Soc., Feb. 4th, 1873, pp. 153 — 162. R.M.]
e [A phenomenon somewhat analogous to seasonal change
of protecting colour does occur in some Lepidoptera, only the
change, instead of occurring in the same individual, is dis-
played by the successive individuals of the same brood. See
Dr. Wallace on Bombyx Cynthia, Trans. Ent. Soc. Vol. v.
p. 485. R.M.]
7 " Uber den Einfluss der Isolirung auf die Artbildung."
Leipzig, 1872, pp. 55—62.
8 Studies in the Theory of Descent.
of the background to which they are exposed con-
tinually changes, and because, even with the best
adaptation to the background, the fluttering motion
of the wings would betray them to the eyes of
their enemies.8 I attempted also to prove at the
same time that the diurnal Lepidoptera of our
temperate zone have few enemies which pursue
them when on the wing, but that they are subject
to many attacks during their period of repose.
In support of this last statement I may here
adduce an instance. In the summer of 1869 I
placed about seventy specimens of Araschnia
Prorsa in a spacious case, plentifully supplied with
flowers. Although the insects found themselves
quite at home, and settled about the flowers in
very fine weather (one pair copulated, and the
female laid eggs), yet I found some dead and
mangled every morning. This decimation con-
8 [Mr. A. R. Wallace maintains that the obscurely coloured
females of those butterflies which possess brightly coloured
males have been rendered inconspicuous by natural selec-
tion, owing to the greater need of protection by the former
sex. See " Contributions to the Theory of Natural Selec-
tion," London, 1870, pp. 112 — 114. It is now generally
admitted that the underside of butterflies has undergone pro-
tectional adaptation ; and many cases of local variation in the
colour of the underside of the wings, in accordance with the
nature of the soil, &c., are known. See, for instance, Mr. D.
G. Rutherford on the colour-varieties of Aterica Meleagris
(Proc. Ent. Soc. 1878, p. xlii.), and Mr. J. Jenner Weir on a
similar phenomenon in Hipparchia Semele (loc. cit. p. xlix.)
R.M.]
On the Seasonal Dimorphism of Butterflies. 9
tinued — many disappearing entirely without my
being able to find their remains — until after the
ninth day, when they had all, with one exception,
been slain by their nocturnal foes — probably
spiders and Opilionidce.
Diurnal Lepidoptera in a position of rest are
especially exposed to hostile attacks. In this
position, as is well known, their wings are closed
upright, and it is evident that the adaptational
colours on the under side are displayed, as is most
clearly shown by many of our native species.9
Now, the differences in the most pronounced
cases of seasonal dimorphism — for example, in
Araschnia Levand — are much less manifest on the
under than on the upper side of the wing. The
explanation by adaptation is therefore untenable ;
but I will not here pause to confute this view more
completely, as I believe I shall be able to show
the true cause of the phenomenon.
If seasonal dimorphism does not arise from the
indirect influence of varying seasons of the year,
it may result from the direct influence of the
varying external conditions of life, which are,
without doubt, different in the winter from those
of the summer brood.
There are two prominent factors from which
such an influence may be expected — temperature
9 [The fact that moths which, like the Geometrae, rest by
day with the wings spread out, are protectively marked on the
upper side, fully corroborates this statement. R.M.]
io Studies in the Theory of Descent.
and duration of development, i. e., duration of the
chrysalis period. The duration of the larval
period need not engage our attention, as it is only
very little shorter in the winter brood — at least, it
was so with the species employed in the ex-
periments.
Starting from these two points of view, I carried
on experiments for a number of years, in order to
find out whether the dual form of the species in
question could be traced back to the direct action
of the influences mentioned.
The first experiments were made with Araschnia
Levana. From the eggs of the winter generation,
which had emerged as butterflies in April, I bred
caterpillars, and immediately after pupation placed
them in a refrigerator, the temperature of the air
of which was 8° — IOQ R. It appeared, however,
that the development could not thus be retarded
to any desired period by such a small diminution
of temperature, for, when the box was taken out
of the refrigerator after thirty- four days, all the
butterflies, about forty in number, had emerged,
many being dead, and others still living. The
experiment was so far successful that, instead of
the Prorsa form which might have been expected
under ordinary circumstances, most of the butter-
flies emerged as the so-called Porima (Figs. 3, 4,
7, 8, and 9, Plate I.) ; that is to say, in a form inter-
mediate between Prorsa and Levana sometimes
found in nature, and possessing more or less the
On the Seasonal Dimorphism of Butterflies. 1 1
marking1 of the former, but mixed with much of
the yellow of Levana.
It should be here mentioned, that similar expe-
riments were made in 1864 by George Dorf-
meister, but unfortunately I did not get this infor-
mation10 until my own were nearly completed. In
these well-conceived, but rather too complicated
experiments, the author arrives at the conclusion
" that temperature certainly affects the colouring,
and through it the marking, of the future butterfly,
and chiefly so during pupation." By lowering the
temperature of the air during a portion of the
pupal period, the author was enabled to produce
single specimens of Porima, but most of the butter-
flies retained the Prorsa form. Dorfmeister em-
ployed a temperature a little higher than I did in
my first experiments, viz. 10° — 11° R., and did
not leave the pupae long exposed, but after 5^ — 8
days removed them to a higher temperature. It
was therefore evident that he produced transition
forms in a few instances only, and that he never
succeeded in bringing about a complete transfor-
mation of the summer into the winter form.
In my subsequent experiments I always ex-
posed the pupae to a temperature of o° — 1° R. ;
they were placed directly in the refrigerator, and
10 " Uber die Einwirkung verschiedener, wahrend der Ent-
wicklungsperioden angewendeter Warmegrade auf die Farbung
und Zeichnung der Schmetterlinge." A communication to the
Society of Natural Science of Steiermark, 1864.
1 2 Stiidies in the Theory of Descent.
taken out at the end of four weeks. I started with
the idea that it was perhaps not so much the re-
duced temperature as the retardation of develop-
ment which led to the transformation. But the
first experiment had shown that the butterflies
emerged between 8° and 10° R., and conse-
quently that the development could not be re-
tarded at this temperature.
A very different result was obtained from the ex-
periment made at a lower temperature. n Of twenty
butterflies, fifteen had become transformed into
Porima, and of these three appeared very similar
to the winter form (Levana), differing only in the
absence of the narrow blue marginal line, which
is seldom absent in the true Levana. Five butter-
flies were uninfluenced by the cold, and remained
unchanged, emerging as the ordinary summer
form (Prorsa]. It thus appeared from this expe-
riment, that a large proportion of the butterflies
inclined to the Levana form by exposure to a
temperature of o° — 1° R. for four weeks, while
in a few specimens the transformation into this
form was nearly perfect.
Should it not be possible to perfect the trans-
formation, so that each individual should take the
Levana form ? If the assumption of the Prorsa or
Levana form depends only on the direct influence
of temperature, or on the duration of the period of
11 See Exp. 9, Appendix I.
On the Seasonal Dimorphism of Butterflies. 1 3
development, it should be possible to compel the
pupae to take one or the other form at pleasure, by ,,
the application of the necessary external conditions.
This has never been accomplished with Araschnia
Prorsa. As in the experiment already described,
and in all subsequent ones, single specimens ap-
peared as the unchanged summer form, others
showed an appearance of transition, and but very
few had changed so completely as to be possibly
taken for the pure Levana. In some species of the
sub-family Pierince, however, at least in the case
of the summer brood, there was, on the contrary,
a complete transformation.
Most of the species of our ' Whites ' (Pierince)
exhibit the phenomenon of seasonal dimorphism,
the winter and summer forms being remarkably
distinct. In Pieris Napi (with which species I
chiefly experimented) the winter form (Figs. 10
and 11, Plate I.) has a sprinkling of deep black
scales at the base of the wings on the upper side,
while the tips are more grey, and have in all cases
much less black than in the summer form ; on the
underside the difference lies mainly in the frequent
breadth, and dark greenish-black dusting, of the
veins of the hind wings in the winter form, while
in the summer form these greenish-black veins
are but faintly present.
I placed numerous specimens of the summer
brood, immediately after their transformation into
chrysalides, in the refrigerator (o° — 1° R.), where
1 4 Studies in the Theory of Descent.
I left them for three months, transferring them to
a hothouse on September nth, and there (from
September 26th to October 3rd) sixty butterflies
emerged, the whole of which, without exception —
and most of them in an unusually strong degree —
bore the characters of the winter form. I, at least,
have never observed in the natural state such a
strong yellow on the underside of the hind wings,
and such a deep blackish-green veining, as pre-
vailed in these specimens (see, for instance, Figs.
10 and n). The temperature of the hothouse
(12° — 24° R.) did not, however, cause the emer-
gence of the whole of the pupae ; a portion hiber-
nated, and produced in the following spring
butterflies of the winter form only. I thus suc-
ceeded, with this species of Pieris, in completely
changing every individual of the summer genera-
tion into the winter form.
It might be expected that the same result could
be more readily obtained with A. Levana, and
fresh experiments were undertaken, in order that
the pupae might remain in the refrigerator fully
two months from the period of their transforma-
tion (9-ioth July). But the result obtained was
the same as before — fifty-seven butterflies emerged
in the hothouse12 from September igthto October
4th, nearly all of these approaching very near to
the winter form, without a single specimen pre-
11 See Exp. ir, Appendix I.
On the Seasonal Dimorphism of Butterflies. 1 5
senting the appearance of a perfect Levana, while
three were of the pure summer form (Prorsa).
Thus with Levana it was not possible, by refri-
geration and retardation of development, to change
the summer completely into the winter form in all
specimens. It may, of course, be objected that
the period of refrigeration had been too short,
and that, instead of leaving the pupae in the refri-
gerator for two months, they should have remained
there six months, that is, about as long as the
winter brood remains under natural conditions in
the chrysalis state. The force of this last objec-
tion must be recognized, notwithstanding the im-
probability that the desired effect would be pro-
duced by a longer period of cold, since the doubling
of this period from four to eight weeks did not
produce13 any decided increase in the strength of
the transformation. I should not have omitted
to repeat the experiment in this modified form,
but unfortunately, in spite of all trouble, I was
unable to collect during the summer of 1873 a
sufficient number of caterpillars. But the omission
thus caused is of quite minor importance from a
theoretical point of view.
For let us assume that the omitted experiment
had been performed — that pupae of the summer
brood were retarded in their development by cold
until the following spring, and that every specimen
13 See Exps. 4, 9, and u, Appendix I«
1 6 Studies in the Theory of Descent.
then emerged in the perfect winter form, Levana.
Such a result, taken in connexion with the cor-
responding experiment upon Pieris Napi, would
warrant the conclusion that the direct action of a
certain amount of cold (or of retardation of deve-
lopment) is able to compel all pupae, from which-
ever generation derived, to assume the winter
form of the species. From this the converse
would necessarily follow, viz. that a certain amount
of warmth would lead to the production of the
summer form, Prorsa, it being immaterial from
which brood the pupae thus exposed to warmth
might be derived. But the latter conclusion was
proved experimentally to be incorrect, and thus
the former falls with it, whether the imagined ex-
periment with Prorsa had succeeded or not.
I have repeatedly attempted by the application
of warmth to change the winter into the summer
form, but always with the same negative result.
It is not possible to compel the winter brood to
assume the form of the summer generation.
A. Levaua may produce not only two but three
broods in the year, and may, therefore, be said to
be polygoneutic™ One winter brood alternates
with two summer broods, the first of which appears
in July, and the second in August. The latter
14 It seems to me very necessary to have a word expressing
whether a species produces one, two, or more generations in
the year, and I have therefore coined the expression mono-, di-,
and polygoneutic from yovevw, I produce.
On the Seasonal Dimorphism of Butterflies, i 7
furnishes a fourth generation of pupae, which, after
hibernation, emerge in April, as the first brood of
butterflies in the form Levana.
I frequently placed pupae of this fourth brood in
the hothouse immediately after their transforma-
tion, and in some cases even during the caterpillar
stage, the temperature never falling, even at night,
below 12° R., and often rising during the day to
24° R. The result was always the same : all, or
nearly all, the pupae hibernated, and emerged the
following year in the winter form as perfectly pure
Levana, without any trace of transition to the
Prorsa form. On one occasion only was there a
Porima among them, a case for which an explana-
tion will, I believe, be found later on. It often
happened, on the other hand, that some few of the
butterflies emerged in the autumn, about fourteen
days after pupation ; and these were always Prorsa
(the summer form), excepting once a Porima.
From these experiments it appeared that similar
causes (heat) affect different generations of A.
Levana in different manners. With both summer
broods a high temperature always caused the
appearance of Prorsa, this form arising but seldom
from the third brood (and then only in a few in-
dividuals), while the greater number retained the
Levana form unchanged. We may assign as the
reason for this behaviour, that the third brood has
no further tendency to be accelerated in its develop-
ment by the action of heat, but that by a longer
c
1 8 Studies in the Theory of Descent.
duration of the pupal stage the Levana form must
result. On one occasion the chrysalis stage was
considerably shortened in this brood by the
continued action of a high temperature, many
specimens thus having their period of develop-
ment reduced from six to three months. The
supposed explanation above given is, however, in
reality no explanation at all, but simply a restate-
ment of the facts. The question still remains, why
the third brood in particular has no tendency to
be accelerated in its development by the action of
heat, as is the case with both the previous broods ?
The first answer that can be given to this
question is, that the cause of the different action
produced by a similar agency can only lie in the
constitution, i. e., in the physical nature of the
broods in question, and not in the external in-
fluences by which they are acted upon. Now,
what is the difference in the physical nature of
these respective broods ? It is quite evident, as
shown by the experiments already described, that
cold and warmth cannot be the immediate causes
of a pupa emerging in the Prorsa or Levana form,
since the last brood always gives rise to the
Levana form, whether acted on by cold or warmth.
The first and second broods only can be made to
partly assume, more or less completely, the Levana
form by the application of cold. In these broods
then, a low temperature is the mediate cause of the
transformation into the Levana form.
On the Seasonal Dimorphism of Butterflies. 1 9
The following is my explanation of the facts.
The form Levana is the original type of the
species, and Prorsa the secondary form arising
from the gradual operation of summer climate.
When we are able to change many specimens of
the summer brood into the winter form by means
of cold, this can only depend upon reversion to/
the original, or ancestral, form, which reversion ap-
pears to be most readily produced by cold, that is,
by the same external influences as those to which
the original form was exposed during a long period
of time, and the continuance of which has preserved,
in the winter generations, the colour and marking
of the original form down to the present time.
I consider the origination of the Prorsa from the
Levana form to have been somewhat as follows : —
It is certain that during the diluvial period in \
Europe there was a so-called 'glacial epoch,' which/
may have spread a truly polar climate over our
temperate zone ; or perhaps a lesser degree of cold
may have prevailed with increased atmospheric
precipitation. At all events, the summer was then
short and comparatively cold, and the existing
butterflies could have only produced one genera-
tion in the year ; in other words, they were mono-
goneutic. At that time A. Levana existed only in
the Levana form.16 As the climate gradually be-
15 [Eng. ed. In the German edition, which appeared in
1874, I was not able to support this hypothesis by geographi-
cal data, and could then only ask the question "whether
C 2
2O Studies in the Theory of Descent.
came warmer, a period must have arrived when
Levana, in the most" northern portion of its area of distribution,
appears in two or only in one generation?" This question is
now answered by the Swedish Expedition to the Yenisei in
1876. Herr Philipp Trybom, one of the members of this
expedition, observed A. Levana at the end of June and
beginning of July, in the middle of Yenisei, in 60° — 63° N.
(Dagfjarilar fr&n Yenisei in Oversigt ap k. Vertensk. Akad.
Forhandlingon, 1877, No. 6.) Trybom* found Levana at
Yenisk on June 23rd, at Worogova (61° 5') on July 3rd, at
Asinova (61° 25') on July 4th, at Insarowa (62° 5') on July
7th, and at Alinskaja (63° 25') on July Qth. The butterflies
were especially abundant at the beginning of June, and were
all of the typical Levana form. Trybom expressly states, " we
did not find a single specimen which differed perceptibly from
Weismann's Figs, i and 2 (' Saison-Dimorphismus ' Taf. I.)."
The Swedish expedition soon left the Yenisei, and con-
sequently was not able to decide by observations whether
a second generation possessing the Prorsa form appeared
later in the summer. Nevertheless, it may be stated with
great probability that this is not the case. The districts in
which Levana occurs on the Yenisei have about the same
isotherm as Archangel or Haparanda, and therefore the same
summer temperature. Dr. Staudinger, whose views I solicited,
writes to me: — "In Finnmark (about 67° N.) I observed no
species with two generations ; even Polyommatus Phlceas, which
occurs there, and which in Germany has always two, and in
the south, perhaps, three generations, in Finnmark has only one
generation. A second generation would be impossible, and
this would also be the case with Levana in the middle of
Yenisei. I certainly have Levana and Prorsa from the middle
of Amur, but Levana flies there at the end of May, and the
summers are very warm." The middle of Amur lies, more-
over, in 50° N. lat., and therefore io°— 13° south of the
districts of the Yenisei mentioned.
It must thus be certainly admitted that on the Yenisei A.
Levana occurs only in the Levana form, and that consequently
this species is at the present time, in the northernmost portion
On the Seasonal Dimorphism of Butterflies. 2 i
the summer lasted long enough for the interpolation
of a second brood. The pupae of Levana, which
had hitherto hibernated through the long winter
to appear as butterflies in the following summer,
were now able to appear on the wing as butterflies
during the same summer as that in which they left
their eggs as larvae, and eggs deposited by the last
brood produced larvae which fed up and hibernated
as pupae. A state of things was thus established
in which the first brood was developed under very
different climatic conditions from the second. So
considerable a difference in colour and marking
between the two forms as we now witness could
not have arisen suddenly, but must have done so
gradually. It is evident from the foregoing ex
periments that the Prorsa form did not originate
suddenly. Had this been the case it would simply
signify that every individual of this species pos-
sessed the faculty of assuming two different forms
according as it was acted on by warmth or cold,
just in the same manner as litmus-paper becomes
red in acids and blue in alkalies. The experiments
of its area of distribution, in the same condition as that in
which I conceive it to have been in mid Europe during the
glacial period. It would be of the greatest interest to make
experiments in breeding with this single-brooded Levana from
the Yenisei, i. e., to attempt to change its offspring into the
Prorsa form by the action of a high temperature. If this
could not be accomplished it would furnish a confirmation of
my hypothesis than which nothing more rigorous could be
desired.]
22 Studies in the Theory of Descent.
have shown, however, that this is not the case, but
rather that the last generation bears an ineradi-
cable tendency to take the Levana form, and is
not susceptible to the influence of warmth, however
long continued ; while both summer generations,
on the contrary, show a decided tendency to assume
the Prorsa form, although they certainly can be
made to assume the Levana form in different
degrees by the prolonged action of cold.
The conclusion seems to me inevitable, that the
origination of the Prorsa form was gradual — that
those changes which originated in the chemistry
of the pupal stage, and led finally to the Prorsa
type, occurred very gradually, at first perhaps
remaining completely latent throughout a series
of generations, then very slight changes of mark-
ing appearing, and finally, after a long period
of time, the complete Prorsa type was produced.
It appears to me that the quoted results of the
experiments are not only easily explained on the
view of the gradual action of climate, but that this
view is the only one admissible. The action of
climate is best comparable with the so-called
cumulative effect of certain drugs on the human
body ; the first small dose produces scarcely any
perceptible change, but if often repeated the effect
becomes cumulative, and poisoning occurs.
This view of the action of climate is not at all
new, most zoologists having thus represented it ;
only the formal proof of this action is new, and
On the Seasonal Dimorphism of Butterflies. 2 3
the facts investigated appear to me of special im-
portance as furnishing this proof. I shall again
return to this view in considering climatic varieties,
and it will then appear that also the nature of the
transformation itself confirms the slow operation
of climate.
During the transition from the glacial period to
the present climate A. Levana thus gradually
changed from a monogoneutic to a digoneutic
species, and at the same time became gradually
more distinctly dimorphic, this character origi-
nating only through the alteration of the summer
brood, the primary colouring and marking of the
species being retained unchanged by the winter
brood. As the summer became longer a third
generation could be interpolated — the species
became polygoneutic ; and in this manner two
summer generations alternated with one winter
generation.
We have now to inquire whether facts are
in complete accordance with this theory — whether
they are never at variance with it — and whether
they can all be explained by it. I will at once
state in anticipation, that this is the case to the
fullest extent.
In the first place, the theory readily explains
why the summer but not the winter generations
are capable of being transformed ; the latter can-
not possibly revert to the Prorsa form, because
this is much the younger. When, however, it
24 Studies in the Theory of Descent.
happens that out of a hundred cases there occuis
one in which a chrysalis of the winter gene-
ration, having been forced by warmth, under-
goes transformation before the commencement
of winter, and emerges in the summer form,16 this
is not in the least inexplicable. It cannot be
atavism which determines the direction of the
development ; but we see from such a case that
the changes in the first two generations have
already produced a certain alteration in the third,
which manifests itself in single cases under favour-
able conditions (the influence of warmth) by the
assumption of the Prorsa form ; or, as it might be
otherwise expressed, the alternating heredity (of
which we shall speak further), which implies the
power of assuming the Prorsa form, remains latent
as a rule in the winter generation, but becomes
continuous in single individuals.
It is true that we have as yet no kind of insight
into the nature of heredity, and this at once shows
the defectiveness of the foregoing explanation ; but
we nevertheless know many of its external phe-
nomena. We know for certain that one of these
consists in the fact that peculiarities of the father
do not appear in the son, but in the grandson,
or still further on, and that they may be thus
transmitted in a latent form. Let us imagine a
character so transmitted that it appears in the
first, third, and fifth generations, remaining latent
18 See Exp. 10, Appendix I.
On the Seasonal Dimorphism of Butterflies. 25
in the intermediate ones ; it would not be improb-
able, according to previous experiences, that the
peculiarity should exceptionally, i. e., from a cause
unknown to us, appear in single individuals of the
second or fourth generation. But this completely
agrees with those cases in which " exceptional"
individuals of the winter brood took the Prorsa
form, with the difference only that a cause (warmth)
was here apparent which occasioned the develop-
ment of the latent characters, although we are not
in a position to say in what manner heat produces
this action. These exceptions to the rule are
therefore no objection to the theory. On the con-
trary, they give us a hint that after one Prorsa
generation had been produced, the gradual inter-
polation of a second Prorsa generation may have
been facilitated by the existence of the first. I do
not doubt that even in the natural state single
individuals of Prorsa sometimes emerge in Sep-
tember or October ; and if our summer were
lengthened by only one or two months this might
give rise to a third summer brood (just as a second
is now an accomplished fact), under which circum-
stances they would not only emerge, but would
also have time for copulation and for depositing
eggs, the larvae from which would have time to
grow up.
A sharp distinction must be made between the
first establishment of a new climatic form and the
transference of the latter to newly interpolated
26 Studies in the Theory of Descent.
generations. The former always takes place very
slowly ; the latter may occur in a shorter time.
With regard to the duration of time which is
necessary to produce a new form by the influence
of climate, or to transmit to a succeeding gene-
ration a new form already established, great
differences occur, according to the physical nature
of the species and of the individual. The expe-
riments with Prorsa already described show how
diverse are individual proclivities in this respect.
In Experiment No. 12 it was not possible out of
seventy individuals to substitute Prorsa for the
Levana form, even in one solitary case, or, in
other words, to change alternating into continuous
inheritance ; whilst in the corresponding experi-
ments of former years (Experiment 10, for
example), out of an equal number of pupae three
emerged as Prorsa, and one as Porima. We
might be inclined to seek for the cause of this
different behaviour in external influences, but we
should not thus arrive at an explanation of the
facts. We might suppose, for instance, that a
great deal depended upon the particular period of
the pupal stage at which the action of the elevated
temperature began — whether on the first, the
thirtieth, or the hundredth day after pupation —
and this conjecture is correct in so far that in the
two last cases warmth can have no further influence
than that of somewhat accelerating the emergence
of the butterflies, but cannot change the Levana
On the Seasonal Dimorphism of Butterflies. 2 7
into the Prorsa form. I have repeatedly exposed
a large number of Levana pupae of the third
generation to the temperature of an apartment, or
even still higher (26° R.), during winter, but no
Prorsa were obtained.17
But it would be erroneous to assume a difference
in the action of heat according as it began on the
first or third day after transformation ; whether
during or before pupation. This is best proved
by Experiment No. 12, in which caterpillars of
the fourth generation were placed in the hothouse
several days before they underwent pupation ;
still, not a single butterfly assumed the Prorsa
form. I have also frequently made the reverse
experiment, and exposed caterpillars of the first
summer brood to cold during the act of pupation
A regular consequence was the dying off of the
caterpillars, which is little to be wondered at, as
the sensitiveness of insects during ecdysis is well
known, and transformation into the pupal state is
attended by much deeper changes.
Dorfmeister thought that he might conclude
from his experiments that temperature exerts the
greatest influence in the first place during the act
17 When Dorfmeister remarks that hibernating pupae which,
at an early stage " were taken for development into a room, or
not exposed to any cold, gave dwarfed, weakly and crippled,"
or otherwise damaged butterflies, this is entirely attributable to
the fact that this able entomologist had neglected to supply the
necessary moisture to the warm air. By keeping pupae over
water I have always obtained very fine butterflies.
2 8 Studies in the Theory of Descent,
of pupation, and in the next place immediately
after that period. His experiments were made,
however, with such a small number of specimens
that scarcely any safe conclusion can be founded
on them ; still, this conclusion may be correct, in
so far as everything depends on whether, from
the beginning, the formative processes in the
pupa tended to this or that direction, the final
result of which is the Prorsa or Levana form. If
once there is a tendency to one or the other
direction, then temperature might exert an accele-
rating or a retarding influence, but the tendency
cannot be further changed.
It is also possible — indeed, probable — that a
period may be fixed in which warmth or cold
might be able to divert the original direction of
development most easily ; and this is the next
problem to be attacked, the answer to which, now
that the main points have been determined, should
not be very difficult. I have often contemplated
taking the experiments in hand myself, but have
abandoned them, because my materials did not
appear to me sufficiently extensive, and in all
such experiments nothing is to be more avoided
than a frittering away of experimental materials
by a too complicated form of problem.
There may indeed be a period most favour-
able for the action of temperature during the first
days of the pupal stage ; it appears from Experiment
No. 12 that individuals tend in different degrees
On the Seasonal Dimorphism of Butterflies. 2 9
to respond to such influences, and that the dis-
position to abandon the ordinary course of
development is different in different individuals.
In no other way can it be explained that, in all
the experiments made with the first and second
generations of Prorsa, only a portion of the pupae
were compelled by cold to take the direction of
development of Levana^ arid that even from the
former only a few individuals completely reverted,
the majority remaining intermediate.
If it be asked why in the corresponding experi-
ments with Pieris Napi complete reversion
always occurred without exception, it may be
supposed that in this species the summer form has
not been so long in existence, and that it would
thus be more easily abandoned ; or, that the
difference between the two generations has not
become so distinct, which further signifies that
here again. the summer form is of later origin. It
might also be finally answered, that the tendency
to reversion in different species may vary just as
much as in different individuals of the same
species. But, in any case, the fact is established
that all individuals are impelled by cold to com-
plete reversion, and that in these experiments it
does not depend so particularly upon the moment
of development when cold is applied, but that diffe-
rences of individual constitution are much more the
cause why cold brings some pupae to complete, and
others to partial, reversion, while yet others are
30 Studies in the Theory of Descent.
quite uninfluenced. In reference to this, the
American Papilio Ajax is particularly interesting.
This butterfly, which is somewhat similar to
the European P. Podalirius, appears, wherever it
occurs, in three varieties, designated as var. Tela-
monides, var. Walshii, and var. Marcellus. The
distinguished American entomologist, W. H. Ed-
wards, has proved by breeding experiments, that
all three forms belong to the same cycle of de-
velopment, and in such a manner that the first
two appear only in spring, and always come only
from hibernating pupae, while the last form, var.
Marcellus, appears only in summer, and then in
three successive generations. A seasonal dimor-
phism thus appears which is combined with
ordinary dimorphism, winter and summer forms
alternating with each other; but the first appears
itself in two forms or varieties, vars. Telamonides
and Walshii. If for the present we disregard
this complication, and consider these two winter
forms as one, we should thus have four generations,
of which the first possesses the winter form, and
the three succeeding ones have, on the other hand,
the summer form, var. Marcellus.
The peculiarity of this species consists in the
fact that in all three summer generations only a
portion of the pupae emerge after a short period
(fourteen days), whilst another and much smaller
portion remains in the pupal state during the
whole summer and succeeding winter, first
On the Seasonal Dimorphism of Butterflies, 3 i
emerging in the following spring, and then always
in the winter form. Thus, Edwards states that
out of fifty chrysalides of the second generation,
which had pupated at the end of June, forty-five
Marcellus butterflies appeared after fourteen days,
whilst five pupae emerged in April of the fol-
lowing year, and then as Telamonides.
The explanation of these facts is easily afforded
by the foregoing theory. According to this, both
the winter forms must be regarded as primary,
and the Marcellus form as secondary. But this
last is not yet so firmly established as Prorsa, in
which reversion of the summer generations to the
Levana form only occurs through special external
influences ; whilst in the case of Ajax some in-
dividuals are to be found in every generation, the
tendency of which to revert is still so strong that
even the greatest summer heat is unable to cause
them to diverge from their original inherited
direction of development, or to accelerate their
emergence and compel them to assume the Mar-
cellus form. It is here beyond a doubt that it is
not different external influences, but internal
causes only, which maintain the old hereditary
tendency, for all the larvae and pupse of many
different broods were simultaneously exposed to
the same external influences. But, at the same
time, it is evident that these facts are not opposed
to the present theory ; on the contrary, they con-
firm it, inasmuch as they are readily explained on
32 Studies in the Theory of Descent.
the basis of the theory, but can scarcely otherwise
be understood.
If it be Lsked what significance attaches to the
duplication of the winter form, it may be answered
that the species was already dimorphic at the time
when it appeared in only one annual generation.
Still, this explanation may be objected to, since a
dimorphism of this kind is not at present known,
though indeed some species exhibit a sexual
dimorphism,18 in which one sex (as, for instance,
the case of the female Papilio Turnus) appears
in two forms of colouring, but not a dimorphism,
as is here the case, displayed by both sexes.19
Another suggestion, therefore, may perhaps be
offered.
In A. Levana we saw that reversion occurred
in very different degrees with different individuals,
seldom attaining to the true Levana form, and
18 [For other remarkable cases of sexual dimorphism (not
antigeny in the sense used by Mr. S. H. Scudder, Proc. Amer.
Acad., vol. xii. 1877, pp. 150 — 158) see Wallace "On the
Phenomena of Variation and Geographical Distribution, as
illustrated by the Papilionidse of the Malayan Region," Trans.
Linn. Soc., vol. xxv. 1865, pp. 5 — 10. R.M.]
19 [Eng. ed. Dimorphism of this kind has since been made
known : the North American Limenitis Artemis and L. Proser-
pina are not two species, as was formerly believed, but only
one. Edwards bred both forms from eggs of Proserpina.
Both are single-brooded, and both have males and females.
The two forms fly together, but L. Artemis is much more
widely distributed, and more abundant than L. Proserpina.
See " Butterflies of North America," vol. ii.]
On the Seasonal Dimorphism of Butter flies. 33
generally only reaching the intermediate form
known as Porima. Now it would, at all events,
be astonishing if with P. Ajax the reversion were
always complete, as it is precisely in this case that
the tendency to individual reversion is so variable.
I might, for this reason, suppose that one of the
two winter forms, viz. the vax.Walshii, is nothing
else than an incomplete reversion-form, corre-
sponding to Porima in the case of A. Levana.
Then Telamonides only would be the original
form of the butterfly, and this would agree with
the fact that this variety appears later in the
spring than Walshii. Experiments ought to be
able to decide this.20 The pupae of the first
80 [Eng. ed. Edwards has since proved experimentally that
by the application of ice a large proportion of the pupae do
indeed give rise to the var. Telamonides. He bred from eggs
of Telamonides 122 pupae, which, under natural conditions,
would nearly all have given the var. Marcellus. After two months'
exposure to the low temperature there emerged, from August 24th
to October i6th, fifty butterflies, viz. twenty-two Telamonides,
one intermediate form between Telamonides and Walshii, eight
intermediate forms between Telamonides and Marcellus more
nearly related to the former, stx intermediate forms between
Telamonides and Marcellus, but more closely resembling the
latter, and thirteen Marcellus. Through various mishaps the
action of the ice was not complete and equal. See the
"Canadian Entomologist," 1875, p. 228. In the newly dis-
covered case of Phyciodes Tharos also, Edwards has succeeded
in causing the brood from the winter form to revert, by the
application of ice to this same form. See Appendix II. for
a resume of Edwards' experiments upon both Papilio Ajax and
Phyciodes Tharos. R,M.]
D
34 Studies in the Theory of Descent.
three generations placed upon ice should give,
for the greater part, the form Telamonides, for the
lesser portion Walshii, and for only a few, or per-
haps no individuals, the form Marcellus, This
prediction is based on the view that the tendency
to revert is on the whole great ; that even with the
first summer generation, which was the longest
exposed to the summer climate, a portion of the
pupae, without artificial means, always emerged as
Telamonides, and another portion as Marcellus.
The latter will perhaps now become Walshii by
the application of cold.
One would expect that the second and third
generations would revert more easily, and in a
larger percentage, than the first, because this latter
first acquired the new Marcellus form ; but the
present experiments furnish no safe conclusion on
this point. Thus, of the first summer generation
only seven out of sixty-seven pupae hibernated,
and these gave Telamonides ; while of the second
generation forty out of seventy-six, and of the
third generation twenty-nine out of forty-two
pupae hibernated. But to establish safer conclu-
sions, a still larger number of experiments is
necessary. According to the experience thus far
gained, one might perhaps still be inclined to
imagine that, with seasonal dimorphism, external
influences operating on the individual might
directly compel it to assume one or the other
form. I long held this view myself, but it is,
On the Seasonal Dimorphism of Butterflies. 35
nevertheless, untenable. That cold does not
produce the one kind of marking, and warmth
the other, follows from the before-mentioned facts,
viz. that in Papilio Ajax every generation pro-
duces both forms ; and, further, in the case of
A. Levana I have frequently reared the fourth
(hibernating) generation entirely in a warm room,
and yet I have always obtained the winter form.
Still, one might be inclined not to make the tem-
perature directly responsible, but rather the re-
tardation or acceleration of development produced
through the action of temperature. I confess that
I for a long time believed that in this action I had
found the true cause of seasonal dimorphism.
Both with A. Levana and P. Napi the difference
between the duration of the pupal period in the
winter and summer forms is very great, lasting
as a rule, in the summer generation of A. Levana,
from seven to twelve days, and in the winter gene-
ration about two hundred days. In this last species
the pupal state can certainly be shortened by
keeping them at an elevated temperature ; but I
have, nevertheless, only in one case obtained two
or three butterflies at the end of December from
caterpillars that had pupated in September, these
generally emerging in the course of February and
March, and are to be seen on the wing in warm
weather during the latter month. The greatest
reduction of the pupal period still leaves for this
stage more than 100 days.
D 2
36 Studies in the Theory of Descent.
From this last observation it follows that it is
not the duration of development which, in indi-
vidual cases, determines the form of the butterfly,
and which consequently decides whether the winter
or summer form shall emerge, but that, on the
contrary, the duration of the pupal stage is depen-
dent on the tendency which the forthcoming
butterfly had taken in the chrysalis state. This
can be well understood when we consider that
the winter form must have had a long, and the
summer form a short pupal period, during innu-
merable generations. In the former the habit of
slow development must have been just as well
established as that of rapid development in the
latter ; and we cannot be at all surprised if we do
not see this habit abandoned by the winter form
when the opportunity presents itself. But that it
may be occasionally abandoned the more proves
that the duration of the pupal development less
determines the butterfly form than does the tem-
perature directly, in individual cases.
Thus, for instance, Edwards explicitly states
that, whereas the two winter forms of P. Ajax, viz.
the vars. Walshii and Telamonides, generally
appear only after a pupal period of 150 to 270
days, yet individual cases occur in which the pupal
stage is no longer than in the summer form, viz.
fourteen days.21 A similar thing occurs with
21 Thus from eggs of Walshii, laid on April loth, Edwards
obtained, after a pupal period of fourteen days, from the ist
On the Seasonal Dimorphism of Butterflies. 3 7
A. Levana, for, as already explained, not only
may the development of the winter form be forced
to a certain degree by artificial warmth, but the
summer generation frequently produces reversion-
forms without protraction of development. The
intermediate reversion-form Porima was known
long before it was thought possible that it could
be produced artificially by the action of cold ;
it appears occasionally, although very rarely, at
midsummer in the natural state.
If, then, my explanation of the phenomena is
correct, the winter form is primary and the
summer the secondary form, and those individuals
which, naturally or artificially, assume the winter
form must be considered as cases of atavism. The
suggestion thus arises whether low temperature
alone is competent to bring about this reversion,
or whether other external influences are not also
effective. Indeed, the latter appears to be the
case. Besides purely internal causes, as previously
pointed out in P. Ajax, warmth and mechanical
motion appear to be able to bring about rever-
sion.
That an unusually high temperature may cause
reversion, I conclude from the following observa-
tion. In the summer of 1869 I bred the first
summer brood of A. Levana; the caterpillars
pupated during the second half of June, and from
to the 6th of June, fifty-eight butterflies of the form Marcellus,
one, of Walshii, and one of Telamonides.
38 Studies in the Theory of Descent.
that time to their emergence, on 28th June — 3rd
July, great heat prevailed. Now, while the inter-
mediate form Porima had hitherto been a great
rarity, both in the free state and when bred, having
never obtained it myself, for example, out of many
hundreds of specimens, there were among the
sixty or seventy butterflies that emerged from the
above brood, some eight to ten examples of
Porima. This is certainly not an exact experi-
ment, but there seems to me a certain amount of
probability that the high summer temperature in
this case brought about reversion.
Neither for the second cause to which I have
ascribed the power of producing reversion can I
produce any absolute evidence, since the experi-
mental solution of all these collateral questions
would demand an endless amount of time. I am
in possession of an observation, however, which
makes it appear probable to me that continuous
mechanical movement acts on the development of
the pupae in a similar manner to cold, that is,
retarding them, and at the same time producing
reversion. I had, in Freiburg, a large number of
pupae of the first summer brood of Pieris Napi,
bred from eggs. I changed residence while many
caterpillars were in course of transformation and
travelled with the pupae in this state seven hours
by rail. Although this brood of P. Napi, under
ordinary circumstances, always emerges in the
summer, generally in July of the same year, as the
On the Seasonal Dimorphism of Butterflies. 39
summer form (var. Napwe)y yet out of these
numerous pupae I did not get a single butterfly
during the year 1872. In winter I kept them in
a warm room, and the first butterflies emerged in
January, 1873, the remainder following in Feb-
ruary, March, and April, and two females not
until June. All appeared, however, as exquisite
winter forms. The whole course of development
was precisely as though cold had acted on the
pupae ; and in fact, I could find no other cause for
this quite exceptional deportment than the seven
hours' shaking to which the pupae were exposed
by the railway journey, immediately after or during
their transformation.
It is obviously a fact of fundamental importance
to the theory of seasonal dimorphism, that the
summer form can be readily changed into the
winter form, whilst the latter cannot be changed
into the summer form. I have thus far only made
experiments on this subject with A. Levana, but
the same fact appears to me to obtain for P. Napi.
I did not, however, operate upon the ordinary
winter form of P. Napi, but chose for this experi-
ment the variety Bryonice, well known to all ento-
mologists. This is, to a certain extent, the poten-
tial winter form of P. Napi ; the male (Fig. 14,
Plate I.) exactly resembles the ordinary winter
form in the most minute detail, but the female is
distinguished from Napi by a sprinkling of greyish
brown scales over the whole of the upper side of
4O Studies in the Theory of Descent.
the wings (Fig. 15, Plate I.). This type, Bryonice,
occurs in Polar regions as the only form of Napi,
and is also found in the higher Alps, where it flies
in secluded meadows as the only form, but in other
localities, less isolated, mixed with the ordinary
form of the species. In both regions Bryonitz
produces but one generation in the year, and must
thus, according to my theory, be regarded as the
parent-form of Pieris Napi.
If this hypothesis is correct — if the variety
Bryonicz is really the original form preserved from
the glacial period in certain regions of the earth,
whilst Napi in its winter form is the first secondary
form gradually produced through a warm climate,
then it would be impossible ever to breed the
ordinary form Napi from pupae of Bryonicz by
the action of warmth, since the form of the species
now predominant must have come into existence
only by a cumulative action exerted on numerous
generations, and not per saltiim.
The experiment was made in the following
manner : In the first part of June I caught a
female of Bryonite in a secluded Alpine valley,
and placed her in a capacious breeding- cage, where
she flew about among the flowers, and laid more
than a hundred eggs on the ordinary cabbage.
Although the caterpillars in the free state feed upon
another plant unknown to me, they readily ate the
cabbage, grew rapidly, and pupated at the end of
July. I then brought the pupae into a hothouse in
On the Seasonal Dimorphism of Butterflies. 4 1
which the temperature fluctuated between 12°
and 24° R. ; but, in spite of this high temperature,
and — what is certainly of more special importance —
notwithstanding the want of cooling at night, only
one butterfly emerged the same summer, and
that a male, which, from certain minute charac-
teristic markings, could be safely identified as var.
Bryonice. The other pupae hibernated in the
heated room, and produced, from the end of
January to the beginning of June, 28 butterflies,
all of which were exquisite Bryonice.
Experiment thus confirmed the view that
Bryonice is the parent-form of Napi, and the
description hitherto given by systematists ought
therefore properly to be reversed. Pieris Bryonice
should be elevated to the rank of a species, and
the ordinary winter and summer forms .should be
designated as vars. Napi and Napecz. Still [
should not like to take it upon myself to increase
the endless confusion in the synonomy of butter-
flies. In a certain sense, it is also quite correct to
describe the form Bryonice as a climatic variety, for
it is, in fact, established, if not produced, by climate,
by which agency it is likewise preserved ; only it
is not a secondary, but the primary, climatic variety
of Napi. In this sense most species might pro-
bably be described as climatic varieties, inasmuch
as under the influence of another climate they
would gradually acquire new characters, whilst,
under the influence of the climate now prevailing
42 Studies in the Theory of Descent.
in their habitats, they have, to a certain extent,
acquired and preserved their present form.
The var. Bryonicz is, however, of quite special
interest, since it makes clear the relation which
exists between climatic variation and seasonal
dimorphism, as will be proved in the next section.
The correctness of the present theory must first
here be submitted to further proof.
It has been shown that the secondary forms of
seasonally dimorphic butterflies do not all possess
the tendency to revert in the same degree, but that
this tendency rather varies with each individual.
As the return to the primary form is synonymous
with the relinquishing of the secondary, the greater
tendency to revert is thus synonymous with the
greater tendency to relinquish the secondary form,
but this again is equivalent to a lesser stability of
the latter ; it must consequently be concluded that
the individuals of a species are very differently
influenced by climatic change, so that with some
the new form must become sooner established than
with others. From this a variability of the gene-
ration concerned must necessarily ensue, i. e., the
individuals of the summer generation must differ
more in colour and marking than is the case with
those of the winter generation. If the theory is
correct, the summer generations should be more
variable than the winter generations — at least, so
long as the greatest possible equalization of indi-
vidual variations has not occurred through the
continued action of warmth, combined with the
On the Seasonal Dimorphism of Butterflies. 43
constant crossing of individuals which have be-
come changed in different degrees. Here also
the theory is fully in accord with facts.
In A. Levana the Levana form is decidedly
more constant than \\\& Prorsa form. The first is,
to a slight extent, sexually dimorphic, the female
being light and the male dark-coloured. If we take
into consideration this difference between the sexes,
which also occurs to a still smaller extent in the
Prorsa form, the foregoing statement will be found
correct, viz. that the Levana form varies but little,
and in all cases considerably less than the Prorsa
form, in which the greatest differences occur in
the yellow stripes and in the disappearance of the
black spots on the white band of the hind wing,
these black spots being persistent Levana mark-
ings. It is, in fact, difficult to find two perfectly
similar individuals of the Prorsa form. It must,
moreover, be considered that the Levana marking,
being the more complicated, would the more
readily show variation. Precisely the same thing
occurs in Pieris Napi, in which also the var.
sEstiva is considerably more variable than the
var. Vernalis. From the behaviour of the var.
Bryoni&y on the other hand, which I regard as the
parent-form, one might be tempted to raise an
objection to the theory ; for this form is well
known to be extraordinarily variable in colour
and marking, both in the Alps and Jura, where it
is met with at the greatest altitudes. According
to the theory, Bryonicz should be less variable
44 Studies in the Theory of Descent.
than the winter form of the lowlands, because it is
the older, and should therefore be the more con-
stant in its characters. It must not be forgotten,
however, that the variability of a species may not
only originate in the one familiar manner of un-
equal response of the individual to the action of
varying exciting causes, but also by the crossing of
two varieties separately established in adjacent
districts and subsequently brought into contact.
In the Alps and Jura the ordinary form of Napi
swarms everywhere from the plains towards the
habitats of Bryonice, so that a crossing of the two
forms may occasionally, or even frequently, take
place ; and it is not astonishing if in some places
(Meiringen, for example) a perfect series of inter-
mediate forms between Napi and Bryonia is met
with. That crossing is the cause of the great
variability of Bryonicz in the Alpine districts, is
proved by the fact that in the Polar regions this
form " is by no means so variable as in the Alps,
but, judging from about forty to fifty Norwegian
specimens, is rather constant." My friend, Dr.
Staudinger, who has twice spent the summer in
Lapland, thus writes in reply to my question.
A crossing with Napi cannot there take place,
as this form is never met with, so that the ancient
parent-form Bryonia has been able to preserve its
original constancy. In this case also the facts
thus accord with the requirements of the theory.
On the Seasonal Dimorphism of Butterflies. 45
II.
SEASONAL DIMORPHISM AND CLIMATIC
VARIATION.
IF, as I have attempted to show, seasonal dimor-
phism originates through the slow operation of a
changed summer climate, then is this phenomenon
nothing else than the splitting up of a species into
two climatic varieties in the same district, and we
may expect to find various connexions between
ordinary simple climatic variation and seasonal
dimorphism. . Cases indeed occur in which sea-
sonal dimorphism and climatic variation pass into
each other, and are interwoven in such a manner
that the insight into the origin and nature of
seasonal dimorphism gained experimentally finds
confirmation. Before I go more closely into this
subject, however, it is necessary to come to an
understanding as to the conception " climatic
variation," for this term is often very arbitrarily
applied to quite dissimilar phenomena.
According to my view there should be a sharp
distinction made between - climatic and local
varieties. The former should comprehend only
such cases as originate through the direct action
46 Studies in the Theory of Descent.
of climatic influences ; while under the general
designation of " local forms," should be comprised
all variations which have their origin in other
causes — such, for example, as in the indirect action
of the external conditions of life, or in circum-
stances which do not owe their present existence
to climate and external conditions, but rather to
those geological changes which produce isolation.
Thus, for instance, ancient species elsewhere long
extinct might be preserved in certain parts of the
earth by the protecting influence of isolation,
whilst others which immigrated in a state of
variability might become transformed into local
varieties in such regions through the action of
' amixia,' l i. e. by not being allowed to cross with
their companion forms existing in the other
portions of their habitat. In single cases it may
be difficult, or for the present impossible, to decide
whether we have before us a climatic form, or a
local form arising from other causes ; but for this
very reason we should be cautious in defining
climatic variation.
The statement that climatic forms, in the true
sense of the word, do exist is well known to me,
and has been made unhesitatingly by all zoologists ;
indeed, a number of authentically observed facts
1 [The word 'Amixie,' from the Greek a/u£t'a, was first adopted
by the author to express the idea of the prevention of crossing
by isolation in his essay " Uber den Einfluss der Isolirung auf
die Artbildung," Leipzig, 1872, p. 49. R.M.]
On the Seasonal Dimorphism of Butterflies. 47
might be produced, which prove that quite constant
changes in a species may be brought about by the
direct action of changed climatic conditions. With
butterflies it is in many cases possible to separate
pure climatic varieties from other local forms, inas-
much as we are dealing with only unimportant
changes and not with those of biological value, so
that natural selection may at the outset be ex-
cluded as the cause of the changes in question.
Then again the sharply defined geographical
distribution climatically governed, often furnishes
evidence of transition forms in districts lying
between two climatic extremes.
In the following attempt to make clear the
relationship between simple climatic variation and
seasonal dimorphism, I shall concern myself only
with such undoubted climatic varieties. A case
of this kind, in which the winter form of a
seasonally dimorphic butterfly occurs in other
habitats as the only form, i.e., as a climatic variety,
has already been adduced in a former paragraph.
I allude to the case of Pieris Napi> the winter
form of which seasonally dimorphic species occurs
in the temperate plains of Europe, whilst in Lap-
land and the Alps it is commonly found as a
monomorphic climatic variety which is a higher
development of the winter type, viz., the var.
Bryonicz.
Very analogous is the case of Eiichloe Belia,
a butterfly likewise belonging to the Pierincz,
48 Studies in the Theory of Descent.
which extends from the Mediterranean countries
to the middle of France, and everywhere mani-
fests a very sharply pronounced seasonal dimor-
phism. Its summer form was, until quite recently,
described as a distinct species, E. Ausonia. Stau-
dinger was the first to prove by breeding that the
supposed two species were genetically related.2
This species, in addition to being found in the
countries named, occurs also at a little spot
in the Alps in the neighbourhood of the Simplon
Pass. Owing to the short summer of the Alpine
climate the species has in this locality but one
annual brood, which bears the characters of the
winter form, modified in all cases by the coarser
thickly scattered hairs of the body (peculiar to
many Alpine butterflies,) and some other slight
differences. The var. Simplonia is thus in the
Alps a simple climatic variety, whilst in the plains
of Spain and the South of France it appears as
the winter form of a seasonally dimorphic species.
This Euchloe var. Simplonia obviously corre-
sponds to the var. Bryonicz of Fieri s Napi, and it
is highly probable that this form of E. Belia
must likewise be regarded as the parent-form of
the species surviving from the glacial epoch,
although it cannot be asserted, as can be done in
the case of Bryonicz, that the type has undergone
3 [Eng. ed. In 1844, Boisduval maintained this relationship
of the two forms. See Speyer's " Geographische Verbreit. d.
Schmetterl.," i. p. 455.]
On the Seasonal Dimorphism of Butter/lies. 49
no change since that epoch, for Bryonice from
Lapland is identical with the Alpine form,3 whilst
E. Simp Ionia does not appear to occur in Polar
countries.
Very interesting also is the case of Polyommatus
Phlczas, Linn., one of our commonest Lyccznidce,
which has a very wide distribution, extending from
Lapland to Spain and Sicily.4 If we compare
specimens of this beautiful copper-coloured but-
terfly from Lapland with those from Germany, no
constant difference can be detected ; the insect
has, however, but one annual generation in Lapland,
whilst in Germany it is double-brooded ; but the
winter and summer generations resemble each
other completely, and specimens which had been
caught in spring on the Ligurian coast were likewise
similarly coloured to those from Sardinia. (Fig. 2 1 ,
Plate II.). According to these facts we might
8 According to a written communication from Dr. Staudinger,
the female Bryonice from Lapland are never so dusky as is
commonly the case in the Alps, but they often have, on the
other hand, a yellow instead of a white ground-colour. In the
Alps, yellow specimens are not uncommon, and in the Jura
are even the rule.
4 [According to W. F. Kirby (Syn. Cat. Diurn. Lepidop.j,
the species is almost cosmopolitan, occurring, as well as
throughout Europe, in Northern India (var. Timeus), Shanghai
(var. C/imensts), Abyssinia (var. Pseudophlceas')^ Massachusetts
(var. Americana), and California (var. Hypophlceas). In a long
series from Northern India, in my own collection, all the
specimens are extremely dark, the males being almost black.
R.M.]
*E
50 Studies in the Theory of Descent.
believe this species to be extraordinarily indifferent
to climatic influence ; but the South European
summer generation differs to a not inconsiderable
extent from the winter generation just mentioned,
the brilliant coppery lustre being nearly covered
with a thick sprinkling of black scales. (Plate II.,
Fig. 22.) The species has thus become seasonally
dimorphic under the influence of the warm
southern climate, although this is not the case in
Germany where it also has two generations in
the year.5 No one who is acquainted only with
the Sardinian summer form, and not with the
winter form of that place, would hesitate to regard
the former as a climatic variety of our P. Phlczas ;
or, conversely, the north German form as a
climatic variety of the southern summer form —
according as he accepts the one or the other as
the primary form of the species.
Still more complex are the conditions in another
species of Lyccenidce, Plebeius Agestis ( — Alexis
Scop,), which presents a double seasonal dimor-
phism. This butterfly appears in three forms ; in
Germany A and B alternate with each other as
winter and summer forms, whilst in Italy B and
C succeed each other as winter and summer
* [Eng. ed. From a written communication from Dr.
Speyer, it appears that also in Germany there is a small dif-
ference between the two generations. The German summer
brood has likewise more black on the upper side, although
seldom so much as the South European summer brood.]
On the Seasonal Dimorphism of Butterflies. 5 1
forms. The form B thus occurs in both climates,
appearing as the summer form in Germany and
as the winter form in Italy. The German winter
variety A, is entirely absent in Italy (as I know
from numerous specimens which I have caught),
whilst the Italian summer form, on the other hand,
(var. Allous, Gerh.), does not occur in Germany.
The distinctions between the three forms are
sufficiently striking. The form A (Fig. 18, Plate
II.) is blackish brown on the upper side, and has
in the most strongly marked specimens only a trace
of narrow red spots round the borders ; whilst the
form B (Fig. 19, Plate II.) is ornamented with vivid
red border spots ; and C (Fig. 20, Plate II.) is dis-
tinguished from B by the strong yellowish-brown
of the under side. If we had before us only the
German winter and the Italian summer forms, we
should, without doubt, regard them as climatic
varieties ; but they are connected by the form B,
interpolated in the course of the development of
both, and the two extremes thus maintain the
character of mere seasonal forms.
E 2
52 Studies in the Theory of Descent.
III.
NATURE OF THE CAUSES PRODUCING CLIMATIC
VARIETIES.
IT has been shown that the phenomenon of sea-
sonal dimorphism has the same proximate cause
as climatic variation, viz. change of climate, and
that it must be regarded as identical in nature
with climatic variation, being distinguished from
ordinary, or, as I have designated it, simple (mono-
morphic) climatic variation by the fact that, be-
sides the new form produced by change of climate,
the old form continues to exist in genetic con-
nexion with it, so that old and new forms alternate
with each other according to the season.
Two further questions now present themselves
for investigation, viz. (i) by what means does
change of climate induce a change in the marking
and colouring of a butterfly ? and (2) to what ex-
tent does the climatic action determine the nature
of the change ?
With regard to the former question, it must, in
the first place, be decided whether the true effect of
climatic change lies in the action of a high or low
temperature on the organism, or whether it may
On the Seasonal Dimorphism of Butterflies. 5 3
not perhaps be produced by the accelerated de-
velopment caused by a high temperature, and the
retarded development caused by a low temperature.
Other factors belonging to the category of external
conditions of life which are included in the term
" climate" may be disregarded, as they are of no
importance in these cases. The question under
consideration is difficult to decide, since, on the one
hand, warmth and a short pupal period, and, on
the other hand, cold and a long pupal period, are
generally inseparably connected with each other ;
and without great caution one may easily be led
into fallacies, by attributing to the influence of
causes now acting that which is but the conse-
quence of long inheritance.
When, in the case of Araschnia Levana, even
in very cold summers, Prorsa, but never the Le-
vana form, emerges, it would still be erroneous to
conclude that it is only the shorter period of de-
velopment of the winter generation, and not the
summer warmth, which occasioned the formation
of the Prorsa type. This new form of the species
did not come suddenly into existence, but (as ap-
pears sufficiently from the foregoing experiments)
originated in the course of many generations, during
which summer warmth and a short development
period were generally associated together. From
the fact that the winter generation always produces
Levana, even when the pupae have not been ex-
posed to cold but kept in a room, it would be
54- Studies in the Theory of Descent.
equally erroneous to infer that the cold of winter
had no influence in determining the type. In this
case also the determining causes must have been in
operation during innumerable generations. After
the winter form of the species has become esta-
blished throughout such a long period, it remains
constant, even when the external influence which
produced it (cold) is occasionally withdrawn.
Experiments cannot farther assist us here, since
we cannot observe throughout long periods of time ;
but there are certain observations, which to me
appear decisive. When, both in Germany and
Italy, we see Polyommatus Pkl&as appearing in
two generations, of which both the German ones
are alike, whilst in Italy the summer brood is
black, we cannot ascribe this fact to the influence
of a shorter period of development, because this
period is the same both in Germany and Italy
(two annual generations), so that it can only be
attributed to the higher temperature of summer.
Many similar cases might be adduced, but the
one given suffices for proof. I am therefore of
opinion that it is not the duration of the period of
development which is the cause of change in the
formation of climatic varieties of butterflies, but
only the temperature to which the species is ex-
posed during its pupal existence. In what manner,
then, are we to conceive that warmth acts on the
marking and colouring of a butterfly ? This is a
question which could only be completely answered
On the Seasonal Dimorphism of Butterflies. 5 5
by gaining an insight into the mysterious chemico-
physiological processes by which the butterfly is
formed in the chrysalis ; and indeed only by such
a complete insight into the most minute details,
which are far beyond our scrutiny, could we arrive
at, or even approximate to, an explanation of the
development of any living organism. Neverthe-
less an important step can be taken towards the
solution of this problem, by establishing that the
change does not depend essentially upon the
action of warmth, but upon the organism itself,
as appears from the nature of the change in one
and the same species.
If we compare the Italian summer form of Poly-
ommatus Phlceas with its winter form, we shall find
that the difference between them consists only in
the brilliant coppery red colour of the latter being
largely suffused in the summer form with black
scales. When entomologists speak of a " black
dusting" of the upper side of the wings, this state-
ment must not of course be understood literally';
the number of scales is the same in both forms,
but in the summer variety they are mostly black,
a comparatively small number being red. We
might thus be inclined to infer that, owing to the
high temperature, the chemistry of the material
undergoing transformation in Phlczas is changed
in such a manner that less red and more black
pigment is produced. But the case is not so
simple, as will appear evident when we consider
56 Stiidies in the Theory of Descent.
the fact that the summer forms have not originated
suddenly, but only in the course of numerous gene-
rations ; and when we further compare the two
seasonal forms in other species. Thus in Pieris
Napi the winter is distinguished from the summer
form, among other characters, by the strong black
dusting of the base of the wings. But we cannot
conclude from this that in the present case more
black pigment is produced in the winter than in the
summer form, for in the latter, although the base of
the wings is white, their tips and the black spots
on the fore-wings are larger and of a deeper black
than in the winter form. The quantity of black
pigment produced does not distinguish between
the two forms, but the mode of its distribution
upon the wings.
Even in the case of species the summer form of
which really possesses far more black than the
winter form, as, for instance, Araschnia Levana,
one type cannot be derived from the other simply
by the expansion of the black spots present, since
on the same place where in Levana a black band
crosses the wings, Prorsa, which otherwise pos-
sesses much more black, has a white line. (See
Figs, i — 9, Plate I.) The intermediate forms which
have been artificially produced by the action of
cold on the summer generation present a graduated
series, according as reversion is more or less com-
plete ; a black spot first appearing in the middle of
the white band of Prorsa, and then becoming en-
On the Seasonal Dimorphism of Butterflies. 5 7
larged until, finally, in the perfect Levana it unites
with another black triangle proceeding from the
front of the band, and thus becomes fused into a
black bar. The white band of Prorsa and the black
band of Levana by no means correspond in position;
in Prorsa quite a new pattern appears, which does
not originate by a simple colour replacement of the
Levana marking. In the present case, therefore,
there is no doubt that the new form is not produced
simply because a certain pigment (black) is formed
in larger quantities, but because its mode of dis-
tribution is at the same time different, white appear-
ing in some instances where black formerly existed,
whilst in other cases the black remains. Whoever
compares Prorsa with Levana will not fail to be
struck with the remarkable change of marking pro-
duced by the direct action of external conditions.
The numerous intermediate forms which can be
produced artificially appear to me to furnish a fur-
ther proof of the gradual character of the trans-
formation. Ancestral intermediate forms can only
occur where they have once had a former exis-
tence in the phyletic series. Reversion may only
take place completely in some particular characters,
whilst in others the new form remains constant —
this is in fact the ordinary form of reversion, and
in this manner a mixture of characters might ap-
pear which never existed as a phyletic stage ; but
particular characters could certainly never appear
unless they were normal to the species at some
58 Studies in the Theory of Descent.
stage of phyletic development. Were this possible
it would directly contradict the idea of reversion,
according to which new characters never make their
appearance, but only such as have already existed.
If, therefore, the ancestral forms of A. Levana
(which we designate as Porima) present a great
number of transitional varieties, this leads to the
conclusion that the species must have gone through
a long series of stages of phyletic development
before the summer generation had completely
changed into Prorsa. The view of the slow cumu-
lative action of climatic influences already sub-
mitted, is thus confirmed.
If warmth is thus without doubt the agency which
has gradually changed the colour and marking of
many of our butterflies, it sufficiently appears from
what has just been said concerning the nature of
the change that the chief part in the transmutation
is not to be attributed to the agency in question,
but to the organism which is affected by it. In-
duced by warmth, there begins a change in the
ultimate processes of the matter undergoing trans-
formation, which increases from generation to
generation, and which not only consists in the
appearance of the colouring matter in one place
instead of another, but also in the replacement of
yellow, in one place by white and in another by
black, or in the transformation of black into white
on some portions of the wings, whilst in others
black remains. When we consider with what
On the Seasonal Dimorphism of Butterflies. 59
extreme fidelity the most insignificant details of
marking are, in constant species of butterflies,
transmitted from generation to generation, a total
change of the kind under consideration cannot but
appear surprising, and we should not explain it by
the nature of the agency (warmth), but only by the
nature of the species affected. The latter cannot
react upon the warmth in the same manner that a
solution of an iron salt reacts upon potassium fer-
rocyanide or upon sulphuretted hydrogen ; the
colouring matter of the butterfly's wing which was
previously black does not become blue or yellow,
nor does that which was white become changed
into black, but a new marking is developed from
the existing one — or, as I may express it in more
general terms, the species takes another course of
development ; the complicated chemico-physical
processes in the matter composing the pupa be-
come gradually modified in such a manner that,
as the final result, a new marking and colouring
of the butterfly is produced.
Further facts can be adduced in support of the
view that in these processes it is the constitu-
tion of the species, and not the external agency
(warmth), which plays the chief part. The latter,
as Darwin has strikingly expressed it, rather per-
forms the function of the spark which ignites a
combustible substance, whilst the character of the
combustion depends upon the nature of the ex-
plosive material. Were this not the case, increased
60 S Indies in the Theory of Descent.
warmth would always change a given colour * in the
same manner in all butterflies, and would there-
fore always give rise to the production of the same
colour. But this does not occur ; Polyommatus
Phl&as, for example, becoming black in the south,
whilst the red-brown Vanessa Urticce becomes black
in high northern latitudes, and many other cases
well known to entomologists might be adduced.2
It indeed appears that species of similar physical
constitution, i.e., nearly allied species, under similar
climatic influences, change in an analogous man-
ner. A beautiful example of this is furnished
by our Pierince. Most of the species display
seasonal dimorphism ; as, for instance, Pieris
Brassica, Rap a, Napi, Krueperi, and Daplidice,
Eiichloe Belia and Belemia, and Leucophasia
Sinapis, in all of which the difference between the
winter and the summer forms is of a precisely
1 [Assuming that in all butterflies similar colours are pro-
duced by the same chemical compounds. R.M.]
a [Mr. H. W. Bates mentions instances of local variation in
colour affecting many distinct species in the same district in
his memoir " On the Lepidoptera of the Amazon Valley ;"
Trans. Linn. Soc., vol. xxiii. Mr. A. R. Wallace also has
brought together a large number of cases of variation in colour
according to distribution, in his address to the biological section
of the British Association at Glasgow in 1876. See "Brit.
Assoc. Report," 1876, pp. 100 — no. For observations on the
change of colour in British Lepidoptera according to distri-
bution see papers by Mr. E. Birchall in " Ent. Mo. Mag ,"
Nov., 1876, and by Dr. F. Buchanan White, " Ent. Mo. Mag./'
Dec., 1876. The colour variations in all these cases are ot
course not protective as in the well-known case of Gnophos
obscurata, &c. R.M.]
On the Seasonal Dimorphism of Butterflies. 6 1
similar nature. The former are characterized by
a strong black dusting of the base of the wings,
and by a blackish or green sprinkling of scales on
the underside of the hind wings, while the latter
have intensely black tips to the wings, and fre-
quently also spots on the fore-wings.
Nothing can prove more strikingly, however,
that in such cases everything depends upon the
physical constitution, than the fact that in the same
species the males become changed in a different
manner to the females. The parent form of Pieris
Napi (var. Bryonice) offers an example. In all
the Pierince secondary sexual differences are found,
the males being differently marked to the females ;
the species are thus sexually dimorphic. Now the
male of the Alpine and Polar var. Bryonicz, which
I conceive to be the ancestral form, is scarcely to
be distinguished, as has already been mentioned,
from the male of our German winter form (P.
Napi, var. Vernalis), whilst the female differs con-
siderably.3 The gradual climatic change which
transformed the parent form Bryonice into Napi
has therefore exerted a much greater effect on the
female than on the male. The external action on
the two sexes was exactly the same, but the re-
sponse of the organism was different, and the
cause of the difference can only be sought for in
the fine differences of physical constitution which
distinguish the male from the female. If we are
1 See Figs. TO and 14, n and 15, Plate I.
62 Studies in the Theory of Descent.
unable to define these differences precisely, we may
nevertheless safely conclude from such observa-
tions that they exist.
I have given special prominence to this subject
because, in my idea, Darwin ascribes too much
power to sexual selection when he attributes the
formation of secondary sexual characters to the
sole action of this agency. The case of Bryonice
teaches us that such characters may arise from
purely innate causes ; and until experiments have
decided how far the influence of sexual selection
extends, we are justified in believing that the sexual
dimorphism of butterflies is due in great part to
the differences of physical constitution between
the sexes. It is quite different with such sexual
characters as the stridulating organs of male Or-
thoptera which are of undoubted importance to
that sex. These can certainly be attributed with
great probability to sexual selection.
It may perhaps not be superfluous to adduce
one more similar case, in which, however, the male
and not the female is the most affected by climate.
In our latitudes, as also in the extreme north,
Polyommaius Phl&as, already so often mentioned,
is perfectly similar in both sexes in colour and
marking ; and the same holds good for the winter
generation of the south. The summer generation of
the latter, however, exhibits a slight sexual dimor-
phism, the red of the fore wings of the female being
less completely covered with black than in the male.
On the Seasonal Dimorphism of Butterflies, 63
IV.
WHY ALL POLYGONEUTIC SPECIES ARE NOT
SEASONALLY DIMORPHIC.
IF we may consider it to be established that
seasonal dimorphism is nothing else than the
splitting up of a species into two climatic varie-
ties in one and the same locality, the further ques-
tion at once arises why all polygoneutic species
(those which produce more than one annual gene-
ration) are not seasonally dimorphic.
To answer this, it will be necessary to go more
deeply into the development of seasonal dimor-
phism. This evidently depends upon a peculiar
kind of periodic, alternating heredity, which we
might be tempted to identify with Darwin's
" inheritance at corresponding periods of life."
It does not, however, in any way completely
agree with this principle, although it presents a
great analogy to it and must depend ultimately
upon the same cause. The Darwinian " inheri-
tance at corresponding periods of life" — or, as it
is termed by Haeckel, " homochronic heredity" —
is characterized by the fact that new characters
always appear in the individuals at the same stage
64 Studies in the Theory of Descent.
of life as that in which they appeared in their pro-
genitors. The truth of this principle has been
firmly established, instances being known in which
both the first appearance of a new (especially
pathological) character and its transmission through
several generations has been observed. Seasonally
dimorphic butterflies also furnish a further valuable
proof of this principle, since they show that not
only variations which arise suddenly (and which
are therefore probably due to purely innate causes)
follow this mode of inheritance, but also that cha-
racters gradually called forth by the influence of
external conditions and accumulating from genera-
tion to generation, are only inherited at that period
of life in which these conditions were or are effec-
tive. In all seasonally dimorphic butterflies which
I have been able to examine closely, I found the
caterpillars of the summer and winter broods to be
perfectly identical. The influences which, by
acting on the pupae, split up the imagines into
two climatic forms, were thus without effect on
the earlier stages of development. I may specially
mention that the caterpillars, as well as the pupae
and eggs of A. Levana, are perfectly alike both in
the summer and winter forms ; and the same is the
case in the corresponding stages of P. Napi and
P. Bryonice.
I shall not here attempt to enter more deeply
into the nature of the phenomena of inheritance.
It is sufficient to have confirmed the law that
On the Seasonal Dimorphism of Butterflies. 65
influences which act only on certain stages in the
development of the individual, even when the
action is cumulative and not sudden, only affect
those particular stages without having any effect
on the earlier or later stages. This law is
obviously of the greatest importance to the com-
prehension of metamorphosis. Lubbock1 has
briefly shown in a very clear manner how the
existence of metamorphosis in insects can be
explained by the indirect action of varying con-
ditions on the different life-stages of a species.
Thus the mandibles of a caterpillar are, by adap-
tation to another mode of nourishment, exchanged
at a later period of life for a suctorial organ. Such
adaptation of the various development-stages of a
species to the different conditions of life would
never give rise to metamorphosis, if the law of
homochronic, or periodic, heredity did not cause
the characters gradually acquired at a given stage
to be transferred to the same stage of the follow-
ing generation.
The origin of seasonal dimorphism depends
upon a very similar law, or rather form, of inheri-
tance, which differs from that above considered
only in the fact that, instead of the ontogenetic
stages, a whole series of generations is influenced.
This form of inheritance may be formulated some-
what as follows : — When dissimilar conditions
1 " On the Origin and Metamorphoses of Insects," London,
18714.
F
66 Studies in the Theory of Descent.
alternatingly influence a series of generations, a
cycle is produced in which the changes are
transmitted only to those generations which are
acted upon by corresponding conditions, and not
to the intermediate ones. Characters which have
arisen by the action of a summer climate are inhe-
rited by the summer generation only, whilst they
remain latent in the winter generation. It is the
same as with the mandibles of a caterpillar which
are latent in the butterfly, and again make their
appearance in the corresponding (larval) stage of
the succeeding generation. This is not mere
hypothesis, but the legitimate inference from the
facts. If it be admitted that my conception of
seasonal dimorphism as a double climatic variation
is correct, the law of " cyclical heredity,"2 as I may
term it — in contradistinction to " homochronic
heredity," which relates only to the ontogenetic
stages — immediately follows. All those cases
which come under the designation of ' alternation
of generation/ can obviously be referred to cyclical
heredity, as will be explained further on. In the
one case the successive generations deport them-
2 I at first thought of designating the two forms of cyclical
or homochronic heredity as ontogenetic- and phyletic-cyclical
heredity. The former would certainly be correct ; the latter
would be also applicable to alternation of generation (in which
actually two or more phyletic stages alternate with each other)
but not to all those cases which I attribute to heterogenesis,
in which, as with seasonal dimorphism, a series of generations
of the same phyletic stage constitute the point of departure.
On the Seasonal Dimorphism of Butterflies. 67
selves exactly in the same manner as do the
successive stages of development of the individual
in the other ; and we may conclude therefrom (as
has long been admitted on other grounds) that a
generation is, in fact, nothing else than a stage of
development in the life of a species. This appears
to me to furnish a beautiful confirmation of the
theory of descent.
Now if, returning to questions previously solved,
the alternating action of cold in winter and warmth
in summer leads to the production of a winter and
summer form, according to the law of cyclical here-
dity, the question still remains : why do we not
find seasonal dimorphism in all polygoneutic
butterflies ?
We might at first suppose that all species are
not equally sensitive to the influence of tempe-
rature : indeed, the various amounts of difference
between the winter and summer forms in different
species would certainly show the existence of
different degrees of sensitiveness to the modifying
action of temperature. But even this does not
furnish an explanation, since there are butterflies
which produce two perfectly similar3 generations
8 When Meyer-Dikr, who is otherwise very accurate, states
in his " Verzeichniss der Schmetterlinge der Schweiz," (1852, p.
207), that the winter and summer generations of P. JEgeria
differ to a small extent in the contour of the wings and in
marking, he has committed an error. The characters which
this author attributes to the summer form are much more appli-
F 2
68 Studies in the Theory of Descent.
wherever they occur, and which, nevertheless,
appear in different climates as climatic varieties.
This is the case with Pararga SEgeria (Fig. 23,
Plate II.), the southern variety of which, Meione
(Fig. 24, Plate II.), is connected with it by an
intermediate form from the Ligurian coast. This
species possesses, therefore, a decided power of
responding to the influence of temperature, and
yet no distinction has taken place between the
summer and the winter form. We can thus
only attribute this different deportment to a
different kind of heredity ; and we may therefore
plainly state, that changes produced by alternation
of climate are not always inherited alternatingly,
i. e. by the corresponding generations, but some-
times continuously, appearing in every generation,
and never remaining latent. The causes which
determine why, in a particular case, the one
or the other form of inheritance prevails, can
be only innate, i. e. they lie in the organism
itself, and there is as little to be said upon
their precise nature as upon that of any other
process of heredity. In a similar manner Darwin
admits a kind of double inheritance with respect
to characters produced by sexual selection ; in
one form these characters remain limited to the
sex which first acquired them, in the other form
they are inherited by both sexes, without it
cable to the female sex. There exists in this species a trifling
sexual dimorphism, but no seasonal dimorphism.
On the Seasonal Dimorphism of Butterflies. 69
being apparent why, in any particular case, the
one or the other form of heredity should take
place.
The foregoing explanation may obtain in the
case of sexual selection, in which it is not incon-
ceivable that certain characters may not be so
easily produced, or even not produced at all,
in one sex, owing to its differing from the other
in physical constitution. In the class of cases"
under consideration, however, it is not possible
that the inherited characters can be prevented
from being acquired by one generation owing
to its physical constitution, since this constitution
was similar in all the successive generations before
the appearance of dimorphism. The constitution
in question first became dissimilar in the two
generations to the extent of producing a change
of specific character, through the action of tem-
perature on the alternating broods of each year,
combined with cyclical heredity. If the law
of cyclical heredity be a general one, it must
hold good for all cases, and characters acquired
by the summer generation could never have been
also transmitted to the winter generation from
the very first.
I will not deny the possibility that if alternating
heredity should become subsequently entirely sup-
pressed throughout numerous generations, a period
may arrive when the preponderating influence of
a long series of summer generations may ultimately
70 Studies in the Theory of Descent.
take effect upon the winter generation. In
such a case the summer characters would appear,
instead of remaining latent as formerly. In this
manner it may be imagined that at first but few,
and later more numerous individuals, approximate
to the summer form, until finally the dimorphism
entirely disappears, the new form thus gaining
ascendency and the species becoming once more
monomorphic. Such a supposition is indeed
capable of being supported by some facts, an
observation on A. Levana apparently contra-
dicting the theory having been already inter-
preted in this sense. I refer to the fact that
whilst some butterflies of the winter generation
emerge in October as Prorsa, others hibernate,
and appear the following spring in the Levana
form. The winter form of Pieris Napi also
no longer preserves, in the female sex, the
striking coloration of the ancestral form Bryonice,
a fact which may indicate the influencing of the
winter generation by numerous summer genera-
tions. The double form of the spring generation
of Papilio Ajax can be similarly explained by the
gradual change of alternating into continuous
heredity, as has already been mentioned. All
these cases, however, are perhaps capable of
another interpretation ; at any rate, the correct-
ness of this supposition can only be decided by
further facts.
Meanwhile, even if we suppose the above ex-
On the Seasonal Dimorphism of Butterflies. 7 1
planation to be correct, it will not apply to the
absence of seasonal dimorphism in cases like that
olPararga sEgeria and Meione, in which only one
isummer generation appears, so that a preponde-
rating inheritance of summer characters cannot be
admitted. Another explanation must thus be
sought, and I believe that I have found it in the
circumstance that the butterflies named do not
hibernate as pupae but as caterpillars, so that the
cold of winter does not directly influence those
processes of development by which the perfect
insect is formed in the chrysalis. It is precisely
on this point that the origin of those differences
of .colour which we designate as the seasonal
dimorphism of butterflies appears to depend.
Previous experiments give great probability to this
statement. From these we know that the eggs,
caterpillars, and pupae of all the seasonally dimor-
phic species experimented with are perfectly
similar in the summer and winter generations, the
imago stage only showing any difference. We
know further from these experiments, that tem-
perature-influences which affect the caterpillars
never entail a change in the butterflies ; and
finally, that the artificial production of the re-
version of the summer to the winter form can
only be brought about by operating on the pupae.
Since many monogoneutic species now hiber-
nate in the caterpillar stage (e. g. Satyrus Proser-
pina, and Hermione, Epinephele Eudora, Jurtina,
72 Studies in the Theory of Descent.
Tithonus, Hyperanthus, Ida, drV.), we may admit
that during the glacial period such species did not
pass the winter as pupae. As the climate grew
warmer, and in consequence thereof a second
generation became gradually interpolated in many
of these monogoneutic species, there would ensue
(though by no means necessarily) a disturbance of
the winter generation, of such a kind that the
pupae, instead of the caterpillars as formerly,
would then hibernate. It may, indeed, be easily
proved a priori that whenever a disturbance of
the winter generation takes place it only does so
retrogressively, that is to say — species which at one
time pass the winter as caterpillars subsequently
hibernate in the egg, while those which formerly
hibernate as pupae afterwards do so as caterpillars.
The interpolation of a summer generation must
necessarily delay till further towards the end
of summer, the brood about to hibernate ; the
remainder of the summer, which serves for the
development of the eggs and young caterpillars,
may possibly under these conditions be insuffi-
cient for pupation, and the species which hiber-
nated in the pupal state when it was monogoneutic,
may perhaps pass the winter in the larval con-
dition after the introduction of the second brood.
A disturbance of this kind is conceivable ; but it is
certain that many species suffer no further altera-
tion in their development than that of becoming
digoneutic from monogoneutic. This follows
On the Seasonal Dimorphism of Butterflies. 73
from the fact that hibernation takes place in the
caterpillar stage in many species of the sub-family
Satyridce which are now digoneutic, as well as in
the remaining monogoneutic species of the same
sub-family. But we cannot expect seasonal dimor-
phism to appear in all digoneutic butterflies the
winter generation of which hibernates in the
caterpillar form, since the pupal stage in these
species experiences nearly the same influences of
temperature in both generations. We are hence
led to the conclusion that seasonal dimorphism
must arise in butterflies whenever the pupae of
the alternating annual generations are exposed
throughout long periods of time to widely
different regularly recurring changes of tem-
perature.
The facts agree with this conclusion, inasmuch
as most butterflies which exhibit seasonal dimor-
phism hibernate in the pupa stage. Thus, this
is the case with all the Pierince^ with Papilio
Machaon, P. Podalirius, and P. Ajax, as well as
with Araschnia Lev ana. Nevertheless, it cannot
be denied that seasonal dimorphism occurs also in
some species which do not hibernate as pupae but
as caterpillars ; as, for instance, in the strongly
dimorphic Plebeius Amyntas. But such cases can
be explained in a different manner.
Again, the formation of a climatic variety — and
as such must we regard seasonally dimorphic
forms — by no means entirely depends on the
74 Studies in the Theory of Descent.
magnitude of the difference between the tempera -
ture which acts >on ;thq pupse of the primary and
that which acts 'on those of the secondary form ;
it rather depends: on the absolute temperature
which the pupae .experience. This follows without
doubt from the fact that many species, such as
our common Swallow-tail (Papilio Mac/iaon), and
also P. Podalirius, in Germany and the rest of
temperate Europe, show no perceptible difference
of colour between the first generation, the pupae
of which hibernate, and the second generation,
the pupal period of which falls in July, whereas the
same butterflies in South Spain and Italy are to
a small extent seasonally dimorphic. Those
butterflies which are developed under the in-
fluence of a Sicilian summer heat likewise show
climatic variation to a small extent. The follow-
ing consideration throws further light on these
conditions. The mean summer and winter tem-
peratures in Germany differ by about i4.9°R. ;
this difference being therefore much more pro-
nounced than that between the German and
Sicilian summer, which is only about 3-6°R.
Nevertheless, the winter and summer generations
of P. Podahrius are alike in Germany, whilst the
Sicilian summer generation has become a climatic
variety. The cause of this change must therefore
lie in the small difference between the mean
summer temperatures of 15.0° R. (Berlin) and
19.4° R. (Palermo). According to this, a given
On the Seasonal Dimorphism of Butterflies. 75
absolute temperature appears to give a tendency
to variation in a certain direction, the necessary
temperature being different for different species.
The latter statement is supported by the facts that,
in the first place, in different species there are
very different degrees of difference between the
summer and winter forms ; and secondly, many
digoneutic species are still monomorphic in Ger-
many, first becoming seasonally dimorphic in
Southern Europe. This is the case with P.
Machaon and P. Podalirius, as already mentioned,
and likewise with Polyommalus Phlceas. Zeller in
1846-47, during his journey in Italy, recognized
as seasonally dimorphic in a small degree a large
number of diurnal Lepidoptera which are not so
in our climate.4
In a similar manner the appearance of seasonal
dimorphism in species which, like Plebei^ls Amyn-
tas, do not hibernate as pupae, but as caterpillars,
can be simply explained by supposing that the
winter generation was the primary form, and that
the increase in the summer temperature since the
glacial period was sufficient to cause this particu-
lar species to become changed by the gradual
interpolation of a second generation. The dimor-
phism of P. Amyntas can, nevertheless, be ex-
plained in another manner. Thus, there may
4 P. C. Zeller, " Bemerkungen iiber die auf einer Reise nach
Italien und Sicilien gesammelten Schmetterlingsarten." Isis,
1847, ii. — xii.
7 6 Studies in the Theory of Descent.
have been a disturbance of the period of develop-
ment in the manner already indicated, the species
which formerly hibernated in the pupal stage
becoming subsequently disturbed in its course of
development by the interpolation of a summer
generation, and hibernating in consequence in the
caterpillar state. Under these circumstances we
must regard the present winter form (var. Poly-
sperchori) as having been established under the
influence of a winter climate, this form, since the
supposed disturbance in its development, having
had no reason to become changed, the spring tem-
perature under which its pupation now takes place
not being sufficiently high. The interpolated
second generation on the other hand, the pupal
period of which falls in the height of summer, may
easily have become formed into a summer variety.
This latter explanation agrees precisely with the
former, both starting with the assumption that in
the present case, as in that of A. Levana and the
Pierincz, the winter form is the primary one, so
that the dimorphism proceeds from the said win-
ter form and does not originate the winter but the
summer form, as will be explained. Whether the
winter form has been produced by the action
of the winter or spring temperature is immaterial
in judging single cases, inasmuch as we are not
in a position to state what temperature is neces-
sary to cause any particular species to become
transformed.
On the Seasonal Dimorphism of Butterflies. 77
The reverse case is also theoretically conceiva-
ble, viz., that in certain species the summer form
was the primary one, and by spreading northwards
a climate was reached which still permitted the
production of two generations, the pupal stage of
one generation being exposed to the cold of win-
ter, and thus giving rise to the production of a
secondary winter form. In such a case hiberna-
tion in the pupal state would certainly give rise to
seasonal dimorphism. Whether these conditions
actually occur, appears to me extremely doubtful ;
but it may at least be confidently asserted that the
first case is of far more frequent occurrence. The
beautiful researches of Ernst Hoffmann 5 furnish
strong evidence for believing that the great
majority of the European butterflies have immi-
grated, not from the south, but from Siberia. Of
281 species, 173 have, according to Hoffmann,
come from Siberia, 39 from southern Asia,
and only 8 from Africa, whilst during the
greatest cold of the glacial period, but very few
or possibly no species existed north of the Alps.
Most of the butterflies now found in Europe have
thus, since their immigration, experienced a
gradually increasing warmth. Since seasonal
dimorphism has been developed in some of these
species, the summer form must in all cases have
been the secondary one, as the experiments upon
1 " Isoporien der europaischen Tagfalter." Stuttgart, 1873.
78 Studies in the Theory of Descent.
the reversion of Pieris Napi and Araschnia
Levana have also shown.
All the seasonally dimorphic butterflies known
to me are found in Hoffmann's list of Siberian
immigrants, with the exception of two species,
viz., Eiichloe Belemia, which is cited as an
African immigrant, and Pieris Krueperi, which
may have come through Asia Minor, since at the
present time it has not advanced farther west than
Greece. No considerable change of climate can
be experienced by migrating from east to west,'
so that the seasonal dimorphism of Pieris Krue-
peri can only depend on a cause similar to that
which affected the Siberian immigrants, that is, the
gradual increase of temperature in the northern
hemisphere since the glacial period. In this
species also, the winter form must be the primary
one. In the case of E. Belemia, on the other
hand, the migration northwards from Africa cer-
tainly indicates removal to a cooler climate,
which may have originated a secondary winter
form, even if nothing more certain can be stated.
We know nothing of the period of migration into
southern Europe ; and even migration without
climatic change is conceivable, if it kept pace with
the gradual increase of warmth in the northern
hemisphere since the glacial epoch. Experi-
ments only would in this case be decisive. If the
summer generation, var. Glauce, were the primary
form, it would not be possible by the action of
On the. Seasonal Dimorphism of Butterflies. 79
cold on the pupae of this brood to produce the
winter variety Belemia, whilst, on the other hand,
the pupse of the winter generation by the influence
of warmth would be made to revert more or less
completely to the form Glance. It is by no means
to be understood that the species would actually
comport itself in this manner. On the contrary, I
am of opinion that in this case also, the winter
form is primary. The northward migration (from
Africa to south Spain) would be quite insufficient,
and the winter form is now found in Africa as well
as in Spain.
8o Studies in the Theory of Descent.
V.
ON ALTERNATION OF GENERATIONS.
SEASONAL dimorphism has already been designated
by Wallace as alternation of generation,1 a term
which cannot be disputed so long as it is confined
to a regular alternation of dissimilar generations.
But little is gained by this definition, however,
unless it can be proved that both phenomena are
due to similar causes, and that they are conse-
quently brought about by analogous processes.
The causes of alternation of generation have, until
the present time, been scarcely investigated, owing
to the want of material. Haeckel alone has quite
recently subjected these complicated phenomena
generally to a searching investigation, and has
arrived at the conclusion that the various forms of
metagenesis can be arranged in two series. He
distinguishes a progressive and a retrogressive
series, comprising under the former those species
" which, to a certain extent, are still in a transition
stage from monogenesis to amphigenesis (asexual
to sexual propagation), and the early progenitors
1 [Trans. Linn. Soc., vol. xxv. 1865, p. 9. R.M.]
On the Seasonal Dimorphism of Butterflies. 81
of which, therefore, never exclusively propagated
themselves sexually " (Trematoda, Hydromedusce).
Under the other, or retrogressive form of meta-
genesis, Haeckel includes a " return from amphi-
genesis to monogenesis," this being the case with
all those species which now manifest a regular
alternation from amphigenesis to parthenogenesis
(Aphides, Rotatoria> Daphnidce, Phyllopoda, &c).
Essentially I can but agree entirely with Haeckel.
Simply regarding the phenomena of alternation of
generation as at present known, it appears to me
to be readily admissible that these multiform modes
of propagation must have originated in at least
two different ways, which can be aptly formulated
in the manner suggested by Haeckel.
1 will, however, venture to adopt a somewhat
different mode of conception, and regard the man-
ner of propagation (whether sexual or asexual)
not as the determining, but only as the secondary
cause. I will further hazard the separation of
the phenomena of alternating generations (in their
widest sense) into two main groups according to
•their origin, designating the cases of one group as
true metagenesis and those of the other as hetero-
genesis.2 Metagenesis takes its origin from a
2 It is certainly preferable to make use of the expression
" metagenesis " in this special sense .instead of introducing a
new one. As a general designation, comprehending meta-
genesis and heterogenesis, there will then remain the expression
" alternation of generation," if one does not prefer to say
G
82 Studies in the Theory of Descent.
phyletic series of dissimilar forms, whilst hetero-
genesis originates from a phyletic series of simi-
lar forms — this series, so far as we can at present
judge, always consisting of similar sexual genera-
tions. The former would thus nearly coincide
with Haeckel's progressive, and the latter with his
retrogressive metagenesis. Metagenesis may fur-
ther originate in various ways. In the first place,
from metamorphosis, as for example, in the propa-
gation of the celebrated Cecidomyia with nursing
larvae. The power which these larvae possess of
propagating themselves asexually has evidently
been acquired as a secondary character, as appears
from the fact that there are many species of the
same genus the larvae of which do not nurse, these
larvae being themselves undoubted secondary forms
produced by the adaptation of this stage of phyletic
development to a mode of life widely different
from that of the later stages. In the form now
possessed by these larvae they could never have
represented the final stage of their ontogeny, nei-
ther could they have formerly possessed the power
of sexual propagation. The conclusion seems
inevitable that metagenesis has here proceeded
from metamorphosis ; that is to say, one stage
of the ontogeny, by acquiring asexual propagation,
has changed the originally existing metamorphosis
into metagenesis.
"cyclical propagation." The latter may be well used in con-
tradistinction to " metamorphosis."
On the Seasonal Dimorphism of Butterflies. 83
Lubbock3 is undoubtedly correct when, for cases
like that just mentioned, he attempts to derive
alternation of generations from metamorphosis.
But if we exclude heterogenesis there still remain
a large number of cases of true metagenesis which
cannot be explained from this point of view.
It must be admitted, with Haeckel, that the
alternation of generations in the Hydromedusae
and Trematoda does not depend, as in the case of
Cecidomyia, upon the larvae having acquired the
power of nursing, but that the inferior stages of
these species always possessed this power which
they now only preserve. The nursing Trematode
larvae now existing may possibly have been formerly
able to propagate themselves also sexually, this
mode of propagation having at the present time
been transferred to a later phyletic stage. In this
case, therefore, metagenesis was not properly pro-
duced by metamorphosis, but arose therefrom in
the course of the phyletic development, the
earlier phyletic stages abandoning the power of
sexual reproduction, and preserving the asexual
mode of propagation. A third way in which
metagenesis might originate is through polymor-
phosis. When the latter is combined with
asexual reproduction, as is especially the case
with the Hydrozoa, metagenesis may be derived
therefrom. The successive stages of transfor-
mation of one and the same physiological in-
3 Loc. cit. chap. iv.
G 2
84 Studies in the Theory of Descent.
dividual do not in these cases serve as the point
of departure for alternation of generation, but the
different contemporary forms living gregariously
into which the species has become divided through
functional differentiation of the various individuals
of the same stock. Individuals are here produced
which alone acquire the power of sexual reproduc-
tion, and metagenesis is thus brought about, these
individuals detaching themselves from the stock
on which they originated, while the rest of the
individuals remain in combination, and retain the
asexual mode of propagation. No sharp distinc-
tion can be otherwise drawn between this and the
cases previously considered.4 The difference con-
sists only in the whole cycle of reproduction being
performed by one stock ; both classes have the
common character that the different phyletic stages
never appear in the same individual (metamor-
phosis), but in the course of further phyletic de-
velopment metagenesis at the same time arises,
i.e. the division of these stages among a succession
of individuals. We are therefore able to distin-
guish this primary metagenesis from the secondary
metagenesis arising from metamorphosis.
4 The idea that alternation of generation is derived from
polymorphism (not the reverse, as usually happens ; i. e. poly-
morphism from alternation of generation) is not new, as I find
whilst correcting the final proof. Semper has already ex-
pressed it at the conclusion of his interesting memoir, " Uber
Generationswechsel bei Steinkorallen," &c. See " Zei-tschrift f.
wiss. Zool." vol. xxii. 1872.
On the Seasonal Dimorphism of Butterflies. 85
It is not here my intention to enter into the
ultimate causes of metagenesis ; in this subject we
should only be able to advance by making vague
hypotheses. The phenomenon of seasonal dimor-
phism, with which this work has mainly to deal,
is evidently far removed from metagenesis, and it
was to make this clear that the foregoing observa-
tions were brought forward. The characters com-
mon in the origin of metagenesis are to be found,
according to the views previously set forth, in the
facts that here the faculty of asexual and of sexual
reproduction is always distributed among several
phyletic stages of development which succeed each
other in an ascending series (progressive meta-
genesis of Haeckel), whereas I find differences only
in the fact that the power of asexual propagation
may (in metagenesis) be either newly acquired
(larva of Cecidomyid] or preserved from previous
ages (Hydroida). It seems that in this process
sexual reproduction is without exception lost by
the earlier, and remains confined solely to the
most recent stages.
From the investigations on seasonal dimorphism
it appears that a cycle of generations can arise in
an entirely different way. In this case a series of
generations originally alike are made dissimilar by
external influences. This appears to me of the
greatest importance, since seasonal dimorphism is
without, doubt closely related to that mode of re-
production which has hitherto been exclusively
86 Studies in the Theory of Descent.
designated as heterogenesis, and a knowledge of
its mode of origination must therefore throw light
on the nature and origin of heterogenesis in general.
In seasonal dimorphism, as I have attempted to
show, it is the direct action of climate, and indeed
chiefly that of temperature, which brings about the
change in some of the generations. Since these
generations have been exposed to the alternating
influence of the summer and winter temperature
a periodical dimorphism has been developed —
a regular cycle of dissimilar generations. It
has already been asserted that the consecutive
generations of a species comport themselves with
respect to heredity in a manner precisely similar
to that of the ontogenetic stages, and at the same
time such succeeding generations point out the
parallelism between metamorphosis and hetero-
genesis. If influences capable of directly or indi-
rectly producing changes operate on any particular
stage of development, these changes are always
transmitted to the same stage. Upon this meta-
morphosis depends. In a precisely similar manner
changes which operated periodically on certain
generations (i, 3, 5, for instance) are transmitted
to these generations only, and not to the inter-
mediate ones. Upon this depends heterogenesis.
We have just been led to the comprehension of
heterogenesis by cyclical heredity, by the fact
that a cycle is produced whenever a series of gene-
rations exists under regularly alternating influences.
On the Seasonal Dimorphism of Butterflies. 8 7
In this cycle newly-acquired changes, however
minute in character at first, are only transmitted
to a later, and not to the succeeding generation,
appearing only in the one corresponding, i.e. in
that generation which exists under similar trans-
forming influences. Nothing can more clearly
show the extreme importance which the conditions
of life must have upon the formation and further
development of species than this fact. At the
same time nothing shows better that the action of
these conditions is not suddenly and violently
exerted, but that it rather takes place by small and
slow operations. In these cases the long-con-
tinued .accumulation of imperceptibly small varia-
tions proves to be the magic means by which the
forms of the organic world are so powerfully
moulded. By the application of even the greatest
warmth nobody would be able to change the winter
form of A. Levana into the summer form ; never-
theless, the summer warmth, acting regularly on
the second and third generations of the year, has,
in the course of a lengthened period, stamped
these two generations with a new form without the
first generation being thereby changed. In the
same region two different climatic varieties have
been produced (just as in the majority of cases
climatic varieties occur only in separate regions)
which alternate with each other, and thus give rise
to a cycle of which each generation propagates
itself sexually.
88 Shi dies in the Theory of Descent.
But even if seasonal dimorphism is to be ascribed
to heterogenesis, it must by no means be asserted
that those cases of cyclical propagation hitherto
designated as heterogenesis are completely iden-
tical with seasonal dimorphism. Their identity
extends only to their origin and manner of de-
velopment, but not to the mode of operation of
the causes which bring about their transformation.
Both phenomena have a common mode of origina-
tion, arising from similar (monomorphic) sexual
generations and course of development, a cycle of
generations with gradually diverging characters
coming into existence by the action of alternating
influences. On the other hand, the nature of the
changes by which the secondary differs from the
primary generation may be referred to another
mode of action of the exciting causes. In seasonal
dimorphism the differences between the two gene-
rations are much less than in other cases of hetero-
genesis. These differences are both quantitatively
less, and are likewise qualitative, affecting only
characters of biological insignificance.5 The va-
riations in question are mostly restricted to the
marking and colouring of the wings and body,
occasionally affecting also the form of the wing,
and in a few cases the size of the body (Plebeius
Amyntas), whilst the bodily structure — so far at
6 See my essay " Uber den Einfluss der Isolirung auf die
Artbildung." Leipzig, 1872.
On the Seasonal Dimorphism of Butterflies. 89
least as my investigations extend— appears to be
the same in both generations.6
The state of affairs is quite different in the re-
maining cases of heterogenesis ; here the entire
structure of the body appears to be more or less
changed, and its size is often very different,
nearly all the internal organs differing in the two
generations. According to Claus,7 " we can
scarcely find any other explanation of the mode
of origination of heterogenesis than the gradual
and slow advantageous adaptation of the organiza-
tion to important varying conditions of life " — a
judgment in which this author is certainly correct.
In all such cases the change does not affect unim-
portant characters, as it does in butterflies, but
parts of biological or physiological value ; and we
cannot, therefore, consider such changes to have
originated through the direct action of altered
conditions of life, but indirectly through natural
selection or adaptation.
Thus, the difference between seasonal dimor-
phism and the other known cases of heterogenesis
0 [In the case of monogoneutic species which, by artificial
' forcing,' have been made to give two generations in the year,
it has generally been found that the reproductive system has
been imperfectly developed in the second brood. A minute
anatomical investigation of the sexual organs in the two broods
of seasonally-dimorphic insects would be of great interest, and
might lead to important results. R.M.]
T " Grundziige der Zoologie." 2nd ed. Leipzig, 1872. In-
troduction.
90 Studies in the Theory of Descent.
consists in the secondary form in which the
species appears in the former originating through
the direct action of external conditions, whilst in
the latter this form most probably originates
through the indirect action of such influences.
The first half of the foregoing proposition is alone
capable of provisional proof, but it is in the
highest degree probable that the latter half is also
correct. Naturally we cannot say to what extent
the direct action of external conditions plays also
a part in true heterogenesis, as there have been
as yet no experiments made on its origin. That
direct action, working to a certain extent co-ope-
ratively, plays only a secondary part, while the
chief cause of the change is to be found in adapta-
tion, no one can doubt who keeps in view, for
instance, the mode of propagation discovered by
Leuckart in Ascaris nigrovenosa. In this worm,
the one generation lives free in the water, and
the other generation inhabits the lungs of frogs,
the two generations differing from one another
in size of body and structure of internal organs
to an extent only possible with the true Nema-
toda.
To prevent possible misunderstanding, let it
be finally noted — even if superfluous — that the
changes causing the diversity of the two genera-
tions in seasonal dimorphism and heterogenesis
are not of such a nature that the value of different
" specific characters " can be attached to them.
On the Seasonal Dimorphism of Butterflies. 9 1
Distinctly defined specific characters, are well
known not to occur generally, and it would
therefore be erroneous to attach but little value
to the differences in seasonal dimorphism because
these chiefly consist in the colouring and marking
of the wings. The question here under consider-
ation is not whether two animal forms have the
value of species or of mere varieties — a question
which can never be decided, since the reply always
depends upon individual opinion of the value of
the distinctions in question, and the idea of both
species and varieties is moreover purely conven-
tional. The question is, rather, whether the distin-
guishing characters possess an equal constancy —
that is, whether they are transmitted with the same
force and accuracy to all individuals ; and whether
they occur, therefore, in such a manner that they
can be practically employed as specific characters.
With respect to this, it cannot be doubtful for a
moment that the colouring and marking of a but-
terfly possess exactly the same value as the constant
characters in any other group of animals, such as
the palate-folds in mice, the structure of the
teeth in mammals, the number and form of the
wing and tail feathers in birds, &c. We have but
to remember with what wonderful constancy often
the most minute details of marking are trans-
mitted in butterflies. The systematist frequently
distinguishes between two nearly allied species, as
for instance in the Lyccenidce, chiefly by the posi-
9 2 Studies in the Theory of Descent.
tion of certain insignificant black spots on the
under side of the wing (P. Alexis female, and P.
Agestis) ; and this diagnosis proves sufficient, since
P. Alexis, which has the spots in a straight row,
has a different caterpillar to P. Agestis, in which
the central spot is nearer the base of the hind
wing !
For the reasons just given, I maintain that it
is neither justifiable nor useful to designate the
di- and polymorphism of butterflies as di- and
polychroism, and thereby to attribute but little im-
portance to these phenomena.8 This designation
would be only justifiable if the differences of colour
were due to other causes than the differences of
form, using this last word in a narrow sense. But
it has been shown that the same direct action of
climate which originates new colours, produces
also in some species differences of form (contour of
wing, size, &c.) ; whilst, on the other hand, it has
long been known that many protective colours can
only be explained by the indirect action of ex-
ternal conditions.
When I raise a distinction in the nature of the
changes between seasonal dimorphism and the re-
maining known cases of heterogenesis, this must be
taken as referring only to the biological or physio-
logical result of the change in the transformed
organism itself. In seasonal dimorphism only
8 With reference to this subject, see the discussion by the
Belgian Entomological Society, Brussels, 1873.
On the Seasonal Dimorphism of B litter flies. 93
insignificant characters become prominently
changed, characters which are without importance
for the welfare of the species ; while in true hetero-
genesis we are compelled to admit that useful
changes, or adaptations, have occurred.
Heterogenesis may thus be defined either in
accordance with my proposal or in the manner
hitherto adopted, since it may be regarded as more
morphological than the cyclical succession of dif-
ferently formed sexual generations ; or, with Claus,
as the succession of different sexual generations,
" living under different conditions of existence " —
a definition which applies in all cases to seasonal
dimorphism. Varying conditions of existence, in
their widest sense, are the result of the action of
different climates ; and a case has been made
known recently in which it is extremely probable
that the climatic differences of the seasons have
produced a cycle of generations by influencing the
processes of nutrition. This case is quite ana-
logous to that which we have observed in the
seasonal dimorphism of butterflies, but with the
distinction that the difference between the winter
and summer generations does not, at least entirely,
consist in the form of the reproductive adult, but
almost entirely in its ontogeny — in the mode of
its development. A comparison of this case with
the analogous phenomenon in butterflies, may
be of interest. In the remarkable fresh- water
Daphnid, Leptodora hyalina Lillejeborg, it was
94 Studies in the Theory of Descent.
proved some years ago by P. E. M tiller,9 who
studied the ontogeny, that this last was direct, since
the embryo, before leaving the egg, already pos-
sesses the form, members, and internal organs of
the adult. This was, at least, the case with the
summer eggs. It was subsequently shown by
Sars10 that this mode of development only holds
good for the summer brood, the winter eggs pro-
ducing an embryo in the spring which possesses
only the three first pairs of limbs, and, instead of
compound eyes, only a single frontal eye, thus
exhibiting briefly, at first, the structure of a Nau-
plius, and gradually acquiring that of Leptodora.
The mature form derived from the winter eggs is
not distinguishable from the later generations, ex-
cept by the presence of the simple larval eye, which
appears as a small black spot. The generations
when fully developed are thus distinguished only
by this minute marking, but the summer generation
undergoes direct development, whilst the winter
generation, on the contrary, is only developed by
metamorphosis, beginning with the simplest Crus-
tacean type, and thus fairly representing the phy-
letic development of the species. We therefore
see, in this case, the combination of a metamorphic
and a direct development taking place to a certain
8 P. E. Muller, " Bidrag til Cladocerners Fortplantingshis-
torie," 1868.
10 Sars, in " Forhandlinger i Videnskabs Selskabet i Christia-
nia," 1873, part i.
On the Seasonal Dimorphism of Butterflies. 95
extent under our eyes. It cannot be proved with
certainty what the cause of this phenomenon may
be, but the conjecture is almost unavoidable that
it is closely related to the origin of the seasonal
dimorphism of butterflies, since both depend on
the alternating climatic influences of summer and
winter: it is most probable that these influences
have directly u brought about a shortening of the
period of development in summer. Thus we
have here a case of heterogenesis nearly related
to the seasonal dimorphism of butterflies in a
twofold manner — first, because the cycle of gene-
rations is also in this case brought about by the
direct action of the external conditions of life ;
and secondly, the winter form is here also the
primary, and the summer form the secondary
one.
In accordance with the idea first introduced into
science by Rudolph Leuckart, we have hitherto
understood heterogenesis to be only the alterna-
tion of dissimilar sexual generations. From this
point of view the reproduction of Leptodora can
be as little ascribed to heterogenesis as can that
of Aphis or Daphnia, although the apparent agamic
reproduction of the winter and a portion of the
summer generation is undoubtedly partheno-
11 [Eng. ed. Recent researches on alternation of generation
in the Daphnoidea have convinced me that direct action
of external conditions does not in these cases come into con-
sideration, but only indirect action,]
96 Studies in the Theory of Descent.
genesis and not propagation by nursing,12 As has
already been said, however, I would attribute no
fundamental importance to the criterion of agamic
reproduction — the more especially because we are
ignorant of the physiological significance of the
two modes of propagation; and further, because this
principle of classification is entirely external, and
only valuable in so far as no better one can be
substituted for it. A separation of the modes of
cyclical propagation according to their genesis ap-
pears to me — especially if practicable — not alone
to be of greater value, but the only correct one,
and for this the knowledge of the origin of sea-,
sonal dimorphism seems to me to furnish a possi-
ble method.
If, as was indicated above, we designate as
metagenesis (in the narrow sense) all those cases in
which it must be admitted that a series of dif-
ferently aged phyletic stages have furnished the
points of departure, and as heterogenesis those
cases in which similar phyletic stages have been
compelled to produce a cycle of generations by the
periodic action of external influences, it is clear
that the scope of heterogenesis is by this means
considerably extended, and at the same time
sharply and precisely defined.
Under heterogenesis then is comprised, not only
12 See my memoir, " Uber Bau und Lebenserscheinungen der
Leptodora hyalina" Zeitschrift f. wiss. Zool., vol. xxiv. part 3,
1874.
On the Seasonal Dimorphism of Butterflies. 97
as heretofore the reproduction of Ascaris nigrove-
nosa, of Leptodora appendwilata, and of the cattle-
lice, but also that of the Aphides, Coccidce, Daph-
nidce, Rotatoria, and Phyllopoda, and, in short, all
those cases in which we can determine the former
identity of the two kinds of generations from their
form, anatomical structure, and mode of reproduc-
tion. This conclusion is essentially supported by
a comparison of the most closely allied species.
Thus, for instance, when we see the genus Aphis
and its allies related on all sides to insects which
propagate sexually in all generations, and when
we further observe the great similarity of the
whole external and internal structure in the two
kinds of generations of Aphis, we are forced to
the conjecture that the apparent asexual repro-
duction of the Aphides is in reality partheno-
genesis, i. e., that it has been developed from
sexual reproduction. Neither can it be any
longer disputed that in this case, as well as in that
of Leptodora and other Daphnidcz, the same
female alternately propagates parthenogenetically,
and produces eggs requiring fertilization. This
was established by Von Heyden13 some years
ago, in the case of Lachnus Querci, and has been
since confirmed by Balbiani.14
There can be no doubt that in all these cases
the cycle of generations has been developed from
1 ''Stettin, entom. Zeit, vol. xviii p. 83, 1857.
14 Compt. Rend., vol. Ixxvii. p. 1164, 1873.
H
98 Studies in the Theory of Descent.
phyletically similar generations. But instances
are certainly conceivable which present themselves
with less clearness and simplicity. In the first
place, we do not know whether parthenogenesis
may not finally settle down into complete asexual
reproduction. Should this be the case, it might
be possible that from heterogenesis a mode oi
propagation would ultimately arise, which was
apparently indistinguishable from pure meta-
genesis. Such a state of affairs might result, if
the generations settling into asexual reproduction
(as, for instance, the plant-lice), at the same time
by adaptation to varying conditions of life, under-
went considerable change of structure, and
entered upon a metamorphosis to some extent
retrogressive. We should then be inclined to
regard these generations as an earlier phyletic
stage, whilst, in fact, they would be a later one,
and the idea of metagenesis would thus have been
formed after the manner of heterogenesis.
On the other hand, it is equally conceivable
that heterogenesis may have been developed from
true metagenesis in the case of larvae which,
having acquired the faculty of asexual propaga-
tion, are similar in function to sexually mature
insects. This possibility is not at first sight ap-
parent. If the nursing-larvae of the Cecidomyice
were as much like the sexual insects as are the
young Orthoptera to the sexually mature forms,
we should not know whether to regard them as
On the Seasonal Dimorphism of Butterflies. 99
degraded sexual insects, or as true larvae which
had attained the power of asexual propagation.
Their propagation would be considered to be par-
thenogenesis ; and as it could not be denied that
heterogenesis was here manifest, the mode of de-
velopment of their particular kind of propagation
might be proved, i. e., it might be demonstrated,
that the generations now parthenogenetic were
formerly mere reproductive larval stages.
I have only offered these last observations in
order to show on what uncertain ground we are
still standing with regard to this subject when-
ever we deal with the meaning of any particular
case, and how much still remains to be done. It
appears certain that the two forms of cyclical pro-
pagation, heterogenesis and metagenesis, origi-
nate in entirely distinct ways, so that it must be
admitted that, under these circumstances, the
idea of the existing conditions respecting the
true genesis may possibly be erroneous. To in-
dicate the manner in which the cyclical mode of
propagation has arisen in any single case, would
only be possible by a searching proof and com-
plete knowledge of existing facts in addition to
experiments.
H 2
ioo Studies in the 7^/ieory of Descent.
VI.
GENERAL CONCLUSIONS.
I SHALL not here give a repetition and summary
of the results arrived at with respect to seasonal
dimorphism, but rather the general conclusions
derived from these results ; and, at the same time,
I may take the opportunity of raising certain
questions which have not hitherto found expres-
sion, or have been but briefly and casually stated.
It must, in the first place, be admitted that
differences of specific value can originate through
the direct action of external conditions of life only.
Of the truth of this proposition there can be no
doubt, after what has been above stated concern-
ing the difference between the two forms of any
seasonally dimorphic species. The best proof is
furnished by the older systematists, to whom the
genetic relationship of the two forms was un-
known, and who, with unprejudiced taxonomy, in
many cases indicated their distinctness by separate
specific names. This was the case with Araschnia
Levana and Prorsa, Euchloe Bella and Auso-
nia, E. Belemia and Glance, Plebeius Polysperchon
and Amyntas. In the presence of these facts it
On the Seasonal Dimorphism of Butterflies. 101
can scarcely be doubted that new species can be
formed in the manner indicated ; and I believe
that this was and is still the case, with butterflies
at least, to a considerable extent ; the more so
with these insects, because the striking colours and
markings of the wings and body, being in most
cases without biological significance, are useless for
the preservation of the individual or the species,
and cannot, therefore, be objects of natural selection.
Darwin must have obtained a clear insight into
this, when he attempted to attribute the markings
of butterflies to sexual and not to natural selec-
tion. According to this view, every new colour
or marking first appears in one sex accidentally,1
and is there fixed by being preferred by the other
sex to the older coloration. When the new or-
namentation becomes constant (in the male for
example), Darwin supposes that it becomes trans-
ferred to the female by inheritance, either partially
or completely, or not at all ; so that the species,
therefore, remains more or less sexually dimor-
phic, or (by complete transference) becomes again
sexually monomorphic.
The admissibility of such different, and, to a
certain extent, arbitrarily limited inheritance, has
already been acknowledged. The question here
concerned is, whether Darwin is correct when he
1 [" Accidental " in the sense of our being in ignorance of
the laws of variation, as so frequently insisted upon by Darwin.
R.M.]
IO2 Studies in the Theory of Descent.
in this manner attributes the entire coloration of
butterflies to sexual selection. The origin of
seasonal dimorphism appears to me to be against
this view, howsoever seductive and grand the
latter may seem. If differences as important as
those which exist between the summer and winter
forms of many butterflies can be called forth by
the direct action of a changed climate, it would be
extremely hazardous to attribute great importance
to sexual selection in this particular case.
The principle of sexual selection appears to me
to be incontestible, and I will not deny that it is
also effective in the case of butterflies; but I believe
that as a final explanation of colour this agency
can be dispensed with, inasmuch as we see that
considerable changes of colour can occur without
the influence of sexual selection.2
8 [Eng. ed. Since this was written I have studied the orna-
mental colours of the Daphnidcs ; and, as a result, I no longer
doubt that sexual selection plays a very important part in the
marking and colouring of butterflies. I by no means exclude
both transforming factors, however ; it is quite conceivable, on
the contrary, that a change produced directly by climate may
be still further increased by sexual selection. The above given
case of Polyommatus Phlceas may perhaps be explained in this
manner. That sexual selection plays a part in butterflies, is
proved above all by the odoriferous scales and tufts of the males
discovered by Fritz M tiller.] [For remarks on the odours
emitted by butterflies and moths, see Fritz Miiller in " Jena.
Zeit. f. Naturwissen.," vol. xi. p. 99 ; also " Notes on Brazilian
Entomology," Trans. Ent. Soc. 1878, p. 211. The odoriferous
organs of the female Heliconincz are fully described in a paper
in "Zeit. f. Wissen. Zool.," vol. xxx. p. 167. The position of
On the Seasonal Dimorphism of Butterflies. 103
The question now arises, how far does the
transforming influence of climate extend ? When
a species has become transformed by climatic
change to such an extent that its new form pos-
sesses the systematic value of a new species, does
it return to its older form by removal to the old
climatic conditions ? or would it under these cir-
cumstances become again transformed in a new
manner ? This question is not without impor-
tance, inasmuch as in the first case climatic
influences would be of little value in the forma-
tion of species, and there would result at most
only a fluctuation between two extremes. In the
same manner as in seasonally dimorphic species
the summer and winter forms now alternate with
each other every year, so would the forms pro-
duced by warmth and cold then alternate in the
greater periods of the earth's history. Other
groups of animals are certainly changed by the
action of different climatic influences ; but in but-
the scent-tufts in the sphinx-moths is shown in Proc. Entom. Soc.
1878, p. ii. Many British moths, such as Phlogophora meticu-
fasa, Cosmia trapezina, &c. &c., have tufts in a similar position.
The fans on the feet of Addalia bisetata, Herminia barbalis,
H. tarsipennalts, &c., are also probably scent organs. A large
moth from Jamaica, well known to possess a powerful odour
when alive (Erebus odorus Linn.), has great scent-tufts on the
hind legs. For the application of the theory of sexual selection
to butterflies, see, in addition, to Darwin's "Descent of
Man," Fritz Miiller in " Kosmos," vol. ii. p. 42 ; also for
January, 1879, p. 285; and Darwin in "Nature," vol. xxi.
January 8th, 1880, p. 237. R.M.]
IO4 Studies in the Theory of Descent.
terflies, as I believe I have proved, temperature
plays the chief part, and as this only oscillates be-
tween rather narrow limits, it admits of no great
differences of coloration.
The question thus suggests itself, whether
species of butterflies only oscillate between two
forms, or whether climatic change, when sufficiently
great to produce variation, does not again origi-
nate a new form. Inasmuch as the reversion
experiments with seasonally dimorphic butterflies
appear to correspond with the latter view, I
believe that this must be admitted. I am of
opinion that an old form never again arises
through change of climate, but always a new
one ; so that a periodically recurring change of
climate is alone sufficient, in the course of a long
period of time, to admit of new species arising
from one another. This, at least, may be the case
with butterflies.
My views rest essentially upon theoretical con-
siderations. It has already been insisted upon,
as results immediately from the experiments, that
temperature does not act on the physical constitu-
tion of the individual in the same manner as acid
or alkali upon litmus paper, i. e., that one and the
same individual does not produce this or that
coloration and marking according as it is exposed
to warmth or cold ; but rather that climate, when
it influences in a similar manner many succeeding
generations, gradually produces such a change in
On the Seasonal Dimorphism of Butterflies. 105
the physical constitution of the species that this
manifests itself by other colours and markings.
Now when this newly acquired physical constitu-
tion, established, as we may admit, throughout
a long series of generations, is again submitted
to a constant change of climate, this influence,
even if precisely similar to that which obtained
during the period of the first form of the species,
cannot possibly reproduce this first form. The
nature of the external conditions may be the
same, but not so the physical constitution of the
species. Just in the same manner as a Pieris (as
has been already shown), a Lyccena, or a Satyrus,
produces quite different varieties under the trans-
forming influence of the same climate, so must the
variation originatingfrom the transformed species of
our present case after the beginning of the primary
climate be different from that primary form of the
species, although perhaps in a less degree. In
other words, if only two different climates alter-
nated with each other during the earth's geological
periods, every species of butterfly submitted to
these changes of climate would give rise to an
endless series of different specific forms. The
difference of climate would in reality be greater
than supposed, and for any given species the
climatic variation would not only occur through
the periodic shifting of the ecliptic, but also through
geological changes and the migrations of the
species itself, so that a continuous change of
io6 Studies in the Theory of Descent.
species must have gone on from this sole cause
of alternation of climate. When we consider
that many species elsewhere extinct have become
locally preserved, and when, further, to these we
add those local forms which have arisen by the
prevention of crossing (amixia), and finally take
into consideration the important effects of sexual
selection, we can no longer be astonished at the
vast numbers of species of butterflies which we
now meet with on the earth.
Should any one be inclined to conclude, from my
reversion experiments with seasonally dimorphic
butterflies, that the secondary species when ex-
posed to the same climate as that which produced
it must revert to the primary, he forgets that this
reversion to the winter form is nothing but a
reversion — i.e., a sudden return to a primary form
through peculiar laws of inheritance — and by no
means a gradual re-acquisition of this primary
form under the gradual influence of the primary
climate. Reversion to the winter form occurs also
through other influences, as, for instance, by high
temperature. Reversions of this kind, depending
on laws of heredity, certainly happen with those
cases of transmutation which do not alternate with
the primary form, as in seasonal dimorphism, but
which occur continuously. They would, how-
ever probably be more quickly suppressed in such
cases than in seasonal dimorphism, where the
constant alternation of the primary and secondary
On the Seasonal Dimorphism of Butterflies. 107
forms must always maintain the tendency of the
latter to produce the former.
That the above conclusion is correct — that a
secondary species, when exposed to the external
conditions under the influence of which the
primary form originated, does not again revert toi
the latter — is proved by experience with plants.
Botanists3 assure us "that cultivated races which
become wild, and are thus brought back to their
former conditions of life, do not become changed
into the original wild form, but into some new
one."
A second point which appears to me to be
elucidated by seasonal dimorphism, is the origin
of variability. It has already been prominently
shown that secondary forms are for the most part
considerably more variable than primary forms.
From this it follows that similar external in-
fluences either induce different changes in the
different individuals of a species, or else change all
individuals in the same manner, variability arising
only from the unequal time in which the indi-
viduals are exposed to the external influence.
The latter is undoubtedly the case, as appears
from the differences which are shown by the
various individuals of a secondary form. These
8 Nageli, " Entstehung und Begriff der naturhistorischen
Art," Munich, 1865, p. 25. The author interprets the facts
above quoted in a quite opposite sense, but this is obviously -
erroneous.
1 08 Studies in the Theory of Descent.
are always only differences of degree and not of
kind, as is perhaps most distinctly shown by the
very variable A. Prorsa (summer form), in which
all the occurring variations differ only by the
Levana marking being more or less absent, and,
at the same time, by approximating more or less
to the pure Prorsa marking ; but changes in a
totally different direction never occur. It is like-
wise further evident, as has been mentioned above,
that allied species and genera, and even entire
families (Pieridce\ are changed by similar external
inducing causes in the same manner — or, better, in
the same direction.
In accordance with these facts the law may be
stated, that, in butterflies at least, all the indivi-
duals of a species respond to the same external
influences by similar changes, and that, conse-
quently, the changes brought about by climatic
influences take a fixed direction, determined by
the physical constitution of the species. When,
however, new climatic forms of butterflies, in which
natural selection is completely excluded, and the
nature of the species itself definitely determines
the direction of the changes, nevertheless show
variability from the very beginning, we may
venture to conclude that every transformation of a
species generally begins with a fluctuation of its
characters. But when we find the primary forms
of butterflies always far more constant, this shows
that the continued crossing of the individuals of a
On the Seasonal Dimorphism of Butterflies. 1 09
species to a certain extent balances the fluctuations
of form. Both facts taken together confirm the
law formerly enunciated by me,4 that in every
species a period of variability alternates with one
of (relative) constancy — the latter indicating the
culmination, and the former the beginning or end,
of its development. I here call to mind this law,
because the facts which I advanced at that time,
viz., Hilgendorf's history of the phyletic develop-
ment of the Steinheim fossil shells, having since
become somewhat doubtful, one might easily be
inclined to go too far in mistrusting them and refuse
to give them any weight at all.5
In the essay just indicated I traced the origin
of a certain class of local forms to local isolation.
I attempted to show that when a species finds
itself in an isolated district in a condition (period)
of variability, it must there necessarily acquire
somewhat deviating characters by being prevented
from crossing with the individuals of other regions,*
or, what comes to the same thing, a local form
must originate. This production of local forms
4 See my essay, " Uber den Einfluss der Isolirung auf die
Artbildung." Leipzig, 1872.
8 [Eng. ed. In the summer of 1877, Dr. Hilgendorf again
investigated the Steinheim fossil shells, and found his former
statements to be completely confirmed. At the meeting of the
German Naturalists and Physicists at Munich, in 1877, he ex-
hibited numerous preparations, which left no doubt that the
chief results of his first research were correct, and that there
have been deposited a series of successively derived species
together with their connecting intermediate forms.]
1 1 o Studies in the Theory of Descent.
results because the different variations which, for
the time being, constitute the variability of the
species, would alwrays be in a different numerical
proportion in the isolated district as compared with
other regions ; and further, because constancy is
produced by the crossing of these (isolated)
varieties among themselves ; so that the resultant
of the various components is (local) variation. If
the components are dissimilar the resultant would
also be different, and thus, from a theoretical
point of view, there seems to me no obstacle in
the way of the production of such local forms by
the process of ' amixia.' I believe that I have
further shown that numerous local forms can
be conceived to have arisen through this process
of preventive crossing, whilst they cannot be ex-
plained by the action of climatic influences.
That I do not deny the existence of true climatic
forms in admitting this principle of ' amixia/ as
has been frequently imagined, appears suffi-
ciently from the treatise in question. The ques-
tion arises, however, whether climatic influences
may not also originate forms by ' amixia ' by
making a species variable. It would be difficult
at present to decide finally upon this subject.
If, however, in all cases a variation in a certain
fixed direction occurred through climatic influences,
a form could not arise by ' amixia ' from such a
variability, since the components could then pro-
duce resultants different only in degree and not
On the Seasonal Dimorphism of Butterflies. 1 1 1
in kind. But we are not yet able to extend our
researches to such fine distinctions.
As a final, and not unimportant result of these
investigations, I may once more insist that dis-
similar influences, when they alternatingly affect
a long series of originally similar generations in
regularly recurring change, only modify the gene-
rations concerned, and not intermediate ones. Or,
more briefly, cyclically acting causes of change
produce cyclically recurring changes : under their
influence series of monomorphic generations be-
come formed into a cycle of di- or polymorphic
generations.
There is no occasion to return here to the im-
mediate evidence and proof of the foregoing law.
In the latter, however, is comprised the question —
is not the cycle of generations produced by cycli-
cal heredity ultimately equivalent to Darwin and
Haeckel's homochronic heredity which forms the
ontogenetic stages into a cycle ? It is possible
that from this point, in the future, the nature of the
processes of heredity, which are still so obscure,
may be penetrated into, and both phenomena
traced to the same cause, as can now be only sur-
mised but not clearly perceived.
Finally, the most general, and in so far chief
result of these investigations, appears to me to lie
in the conclusion, which may be thus formulated : —
A species is only caused to change through the
influence of changing external conditions of life,
1 1 2 Studies in the Theory of Descent.
this change being in a fixed direction which en-
tirely depends on the physical nature of the varying
organism, and is different in different species, or
even in the two sexes of the same species.
I am so little disposed to speak in favour of an
unknown transforming power that I may here
again insist that the transformation of a species
only partly depends upon external influences, and
partly on the specific constitution of the particular
form. I designate this constitution ' specific/
inasmuch as it responds to the same inciting cause
in a manner different to the constitution of another
species. We can generally form a clear concep-
tion why this should be the case ; for not only is
there in another species a different kind of latent
vital activity, but each species has also a different
developmental history. It must be admitted that,
from the earliest period of the formation of an or-
ganism, and throughout all its intermediate stages,
properties which have become established, such as
growth, nutrition, or tendency to development,
have been transferred to the species now existing,
each of which bears these tendencies in itself to
a certain extent. It is these innate tendencies
which determine the external and internal appear-
ance of the species at every period of its life, and
which, by their reaction to external factors, repre-
sent the life of the individual as well as that of the
species. Since the sum of these inherited ten-
dencies must vary more or less in every species,
On the Seasonal Dimorphism of Butterflies. 1 1 3
not only is the different external appearance of
species as well as their physiological and biological
diversity thus explained, but it necessarily follows
therefrom, that different species must respond dif-
ferently to those external causes which tend to
produce a change in their form.
Now, this last conclusion is equivalent to the
statement that every species, through its physical
constitution, (in the sense defined) is impressed
with certain fixed powers of variation, which are
evidently extraordinarily numerous in the case of
each species, but are not unlimited ; they permit
of a wide range for the action of natural selection,
but they also limit its functions, since they certainly
restrain the course of development, however wide
the latter may be. I have elsewhere previously
insisted6 that too little is ascribed to the part played
by the physical constitution of species in the his-
tory of their transformation, when the course of
this transformation is attributed entirely to external
conditions. Darwin certainly admits the impor-
tance of this factor, but only so far as it concerns
the individual variation, the nature of which ap-
pears to him to depend on the physical constitution
of the species. I believe, however, that in this
directive influence lies the precise reason why,
under the most favourable external circumstances,
a bird can never become transformed into a mam-
6 See my essay, " Uber die Berechtigung der Darwin'schen
Theorie." Leipzig, 1868.
T
1 14 Studies in the Theory of Descent.
mal — or, to express myself generally, why, from a
given starting-point, the development of a par-
ticular species cannot now attain, even under the
most favourable external conditions, any desired
goal ; and why, from this starting-point, given
courses of development, even when of conside-
rable latitude, must be restricted, just as a ball
rolling down a hill is diverted by a fixed
obstacle in a direction determined by the posi-
tion of the latter, and depending on the direction
of motion and the velocity at the moment of
being diverted.
In this sense I agree with Askenasy's " fixed"
direction of variation ; but not if another new
physical force directing variation itself is thereby
intended.7 The explanation of the phenomena
does not appear to me to require such an admission,
and, if unnecessary, it is certainly not legitimate.
According to my view, transmutation by purely
internal causes is not to be entertained. If we
could absolutely suspend the changes of the ex-
ternal conditions of life, existing species would
remain stationary. The action of external inciting
causes, in the widest sense of the word, is alone able
to produce modifications ; and even the never-
failing " individual variations," together with the
inherited dissimilarity of constitution, appear to
7 I expressly insist upon this here, because the notice of
Askenasy's thoughtful essay which I gave in the " Archiv fur
Anthropologie " (1873) has frequently been misunderstood.
On the Seasonal Dimorphism of Butterflies. 1 1 5
me to depend upon unlike external influences,
the inherited constitution itself being dissimi-
lar because the individuals have been at all
times exposed to somewhat varying external
influences.
A change arising from purely internal causes
seems to me above all quite untenable, because I
cannot imagine how the same material substratum
of physical constitution of a species can be trans-
ferred to the succeeding generation as two op-
posing tendencies. Yet this must be the case if the
direction of development transferred by heredity
is to be regarded as the ultimate ground both of
the similarity and dissimilarity to the ancestors.
All changes, from the least to the greatest, appear
to me to depend ultimately only on external in-
fluences ; they are the response of the organism to
external inciting causes. It is evident that this
response must be different when a physical consti-
tution of a different nature is affected by the same
inciting cause, and upon this, according to my
view, depends the great importance of these con-
stitutional differences.
If, under " heredity," we comprise the totality of
inheritance — that is to say, the physical constitu-
tion of a species at any time, and therefore the
restricted and, in the foregoing sense, pre-de-
termined power of variation, whilst under " adap-
tation" we comprehend the direct and indirect
response of this physical constitution to the changes
I 2
1 1 6 Stitdies in the Theory of Descent.
in the conditions of life, I can agree with Haeckel's
mode of expression, and with him trace the trans-
formation of species to the two factors of heredity
and adaptation.
APPENDIX I.
EXPERIMENTS.
EXPERIMENTS WITH ARASCHNIA LEVANA.
i. BRED from eggs laid by a female of the winter form
on I2th — 1 5th May, 1868, in a breeding-cage. The
caterpillars emerged on 2Oth — 22nd May, and pupated
on 7th — gth June. The pupae, kept at the ordinary
temperature, produced : —
On the 1 9th of June 4 butterflies.
» 20th „ 5
2lSt „ 10
„ 22nd „ 9 „
23rd „ 7
» 25th „ 13
Total . . 48 „
All these butterflies were of the Prorsa type, 3 females
having a considerable amount of yellow, but none with
so much as figs. 3, 4, 7, 8, or 9. PI. I.
2. August 1 2th, 1868, found larvae of the third gene-
ration, which pupated at the beginning of September,
and were kept in a room not warmed. In September
three butterflies emerged in the Prorsa form, the re-
mainder hibernating and producing, after being placed
in a heated room at the end of February, from the 1st to
the 1 7th of March, 1869, more butterflies, all of the
Lev ana form.
1 1 8 Appendix.
3. Larvae found on the i/th June, 1869, were sorted
according to colour ; the yellow ones, with light brown
spines, produced, at the ordinary temperature, on 8th —
I2th July, 13 butterflies, 12 of which showed the ordinary
Prorsa type, and one, a male, possessing more yellow
than fig. 3, PI. I., must be considered as a Porima
type.
4. From caterpillars of the second generation, found
at the same time as those of Exp. 3, 30 pupae were
placed in the refrigerator (temperature 8° — 10° R.) on
June 25th. When the box was opened on August 3rd,
almost all had emerged, many being dead, and all,
without exception, were of the intermediate form
(Porima), although nearer the Prorsa than the Lev ana
type.
5. A large number of caterpillars of the second genera-
tion, found at the same time, pupated, and were kept at
a high summer temperature. After a pupal period of
about 19 days, some 70 butterflies emerged from 28th
June to 5th July, all of the Prorsa form, with the excep-
tion of 5, which were strongly marked with yellow
(Porima).
6. The 70 butterflies of the foregoing experiment were
placed in an enclosure 6 feet high, and 8 feet long, in
which, during warm weather, they freely swarmed on
flowers. Copulation was only once observed, and but
one female laid eggs on nettle on July 4th. At the
high summer temperature prevailing at the time, these
eggs produced butterflies after 30 — 31 days (third
generation). All were Prorsa, with more or less yellow ;
among 1 8 none were completely Porima.
7. Young larvae of the fourth generation, found on the
8th of August, were reared in a hothouse (17° — 20° R.).
They pupated on 2ist — 23rd August. Of these : —
A. 56 pupae were placed on ice (o° — 1° R.) for five
weeks, and then allowed to hibernate in a room
Appendix. 119
not warmed. In April, 1870, they all gave the Levana
form, with the exception of a single Porinia.
B. About an equal number of pupae were placed in
the hothouse, but without any result ; for, notwithstand-
ing a temperature of 12° — 24° R., not a single butterfly
emerged in the course of October and November. The
pupae were then allowed to hibernate in an unheated
room, and in April and May gave nothing but Levana.
8. Caterpillars of the second generation, found at the
beginning of June, 1870, pupated on I3th — 15th June,
and gave, at the ordinary temperature, on June 29th —
3<Dth. 7 butterflies of the Prorsa form.
9. Pupae of the same (second) generation were placed
immediately after pupation on June iSth, 1870, in a
refrigerator (o° — 1° R.), and after remaining there four
weeks (till July 1 8th) gave, at the ordinary summer
temperature : —
On the 22nd of July, 2 Prorsa.
23rd „ 3 „
„ 24th „ 6 Porima, 4 of which were
very similar to Levana.
„ 25th „ I Levana, without the blue
marginal line.
„ 26th „ 2 Levana, also without the
blue marginal line.
„ 2nd August, 6 Porima.
Total . . 20
Of these 20 butterflies only 5 were of the pure Prorsa
form.
10. Full grown larvae of the fourth generation, found
on August 20th, 1870, pupated on August 26th to Sep-
tember 5th. The pupae were divjded into three portions : —
A. Placed in the hothouse (12°— 25° R.), immediately
after pupation and left there till October 2Oth. Of
I2O Appendix.
about 40 pupae only 4 emerged, 3 of which were Prorsa
and I Porima. The remaining pupae hibernated and
all changed into Levana the following spring.
B. Kept in a room heated to 6° — 15° R. from
November. Not a single specimen emerged the same
year. This lot of pupae were added to C from No-
vember.
C. Placed on ice for a month immediately after pu-
pation ; then, from September 28th to October igth in
the hothouse, where no more butterflies emerged. The
pupae hibernated, together with those from lot B, in a
room heated by water to 6° — 15° R., and gave : —
On the 6th of February, i female Levana.
„ 22nd „ I male Levana.
„ 23rd „ i male Levana.
„ 24th „ i female Levana.
„ 25th „ i male and i female Levana.
„ 28th „ i male and i female Levana.
„ 1st of March, I male Levana.
„ 1 3th „ i female Levana.
„ 1 5th „ i female Levana.
„ i Qth „ i male Levana.
„ 2nd of April, 2 male and i female Levana.
„ 7th „ i female Levana.
„ 2 1st „ i female Levana.
„ 2nd of May i female Levana.
Total . . 1 8 Levana, TO of which were
females.
The exact record of the time of emergence is interest-
ing, because it is thereby rendered apparent that different
individuals respond more in different degrees to a higher
than to the ordinary temperature. Whilst with many
an acceleration of development of I — 2 months occurred,
others emerged in April and May, i. e. at the time, of
their appearance in the natural state.
Appendix. 1 2 1
ii. Reared the second generation from eggs of the first
generation. Emerged from the eggs on June 6th, 1872,
pupated on July Qth. The pupae were placed on ice
(o° — 1° R.) from July nth till September nth, and
then transferred to a hothouse, where all emerged : —
On the 1 9th of September, 3 male Prorsa, I male/V
rima.
„ 2 1st „ 13 Porima (12 males, I
female) 2 female Levana.
„ 22nd „ 14 Porima (12 males, 2 fe-
males) and i female Le-
vana.
„ 23rd „ 10 female Levana, 3 male
Porima.
„ 24th „ 5 female Levana.
„ 25th „ i female Levana.
„ 27th „ 3 female Levaua.
„ 4th of October, i male Porima.
Total . . 57 butterflies (32 males and
25 females), only 3 of which were Prorsa, 32 Porima^
and 22 Levana.
It must be pointed out, however, that among those
specimens marked as " Levana " there were none which
entirely corresponded with the natural Levanay or which
indeed approximated so nearly to this form as did
some of the specimens in Exp. 9. All were larger
than the natural Levana, and possessed, notwithstanding
the large amount of yellow, more black than any true
Levana. In all artificially bred Levana the black band
of the basal half of the hind wings is always interrupted
with yellow, which is seldom the case with true Levana.
The whole appearance of the artificial Levana is also
coarser, and the contour of the wirigs somewhat different,
the fore-wings being broader and less pointed. (See figs.
7 to 9, PL I.)-
122 Appendix.
1 2. Larvae of the fourth generation, found on September
22nd, 1872, were divided into two portions : —
A. Placed for pupation in an orchid-house at 12° —
25° R., and allowed to remain there till December. In
spite of the high temperature not a single butterfly
emerged during this time, whilst pupae of Vanessa C-al-
bum and Pyrameis Atalanta, found at the same time, and
placed in the same hothouse, emerged in the middle of
October. From the middle of December the pupae were
kept in an unheated room, and they emerged very late
in the spring of 1873, all as Levana: —
On the 6th of June, 7 Levana.
„ 8th „ 2 „
„ nth „ 2 „
„ I2th „ i
„ I5th „ 6 „
1 6th „ i
_^
Total . . 21 „
B. Kept in an unheated room during the winter. The
butterflies emerged from the 28th of May, all as Levana.
EXPERIMENTS WITH
13. Females of Pieris Rapes, captured in April, laid
eggs on Sisymbrium Alliaria. From these caterpillars
were obtained, which pupated on 1st — 3rd June. The
pupae were placed on ice from June 3rd till September
IIth (o° — 1° R.), and from September nth till Oc-
tober 3rd in the hothouse (12°— 24° R.), where there
emerged : —
On the 23rd of October, i female.
„ 24th „ i female.
M 25th „ 2 males, i female.
„ 26th „ i female.
28th „ i male, I female.
Total . . 3 males, 5 females.
Appendix. 123
All these were sharply impressed with the characters
of the winter form, the females all strongly yellow on the
upper side, the males pure white ; on the under side a
strong black dusting on the hind wings, particularly on
the discoidal ceil. One pupa did not emerge in the
hothouse, but hibernated, and gave in a heated room on
January 2Oth, 1873, a female, also of the winter form.
14. Females of Pieris Napi, captured on 2/th — 28th
April, 1872, laid eggs on Sisymbrium Alliaria. The
larvae bred from these pupated on May 28th to June 7th.
The pupae, shortly after transformation, were placed on
ice, where they remained till Sept. nth (three months).
Transferred to the hothouse on October 3rd, they pro-
duced, up to October 2oth, 60 butterflies, all with the
sharply-defined characters of the winter form. The re-
maining pupae hibernated in a room, and produced : —
On the 28th of April, 3 males, 6 females.
„ 4th of May, I female.
„ 1 2th „ 4 males.
„ 1 5th „ i male, I female.
„ 1 6th „ i male.
„ 1 8th „ i male, I female.
„ 1 9th „ i female.
„ 2Oth „ 2 males, i female.
„ 23rd „ 2 males.
„ 26th „ i male.
„ 29th „ i female.
„ 3rd of June, 3 females.
„ 6th „ i female.
„ 9th „ i female.
„ 2 ist „ i female.
„ 2nd of July, I female.
Total . . 15 males, 19 females.
15. Several butterflies from Exp. 14, which emerged
in May, 1873, were placed in a capacious breeding-
124 Appendix.
house, where they copulated and laid eggs on rape.
The caterpillars fed on the living plants in the breeding-
house, and after pupation were divided into two por-
tions : —
A. Several pupae, kept at the ordinary summer tem-
perature, gave butterflies on July 2nd, having the charac-
ters of the summer form.
B. The remainder of the pupae were placed on ice im-
mediately after transformation, and remained over three
months in the refrigerator (from July 1st till October
roth). Unfortunately most of them perished through
the penetration of moisture into the box. Only 8 sur-
vived, 3 of which emerged on the 2oth of October as the
winter form ; the others hibernated in an unheated
room, and emerged at the beginning of June, 1874. All
5 were females, and all exhibited the characters of the
winter form. Notwithstanding a pupal period of eleven
months, they did not possess these characters to a greater
extent than usual, and did not, therefore, approximate
to the parent form Bryonice.
1 6. On June I2th, 1871, specimens ofPieris Napi,vzx.
JBry0nuB,wer£ captured on a mountain in the neighbour-
hood of Oberstorf (Allgauer Alpen), and placed in a
breeding-house, where they flew freely about the flowers ;
but although copulation did not take place, several
females laid eggs on the ordinary garden cabbage.
From these caterpillars were hatched, which at all stages
of growth were exactly like those of the ordinary form
of Napi. They throve well until shortly before pupation,
when a fungoid epidemic decimated them, so that from
300 caterpillars only about 40 living pupae were ob-
tained. These also completely resembled the ordinary
form of Napi, and showed the same polymorphism, some
being beautifully green, others (the majority) straw
yellow, and others yellowish grey. Only one butterfly
emerged the same summer, a male, which, by the black
Appendix.
125
dusting of the veins on the margin of the wings (upper
side), could be with certainty recognized as var. Bryonia.
The remaining pupae hibernated in a heated room, and
gave, from the end of January to the beginning of June,
10 males and 5 females, all with the characters of the
var. Bryonice. They emerged : —
22nd of January,
male.
26th
male.
3rd of February,
male.
4th
male.
5th
male.
7th „ ]
female.
9th
male.
24th
male.
4th of March,
female.
nth
male, I female.
6th of April,
female.
i;th
male.
nth of May,
female.
3rd of June,
male.
We here perceive that the tendency to accelerate
development through the action of warmth is, in this
case, also very different in different individuals. Of the
1 6 butterflies only I kept to the normal period of de-
velopment from July 2/th to June 3rd, fully ten months ;
all the others had this period abbreviated, i male to
eleven days, 8 specimens to six months, 4 to seven
months, 2 to eight months, and I to nine months.
APPENDIX II.
EXPERIMENTS WITH PAPILIO AjAX.1
FROM eggs of var. Telamonides laid on the last of May
larvae were obtained, which gave on June 2.?nd — 26th,
122 pupae. These, as fast as formed, were placed on ice
in the refrigerator in small tin boxes, and when all the
larvae had become transformed the pupae were trans-
ferred to a cylindrical tin box (4 in. diam. and 6 in.
high), and packed in layers between fine shavings. The
tin box was set in a small wooden one, which was put
directly on the ice aiid kept there till July 2Oth. From
that date, by an unfortunate accident, the box, instead
of being kept on the surface of the ice in an ice-house,
as was intended, was placed on straw near the ice, so
that the action of the cold was modified, the outside
pupae certainly experiencing its full effects, but the in-
side ones were probably at a somewhat higher tempera-
ture. The ice failed on August 2oth, so that the pupae
had been subjected to an equable low temperature in
the refrigerator for three to four weeks, and to a lesser
degree of cold in the ice-house for five weeks, the tem-
1 The experiments upon Papilio Ajax and Phydodes Tharos,
described in this Appendix, were made by Mr. W. H. Edwards
(see his " Butterflies of North America;" also the " Canadian
Entomologist," vol. vii. p. 228 — 240, and vol. ix. p. i — 10, 51
—5, and 203 — 6) ; and I have added them, together with some
hitherto unpublished results, to Dr. Weismann's Essay, in order
to complete the history of the subject of seasonal dimorphism
up to the present time. — R.M.
Appendix. 1 2 7
perature of the last place rising daily, as the ice had all
thawed by August 2Oth. On opening the box it was
found (probably owing to the cold not having been
sufficiently severe) that the butterflies had commenced
to emerge. Twenty -seven dead and crippled specimens
were removed, together with several dead pupae. One
butterfly that had just emerged was taken out and
placed in a box, and when its wings had fully expanded
it was found to be a " Telamodides of the most pro-
nounced type." The experimenter then states : —
" Early in the morning I made search for the dead and
rejected butterflies, and recovered a few. It was not
possible to examine them very closely from the wet and
decayed condition they were in, but I was able to dis-
cover the broad crimson band which lies above the
inner angle of the hind wings, and which is usually lined
on its anterior side with white, and is characteristic of
either Walshii or Telamonides, but is not found in
Marcellus. And the tip only of the tail being white in
Walshii, while both tip and sides are white in Telamo-
nides, enabled me to identify the form as between these
two. There certainly were no Walskii, but there seemed
to be a single Marcellus, and excepting that all were
Te lamonides. ' '
The remaining pupae were kept in a light room where
3 Telamonides emerged the following day, and by Sep-
tember 4th 14 specimens of the same variety had
emerged, but no Marcellus or intermediate forms. From
the 4th to the 2Oth of September a few more Telamo-
nides appeared, but between the 4th and I5th of the
month 12 out of 26 butterflies that had emerged were
intermediate between Telamonides and Marcellus, some
approximating to one form and some to the other form.
The first pure Marcellus appeared on September 4th,
and was followed by one specimen on the 6th, 8th,
1 3th and I5th respectively. From this last date to
128 Appendix.
October 3rd, 6 out of 10 were Marcellus and 3 inter-
mediate. On September 3rd, a specimen intermediate
between Telamonides and Walshii emerged, " in which
the tails were white tipped as in Walshii, but in size
and other characters it was Telamonides, though the
crimson band might have belonged to either form."
Butterflies continued to emerge daily up to September
2Oth, after which date single specimens appeared at in-
tervals of from four to six days, the last emergence
being on October i6th. Thus, from the time the box was
removed from the ice-house, the total period of emerging
was fifty-seven days, some specimens having emerged
before the removal of the box. With specimens of P.
Ajax which appear on the wing the first season the
natural pupal period is about fourteen days, individuals
rarely emerging after a period of four to six weeks.
Between August 2Oth and October i6th, the 50 fol-
lowing butterflies emerged : —
On the 2Oth of August, i male Telamonides.
„ 2 1st „ i male and 2 female Tela-
monides.
„ 22nd „ i female Telamonides.
„ 24th „ i female Telamonides.
„ 2Qth „ i male Telamonides.
„ 3 ist „ i female Telamonides.
„ ist September i female Telamonides.
„ 2nd „ i female Telamonides.
„ 3rd „ i female intermediate be-
tween Telamonides and
Walshii.
„ „ „ i male Telamonides.
„ 4th „ 4 males and I female Tela-
monides.
„ „ „ 2 males, medium, nearest
Telamonides.
Appendix. 129
On the 4th of September, 2 males, medium, nearest
Marcellus.
„ „ „ 2 males, Marcellus.
„ 5th „ i male and I female Tela-
monides.
„ „ „ i male medium, nearest
Telamonides.
„ 6th „ I male Marcellus.
„ yth „ I male Telamonides.
„ 8th „ i male Marcellus and I fe-
male Telamonides.
„ 9th „ i male Marcellus and i fe-
male medium, nearest
Marcellus.
„ -i3th „ i male medium, nearest
Marcellus.
„ „ „ i male medium, nearest
Telamonides.
„ „ „ i male Marcellus
„ 1 4th „ i male Marcellus and I fe-
male medium, nearest
Marcellus.
„ „ „ i male medium, nearest
Telamonides.
„ 1 5th „ i male Marcellus.
„ 1 6th „ i female Marcellus and i
male Telamonides.
„ 1 8th „ i male medium, nearest
Marcellus.
„ i Qth „ i female Marcellus.
„ 2Oth „ i male Telamonides.
„ 24th „ i male Marcellus.
„ 3Oth ,, i female Marcellus.
„ 2nd of October, I female Marcellus.
„ 3rd „ i female medium, nearest
Telamonides.
K
1 30 Appendix.
On the 8th of October, I female medium, nearest
Telamonides.
„ i6th „ i female medium, nearest
Telamonides.
Total.
Telamonides . . . .22 12 males, 10 females
Telamonides partly Walshii . I I female.
Medium, nearest Telamonides 8 5 males, 3 females
Medium, nearest Marcellus . 6 4 males, 2 females
Marcellus . . . .139 males, 4 females.
50 30 males, 20 females.
All these butterflies were very uniform in size, being
about that of the ordinary Telamonides. The specimens
of Telamonides especially were " strongly marked, the
crimson band in a large proportion of them being as
conspicuous as is usual in Walshii, and the blue lunules
near the tail were remarkably large and bright coloured.
OftheMarce/IuSjin addition to the somewhat reduced size,
the tails were almost invariably shorter than usual and
narrower, and instead of the characteristic single crimson
spot, nearly all had two spots, often large. In all these
particulars they approach Telamonides''
Adding to the Telamonides which emerged after
August 2Oth most of those specimens which were found
dead in the box at that date, the total number of this
form is thus brought up to nearly 50. Of the 122 pupae
with which Mr. Edwards started, 28 remained in a state
fit for hibernation, several having died without emerg-
ing. Previous experiments had shown that 28 out of 122
pupse is not an unreasonable number to hibernate, so that
the author concludes that the butterflies which emerged
the same season would have done so naturally, and
the effect of the artificial cold was not " to precipitate
the emerging of any which would have slept" till the
Appendix. 131
following spring. Now under ordinary circumstances
all the butterflies which emerged the same season would
have been of the Marcellus form, so that the cold changed
a large part of these into the form Telamonides, some
(probably from those pupae which experienced the lowest
temperature) being completely changed, and others
(from those pupae which were only imperfectly subjected
to the cold) being intermediate, i. e.> only partly changed.
It appears also that several pupae experienced sufficient
cold to retard their emergence and stunt their growth,
but not enough to change their form, these being the 13
recorded specimens of Marcellus. Had the degree of
cold been equal and constant, the reversion would pro-
bably have been more complete. The application of
cold produced great confusion in the duration of the
pupal period, the emergence, instead of taking place
fourteen days after the withdrawal of the cold, as might
have been expected from Dr. Weismann's corresponding
experiment whhPteris Napi (Appendix I. Exps. 13 and
14), having been extended over more than two months.
From the results of this experiment it must be con-
cluded that Telamonides is the primary form of the
species.
ADDITIONAL EXPERIMENTS WITH PAPILIO AJAX.
{Communicated by Mr. W. H. EDWARDS, November i%th, 1879.]
EXP. I. — In 1877 chrysalides of P. Ajax and Grapta
Interrogationis (the eggs laid by females of the form
Fabricii) were experimented upon ; but the results were not
satisfactory, for the reason that the author having been
absent from home most of the time while the pupae were
in the ice-box, on his return found the temperature above
5° — 6° R. And so far as could be told, the ice had been
put in irregularly, and there might have been intervals
during which no ice at all was in the box. Six chry-
K 2
132 Appendix.
salides of the Grapta so exposed produced unchanged
Umbrosa, the co-form with Fabricti. But all chrysalides
from the same lot of eggs, and not exposed to cold, also
produced Umbrosa. Nothing was learnt, therefore, re-
specting this species.
But chrysalides of Ajax, exposed at same time, did
give changed butterflies to some extent. From a lot of
8, placed in the box when under twelve hours from
pupation, and left for twenty-four days, there came 5
males and 3 females. Of these was I Telamonides in
markings and coloration, and all the rest were between
Marcellus and Telamonides. Two other chrysalides on
ice for twenty-three days gave Telamonides, but 3 more
exposed twenty-six days, and all one hour old when put
on ice, were unchanged, producing Marcellus.
During the same season 6 other Ajax chrysalides were
placed in the box, and kept at about o° — 1° R. One was
one hour old, and remained for five days ; I was one
hour old, and remained for two days and three-quarters ;
3 at three hours old for eight days ; and I (age omitted),
six days. All these gave unchanged butterflies of the
form Marcellus.
EXP. 2. — In May, 1878, many chrysalides were placed
in the ice-box, being from eggs laid by Ajax, var. Walshii.
The youngest were but ten to fifteen minutes from pu-
pation, and were soft ; others at intervals up to twenty-
four hours (the chrysalis is hard at about twelve hours) ;
after that, each day up to eight days after pupation.
All were removed from the box on the same day, 28th
May. The exposure was from nineteen to five days, those
chrysalides which were put on ice latest having the shortest
exposure. The author wished to determine if possible
whether, in order to effect any change, it was necessary
that cold should be applied immediately after pupation
or if one or several days might intervene between pu-
pation and refrigeration. Inasmuch as no colour begins
Appendix. 133
to show itself in the pupae till a few hours, or at most a
day or two, before the butterfly emerges, it was thought
possible that cold applied shortly before that time would
be quite as effective as if applied earlier and especially
very soon after pupation. The result was, that more than
half of the chrysalides exposed before they had hardened
died : I exposed at ten minutes, 2 at one hour, I at two
hours, 2 at three hours after pupation. On the other hand
I at fifteen minutes produced a butterfly, I at two hours,
another at twelve hours. The temperature was from
o° — 1° R. most of the time, but varied somewhat each
day as the ice melted. The normal chrysalis period is
from eleven to fourteen days, in case the butterfly
emerges the same season, but very rarely an individual
will emerge several weeks after pupation.
On the 1 4th day after taking the pupae from the ice,
i Telamonides emerged from a chrysalis which
had been placed in the ice-box three days after
pupation, and was on ice sixteen days.
On I Qth day, I Telamonides emerged from a pupa put on
the ice twelve hours after pupation, and kept
there eleven days.
On i Qth day, I Walshii emerged from a pupa two hours
old, and on ice eleven days.
All the rest emerged Marcellus, unchanged, but at
periods prolonged in a surprising way.
i on 43rd day exposed 15 minutes after pupation.
„ 46th „ 2 hours „
„ 53rd „ 24 hours
„ 62nd „ 6 days „
„ 63rd „ 4 days
„ 66th „ 7 days
„ 77th „ 4 days
„ 8 ist „ 12 hours
„ 9 ist „ 5 days
„ 96th „ 19 hours
1 34 Appendix.
Five chrysalides lived through the winter, and all gave
Telamonides in the spring of 1879.
It appeared, therefore, that the only effect produced
by cold in all chrysalides exposed more than three days
after pupation was to retard the emergence of the but-
terfly. But even in some of these earliest exposed, and
kept on the ice for full nineteen days, the only effect
seemed to be to retard the butterfly.
EXP. 3. — In June, 1879, eggs of the form Marcellus
were obtained, and in due time gave 104 chrysalides. Of
these one-third were placed in the ice-box at from twelve
to twenty-four hours after pupation, and were divided
into 3 lots.
ist, 9 pupae, kept on ice 14 days.
2nd, 12 „ „ 20 days.
3rd, II,, „ 25 days.
Temperature o° — 1° R. most of the time, but varying
somewhat as the ice melted. (Both in 1878 and 1879
Mr. Edwards watched the box himself, and endeavoured
to keep a low temperature.)
Of the 69 chrysalides not exposed to cold, 34 gave
butterflies at from eleven to fourteen days after pupation,
and I additional male emerged nth August, or twenty-
two days at least past the regular period of the species.
Of the iced chrysalides, from lot No. I emerged 4
females at eight days and a half to nine days and a half
after removal from the ice, and 5 are now alive (Nov. 18)
and will go over the winter.
From lot No. 2 emerged I male and $ females at
eight to nine days ; another male came out at forty
days ; and 5 will hibernate.
From lot No. 3 emerged 4 females at nine to twelve
days ; another male came out at fifty-four days ; and 6
were found to be dead.
In this experiment the author wished to see as exactly
as possible — First, in what points changes would occur.
Appendix. 135
Second, if there would be any change in the shape of
the wings, as well as in markings or coloration — that is,
whether the shape might remain as that of Marcellus,
while the markings might be of Telamonides or Walshii;
a summer form with winter markings. Third, to ascer-
tain more closely than had yet been done what length of
exposure was required to bring about a decided change,
and what would be the effect of prolonging this period.
After the experiments with Phyciodes Tharos, which had
resulted in a suffusion of colour, the author hoped that
some similar cases might be seen in Ajax. The
decided changes in 1878 had been produced by eleven
and sixteen days' cold. In 1877, an exposure of two
days and three-quarters to eight days had failed to
produce an effect.
From these chrysalides 1 1 perfect butterflies were ob-
tained, i male and 10 females. Some emerged crippled,
and these were rejected, as it was not possible to make
out the markings satisfactorily.
From lot No. I, fourteen days came : —
1 female between Marcellus and Telamonides.
2 females, Marcellus.
These 2 Marcellus were pale coloured, the light parts
a dirty white ; the submarginal lunules on hind wings
were only two in number and small ; at the anal angle
was one large and one small red spot ; the frontal hairs
were very short. The first, or intermediate female, was
also pale black, but the light parts were more green and
less sordid ; there were 3 large lunules ; the anal red
spot was double and connected, as in Telamonides ; the
frontal hairs short, as in Marcellus. These are the
most salient points for comparing the several forms
of Ajax. In nature, there is much difference in shape
between Marcellus and Telamonides, still more between
Marcellus and Walshii ; and the latter may be distin-
guished from the other winter forms by the white tips of
136 Appendix.
the tails. It is also smaller, and the anal spot is larger,
with a broad white edging.
From lot No. 2, twenty days, came : —
i female Marcellus, with single red spot.
I female between Marcelhis and Telamonidcs ;
general coloration pale ; the lunules all obsoles-
cent ; 2 large red anal spots not connected ;
frontal hairs medium length, as in Telamonides.
I female between Marcellus and Telamonidcs ;
colour bright and clear ; 3 lunules ; 2 large red
spots ; frontal hairs short.
1 female Telamonides ; colours black and green ; 4
lunules ; a large double and connected red spot ;
frontal hairs medium.
2 female Telamonides ; colours like last ; 3 and 4
lunules; 2 large red spots ; frontal hairs medium.
From lot No. 3, twenty-five days, came: —
, I male Telamonides; clear colours; 4 large lu-
nules ; I large, I small red spot ; frontal hairs
long.
I female Telamonides ; medium colours ; 4 lunules ;
large double connected red spot ; frontal hairs
long.
In general shape all were Marcellus, the wings pro-
duced, the tails long.
From this it appeared that those exposed twenty-five
days were fully changed ; of those exposed twenty days,
3 were fully, 2 partly, I not at all ; and of those exposed
fourteen days, I partly, 2 not at all.
The butterflies from this lot of 104 chrysalides, but
which had not been iced, were put in papers. Taking 6
males and 6 females from the papers just as they came
to hand, Mr. Edwards set them, and compared them
with the iced examples.
Of the 6 males, 4 had I red anal spot only, 2 had i large
i small ; 4 had 2 green lunules on the hind wings, 2 had
Appendix. 137
3, and in these last there was a 4th obsolescent, at outer
angle ; all had short frontal hairs.
Of the 6 females, 5 had but I red spot, I had I large I
small spot ; 5 had 2 lunules only, i had 3 ; all had short
frontal hairs.
Comparing 6 of the females from the iced chrysalides,
being those in which a change had more or less occurred,
with the 6 females not iced :
1. All the former had the colours more intense, the
black deeper, the light, green.
2. In 5 of the former the green lunules on hind
wings were decidedly larger; 3 of the 6 had 4
distinct lunules, i had 3, I had 3, and a 4th
obsolescent. Of the 6 females not iced none
had 4, 2 had 2, and a 3rd,, the lowest of the row^
obsolescent ; 3 had 3, the lowest being very
small ; one had 3, and a 4th, at outer angle^
obsolescent.
3 . In all the former the subapical spot on fore wing
and the stripe on same wing which crosses the
cell inside the common black band, were distinct
and green ; in all the latter these marks were
either obscure or obsolescent.
4. In 4of the former there was a large double connected
red spot, and in one of the 4 it was edged with
white on its upper side ; 2 had i large and i small
red spot. Of the latter 5 had I spot only, and
the 6th had I spot and a red dot.
5. The former had all the black portions of the wing
of deeper colour but less diffused, the bands being
narrower; on the other hand, the green bands were
wider as well as deeper coloured. Measuring the
width of the outermost common green band along
the middle of the upper medium interspace on
fore wing in tenths of a millimetre, it was found
to be as follows :
138 Appendix.
On the iced pupae . . . Si, 66, 76, 76, 66, 66.
On the not iced . . . 56,56,51,51,46,51.
Measuring the common black discal band across the
middle of the lower medium interspace on fore wing :
On the iced pupae . . . 51, 66, 51, 51, 56, 61.
On the not iced ... 76, 71, 66, 63, 71, 76.
In other words the natural examples were more
melanic than the others.
No difference was found in the length of the tails or
in the length and breadth of wings. In other words, the
cold had not altered the shape of the wings.
Comparing I male iced with 6 males not iced :
1. The former had a large double connected red anal
spot, edged with white scales at top. Of the 6
not iced, 3 had but I red spot, 2 had I large I
small, I had I large and a red dot.
2. The former had 4 green lunules ; of the latter 3
had 3, 3 had only 2.
3. The former had the subapical spot and stripe in
the cells clear green ; of the latter i had the same,
5 had these obscure or obsolescent.
4. The colours of the iced male were bright ; of the
others, 2 were the same, 4 had the black pale, the
light sordid white or greenish-white.
Looking over all, male and female, of both lots, the
large size of the green submarginal lunules on the fore
wings in the iced examples was found to be conspicuous
as compared with all those not iced, though this feature
is included in the general widening of the green bands
spoken of.
In all the experiments with Ajax, if any change at all
has been produced by cold, it is seen in the enlarg-
ing or doubling of the red anal spot, and in the increased
number of clear green lunules on the hind wings. Almost
always the frontal hairs are lengthened and the colour of
the wings deepened, and the extent of the black area is
Appendix. \ 39
also diminished. All these changes are in the direction
of TelamonideS) or the winter form.
That the effect of cold is not simply to precipitate the
appearance of the winter form, causing the butterfly to
emerge from the chrysalis in the summer in which it be-
gan its larval existence instead of the succeeding year, is
evident from the fact that the butterflies come forth with
the shape of Marcellus, although the markings may be of
Telamonides or Walshii. And almost always some of
the chrysalides, after having been iced, go over the
winter, and then produce Telamonides, as do the hiber-
nating pupae in their natural state. The cold appears to
have no effect on these individual chrysalides.2
With every experiment, however similar the condi-
tions seem to be, and are intended to be, there is a
difference in results ; and further experiments — perhaps
many — will be required before the cause of this is under-
stood. For example, in 1878, the first butterfly emerged
on the fourteenth day after removal from ice, the period
being exactly what it is (at its longest) in the species in
nature. Others emerged at 19 — 96 days. In 1879, the
emergence began on the ninth day, and by the twelfth day
all had come out, except three belated individuals, which
came out at twenty, forty, and fifty-four days. In the
last experiment, either the cold had not fully suspended
the changes which the insect undergoes in the chrysalis,
or its action was to hasten them after the chrysalides were
taken from the ice. In the first experiment, apparently
the changes were absolutely suspended as long as the
cold remained.
It might be expected that the application of heat
to the hibernating chrysalides would precipitate the
appearance of the summer form, or change the mark-
2 This is a striking illustration pf the diversity of individual
constitution so frequently insisted on by Dr. Weismann in the
foregoing portion of this work.
1 40 Appendix.
ings of the butterfly into the summer form, even if the
shape of the wings was not altered ; that is, to pro-
duce individuals having the winter shape but the sum-
mer markings. But this was not found to occur. Mr.
Edwards has been in the habit for several years of placing
the chrysalides in a warm room, or in the greenhouse, early
in the winter, thus causing the butterflies to emerge in
February, instead of in March and April, as otherwise
they would do. The heat in the house is 19° R. by day,
and not less than 3*5°R. by night. But the winter form
of the butterfly invariably emerged, usually Tdamonides,
occasionally Walshii.
EXPERIMENTS WITH PHYCIODES THAROS.
EXP. i. — In July, 1875, eggs of P. Tharos were obtained
on Aster Nova-Anglice in the Catskill Mountains, and
the young larvae, when hatched, taken to Coalburgh,
West Virginia. On the journey the larvae were fed on
various species of Aster, which they ate readily. By the
4th of September they had ceased feeding (after having
twice moulted), and slept. Two weeks later part of
them were again active, and fed for a day or two, when
they gathered in clusters and moulted for the third time,
then becoming lethargic, each one where it moulted with
the cast skin by its side. The larvae were then placed
in a cellar, where they remained till February ^th, when
those that were alive were transferred to the leaves of an
Aster which had been forced in a greenhouse, and
some commenced to feed the same day. In due time
they moulted twice more, making, in some cases, a total
of five moults. On May 5th the first larva pupated,
and its butterfly emerged after thirteen days. Another
emerged on the 3<Dth, after eight days pupal period,
this stage being shortened as the weather became
warmer. There emerged altogether 8 butterflies, 5 males
Appendix. 1 4 1
and 3 females, all of the form Marcia, and all of the
variety designated C, except I female, which was var.
B.3
EXP. 2. — On May i8th the first specimens (3 male
Marcia} were seen on the wing at Coalburgh ; i female
was taken on the I9th, 2 on the 23rd, and 2 on the
24th, these being all that were seen up to that date, but
shortly after both sexes became common. On the 26th,
7 females were captured and tied up in separate bags on
branches of Aster. The next day 6 out of the 7 had
laid eggs in clusters containing from 50 to 225 eggs in
each. Hundreds of caterpillars were obtained, each
brood being kept separate, and the butterflies began to
emerge on June 29th, the several stages being : — egg six
days, larva twenty-two, chrysalis five. Some of the
butterflies did not emerge till the 1 5th of July. Just
after this date one brood was taken to the Catskills,
where they pupated, and in this state were sent back to
Coalburgh. There was no difference in the length of
the different stages of this brood and the others which
had been left at Coalburgh, and none of either lot be-
came lethargic. The butterflies from these eggs of May
were all Tharos, with the exception of I female Marcia,
var. C. Thus the first generation of Marcia from the
hibernating larvae furnishes a second generation of
Tharos.
EXP. 3. — On July 1 6th, at Coalburgh, eggs were ob-
tained from several females, all Tharos, as no other form
was flying. In four days the eggs hatched ; the larval
stage was twenty-two, and the pupal stage seven days ;
but, as before, many larvae lingered. The first butterfly
emerged on August i8th. All were Tharos, and none
3 The reader who wishes to acquire a detailed knowledge of
the different varieties of this butterfly, of which a very large
number are known, must consult the plates and descriptions
in Edwards' "Butterflies of North America," vol. ii..
142 Appendix.
of the larvae had been lethargic. This was the third
generation from the second laying of eggs.
EXP. 4. — On August 1 5th, at Coalburgh, eggs were
obtained from a female Tharos, and then taken directly
to the Catskill Mountains, where they hatched on the
2Oth. This was the fourth generation from the third
laying of eggs. In Virginia, and during the journey, the
weather had been exceedingly warm, but on reaching the
mountains it was cool, and at night decidedly cold. Sep-
tember was wet and cold, and the larvae were protected
in a warm room at night and much of the time by day,
as they will not feed when the temperature is less than
about 8° R. The first pupa was formed September
1 5th, twenty-six days from the hatching of the larvae,
and others at different dates up to September 26th, or
thirty-seven days from the egg. Fifty-two larvae out of
127 became lethargic after the second moult on Sep-
tember i6th, and on September 26th fully one half of
these lethargic larvae commenced to feed again, and
moulted for the third time, after which they became
again lethargic and remained in this state. The pupae
from this batch were divided into three portions : —
A. This lot was brought back to Coalburgh on Octo-
ber 1 5th, the weather during the journey having been
cold with several frosty nights, so that for a period of
thirty days the pupae had at no time been exposed to
warmth. The butterflies began to emerge on the day
of arrival, and before the end of a week all that were
living had come forth, viz., 9 males and 10 females. "Of
these 9 males 4 were changed to Marcia var. C, 3 were
var. D, and 2 were not changed at all. Of the 10 fe-
males 7 were changed, 5 of them to var. B, 3 to var. C.
The other 2 females were not different from many
T/iaros of the summer brood, having large discal patches
on under side of hind wing, besides the markings com-
mon to the summer brood."
Appendix. 143
B. This lot, consisting of 10 pupae, was sent from
the Catskills to Albany, New York, where they were
kept in a cool place. Between October 2ist and
Nov. 2nd, 6 butterflies emerged, all females, and all
of the var. B. Of the remaining pupae I died, and 3
were alive on December 2/th. According to Mr.
Edwards this species never hibernates in the pupal
state in nature. The butterflies of this lot were
more completely changed than were those from the
pupae of lot A.
C. On September 2Oth 18 of the pupae were placed
in a tin box directly on the surface of the ice, the tem-
perature of the house being 3° — 4° R. Some were
placed in the box within three hours after transforma-
tion and before they had hardened ; others within six
hours, and others within nine hours. They were all
allowed to remain on the ice for seven days, that being
the longest summer period of the chrysalis. On being
removed they all appeared dead, being still soft, and
when they had become hard they had a shrivelled sur-
face. On being brought to Coalburgh they showed no
signs of life till October 2ist, when the weather became
hot (24° — 25° R.), and in two days 15 butterflies emerged,
" every one Marcia, not a doubtful form among them in
either sex." Of these butterflies 10 were males and 5
females ; of the former 5 were var. C, 4 var. D, and I
var. B, and of the latter I was var. C, and 4 var. D.
The other 3 pupae died. All the butterflies of this brood
were diminutive, starved by the cold, but those from the
ice were sensibly smaller than the others. All the ex-
amples of var. B were more intense in the colouring
of the under surface than any ever seen by Mr.
Edwards in nature, and the single male was as deeply
coloured as the females, this also never occurring in
nature.
Mr. Edwards next proceeds to compare the behaviour
1 44 Appendix.
of the Coalburgh broods with those of the same species
in the Catskills : —
EXP. 5.— On arriving at the Catskills, on June iSth,
a few male Marcia, var. D, were seen flying, but no
females. This was exactly one month later than the
first males had been seen at Coalburgh. The first fe-
male was taken on June 26th, another on June 2/th, and
a third on the 28th, all Marcia, var. C. Thus the first
female was thirty-eight days later than the first at Coal-
burgh. No more females were seen, and no T/taros.
The three specimens captured were placed on Aster,
where two immediately deposited eggs 4 which were for-
warded to Coalburgh, where they hatched on July 3rd.
The first chrysalis was formed on the 2Oth, its butterfly
emerging on the 29th, so. that the periods were: egg
six, larva seventeen, pupa nine days. Five per cent, of
the larvae became lethargic after the second moult.
This was, therefore, the second generation of the butter-
fly from the first laying of eggs. All the butterflies
which emerged were Tharos, the dark portions of the
wings being intensely black as compared with the Coal-
burgh examples, and other differences of colour existed,
but the general peculiarities of the Tharos form were
retained. This second generation was just one month
behind the second at Coalburgh, and since, in 1875,
eggs were obtained by Mr. Mead on July 2/th and
following days, the larvae from which all hibernated,
this would be the second laying of eggs, and the
resulting butterflies the first generation of the follow-
ing season.
Thus in the Catskills the species is digoneutic, the
first generation being Marcia (the winter form), and the
second the summer form. A certain proportion of the
4 Mr. Edwards has shown also that Argynnis Myrina can
lay fertile eggs when but a few hours out of the chrysalis.
Canad. Ent, September, 1876, vol. viii. No. 9.
Appendix. 145
larvae from the first generation hibernate, and appa-
rently all those from the second.
Discussion of Results. —There are four generations of
this butterfly at Coalburgh, the first being Marcia and
the second and third Tharos. None of the larvae from
these were found to hibernate. The fourth generation
under the exceptional conditions above recorded (Exp.
4) produced some Tharos and more Marcia the same
season, a large proportion of the larvae also hibernating.
Had the larvae of this brood been kept at Coalburgh,
where the temperature remained high for several weeks
after they had left the egg, the resulting butterflies
would have been all Tharos^ and the larvae from their
eggs would have hibernated.
The altitude of the Catskills, where Mr. Edwards was,
is from 1650 to 2000 feet above high water, and the al-
titude of Coalburgh is 600 feet. The transference of the
larvae from the Catskills to Virginia (about 48° lat.) and
vice-versa^ besides the difference of altitude, had no per-
ceptible influence on the butterflies of the several broods
except the last one, in which the climatic change exerted
a direct influence on part of them both as to form and
size. The stages of the June Catskill brood may have
been accelerated to a small extent by transference to
Virginia, but the butterflies reserved their peculiarities
of colour. (See Exp. 5.) So also was the habit of
lethargy retained.5 The May brood, on the other hand,
5 Mr. Edwards remarks that the habit of becoming lethargic
is of great service to a digoneutic species in a mountain region
where it is exposed to sharp changes of temperature. " If the
fate of the species depended on the last larval brood of the
year, and especially if the larvae must reach a certain stage
of growth before they were fitted to enter upon their hiberna-
tion, it might well happen that now and then an early frost or
a tempestuous season would destroy all the larvae of the
district."
1 46 Appendix.
taken from Virginia to the Catskills, suffered no retarda-
tion of development. (See Exp. 2.) It might have
been expected that all the larvae of this last brood taken
to the mountains would have become lethargic, but the
majority resisted this change of habit. From all these
facts it may be concluded " that it takes time to natura-
lize a stranger, and that habits and tendencies, even in a
butterfly, are not to be changed suddenly." 6
It has been shown that Tharos is digoneutic in the
Catskills and polygoneutic in West Virginia, so that at
a great altitude, or in a high latitude, we might expect
to find the species monogoneutic and probably restricted
to the winter form Marcia. These conditions are ful-
filled in the Island of Anticosti, and on the opposite
coast of Labrador (about lat. 50°), the summer tempera-
ture of these districts being about the same. Mr. Ed-
wards states, on the authority of Mr. Cooper, who col-
lected in the Island, that Tharos is a rare species there,
but has a wide distribution. No specimens were seen
later than July 29, after which date the weather became
cold, and very few butterflies of any sort were to be seen.
It seems probable that none of the butterflies of Anti-
costi or Labrador produce a second brood. All the
specimens examined from these districts were of the
winter form.
In explanation of the present case Dr. Weismann
wrote to Mr. Edwards : — " Marcia is the old primary
form of the species, in the glacial period the only one.
Tharos is the secondary form, having arisen in the
course of many generations through the gradually work-
ing influence of summer heat. In your experiments
cold has caused the summer generation to revert to the
primary form. The reversion which occurred was com-
plete in the females, but not in all the males. This
6 Compare this with Weismann's remarks, pp. 19 — 22, and 53.
Appendix, 1 4 7
proves, as it appears to me, that the males are changed
or affected more strongly by the heat of summer than
the females. The secondary form has a stronger con-
stitution in the males than in the females. As I read
your letter, it at once occurred to me whether in the
spring there would not appear some males which were
not pure Marcia, but were of the summer form, or nearly
resembling it ; and when I reached the conclusion of
the letter I found that you especially mentioned that
this was so ! And I was reminded that the same thing
is observable in A. Levana, though in a less striking de-
gree. If we treated the summer brood of Levana with
ice, many more females than males would revert to the
winter form. This sex is more conservative than the
male — slower to change."
The extreme variability of P. Tharos was alluded to
more than a century ago by Drury, who stated : — " In
short, Nature forms such a variety of this species that it
is difficult to set bounds, or to know all that belongs to
it." Of the different named varieties, according to Mr.
Edwards, " A appears to be an offset of B, in the direc-
tion most remote from the summer form, just as in
Papilio Ajax, the var. Walshii is on the further side of
Telamonides, remote from the summer form Marcellus"
Var. C leads from B through D directly to the summer
form, whilst A is more unlike this last variety than are
several distinct species of the genus, and would not be
suspected to possess any close relationship were it not
for the intermediate forms. The var. B is regarded as
nearest to the primitive type for the following reasons : —
In the first place it is the commonest form, predomi-
nating over all the other varieties in W. Virginia, and
moreover appears constantly in the butterflies from
pupae submitted to refrigeration. Its distinctive pecu-
liarity of colour occurs in the allied species P. Phaon
(Gulf States) and P. Vesta (Texas), both of which are
L 2
1 48 Appendix.
seasonally dimorphic, and both apparently restricted in
their winter broods to the form corresponding to B of
TJiaros. In their summer generation both these species
closely resemble the summer form of Tharos, and it is
remarkable that these two species, which are the only
ones (with the exception of the doubtful Batesii) closely
allied to Tharos, should alone be seasonally dimorphic
out of the large number of species in the genus.
Mr. Edwards thus explains the case under considera-
tion : — "When Phaon, Vesta, and Tharos were as yet
only varieties of one species, the sole coloration was that
now common to the three. As they gradually became
permanent, or in other words, as these varieties became
species, Tharos was giving rise to several sub-varieties,
some of them in time to become distinct and well
marked, while the other two, Pkaon and Vesta, remained
constant. As the climate moderated and the summer
became longer, each species came to have a summer
generation ; and in these the resemblance of blood-
relationship is still manifest. As the winter generations
of each species had been much alike, so the summer
generations which sprung from them were much alike.
And if we consider the metropolis of the species Tharos,
or perhaps of its parent species, at the time when it had
but one annual generation, to have been somewhere be-
tween 37° and 40° on the Atlantic slope, and within
which limits all the varieties and sub-varieties of both
winter and summer forms of Tharos are now found' in
amazing luxuriance, we can see how it is possible, as the
glacial cold receded, that only part of the varieties of
the winter form might spread to the northward, and but
one of them at last reach the sub-boreal regions and
hold possession to this day as the sole representative of
the species. And at a very early period the primary
form, together with Phaon and Vesta, had made its way
southward, where all three are found "now."
Appendix. 1 49
EXPERIMENTS WITH .GRAPTA INTERROGATION^/
{Communicated by Mr. W. H EDWARDS, November i$th, 1879.]
The experiments with this species were made in June,
1879, on pupse from eggs laid by the summer form
Umbrosa of the second brood of the year, and obtained
by confining a female in a bag on a stem of hop. As
the pupae formed, and at intervals of from six to twenty-
four hours after pupation (by which time all the older
ones had fully hardened), they were placed in the ice-
box. In making this experiment Mr. Edwards had
three objects in view. ist. To see whether it was essen-
tial that the exposure should take place immediately
after pupation, in order to effect any change. 2ndly.
To see how short a period would suffice to bring about
any change. 3rdly. Whether exposing the summer
pupse would bring about a change in the form of the
resulting butterfly. Inasmuch as breeding from the egg
of Umbrosa, in June, in a former year,7 gave both Um-
brosa (n) and Fabricii (6), the butterflies from the eggs
obtained, if left to nature, might be expected to be of
both forms. The last or fourth brood of the year having
been found up to the present time to be Fabricii, and the
ist brood of the spring, raised from eggs of Fabricii (laid
in confinement), having been found to be wholly Um-
brosa, the latter is probably the summer and Fabricii the
winter form. The two intervening broods, i. e. the 2nd
and 3rd, have yielded both forms. This species hiber-
nates in the imago state.
After the pupse had been in the ice-box fourteen days
they were all removed but 5, which were left in six days
longer. Several were dead at the end of fourteen days.
The temperature most of the time was i° — 29 R. ; but for
7 See Canad. Ent, vol. ix. p. 69.
1 50 Appendix.
a few hours each day rose as the ice melted, and was
found to be 3°— 6° R.
From the fourteen-day lot 7 butterflies were obtained,
3 males and 4 females. From the twenty-day lot 4
males and I female ; every one Umbrosa. All had
changed in one striking particular. In the normal Urn-
brosa of both sexes,8 the fore wings have on the upper
side on the costal margin next inside the hind marginal
border, and separated from it by a considerable fulvous
space, a dark patch which ends a little below the dis-
coidal nervule ; inside the same border at the inner
angle is another dark patch lying on the submedian
interspace. Between these two patches, across all the
median interspaces, the ground colour is fulvous, very
slightly clouded with dark.
In all the 4 females exposed to cold for fourteen
days a broad black band appeared crossing the whole
wing, continuous, of uniform shade, covering the two
patches, and almost confluent from end to end with the
marginal border, only a streak of obscure fulvous any-
where separating the two. In the case of the females
from pupae exposed for twenty days, the band was
present, but while broad, and covering the space be-
tween the patches, it was not so dark as in the other
females, and included against the border a series of
obscure fulvous lunules. This is just like many normal
females, and this butterfly was essentially unchanged.
In all the males the patches were diffuse, that at the
apex almost coalescing with the border. In the 3
from chrysalides exposed fourteen days these patches
were connected by a narrow dark band (very different
from the broad band of the females), occupying the same
position as the clouding of the normal male, but
blackened and somewhat diffused. In the 4 examples
8 Figures of the different forms of this species are given in
vol. i. of Edward's ''Butterflies of North America."
Appendix. 1 5 1
from the twenty-day pupae, this connecting band was
scarcely as deeply coloured and continuous as in the
other 3. Beyond this change on the submarginal area,
whereby a band is created where naturally would be
only the two patches, and a slight clouding of the inter-
vening fulvous surfaces, there was no difference of the
upper surface apparent between these examples of both
sexes, and a long series of natural ones placed beside
them.
On the under side all the males were of one type, the
colours being very intense. There was considerably
more red, both dark and pale, over the whole surface,
than in a series of natural examples in which shades of
brown and a bluish hue predominate. No charge was
observed in the females on the under side.
It appears that fourteen days were as effective in pro-
ducing changes as a longer period. In fact, the most
decided changes were found in the females exposed the
shorter period. It also appears that with this species
cold will produce change if applied after the chrysalis
has hardened. The same experiments were attempted
in 1878 with pupae of Grapta Comma. They were put
on ice at from ten minutes to six hours after forming,
and subjected to a temperature of about o° — 1° R. for
eighteen to twenty days, but every pupa was killed.
Chrysalides of Papilio Ajax in the same box, and
partly exposed very soon after pupation, were not
injured. It was for this reason that none of the
Interrogationis pupae were placed in the box till six
hours had passed.
It appears further that cold may change the markings
on one part of the wing only, and in cases where it does
change dark or dusky markings melanises them;or it
may deepen the colours of the under surface (as in the
females of the present experiment). The females in
the above experiment were apparently most susceptible
152 Appendix.
to the cold, the most decided changes having been
effected in them.
The resulting butterflies were all of one form, although
both might have been expected to appear under natural
circumstances.
Dr. Weismann's remarks on the foregoing experiments.
— The author of the present work has, at my request,
been good enough to furnish the following remarks upon
Mr. Edward's experiments with G. Interrogations : —
The interesting experiments of Mr. Edwards are here
principally introduced because they show how many
weighty questions in connexion with seasonal dimorphism
still remain to be solved. The present experiments do
not offer a direct but, at most, only an indirect proof of the
truth of my theory, since they show that the explanation
opposed to mine is also in this case inadmissible. Thus
we have here, as with Papilio Ajax, two out of the four
annual generations mixed, i.e., consisting of summer and
winter forms, and the conclusion is inevitable that these
forms were not produced by the gradual action of heat
or cold. When, from pupae of the same generation
which are developed under precisely the same external
conditions, both forms of the butterfly are produced, the
cause of their diversity cannot lie in these conditions.
It must rather depend on causes innate in the organism
itself, i.e., on inherited duplicating tendencies which
meet in the same generation, and to a certain extent
contend with each other for precedence. The two forms
must have had their origin in earlier generations, and
there is nothing against the view that they have arisen
through the gradual augmentation of the influences of
temperature.
In another sense, however, one might perceive, in the
facts discovered by Edwards, an objection to my theory.
By the action of cold the form Umbrosa, which flies in
June, was produced. Now we should be inclined to
Appendix. 153
regard the var. Umbrosa as the summer form, and the
var. Fabricii, which emerges in the autumn, hibernates in
the imago state, and lays eggs in the spring, as the
winter form. It would then be incomprehensible why
the var. Umbrosa (i. e.y the summer form) should be pro-
duced by cold.
But it is quite as possible that the var. Umbrosa as
that the var. Fabricii is the winter form. We must not
forget that, in this species, not one of the four annual
generations is exposed to the cold of winter in the pupal
state. When, therefore, we have in such cases seasonal
dimorphism, to which complete certainty can only be
given by continued observations of this butterfly, which
does not occur very commonly in Virginia, this must
depend on the fact that the species formerly hibernated
in the pupal stage. This question now arises, which of
the existing generations was formerly the hibernating
one — the first or the last ?
Either may have done so d priori, according as the
summer was formerly shorter or longer than now for
this species. If the former were the case, the var. Fa-
bricii is the older winter form ; were the latter the case,
the var. Umbrosa is the original winter form, as shall
now be more closely established.
Should the experiments which Mr. Edwards has per-
formed in the course of his interesting investigations be
repeated in future with always the same results, I should
be inclined to explain the case as follows : —
It is not the var. Fabricii, but Umbrosa, which is the
winter generation. By the northward migration of the
species and the relative shortening of the summer, this
winter generation would be pushed forward into the
summer, and would thereby lose only a portion of the
winter characters which it had till that time possessed.
The last of the four generations which occurs in Virginia
is extremely rare, so that it must be regarded either as
1 54 Appendix.
one of the generations now supposed to be originating,
or as one now supposed to be disappearing. The
latter may be admitted. Somewhat further north this
generation would be entirely suppressed, and the third
brood would hibernate, either in the imago state or as
pupse or caterpillars. In Virginia this third generation
consists of both forms. We may expect that further
north, at least, where it hibernates as pupae, it will con-
sist entirely, or almost entirely, of the var. Umbrosa. Still
further north in the Catskill Mountains, as Edwards
states from his own observations, the species has only two
generations, and one might expect that the var. Um-
brosa would there occur as the winter generation.
Should the foregoing be correct, then the fact that the
second generation assumes the Umbrosa form by the
action of cold, as was the case in Edward's experiments,
becomes explicable. The new marking peculiar to this
form produced by this means must be regarded as a com-
plete reversion to the true winter form, the characters
of which are becoming partly lost as this generation is
no longer exposed to the influence of winter, but has
become advanced to the beginning of summer.
The foregoing explanation is, of course, purely hypothe-
tical; it cannot at present be asserted that it is the correct
one. Many investigations based on a sufficiently large
number of facts are still necessary to be able to attempt
to explain this complicated case with any certainty.
Neither should I have ventured to offer any opinion on
the present case, did I not believe that even such a pre-
mature and entirely uncertain explanation may always
be of use in serving the inventive principle, i. ^., in
pointing out the way in which the truth must be
sought.
As far as I know, no attempt has yet been made to
prove from a general point of view the interpolation of
new generations, or the omission of single generations
Appendix. 155
from the annual cycle, with respect to causes and effects.
An investigation of this kind would be of the greatest
importance, not only for seasonal dimorphism, but also
for the elucidation of questions of a much more general
nature, and would be a most satisfactory problem for the
scientific entomologist. I may here be permitted to
develope in a purely theoretical manner the principles in
accordance with which such an investigation should be
made : —
On the change in the number of generations of the annual
cycle. — A change in the number of generations which a
species produces annually must be sought chiefly in
changes of climate, and therefore in a lengthening or
shortening of the period of warmth, or in an increase or
diminution of warmth within this period ; or, finally, in
both changes conjointly. The last case would be of the
most frequent occurrence, since a lengthening of the
period of warmth is, as a rule, correlated with an eleva-
tion of the mean temperature of this period, and vice
versa. Of other complications I can here perceive the
following :—
Climatic changes may be active or passive, i. e.y they
occur by a change of climate or by a migration and ex-
tension of the species over new districts having another
climate.
By a lengthening of the summer, as I shall designate
the shorter portion of the whole annual period of warmth,
the last generation of the year would be advanced fur-
ther in its development than before ; if, for instance, it
formerly hibernated in the pupal state, it would now
pass the winter in the imago stage. Should a further
lengthening of the summer occur, the butterflies might
emerge soon enough to lay eggs in the autumn, and by
a still greater lengthening the eggs also might hatch, the
larvae grow up and hibernate as pupae. In this manner
we should have a new generation interpolated, owing to
156 Appendix.
the generation which formerly hibernated being made
to recede step by step towards the autumn and the
summer. By a lengthening of the summer there occurs
therefore a retrogressive interruption of generations.
The exact opposite occurs if the summer should become
shortened. In this case the last generation would no
longer be so far developed as formerly ; for instance, it
might not reach the pupal stage, as formerly, at the be-
ginning of winter, and would thus hibernate in a younger
stage, either as egg or larvae. Finally, by a continual
shortening of the summer it would no longer appear at
the end of this period but in the following spring ; in
other words, it would be eliminated. By a shortening of
the summer accordingly the interruption of generations
occurs by advancement.
The following considerations, which submit themselves
with reference, to seasonal dimorphism, are readily con-
ceivable, at least, in so far as they can be arrived at by
purely theoretical methods. Were the summer to be-
come shorter the generation which formerly hibernated
in the pupal stage would be advanced further into the
spring. It would not thereby necessarily immediately
lose the winter characters which it formerly possessed.
Whether this would happen, and to what extent, would
rather depend upon the intensity of the action of the
summer climate on the generation in question, and on
the number of generations which have been submitted
to this action. Hitherto no attempts have been made
to expose a monomorphic species to an elevated tem-
perature throughout several generations, so as to obtain
an approximate measure of the rapidity with which
such climatic influences can bring about changes. For
this reason we must for the present refrain from all
hypothesis relating to this subject.
The disturbance of generations by the shortening of
summer might also occur to a species in such a manner
Appendix. 157
that the generation which formerly hibernated advances
into the spring, the last of the summer generations at
the same time reaching the beginning of winter. The
latter would then hibernate in the pupal state, and would
sooner or later also assume the winter form through the
action of the cold of winter. We should, in this case,
have two generations possessing more or less completely
the winter form, the ancient winter generation now
gradually losing the winter characters, and the new win-
ter generation gradually acquiring these characters.
In the reverse case, i. e.^ by a lengthening of the sum-
mer, we should have the same possibilities only with the
difference that the disturbance of generations would
occur in a reverse direction. In this case it might
happen that the former winter generation would
become the autumnal brood, and more or less preserve
its characters for a long period. Here also a new
winter generation would be produced as soon as the
former spring brood had so far retrograded that its
pupae hibernated.
I am only too conscious how entirely theoretical are
these conjectures. It is very possible that observation
of nature will render numerous corrections necessary.
For instance, I have assumed that every species is able,
when necessary, to adapt any one of its developmental
stages to hibernation. Whether this is actually the case
must be learnt from further researches ; at present we
only know that many species hibernate in the egg stage,
others in the larval state, others as pupae, and yet others
in the perfect state. We know also that many species
hibernate in several stages at the same time, but we do
not know whether each stage of every species has an
equal power of accommodation to cold. Should this not
be the case the above conjectures would have to be con-
siderably modified. To take up this subject, so as to
completely master all the facts connected therewith,
I.S8
Appendix.
naturalists would have to devote their whole time and
energy to the order Lepidoptera, which I have been
unable to do.
From the considerations offered, it thus appears that
the phenomena of seasonal dimorphism may depend on
extremely complex processes, so that one need not be
surprised if only a few cases now admit of certain
analysis. We must also admit, however, that it is more
advantageous to science to be able in the first place to
analyze the simplest cases by means of breeding experi-
ments, than to concern oneself in guessing at cases
which are so complicated as to make it impossible at
present to procure all the materials necessary for their
solution.
Plate. I.
Weismann
pinx.
Lith, J.A.Hofmanrx,Wurzburg.
Plate E
Aii£>.Weisman.n pinx.
Lith . J.A. Hofmann ,Wiirzbur s=>.
EXPLANATION OF THE PLATES.
PLATE I.
Fig. i. Male Araschnia Levana, winter form.
Fig. 2. Female A. Levana, winter form.
Fig. 3. Male A. Levana, artificially bred intermediate
form (so-called Porima).
Fig. 4. Female A. Levanay intermediate form (Porima) ,
artificially bred from the summer generation, agreeing
perfectly in marking with the winter form, and only to
be distinguished from it by the somewhat darker ground
colour.
Fig. 5. Male A. Levana, summer form (Prorsa).
Fig. 6. Female A. Levana, summer form (Prorsa}.
Figs. 7 to 9. Intermediate forms (Porima}, artificially
bred from the first summer generation.
Figs. 10 and 1 1. Male and female Pieris Napi, winter
form, artificially bred from the summer generation ; the
yellow ground colour of the underside of the hind wings
brighter than in the natural winter form.
Figs. 12 and 13. Male and female Pieris Napi, sum-
mer form.
Figs. 14 and 15. Pieris Napi, var. Bryonice, male and
female reared from eggs.
PLATE IJ.
Fig. 1 6. Papilio Ajax, var. Telamonides, winter form.
Fig. 17. P. Ajax, van Marcellus> summer form.
1 60 Explanation of the Plates.
Fig. 1 8. Plebeius Agestis (Alexis, Scop.), German winter
form.
Fig. 19. P. Agestis (Alexis, Scop.), German summer
form.
Fig. 20. P. Agestis (Alexis, Scop.), Italian summer
form. (The chief difference between figs. 19 and 20 lies
on the under-side, which could not be here represented.)
Fig. 21. Polyommatus Phlaas, winter form, from
Sardinia ; the German winter and summer generations
are perfectly similar.
Fig. 22. P. Phlceas, summer form, from Genoa.
Fig. 23. Pararga ^Egeria, from Freiburg, Baden.
Fig. 24. P. Meione, southern climatic form of
from Sardinia.
END OF PART I.
STUDIES IN THE THEORY OF DESCENT,
H.
ON THE FINAL CAUSES OF
TRANSFORMATION.
I.
THE ORIGIN OF THE MARKINGS OF CATERPILLARS.
INTRODUCTION.
THE general idea which has instigated the re-
searches described in the present essay has
already been expressed in the Preface, where it
has also been explained why the markings of
caterpillars, and especially those of the Sphinx-
larvae, were chosen for testing this idea.
The task presented itself in the following
form : — In order to test the idea referred to, it
must be investigated whether all the forms of
marking which occur in the Sphinx-larvae can or
cannot be traced to known transforming factors.
That natural selection produces a large num-
ber of characters can be as little doubted as that
& M
1 62 Studies in the Theory of Descent.
many varying external influences can bring about
changes in an organism by direct action. That
these two transforming factors, together with
their correlatively induced changes, are competent
to produce all characters, howsoever insignificant,
has indeed been truly asserted, but has never yet
been proved. The solution of the problem, how-
ever, appeared to me to depend particularly on this
point. We are now no longer concerned in prov-
ing that a changing environment reacts upon the
organism — this has already been shown — but we
have to deal with the question whether every
change is the result of the action of the environ-
ment upon the organism. Were it possible to
trace all the forms of markings which occur, to
one of the known factors of species transforma-
tion, it could be thus shown that here at least an
" innate power of development " was of no effect ;
were this not possible, i. e. did there remain
residual markings which could not be explained,
then the notion of an " innate principle of de-
velopment •" could not be at once entirely discoun-
tenanced.
The attempt to solve this problem should com-
mence by the acquisition of a morphological
groundwork, so that the phyletic development of
the markings might by this means be represented
as far as possible. It cannot be stated with cer-
tainty, primd facie, whether some form of de-
velopment conformable to law is here to be found,
The Origin of the Markings of Caterpillars. 163
but it soon becomes manifest that such is certainly
the case in a great measure. In all species the
young caterpillars are differently marked to the
adults, and in many the markings change with
each of the five stages of growth indicated by the
four ecdyses, this gradational transformation of
the markings being a " development " in the true
sense of the word, i. e., an origination of the com-
plex from the simple, the development of characters
from those previously in existence, and never an
inconstant, unconnected series of per saltum
changes. This development of the markings in
individuals very well reveals their phyletic de-
velopment, since there can be no doubt but that
we have here preserved to us in the ontogeny, as
I shall establish more fully further on, a very
slightly altered picture of the phyletic develop-
ment. The latter can have been but slightly
" falsified " in these cases, although it is indeed
considerably abbreviated, and that in very different
degrees ; to the greatest extent in those species
which are most advanced in their phyletic de-
velopment, and to the least extent in those which
are less advanced. From this the value of being
able to compare a large number of species with
respect to their ontogeny will appear. Unfortu-
nately, however, this has only been possible to a
very limited extent. \
The youngest larval stages are those which
are of the most importance for revealing the
M 2
164 Studies in the Theory of Descent.
phyletic development, because they make us ac-
quainted with the markings of the progenitors of
the existing species. For these investigations it
is therefore in the first place necessary to obtain
fertile eggs. Female Sphingidce, however, do not
generally lay eggs in confinement,1 or at most
only a very small number. In the case of many
species (Deilephila Galii, D. Lineata^ D. Vesper-
tiliO) D. Hippophaes) I have for this reason un-
fortunately been unable to observe the entire
development, and such observations would in all
probability have given especially valuable infor-
mation.
I was certainly successful in finding the young
larvae of some of the above as well as of other
species on their food-plants, but even in the most
favourable instances only individuals of the second
stage and generally older. When, however, not-
withstanding this imperfection of the materials,
and in spite of the important gaps thus inevitably
caused in these series of observations, it has
nevertheless been possible to form a picture, on
the whole tolerably complete, of the phyletic de-
velopment of the Sphinx-markings, this well indi-
1 Only the species of Smerinthus can be made to lay eggs
regularly in confinement ; Macroglossa Stellatarum laid a num-
ber in a large gauze-covered breeding-cage; the species of
Deilephila could not be induced to lay more than single ones
in such a cage. From species of Charocampa also I never
obtained but a few eggs, and from Sphinx and Acherontia never
more than single ones.
The Origin of the Markings of Caterpillars. 165
cates what a fertile field is offered by the investi-
gation of this subject, and will, I trust, furnish
an inducement to others, not only to fill up the
various gaps in the small family of the Sphin-
gidcz, but also to treat other Lepidopterous
families in a similar manner. Such an investiga-
tion of the Papilionidcz appears to me to be
especially desirable ; not only of the few European
but also of the American and Indian species. We
know practically nothing, of the youngest stages
of the Papilio larvae from this point of view. No
entomological work gives any description of the
form and marking of the newly hatched larvae,
even in the case of our commonest species (Papilio
Machaon and P. Podalirius)^ and I believe that
I do not go too far when I assert that up to the
present time nobody has observed them at this
early stage.2 When, however, we consider that
2 [Eng. ed. Since the appearance of the German edition of
this work, numerous descriptions of the young stages of cater-
pillars have been given, but in all cases without representing
the relationship of th'e forms.] [In the excellent figures of
larvae at various stages of growth, given in some of the more
recent works on Lepidoptera, there will be found much material
which may be regarded as a contribution to the field of research
entered on by the author in the present essay, /. e. the ontogeny
and comparative morphology of larval markings, although it is
much to be regretted that the figures and descriptions have not
been given from this point of view. In his " Butterflies of
North America," for example, Wi H. Edwards figures the
young as well as the adult larvae of species of Apatura, Argy ri-
ms, Libythea, Phydodes, Limenitis, Colias, Papilio >, &c.
1 66 Studies in the Theory of Descent.
in these young caterpillars we have preserved to
us the parent-form, extinct for centuries, of the
Burmeister, in his recently published " Le'pidopteres de la
Republique Argentine," figures the young stages of species of
Catigo, Opsiphanes, Callidryas, Philampelus, &c. Messrs.
Hellins and Buckler have figured and described the early stages
of large numbers of the caterpillars of British Lepidoptera, but
their figures remain unpublished. The larvae of many of our
native species belonging to the genera Liparis, Tceniocampa,
Epunda, Cymatophora, Calocampa, &c., are dull when young,
but become brightly coloured at the last moult. Such changes
of colour are probably associated with some change, either in
the habits or in the environment ; and a careful study of the
ontogenetic development of such species in connection with
their life-history would furnish results of great value to the
present inquiry. The same remarks apply to those Noctucz
larvae which are brightly coloured in their young stages, and
become dull when adult.
Among other papers which may be considered as contribu-
tions to the present subject, I may mention the following : — •
In 1864 Capt. Hutton published a paper, '''On the Reversion
and Restoration of the Silkworm, Part II. " (Trans. Ent. Soc.
1864, p. 295), in which he describes the various stages of
development of several species of Bombycida. In 1867
G. Semper published accounts of the early stages of several
Sphinx-larvae (" Beitrage zur Entwicklungsgeschichte einiger
ostasiatischer Schmetterlinge," Verhandl. k.k. Zoolog.-botan.
Gesell. in Wien, vol. xvii.). The question as to the number
of claspers in young Noctucz larvae has been raised in notes
by Dr. F. Buchanan White (" Ent. Mo. Mag.," vol. v. p. 204) and
B. Lockyer (" Entomologist," 1871, p. 438). A valuable paper,
" On the Embryonic Larvae of Butterflies," was published in
1871 by S. H. Scudder (" Ent. Mo. Mag.," vol. viii. p. 122). For
remarks on the development of the larva of Papilio Metope,
see J. P. Mansel Weale in Trans. Ent. -Soc., 1874, p. 131, and
PI. I. ; also this author on the young sta,ges of the larva
of Gynanisa fsis, Trans. Ent. Soc., 1878, p. 184. For an
Origin of the Markings of Caterpillars. 167
existing species of Papilio, it must assuredly be
of the greatest interest to become accurately ac-
quainted with them, to compare them with the
earliest stages of allied species, and to follow the
gradual divergence of the succeeding stages in
different directions, thus forming a picture of the
phyletic development of an evolving group. In
the course of such observations numerous col-
lateral results would doubtless come out. Investi-
gations of this kind, whether conducted on this
or on any other group, would, above all, show the
true systematic affinities of the forms, i. e.y their
genealogical affinities, and that in a better way
than could be shown by the morphology of the
perfect insects or the adult caterpillars alone. If
I am diffident in founding these conclusions upon
the development of the Sphinx-markings treated
account of the development of the larvae of certain North
American species of Satyrus, see W. H. Edwards in the
" Canadian Entom.," vol. xii. p. 2i. Mr. P. H. Gosse's recent
description of the newly hatched caterpillar of Papilio Homerus
(Proc. Ent. Soc. 1879, p. Iv), furnishes a good illustration of
the value of studying the ontogeny. The natural affinities
of the Papilionidce, were at one time much disputed, some
systematists placing this family at the head of the Lepidoptera,
and others regarding them as being more closely allied to the
moths. Mr. Gosse's observation tends to confirm the latter
view, now generally received by Lepidopterists, since he states
that the larva in question " suggests one of the great Satur-
niadce, such as Samia Cecropia" Mr. Scudder, in the paper
above referred to, adopts an analogous argument to show
the close relationship between the Papilionida and Hesper-
id<z. R.M.]
1 68 Studies in the Theory of Descent.
of in the present essay, this arises entirely from a
knowledge of the imperfections in the basis of
facts. If however, through the united labours of
many investigators, the individual development
of all the species of Sphingidce now existing should
at some future period be clearly laid before us,
we should then not only have arrived at a know-
ledge of the relative ages of the different species,
genera and families, but we should also arrive at
an explanation of the nature of their affinities.
It is erroneous to assert that Classification has
only to take form-relationship into consideration ;
that it should and can be nothing else than the
expression of form-relationship. The latter is
certainly our only measure of blood-relationship,
but those who maintain the assertion that form-
and blood-relationship are by no means always
synonymous, are undoubtedly correct. I shall in
a future essay adduce facts which leave no doubt
on this point, and which prove at the same time
that modern systematists — especially in the order
Lepidoptera — have always endeavoured — although
quite unconsciously — to make the blood-relation-
ship the basis of their classification. For this
reason alone, larvae and pupae would have an
important bearing upon the establishment of sys-
tematic groups, although certainly in a manner
frequently irregular.
It must be admitted that so long as we are
able to compare the species of one group with
\
The Origin of the Markings of Caterpillars. 169
those of another in one form only, we are often
unable to ascertain the blood-relationship.3 In
such cases we can only determine the latter from
the form-relationship, and as these are not always
parallel, any conclusion based on a single form
must be very unsound. If, for instance, butter-
flies emerged from the egg directly, without pass-
ing through any larval stage, a comparison of their
resemblances of form would alone be of systematic
value ; we should unite them into groups on the
ground of these resemblances only, and the
formation of these groups would then much de-
pend upon the weight assigned to this or that
character. We might thus fall into error, not
only through a different valuation of characters
but still more because two species of near blood-
relationship frequently differ from one another in
form to a greater extent than from other species.
We should have no warrant that our conception of
8 [Mr. A. G. Butler has recently furnished a good illustra-
tion of the danger of classifying Lepidoptera according to the
affinities of the perfect insects only, in his paper, " On the
Natural Affinities of the Lepidoptera hitherto referred to the
Genus Acronycta of authors," Trans. Ent. Soc. 1879, P- 3I3>
If the author's views are ultimately accepted, the species at
present grouped under this genus will be distributed among
the Arctiidce, Liparida, Notodontidce, and Noctuce. Mr. Butler's
determination of the affinities of the species supposed to belong
to the genus mentioned, is based chiefly upon a comparative
examination of the larvae, and this is far more likely to show
the true blood-relationship of the species than a comparison
of the perfect insects only. A study of the comparative
ontogeny can alone give a final answer to this question. R.M.]
1 70 Studies in the Theory of Descent.
the form-relationship expressed the genealogical
connection of the species. But it would be quite
different if every species presented itself in two or
three different forms. If in two species or genera
the butterflies as well as the larvae and pupae ex-
hibited the same degree of form-relationship, the
probability that this expressed also the blood-
relationship would then be exceedingly great.
Now this agreement certainly does not always
occur, and when these different stages are re-
lated in form in unequal degrees, the problem
then is to decide which of these relationships
expresses the genealogy. This decision may be
difficult to arrive at in single cases, since the cater-
pillar may diverge in form from the next blood-
related species to a greater extent than the butter-
fly, or, conversely, the butterfly may diverge more
widely from its nearest blood-related species than
the caterpillar.
For such cases there remains the develop-
mental history of the caterpillar, which will almost
always furnish us to a certain extent with infor-
mation respecting the true genealogical relation-
ship of the forms, because it always reveals a
portion of the phyletic (ancestral) development of
the species. If we see two species of butterflies
quite dissimilar in form of wing and other charac-
ters, we should be inclined, in spite of many points
of agreement between them, to place them in
entirely different genera. But should we then
The Origin of the Markings of Caterpillars. 1 7 1
find that not only did their adult larvae agree in
every detail of marking, but also that the entire
phyletic development of these markings, as re-
vealed by the ontogeny of the larvae, had taken
precisely the same course in both species, we
should certainly conclude that they possessed a
near blood-relationship, and should place them
close together in the same genus. Such an in-
stance is afforded by the two Hawk-moths, Chcero-
campa Elpenor and C. Porcellus, as will appear in
the course of these investigations. These two
species were placed by Walker in different genera,
the form relationship of the1 imagines being thus
correctly represented, since Porcellus (imago), is
indeed more nearly related in form to the species
of the genus Pergesa, Walker, than to those of the
genus C/uerocamfat Nevertheless, these species
must remain in the same genus, as no other ar-
rangement expresses their degree of blood-
relationship.
An intimate knowledge of the development-
stages of caterpillars thus offers, even from a sys-
tematic point of view, an invaluable means of
judging the degree of blood-relationship, and from
this standpoint we must regard the study of the
caterpillar as of more importance than that of the
perfect insect. Certainly all groups would not be
4 [In his recent revision of the Sphingidce, Mr. A. G. Butler
(Trans. Zoo. Soc., vol. ix. part x.) retains Walker's arrange-
ment. R.M.]
172 Studies in the Theory of Descent.
so rich in information as the Sphingidce, or, as I
am inclined to believe, the Papilionidce, since all
families of caterpillars do not possess such a
marked and diversified pattern, nor do they present
such a varied and characteristic bodily form. The
representation of the true, i. e., the blood-relation-
ship, and through this the formation of natural
groups with any completeness, can certainly only
be looked for when we are intimately acquainted
with the different stages of development of the
larvae of numerous species in every group, from
their emergence from the egg to their period of
pupation. The genealogical relationship of many
forms at present of doubtful systematic position
would then be made clear. This investigation,
however, could not be the work of a single indi-
vidual ; not only because the materials for observa-
tion are too great, but, above all, because they are
spread over too wide a field. It is not sufficient
to study the European types only — we should
endeavour to learn as much as possible of the
Lepidoptera of the whole world. But such obser-
vations can only be made on the spot. Why
should it not be possible to trace the development
from the egg, even under a tropical sky, and to
devote to breeding and observing, a portion of that
time which is generally spent in mere collecting ?
I may perhaps be able to convince some cf the
many excellent and careful observers among ento-
mologists, that beyond the necessary and valuable
The Origin of the Markings of Caterpillars. 173
search for new forms, there is another field which
maybe successfully worked, viz., the precise inves-
tigation of the development of known species.
The first portion of the present essay consists
of the determination of this development in those
species of Sphingidce which have been accessible
to me. Seven genera are successively treated of,
some completely, and others only in some of their
stages ; and thus I have sought to present a picture
of the course of development of the markings in
each genus, by comparing the species with each
other, and with allied forms in cases where the
young stages were unknown. In this portion, as
far as possible, the facts only have been given, the
working up of the latter into general conclusions
upon the development of marking being reserved
for the second portion. A complete separation of
facts from generalizations could not, however, be
carried out ; it appeared convenient to close the
account of each genus with a summary of the
results obtained from the various species.
After having established that the markings of
the Sphinx-caterpillars had undergone an ex-
tremely gradual phyletic development, conform-
able to law, in certain fixed directions, it appeared
desirable to investigate the causes of the first
appearance of these markings, as well as of their
subsequent development. The question as to the
biological significance of marking here presented
itself in the first place for solution, and the third
174 Studies in the Theory of Descent.
section is devoted to this subject. If it is main-
tained that marking is of no importance to the life
of the insect, or that it is so only exceptionally, and
that it is in reality, as it appears to be, a character
of purely morphological, i. e., physiological, insig-
nificance, then its striking phylogenetic develop-
ment conformable to law cannot be explained by
any of the known factors of species transformation,
and we should have to assume the action of an
innate transforming power. In the present inves-
tigations, this subject in particular has been exten-
sively treated of, and not only the markings of
Sphinx-caterpillars, but also those of caterpillars in
general, have been taken into consideration. The
results arrived at are indeed quite opposed to this
assumption — marking is shown to be a character
of extreme importance to the life of the species,
and the admission of a phyletic vital force must,
at least from the present point of view, be excluded.
This leads to the fifth section, in which I have at-
tempted to test certain objections to the admission
of a " phyletic vital force." The sixth section
finally gives a summary of the results obtained.
I may now add a few explanations which are
necessary for understanding the subsequent de-
scriptions. It was found impossible to avoid the
introduction of some new technicalities for de-
scribing the various elements of larval markings,
especially as the latter had to be treated of scien-
tifically. I have therefore chosen the simplest
The Origin of the Markings of Caterpillars. 175
and most obvious designations, all of which have
already been employed by various authors, but not
in any rigorously defined sense. I understand
by the " dorsal line " that which runs down the
middle of the back ; the lines above and below the
spiracles will be respectively distinguished as the
" supra- " and " infra-spiracular " lines, and the
line between the dorsal and spiracular as the " sub-
dorsal line." The distinction between " ring-
spots " and " eye-spots " will be made manifest in
the course of the investigation. A glance at any
of the existing descriptions of larvae will show how
necessary it was to introduce a precise terminology.
Even when the latter is exact as far as it goes,
the want of precise expressions not only makes
the descriptions unnecessarily long, but it also
considerably increases the difficulty of comparing
one species with another, since we can never be
sure whether the same designation applies to the
same homologous character. For instance, when
the larva of Chcerocampa Elpenor is said to have
" a light longitudinal line on the sides of the
thoracic segments," this statement is indeed correct;
but it is not apparent whether the line is above or
below, and consequently it does not appear
whether it is the equivalent of the longitudinal
line " on the sides " of the segments in other
species. If, however, it is said that this line is
" subdorsal on the thoracic segments, and on the
eleventh abdominal segment," it is thereby indicated
176 Studies in the Theory of Descent.
that we have here a residue of the same marking
which is found completely developed in many other
Sphinx-larvae, and indeed in the young stages of
this same species. The mode of describing cater-
pillars hitherto in vogue is in fact unscientific ; the
descriptions have not been made with a view to
determining the morphology of the larvae, but
simply to meet the practical want of being able to
readily identify any species that may be found :
even for this purpose, however, it would have
been better to have employed a more precise
mode of description.
The Origin of the Markings of Caterpillars. 177
I.
ONTOGENY AND MORPHOLOGY OF SPHINX MARKINGS.
THE GENUS CH^ROCAMPA, DUPONCHEL.
ALTHOUGH by no means in favour of the excessive
subdivision of genera, I am of opinion that
Ochsenheimer's genus Deilephila has been
correctly separated by Duponchel into the two
genera Chcerocampa and Deilephila, sensu strictiori.
Such a division may appear but little necessary
if we examine the perfect insects only ; but the
developmental history of the caterpillars shows
that there is a wide division between the two
groups of species, these groups however being
branches of one stem.
CILEROCAMPA ELPENOR, LINN.
Some captured females laid single eggs sparsely
on grass, wood, and especially on the tarlatan with
which the breeding-cage was covered. The eggs
are nearly spherical, but somewhat compressed,
of a grass-green colour, a little lighter, and some-
what larger (1.2 millim.) than those of Deilephila
Euphorbia. During the development of the
N
178 Studies in the Theory of Descent.
embryo the eggs first became yellowish-green, and
finally yellowish.
First Stage.
The young caterpillars are four millimeters in
length, and immediately after hatching are not
green, but of a yellowish-white opalescent colour,
the large and somewhat curved caudal horn being
black. The caterpillars were so transparent that
under a low magnifying power the nervous,
tracheal, and alimentary systems could be beauti-
fully seen. As soon as the larvae began to feed
(on Epilobium parviflorum) they became green in
consequence of the food appearing through the
skin, but the latter also gradually acquired a dark
green colour (PL IV., Fig. 17). All the specimens
(some twenty in number) were exactly alike, and
showed no trace of marking.
Second Stage.
The first ecdysis occurred after 5 — 6 days, the
length of the caterpillars being from nine to ten
millimeters. After this first moult they appeared
of a shining green, the horn, which was black
during the first stage, becoming a little red at the
base, while a fine white subdorsal line extended
from the horn to the head (Fig. 18). The head
and legs were green ; the divisions between the
segments appeared as fine light rings, and the
entire upper surface of the segments was also crossed
The Origin of the Markings of Caterpillars. 1 79
by fine transverse rings, as was also the case in the
first stage.
At the beginning of the present stage no trace
of the eye-spots could be detected ; but a few days
after the first moult it was observed that the white
subdorsal line was no longer straight on the fourth
and fifth segments, but had become curved upwards
into two small crescents. The latter soon stood
out more strongly, owing to the filling up of their
concavities with darker green. These are the
first rudiments of the eye-spots (Figs. 19 and 30).
A very fine white line now connected the spiracles
(infra-spiracular line), and could be traced from
the last segment to the head. This line takes
no further part in the subsequent development of
the markings, but disappears in the following
stage. The blood-red colour of the base of the
black caudal horn is retained till the fifth stage,
and then also disappears.
Before the second moult, which occurs after
another period of 5 — 6 days, the caterpillars, which
were about 1.3 centimeters in length, had assumed
their characteristic tapering, slug-like form. I did
not notice that the larvae at this stage possessed
the power of withdrawing the three foremost
segments into the two succeeding ones, as is so
frequently to be observed in the adults ; neither
were these two segments so strjkingly enlarged as
they are at an earlier period.
N 2
1 80 Studies in the Theory of Descent.
Third Stage.
After the second ecdysis the marking and
colouring only undergo change with respect to the
eye-spots. The concavities of the crescent-shaped
portions of the subdorsal line become black,1 the
remainder of this line at the same time losing
much of its whiteness, and thus becoming less
distinct, whilst the crescents assume the appear-
ance of small eye-spots (Fig 20). During this
stage the curved, crescent-formed portions be-
come prepared for complete separation from the
remainder of the subdorsal line ; and just before
the third moult the eye-spots become sharply
defined both in front and behind, whilst the black
ground-colour curves upwards, and the white spots
gradually become lenticular and commence to
enlarge (Fig. 21).
Fourth Stage.
The third moult takes place after another
interval of 5 — 6 days, the eye-spots then becoming
very prominent. The white nucleus of the front
spot is kidney-shaped, and that of the hind spot
egg-shaped ; whilst the black ground-colour extends
as a slender border upwards along the sides of the
spots, but does not completely surround them till
towards the end of the present stage (Fig. 21). The
1 The deposition of black pigment may commence imme-
diately before ecdysis.
The Origin of the Markings of Caterpillars. 1 8 1
central portion of the white spots at the same time
becomes of a peculiar violet-brown colour inclin-
ing to yellow above, the peripheral region alone
remaining pure white.
Of the subdorsal line only traces are now to be
recognized, and these are retained, with almost
unchanged intensity, sometimes into the last stage,
remaining with the greatest persistence on the
three front and on the penultimate segments,
whilst on those containing the eye-spots, i. e.y the
fourth and fifth, not a trace remains. At the
present stage the peculiar mingling of colours
becomes apparent over the whole of the upper
surface ; the green is no longer uniform, but a
mixture of short and gently sinuous, dark-green
striations on a lighter ground now appear. On
the sides of the caterpillar these stripes, which
are at first indistinct, but become more strongly
pronounced in the next stage, are arranged
obliquely on the spiracles, with the lower portions
directed forwards.
Fifth Stage.
The fourth moult occurs 7 — 8 days after the
third, the caterpillar being 4 — 5 centimeters in
length. Whilst all the specimens hitherto observed
were with one exception light green, they now
mostly changed their colour and became dark brown.
In one case only did the brown colour appear
in the previous (fourth) stage. The striations
182 Studies in the Theory of Descent.
previously mentioned appear as dull and inter-
rupted dirty yellow streaks, the same dirty yellow
colour showing itself continuously on the sides of
the four front segments. Of the subdorsal line
only a distinct trace is now to be seen on the
eleventh and on the three front segments, whilst
on the third segment the formation of another
eye-spot commences to be plainly perceptible by
a local deposition of black (Fig. 23). This third
spot does not, however, become completely
developed, either in this or in the last stage, but
the subdorsal line remains continuous on the three
front segments. Among other changes at this
stage, there occurs a considerable shortening of
the caudal horn, which at the same time loses its
beautiful black and red colours and becomes
brownish.
The two large eye-spots have now nearly
attained complete development. The kidney-
shaped white spot has become entirely surrounded
by black ; and on the brown, red, and yellow tints
present in this spot during the last stage, a nearly
black spot has been developed — the pupil of the
eye (Fig. 33). In order to establish a definite
terminology for the different portions of the eye-
spot, I shall designate the pupil as the " nucleus,"
the light ground on which the pupil stands as the
" mirror," and the black ground which surrounds
the mirror as the "ground-area."
In this fifth stage the larva attains a length
The Origin of the Markings of Caterpillars. 183
of six centimeters, after which the fifth moult
takes place, the caterpillar becoming ready for
pupation in the sixth stage. No striking changes
of colouring or marking occur after the present
stage, but only certain unimportant alterations,
which are, however, of the greatest theoretical
interest.
Sixth Stage.
In this stage the eye-like appearance of the
spots on the front segments becomes still more
distinct than in the fifth stage ; at the same time
these spots repeat themselves on all the other
segments from the fifth to the eleventh, although
certainly without pupils, and appearing only as
diffused, deep black spots, of the morphological
significance of which, however, there cannot be
the least doubt. They are situated in precisely
the same positions on the 5 — u segments as
those on the third and fourth — near the front, and
above and below the subdorsal line. A feeble
indication of the latter can often be recognized
(Fig- 23).
In all dark-brown specimens the repeated
spots can only be detected in a favourable light,
and after acquiring an intimate knowledge of the
caterpillar ; but in light-brown and green specimens
they appear very sharply defined.
There is one other new character which I have
never observed at an earlier period than the sixth
184 Studies in the Theory of Descent.
stage, viz. the small dots which appear in pairs
near the posterior edge of segments 5 — n.
These dots cannot have been developed from
the subdorsal line, as they are situated higher
than the latter. Their colour varies according to
the ground-colour of the caterpillar, but it is always
lighter, being light-green in green specimens,
dull yellow in those that are light brown, and
grey in the blackish-brown caterpillars. These
" dorsal spots," as I shall term them, are chiefly
of interest because they are present in Chcero-
campa Porcellus, in which species they appear one
stage earlier than in C. Elpenor.
CH^ROCAMPA PORCELLUS, LINN.
Females captured on the wing, laid in the breed-
ing-cage single eggs of a light green colour,
spheroidal in form, and very similar to those of
C. Elpenor.
First Stage.
The caterpillars on first hatching measure 3.5
millimeters in length, and are of a uniform light
green colour, with a fine white transverse line on
the posterior edge of each segment, precisely
similar to that which appears in the second stage
of C. Elpenor. They resemble the latter species
still further in showing a fine white subdorsal
line, which can 'easily be recognized by the naked
eye (Fig. 24). Although the adult larva is
The Origin of the Markings of Caterpillars. 185
distinguished from all the other known species of
Chcerocampa by the absence of a caudal horn, a
distinct but very small one is nevertheless present
at this first stage, and is indeed retained through-
out the entire course of development, but does not
increase further in size, and thus gradually becomes
so small in proportion to the size of the caterpillar
that it may be entirely overlooked.
The first moult takes places after 4 — 5 days.
Second Stage.
The blue-green coloration remains unchanged ;
but a somewhat darker green dorsal line becomes
apparent down the middle of the back (the dorsal
vessel ?), and the subdorsal line now becomes very
broad and pure white, being much more con-
spicuous than in any stage of C. Elpenor (Fig. 25).
The tapering of the three front segments occurs
at this stage, arid oblique, dark-green striations on
a lighter ground stand out distinctly on the spira-
cles. As with C. Elpenor, the first traces of the
future eye-spots appear during the second stage ;
not in the present case as a curvature of the
subdorsal line, but as a spot-like widening of the
latter, of a brighter white than the somewhat
greenish colour of the remainder of the line.
Third Stage.
After the second moult, the formation of the
dark " ground area " of the eye-spots commences by
1 86 Studies in the Theory of Descent.
the appearance of a little brown on the under edge
of the foremost of the white spots, this coloration
gradually increasing in extent and in depth. At
the same time both spots become more sharply
distinguishable from the subdorsal line, which
becomes constantly greener (Fig. 27). The brown
colour soon grows round the white of the front
eye-spot, which becomes so far perfected ; whilst
the completion of the hind spot is effected slowly
afterwards. The formation of the eye-spots does
not therefore proceed any more rapidly in this
species than in C. Elpenor.
At the end of the present stage the length of
the caterpillar is about four centimeters ; the ground
colour is still sea-green ; the subdorsal line is much
diminished, completely fading away at its lower
edge, but remaining sharply defined above, against
the green ground-colour (Fig. 26).
Fourth Stage.
After the third moult all the caterpillars (5)
became brown, this change occurring therefore one
stage earlier than is generally the case with C.
Elpenor. In single instances the brown colour
appeared in the third stage. The subdorsal line
had disappeared from all the segments but the three
first and the last. The eye-spots now rapidly
attained complete development ; they contained a
black pupil, and gave the insect a truly repulsive
appearance when, on being threatened by danger,
The Origin of the Markings of Caterpillars. 187
it drew in the front segments, and expanded the
fourth (Fig. 28). The eye-spots of the fifth seg-
ment are much less developed than in C. Elpenor ;
they remain small, and are not readily detected.
On the other hand, there now appear on all the
segments with the exception of the last, just as in
the sixth stage of C. Elpenor, distinct rudiments of
eye-spots, which present the appearance of irregular,
roundish, black spots on the front borders of the
segments, at the height of the former subdorsal
line. In this latter region the black pigment is
disposed as a longitudinal streak, and to this a
median line is added, the whole forming a mark-
ing which perhaps makes the caterpillar appear
still more alarming to its foes. This marking is,
however, only to be distinctly recognized on the
three first segments. The " dorsal spots " men-
tioned in the case of C. Elpenor then appear very
distinctly on segments 5 — n.
The caterpillars continued to feed for eleven
days after the third moult, at the end of which
period the fourth moult took place, but without
the occurrence of any change of marking. The
larvae then buried themselves, the complete
development having taken 28 — 29 days.
The development of the Porcellus caterpillar
was twice followed; in 1869 in twelve, and in
1874 in five specimens. In no case did I obtain
caterpillars which remained green throughout the
entire course of development, although this colour
1 88 Studies in the Theory of Descent.
is stated in the books to occur occasionally in these
larvae ; neither have I been able to find any figure
of an adult green specimen, so that it must in the
meantime be admitted that such specimens, if they
occur at all, are exceptional instances.2 The
theoretical bearing of this admission will appear
later on.
RESULTS OF THE DEVELOPMENT OF CHJEROCAMPA ELPENOR
AND C. PORCELLUS ; COMPARISON OF THESE WITH THE
OTHER KNOWN SPECIES OF CH^EROCAMPA.
The first stage of Elpenor shows that the most
remote ancestor of the genus possessed no kind of
marking, but was uniformly green. At a later
period, the white longitudinal stripe which I have
designated the " subdorsal line " made its appear-
ance, and at a still later period this line vanished,
with the exception of a few more or less distinct
remnants, whilst, at the same time, from certain
8 [Mr. Herbert Goss states (Proc. Ent. Soc. 1878, p. v.)
that according to his experience, the green and brown varieties
of C. Porcellus (erroneously printed as Elpenor in the passage
referred to) are about equally common, the former colour not
being in any way confined to young larvae. Mr. Owen Wilson
in his recent work, " The Larvae of British Lepidoptera and
their food-plants," figures (PI. VIII., Figs. 3 and 3a) the two
forms, both apparently in the adult state. During the years
1878-79, my friend, Mr. J. Evershed, jun., took five of these
full-grown larvae in Surrey, one of these being the green variety.
In order to get more statistics on this subject, I applied this
year (1880) to Messrs. Davis of Dartford, who informed me that
among 18 — 20 adult caterpillars of Porcellus in their possession,
there was only one green specimen. R.M.]
The Origin of the Markings of Caterpillars. 1 89
portions of it, the eye- spots of the fourth and fifth
segments became developed. After the per-
fecting of the eye-spots, weak repetitions of the
latter appeared as black spots on all the segments
except the last.
In Porcellus the caterpillar emerges from the
egg with the subdorsal line, the first stage of
Elpenor being omitted, From this fact we may
venture to conclude that Porcellus is the younger
species, or, what comes to the same thing, that
it has further advanced in development. The
whole subsequent history of Porcellus agrees with
this view, its course of development being essen-
tially but a repetition of the phenomena displayed
by Elpenor, and differing only in one point, viz.
that all new characters make their appearance
one stage earlier than in the latter species. This
is the case with the transformation of the green
into a brown ground-colour ; with the repetition of
the eye-spots on the remaining segments in the
form of suffused black spots ; and with the appear-
ance of the light " dorsal spots." Only the eye-
spots themselves appear, and the snout-like taper-
ing of the front segments occurs in the same stage
as in Elpenor ; i. e. the second.
From these data alone, we may venture to infer
the occurrence of four chief stages in the phyletic
development of the genus. The first stage was
simply green, without any marking ; the second
showed a subdorsal line ; the third, eye-spots on
1 90 Studies in the Theory of Descent.
the third and fourth segments ; and the fourth
stage showed a repetition of the eye-spots, although
but rudimentary, on all the remaining segments
with the exception of the twelfth.
Now if we compare the other known species
of Ch&rocampa larvae with the above, we shall
arrive at the interesting conclusion that all these
species can be arranged in three groups, which
correspond exactly with the three last phyletic
stages as just deduced from the ontogeny of C.
Elpenor and Porcelhis.
Of the genus Chczrocampa? over fifty species
have been ^described,4 of which the larvae of only
* I unite the genera Pergesa and Darapsa of Walk, with
Chcerocampa, Dup. ; the first appears to me to be quite untenable,
since it is impossible that two species, of which the caterpillars
agree so completely as those of C. Elpenor and Porcellus, can
be located in different genera. Porcellus indeed was referred
to the genus Pergesa because of its different contour of wings,
an instance which distinctly shows how dangerous it is to
attempt to found Lepidopterous genera without considering the
caterpillars. The genus Darapsa also appears to me to be of
very doubtful value, and in any case requires further confirma-
tion with respect to the larval forms.
4 [Mr. A. G. Butler (Trans. Zoo. Soc., vol. ix., part, x., 1876)
gives a list of about eighty-four species of Charocampa, and
sixteen of Pergesa, besides numerous other species belonging to
several genera placed between Charocampa and Pergesa. ' Of
Darapsa, he states " that this genus was founded upon most
heterogeneous material, the first three species being referable to
Hiibner's genus Otus, the fifth to Walker's genus Diodosida, the
sixth and eighth to the genus Daphnis of Hiibner, the seventh,
ninth, and tenth to Cfuzrocampa of Duponchel ; there therefore
remains only the fourth species, allied to Charocampa, but
The Origin of the Markings of Caterpillars. 191
fifteen are known in the form which they possess
at the last ontogenetic stage.
GROUP i. — I can furnish but little information
with respect to this group. The first species with
which I became acquainted was Chczrocampa
Syriaca,5 of which I saw two blown caterpillars in
Staudinger's collection, and which I have figured in
PL IV., Fig. 29. The larva is green, and has the
short oblique stripes over the legs common to so
many species of Chczrocampa, the only marking
besides these being a simple white subdorsal line,
•without any trace of eye-spots. This species exactly
corresponds therefore with the second ontogenetic
stage of C. Elpenor and Porcellus. The account of
the species, both in the larval and perfect state, is
unfortunately so imperfect, that we cannot with
certainty infer the age of the two caterpillars from
their size. If the moth were of the same size as
Elpenor, then the caterpillar figured, having a
length of 5.3 centimeters, would not be in the last
but in the penultimate stage, and it remains doubt-
ful whether it may not acquire eye-spots in the last
stage.
That species exist, however, which in their last
stage correspond to the second stage of Elpenor,
is shown by two of the forms belonging to
Walker's genus Darapsa, which was founded on
apparently sufficiently distinct." The species still retained in
the genus Darapsa is D. rhodocera, Wlk., from Haiti. R.M.]
* \Otus Syriacus of Butler's revision. R.M.]
192 Studies in the Theory of Descent.
the characters of the imagines only. Ten species
of this genus are given in Gray's catalogue, the
adult larva of two of these being known through
the excellent figures of Abbot and Smith.6 These
two caterpillars possess the characteristic tapering
form in a very marked degree ; one is figured in
the attitude so often assumed by our species of
Ch&rocampa on the approach of danger, the three
front segments being withdrawn into the fourth.
(Fig. 34, PL IV., is copied from this Plate).
There are no eye-spots either in D. Myron or D.
Chcerilus, 7 but only a broad white subdorsal line ;
underneath which, and to a certain extent pro-
ceeding from it, there are oblique white stripes,
precisely similar to those which meet the subdorsal
line in the third stage of C. Porcellus?
fl Abbot and Smith. "The Natural History of the rarer
Lepidopterous Insects of Georgia, collected from the observa-
tions of John Abbot, with the plants on which they feed."
London, 1797, 2 vols. fol.
7 [Otus Ch&rilus and O. Myron of Butler's revision. R.M.]
8 [To this group may also be added Ampelophaga Rubiginosa,
Menetrie's, from China and Japan, the caterpillar of which,
having the distinct subdorsal line without any trace of eye-
spots, is figured by Butler (loc. cit., PI. XCL, Fig. 4). This
author also gives a figure of another species belonging to the
subfamily Charocampina (PI. XC., Fig. n), viz. Acosmeryx
AnceuS) Cram., from Amboina, Java, Silhet, and S. India ; the
caterpillar is green, with seven oblique yellow stripes along the
sides, and a very conspicuous white subdorsal line with a red
border above. As there are no eye-spots, this species may be
referred to the present group provisionally, although its general
marking is very distinct from that of the Charocampa group.
R.M.]
The Origin of the Markings of Caterpillars. 193
GROUP 2. — This group contains numerous
species which; like our native C. Elpenor and
Porcellus, show eye-spots on the fourth and fifth
segments, whilst these markings are absent, or at
most only present in traces, on the remainder. To
this section there belong, besides the two species
mentioned, five others, viz. in Europe, C. Celerio
and Alecto (not certainly known ?) ; 9 in India,
C Nessus, Drury, and Lucasii, Boisduval ; 10 and
an unnamed species from Port Natal.
In the species belonging to this group the sub-
dorsal line may be more or less retained. Thus,
C. Celerio, according to Htibner's figure, has a
broad yellow line extending from the horn to the
sixth segment, whilst it is completely absent on
the three front segments. In the unnamed species
from Port Natal11 the subdorsal line extends to
the front edge of the fifth segment, and on the
fourth segment only is there a perfect eye-spot,
whilst on the succeeding segments traces of such
markings can be recognized as dark spots similar
9 [Eng. ed. Dr. Staudinger has since obtained the caterpillar
of C Alecto from Beyrout ; it possesses " a very distinct sub-
dorsal line, and on the fourth segment a beautiful eye-spot,
which is repeated with gradual diminution to segments
7-8.]
10 Figured in " A Catalogue of Lepidopterous Insects in the
Museum of the East India Company," by Thomas Horsfield
and Frederick Moore. London, 1857. Vol. i., PL XL
11 Figured in Trans. Ent. Soc., New Series, vol. iv., PI.
XIII.
o
1 94 Studies in the Theory of Descent.
to those in Elpenor and Porcellus. The tran-
sition to the third group is through another un-
named species from Mozambique,12 in which
rather large eye-spots have become developed
on the fourth and fifth segments and these
are followed by a subdorsal line, which only
appears distinctly at certain places. On this
broken subdorsal line, and not completely sepa-
rated from it, there are small, roundish eye-
spots, situated near the front edge of each seg-
ment ; these being, therefore, a somewhat more
perfect repetition of the front eye-spots.
13
12 Ibid.
13 [The following species figured by Butler (loc. dt. Pis. XC.
and XCI.) appear to belong to the second group — Chceroeampa
Japonica, Boisd., which is figured in two forms, one brown, and
the other green. The former has two distinct ocelli on the
fourth and fifth segments, and a distinct rudiment on the sixth,
whilst the subdorsal line extends from the second eye-spot to
the caudal horn, and beneath this line the oblique lateral
stripes stand out conspicuously in dark brown on a lighter
ground. The ocelli are equally well developed on the fourth
and fifth segments in the green variety, the subdorsal line
commencing on the sixth segment, and extending to the caudal
horn ; there is no trace of a third eye-spot, nor are there any
oblique lateral stripes ; the insect is almost the exact counter-
part of C. Elpenor in its fourth stage. (See Fig. 21, PI. IV.)
Pergesa Mongoliana, Butl., is brown, without a trace of the
subdorsal line except on the three front segments, and with
only one large eye-spot on the fourth segment. Charocampa
Lewisii, Butl., from Japan, is likewise figured in two forms.
The brown variety has the subdorsal line on the three front
segments only, distinct ocelli on the fourth and fifth segments,
and gradually diminishing rudiments on the remaining seg-
The Origin of the Markings of Caterpillars. 195
GROUP 3. — In the species of this group the
eye-spots are repeated on all the segments. I
am acquainted with seven such Ch&rocampa larvae,
of which C. Bisecta, Horsfield,14 shows some
affinity to the foregoing group, since the eye-
spots on segments 6 — n have not yet attained
ments. The green form appears to be transitional between
the present and the third group, as it possesses a distinct, but
rudimentary eye-spot on the third segment, besides the fully
developed ones on the fourth and fifth, and very conspicuous,
but gradually decreasing repetitions of rudimentary ocelli on
segments 6 — 10. To this group may be added Charocampa
Aristor, Boisd., the caterpillar of which is figured by Burmeister
(Lep. Re>. Arg., PL XV.. Fig. 4) in the characteristic attitude
of alarm, with the front segments retracted, and the ocelli on
the fourth segment prominently exposed. The subdorsal line
is present in this species. Burmeister also figures two of the
early stages (PI. XV., Fig. 7, A and B), and describes the com-
plete development of Philampelus Labruscce, another species
belonging to the subfamily Charocampintz. The earliest stage
(3—4 days old) is simple green, with no trace of any marking
except a black spot on each side of the fourth segment, the
position of the future ocelli. A curved horn is present both in
this stage and the following one, during which the caterpillar
is still green, but now has seven oblique red lateral stripes. The
caudal horn is shed at the second moult, after which the colour
becomes darker, the adult larva (figured by Madame Merian,
in her work on Surinam, pi. 34 and Sepp., pi. 32) being
mottled brown. In addition to the ocellus on the fourth seg-
ment, there is another slightly larger on the eleventh segment,
so that this species may perhaps be another transition to the
third group; but our knowledge is still too imperfect to
attempt to generalize with safety. R.M.]
u Cat. Lep. Ins. East Ind. Comp., PL XIII. [Figured also
by Butler (—Charocampa Silhetensis, Walker), loc. at. PI. XCII.,
Fig. 8. R.M.]
O 2
196 Studies in the Theory of Descent.
full perfection. In C. O Idenlandice , Fabr.,1' and in
C. Alecto from India,16 the eye-spots appear to be
perfectly alike on all the segments ; whilst in
C. Acteus, Cram.,17 and in the North American
C. Tersa™ (PI. IV., Fig. 35) they are smaller on
the other segments than on the fourth ; and in
C. Celerio, Linn., from India,19 the size of the
spots diminishes from the head to the tail.
In this group also the subdorsal line is retainecl
in a very variable degree. In some species it
appears to have completely vanished (C. Acteus,
Celerio] ; in others it is present as a light stripe
extending along all the segments (C. Alecto) ;
whilst in others it is retained as a broad white
stripe, which extends only to the fourth segment
(C. Tersa, Fig. 35). In species possessing eye-
spots, the subdorsal line is thus a very variable
character. It is, however, an interesting fact that
even in the present group, which has made the
greatest step forward, the subdorsal line is of
general occurrence, because the eye-spots in all
these species may have almost a similar develop-
ment to those of Elpenor and Porcellus. The
ontogeny of the tropical species would alone
16 Cat. Lep. Ins. East Ind. Comp., PI. XIII. [Figured also
by Butler, loc. cit. PI. XCL, Fig. i. R.M.]
., 16 Horsfield and Moore, loc. cit. PI. X.
17 Ibid. [= Pergesa Acteus, Walker. R.M.]
18 [Figured also by Burmeister, loc. cit. PI. XV., Fig. 3.
R.M.]
ltf Horsfield and Moore, loc. cit., PI. XI.
The Origin of the Markings of Caterpillars. [97
give a definite reply on this point, but un-
fortunately we are not acquainted with any of
the young forms, so that we can but presume
that some of them at least would show only in the
first stage the simple subdorsal line without eye-
spots ; that in the second stage the primary pairs
of eye-spots would be formed on the fourth and
fifth segments, whilst the transference of these
spots to the remaining segments would take place
in the last stage.
The foregoing assumption is based immediately
on the ontogeny of Elpenor and Porcellus ; it is
supported by the considerable size attained by the
eye-spots in many species of the third group,
and would receive additional confirmation by
observations on the Indian C. Celerio, supposing
that Horsfield's statements do not arise from a
confusion of species. This skilful observer, who
was the first to breed systematically a large
number of tropical larvae, has given a figure of the
Indian caterpillar of C. Celerioy according to which
this species possesses eye-spots on all the segments
from the fourth to the tenth. The European
form of this same species has eye-spots only on
segments four and five, a fact which does not
appear to have been known to Horsfield, as no
mention of it is made in his notice of the Indian
species. If the caterpillar figured is really that
of Celerio, which I consider to be by no means
improbable, not only is it thus shown that in the
1 98 Studies in the Theory of Descent.
species of the third group the ocelli on the hind
segments have a secondary origin through a
repetition of the primary ones of the front
segments, but we can also establish that the same
species in two different regions may arrive at two
different phyletic stages.
If, finally, we sum up the facts taught by the
ontogeny of the two German species, and the
adult forms of the other species, we can form
therefrom a tolerably complete picture of the
course of development of the genus Chczrocampa.
Of the four phyletic stages indicated by the
ontogeny of Elpenor and Porcellus, three still
form the terminus of the development of exist-
ing species. The great differences among the
caterpillars of this genus can be very simply ex-
plained on the view that they stand at different
levels of phyletic development ; some species
having remained far behind (Group i), others
having advanced further (Group 2), and others
having reached the highest point of development
(Group 3). The fact that the species of the third
group are only tropical accords well with this view,
since many facts prove that phyletic development
proceeds more rapidly in the tropics than in
temperate climates.
The striking markings of the Ch&rocampa
larvae may, in brief, be stated to originate from a
local transformation of two portions of the sub-
dorsal line into eye-spots, and the subsequent
The Origin of the Markings of Caterpillars. 199
transference of these two primary ocelli to the other
segments. The eye-spots always originate on
segments four and five, and from these the trans-
ference mostly occurs backwards, although in
certain cases it takes place at the same time
forwards. Herein, i. e. in the origin of the eye-
spots, there lies a great distinction between the
genus Chczrocampa and the genus Deilephila, with
which it was formerly associated, and in which the
origin of a very similar kind of marking can be
traced to quite another source.
THE GENUS DEILEPHILA, OCHSENHEIMER.
I am acquainted with the caterpillars of nine
European and one North American species,
these differing in marking to such a wonderful
extent that they appear to offer at first sight but
little hope of being able to trace them to a common
form. These ten species can be separated,
according to their markings, into five groups,
which I will briefly define before entering upon
their ontogeny.
The first group consists of three species, and
comprises the -commonest and most widely-ranging
of all the European species, Deilephila Euphorbia,
as well as D. Dahlii from Sardinia and Corsica,
and D. Niccea, a species of very restricted range,
which appears to occur only in one small district
on the French coast of the Mediterranean. These
2oo Studies in the Theory of Descent.
three species agree in marking to the extent of
their possessing in the adult form two rows of
ring-spots on each side, whilst the subdorsal line is
completely absent.
The second group, consisting also of three
species, shows a great resemblance to Euphorbia >
but has only one row of ring-spots. It contains
D. Vespertilio, D. Galii, and the Algerian
D. Mauritanica.
For the third group I only know one repre-
sentative, D. Livornica, Esp., which possesses a
single row of ring-spots connected by a subdorsal
line.
Another group is composed of D. Zygophylli,
which occurs on the shores of the Caspian Sea,
and the North American D. Lineata ; these species
possessing a strongly-marked subdorsal line, asso-
ciated with more or less distinct ring-spots, which
I shall designate as " open rings," because their
black border does not intersect the subdorsal line,
but has the form of an arch above and below it.
In the last group, represented by D. Hippophaes,
which occurs at the foot of the Alps (Wallis), and
southward as far as Andalusia, there is only a broad
subdorsal line, generally without any trace of a
row of spots.
The important differences of marking displayed
by these five groups are not in any way accidental,
but they represent different stages of phyletic
development ; or, in other words, the five groups
The Origin of the Markings of Caterpillars. 201
are of different ages, the first (Euphorbia^ &c.)
being the youngest, and the last (Hippophaes) the
oldest of the genus.
According to their phyletic age, the groups
follow each other in inverse order, the first being
Hippophaes, the second that of Zygophylli, the
third that of Livornica, the fourth that of Galii,
and the fifth and youngest that of Euphorbia.
Only in this last am I acquainted with the
complete development of one species, for which
reason I commence with this group, thus pro-
ceeding from the youngest to the oldest forms,
instead of taking the more natural course from
the simplest and oldest to the youngest and most
complicated.
DEILIPHJLA EUPHORBLE, LINN.
Some captured females were at once placed in an
enclosure about the size of a small sitting-room.
It was evident that they did not feel quite at home
under these conditions, frequently beating their
heads and wings against the tarlatan, but some of
them nevertheless laid eggs at the base of the
leaves of Euphorbia Cyparissias. The eggs
much resemble those of Chcerocampa Elpenor,
being spheroidal in form, but rather smaller, and
of a somewhat darker green. They were laid in
small clusters composed sometimes of as many as
seven, the single eggs being placed near together,
but never touching, and seldom at the point of the
202 Studies in the Theory of Descent.
leaf, but generally near the end of a twig, where
young shoots are in close proximity. During
the embryonic development the eggs become
coloured, first yellow and partly blackish, and
finally completely black.
First Stage.
The young caterpillars (Fig. 37, PI. V.)
immediately after hatching measure four milli-
meters in length ; they are at first rather light,
but in the course of half-an-hour they are seen
by the naked eye to become of a deep velvety
black; later, on increasing in size, they again
become paler, appearing of a greenish-black, and
subsequently blackish-green. On further increas-
ing in size (Fig. 38), they are blackish-green,
with the horn, head, legs, and a crescent-shaped
chitinous plate on the back of the prothorax
black. There are also on the last segment a
double and two single black chitinous plates. Of
the later marking of the caterpillar there is
scarcely anything present. The spiracles appear
as white spots, and on each segment there are a
number (mostly ten) of small warts, each of which
emits a single bristle.
When the young larvae have attained a length
of seven millimeters they are olive-green, and do
not contrast so brilliantly with the green of the
Euphorbia leaves as before ; neither do they as yet
possess any markings.
The Origin of the Markings of Caterpillars. 203
Second Stage.
The first ecdysis occurs after five days, and
with this there appears quite suddenly a very
complicated pattern. The ground colour is now
a light yellowish-green (Fig. 39), and on each
of the twelve segments, near the front border, there
is a pure white round spot in the middle of a large
black transverse spot. I shall designate these, in
accordance with the nomenclature employed for
Ch&rocampa> as the white " mirrors " on black
"ground-areas," both together constituting " ring-
spots," as distinguished from " eye-spots " proper,
in which a " nucleus," the pupil of the eye, is also
added. In many, but not in all specimens, very
distinct traces of a subdorsal line can be seen as
a light whitish stripe connecting the white spots.
The horn, the thoracic and prolegs, and some
spots on the head, are black.
The caterpillars remain unaltered till after four
days, when, having a length of 1 7 millimeters, the
second moult takes place, bringing with it changes
quite as great as those which occurred with the
first.
Third Stage.
The caterpillar now assumes the shagreened
appearance which it possesses in the adult state.
Small white warts are arranged in rows from the
dorsal to the spiracular line, and again underneath
2O4 Studies in the Theory of Descent.
this line on the abdominal legs. These dots are
not only of value as a character for differentiating
the genera Deilephila and Chcerocampa^ but they
also play a part in the peculiar spot-marking which
will be shown later on. The ground-colour of the
caterpillar is now light green (Fig. 40), replaced
by black on certain parts. From the black
" ground-area " of the ring-spots, two black
triangles extend towards the posterior borders
of the segments, but usually without reaching
them.
The ring-spots are not essentially changed, al-
though it may be observed that in most specimens
the shagreen-dots under each ring-spot are some-
what larger, and stand closer together than in
other places. In the following stage they become
fused into a second white " mirror," so that two
ring-spots stand one above the other, their black
ground-areas meeting. The formation of the
second ring-spot sometimes takes place in the
present stage (Fig. 42).
The subdorsal line has now completely vanished,
whilst the spiracular-line 20 appears as a broad stripe
above the legs. The horn is yellow with a black
point, and the black spots on the head have in-
creased in size.
10 To be accurate this should be designated the infra-
spiracular line ; but this term cannot be well applied except
in cases where there is also a supra-spiracular line, as, for
instance, in Anceryx (Hyloicus) Pinastri*
The Origin of the Markings af Caterpillars. 205
Fourth Stage.
The third moult, which again occurs after four
days, is not accompanied by such important
changes. The green ground-colour has now
completely disappeared, and is replaced by a dull
black. The caterpillars are now, as also in the
previous stage, extremely variable. Thus, for
example, a triangular patch of the green ground-
colour may be retained on the posterior edge of
the segments (Fig. 41), those specimens which
possess this character generally having their mark-
ings retarded in development, as shown by the
absence of the second " mirror " of the ring-spots.
In Fig. 41 the shagreen-dots from which
this second " mirror" is subsequently formed,
are distinctly larger than the others, and on the
eleventh segment two of them have already
coalesced.
Fifth Stage.
After another period of four days, the fourth
moult takes place. The marking remains the same,
but the colours become more vivid; the brick-red of
the head, horn, dorsal line and legs, changing into
a fiery red. The spiracular line, formerly green
alternating with yellow, generally becomes re-
solved into a row of reddish-yellow spots. Ten
days later the caterpillar (8*5 centimeters in
length), ceases to feed, and prepares for pupation.
206 Studies in the Theory of Descent.
In this last stage also there is great variability
of colour, but although each particular character
is subject to fluctuation, the individuals of the same
brood show but little variation among themselves.21
Thus, the dorsal line is sometimes black, and
sometimes red, or again, this colour interrupted
with black, so that only small red spots mark its
course. The head may be entirely red, or this
colour mixed with black. On the under side of
the caterpillar, red generally predominates, but in
some specimens this is replaced by black. The
ground-colour is also variable, being generally
a shining brownish-black, but sometimes dull
coaly black. The shagreen-dots are sometimes
white and sometimes yellow, and the " mirrors" of
the ring-spots are also often yellowish.
The most interesting variation, however, appears
to me to be the following : — In many specimens
from Kaiserstuhl (Breisgau), the red was unusually
vivid, and was not limited to the ordinary places,
but occupied also the triangles on the posterior
edges of the segments (Fig. 44), which are green
in the third and fourth stages (Fig. 42). This
variety has also been figured by Htibner. In
21 Upon this fact obviously depends the statement of that
extremely accurate observer Rosel, that the caterpillar of
Euphorbia is but very slightly variable ("Insektenbelusti-
gungen," Bd. iii. p. 36). I formerly held the same opinion, till
I convinced myself that this species is very constant in some
localities, but very variable in others. It appears that local
influences make the caterpillar variable.
The Origin of the Markings of Caterpillars. 207
one individual (Fig. 43), the under ring-spots
were wanting, whilst the upper ones possessed a
beautiful red nucleus fading away anteriorly, and
showing the first step in the formation of a complete
eye-spot.
I cannot positively assert that a fifth moult occurs
in the last ten days, although I am very doubtful
whether this is the case. It is certain, however,
that some time before pupation, and whilst the
larva is still feeding, the striking colours fade out,
and become replaced chiefly by black.
The ontogeny of this species is obviously but
a very incomplete representation of its phyletic
development This is at once apparent from the
large gap between the first and second stages. It
is not possible that a row of ring-spots can have
arisen suddenly ; in all probability they have been
developed from a subdorsal line, which in Euphor-
bia is now only indicated in the second stage by
a faint line. This conjecture is raised to a cer-
tainty when we call in the aid of the remaining
species of Deilephila.
DEILEPHILA NIC^EA, DE PRUNNER.
I only know this species from blown larvae in
Staudinger's collection, and DuponchePs figure, of
which Fig. 51, PI. VI. is a copy. The adult insect
possesses two perfectly separated rows of ring-
spots. Duponchel figures also two younger stages,
of which the youngest is probably the third stage.
208 Studies in the Theory of Descent.
The larva is 18 millimeters in length, of a leaf-
green colour, and shows no trace of a subdorsal
line, but possesses the two rows of ring-spots,
which only differ from those of the succeeding
stages in the green colour of the " mirror."
DEILEPHILA DAHLII, TREITSCHKE.
I am familiar with numerous specimens in various
stages, collected in Sardinia by Dr. Staudinger,
and preserved by inflation.
The first stage is blackish, and shows no kind of
marking ; thus agreeing with the corresponding
stage of Euphorbia. The second stage is unfortu-
nately not represented in Staudinger's collection.
The third stage shows a row of ring-spots, which
are, however, connected by a very distinct and
sharply defined subdorsal line. In the fourth
stage a second row of (under) ring-spots is added,
whilst the subdorsal line generally at the same
time disappears.
The caterpillar remains unchanged during the
fifth stage, when it shows a great resemblance in
marking to Euphorbia ; neither does it appear to
differ essentially from this species in colour, so far
as can be judged from preserved specimens and
single figures (in Duponchel and Hiibner). I
have, moreover, seen several larvae in the last
stage, and the subdorsal could be distinctly re-
cognized as a broad light stripe.
Of the four groups, the second (that of Galii),
The Origin of the Markings of Caterpillars. 209
appears to me to be of but very little importance,
as I shall now proceed to show from the develop-
ment of D. Vesper tilio.
DEILEPHILA VESPERTILIO, FABRICIUS.
Hitherto I have unfortunately been unable to
obtain fertile eggs of this species, so that I can
say nothing about the first stage. The latter
would have been of interest, not only because of
the marking, but also because of the presence of a
residual caudal horn.
I am likewise only acquainted with the end of
the second stage, having found, at the end of June
1873, a single caterpillar on Epilobium Rosmarini-
folium}}\!&\. previous to its second ecdysis. In the
case of such young caterpillars, however, the new
characters which appear in the succeeding stage
are generally perceptible through the transparent
chitinous skin at the end of the preceding stage,
so that the markings of the insect are thus caused
to change. The caterpillar found was about 16
millimeters long, and of a beautiful smooth and
shining grass-green (Fig. 13). A broad white
subdorsal line extended from the first to the penul-
timate segment, from which the horn was com-
pletely absent. On close inspection the first traces
of the ring-spots could be detected near the anterior
edge of each segment as feeble, round, yellow,
ill-defined spots, situated on the subdorsal line it-
self (Fig. 13). On the first segment only there is
2 T o Studies in the Theory of Descent.
no spot, and here no ring-spot is afterwards
formed. Besides these markings, there was only
to be seen a yellowish-white spiracular line.
This solitary specimen unfortunately buried itself
before the moult for which it had prepared itself
had occurred ; but this ecdysis is associated with
a very important transformation. This statement
is founded on a blown specimen in Staudinger's
collection ; it is only 18 millimeters in length,
but already shows the later grey colouring in
place of the beautiful green. In this, the third
stage, the broad white subdorsal line bears on
each segment a red spot enclosed between black
crescents above and below (Fig. 49 A). In the
fourth stage, during which I have seen many
living caterpillars, the subdorsal line is still dis-
tinctly present in some individuals (Fig. 14), but
the spots (" mirrors ") are now completely sur-
rounded by a narrow black ring (" ground-area "),
which sharply separates them from the sub-
dorsal line (Fig. 49 B). In the fifth stage this
ring becomes a somewhat irregularly formed black
" ground-area," whilst the subdorsal line com-
pletely vanishes (Figs. 51 and 49 C). The mirrors
are white, but generally have a reddish nucleus,
which obviously corresponds to the primary yellow
spots from which the whole development of the
ring-spots originates. This character is, however,
sometimes absent ; and many other variations also
occur in the earlier stages, all of which can be
The Origin of the Markings of Caterpillars.
211
easily explained as cases of arrested, or retarded
development. Thus, the subdorsal line often dis-
appears earlier, and is only present in the fourth
stage as a feeble light stripe.
DEILEPHILA GALII, FABRICIUS.
The markings of this species appear to be
developed in a precisely similar manner to those
of D. Vespertilio. The adult larva, as in the last
species, shows no trace of a subdorsal line. A row
of large black spots, each having an irregular
round, yellowish-white nucleus, is situated on an
olive-green, blackish-brown, brown, or dirty yellow
ground. I have, unfortunately, also in this case
been unable to procure fertile eggs. There is,
however, one figure of a caterpillar, 2.5 centimeters
long, by Hiibner, which is of a light-green colour,
and has five longitudinal lines ; one dorsal, two
subdorsal, and a spiracular line. The subdorsal
is white, and bears in the place of the ring-spots
small red dots, whilst the line itself is bordered
with black where the red spots are situated.
Hiibner has probably figured the third stage, so
that we may venture to conclude that in the second
stage there is a subdorsal line either quite free
from spots, or only showing such feeble rudiments
as are to be seen in the second stage of
Vespertilio.
I found two specimens in the fourth stage in
the Upper Engadine. One of these (Fig. 45)
p 2
212 Sludics in the Theory of Descent.
was already of a dark, blackish-green ground-
colour22 with a broad, greenish-white subdorsal
line sharply defined throughout its entire length,
and containing ring-spots of a sulphur-yellow with
an orange-red nucleus; the black "ground-area"
did not encroach upon the subdorsal line, but was
confined to two faint crescents situated above
and below the " mirror." Only the two foremost
" mirrors " (on the second and third segments)
were without nuclei.
The remaining peculiarities of coloration are
shown in the figure. I may here only point out
the shagreening present on the sides and a
portion of the under surface.
The specimen figured was 3.3 centimeters long;
a second example measured 2.8 centimeters in
length, and was essentially similar, but showed
that a considerable amount of variability must
prevail at this stage of development. It was pitchy
black, with a very indistinct subdorsal line and a
few ring-spots, the " mirrors " of which were
also sulphur-yellow, with the orange-red nucleus.
The shagreening was quite as strong as in the
first specimen, the dots being yellow instead of white.
It is specially to be observed, because of its im-
portant theoretical bearing, that in this larva the
ring-spots were absent on the three front segments,
and on the fourth only, a faint indication of one
could be perceived. In the caterpillar figured
* The green is considerably too light in Fig. 45.
The Origin of the Markings of Caterpillars. 2 1 3
the ring-spots increase also in distinctness from
the tail to the head.
Fifth Stage.
The two specimens just mentioned, after moult-
ing, acquired the well-known markings of the adult
caterpillar already briefly described above. The
fifth is the last stage.
The larva is known to occur in several variations,
Rosel having figured it in three forms ; light green,
olive-green, and dirty yellow. It has not been
since considered worth the trouble to attend to
the subject of caterpillar coloration. Thus, Wilde,23
in his well-known work, takes no notice of Rosel's
observation, but simply describes the caterpillar
of Galii as " blackish olive-green."
Having had an opportunity of observing twenty-
five adult specimens of this somewhat scarce
species at one time, I am able to state that it is
not in this instance di- or polymorphism, but a
case presenting a great degree of variability, with
which we have to deal. There are not several
sharply-defined types of coloration; but the
extremes are connected by numerous intermediate
forms. The extreme forms, however, certainly
preponderate.
I have never met with Rosel's light-green form ;
neither was there a dark-green specimen among
23 " Die Pflanzen und Raupen Deutschlands." Berlin, 1860,
P- 83.
2 1 4 Studies in the Theory of Descent.
the twenty-five mentioned, and I only know this
variety from single individuals, found at a former
period. Among the twenty-five caterpillars., all
gradations of colour occurred, from pitchy black to
light clay-yellow, and even to an almost whitish-
yellow ; some were brownish-black, others of a
beautiful chestnut-brown, and others yellowish
brown, dark clay-yellow, or brownish-red. Out
of twenty-one specimens of which the ground-
colours were noted, there were nine black, nine
clay-yellow, and three brown ; each of the three
groups again showing various minor modifications
of colour. The other colours also varied some-
what. Thus, the " mirrors " were sometimes
white, sometimes strong yellow, and occasionally
they also contained a reddish nucleus.
The variations in the shagreening were espe-
cially interesting, inasmuch as these appeared
to have a striking connection with the general
colouring of the caterpillar. Black specimens
seldom show such sparse shagreening as that
represented in PI. V., Fig. -46, but are generally
thickly scattered with large shagreen-dots right up
to the dorsal line (Fig. 47, PI. VI.), then strikingly
resembling the adult larva of D. Euphorbia. The
light ochreous-yellow individuals, on the other
hand, were sometimes entirely without shagreen-
ing (Fig. 48, PI. VI.), being smooth, and much
resembling the light ochreous-yellow or yellowish-
red caterpillar of D. Niccza (Fig. 51, PI. VI.).
The Origin of the Markings of Caterpillars. 215
I have never seen a caterpillar of Galii which
showed traces of the subdorsal line in the last
stage, nor have I ever met with one which
possessed a second row of " mirror " spots ; so that
retrogression or a sudden advance in development
does not appear to occur.
Of the North African D. Mauritanica, which
likewise belongs to the Galii group, I have not
been able to obtain specimens or figures of the
younger stages. The adult caterpillar is very
similar to that of Euphorbice, but differs in the
absence of the second row of ring-spots. For
this reason it must be regarded as a retarded
form at an older stage of phyletic development.
I now proceed to the Livornica group.
DEILEPHILA LIVORNICA, ESPER.
This, the only European species here to be
considered, possesses almost the same markings
as Galii in its fourth stage, i. e.y a subdorsal line
with interpolated ring-spots. The species is
known to be rare, and I have not been able to
obtain living specimens, but I have examined
several blown larvae, all of which agree in having
the ring-spots sharply distinct from the whitish
subdorsal line, so that the latter is thereby
interrupted. Figures of the adult larva are
given in the works of Hiibner, Boisduval, and
Duponchel. In most specimens the ground-
2 1 6 Studies in the Theory of Descent.
colour is brown, although Boisduval 24 also figures a
1 'glit-green specimen; from which it may be inferred,
from analogy with Galii and Vespertilio, that the
first stages are green. In Dr. Staudinger's col-
lection there is a young larva, probably in the
fourth stage, the ground-colour of which is light
ash-grey. The dorsal and subdorsal lines are
white, the latter showing in the positions where
the ring-spots subsequently appear, small white
" mirrors " with red nuclei, exactly correspond-
ing to the stage of Vespertilio represented in
Fig. 49 A, PL VI. The "mirrors" are nothing
more than dilatations of the subdorsal line, which
is not therefore interrupted by them. The black
" ground-area " does not surround the " mirrors "
completely, but borders them only above and
below, and is much more strongly developed
above, extending in this direction to the dorsal
line.
The fourth group comprises the two species
D. Lineata, Fabr., and D. Zygophylli, Ochs., the
former being the North American representative
of our D. Livornica, but differing in remaining
permanently at the fourth stage of this last species.
I am acquainted with D. Lineata only through
the figure of the adult larva given by Abbot and
Smith, which figure, judging from the position and
form of the spots, I am compelled to believe is
not quite correct, notwithstanding the excellence
24 Fig. 62, PI. VII. , is copied from Boisduval.
The Origin of the Markings of Caterpillars. 2 1 7
of the other illustrations. The ground-colour of
the caterpillar is green ; the subdorsal yellow,
bordered with black, slightly curved, arched lines,
which nowhere interrupt its continuity. This
North American species appears therefore to be
an older form than our Livornica.
DEILEPHILA ZYGOPHYLLI, OCHSENHEIMER.
This species, which is the next allied form to
D. Lineata, is an inhabitant of Southern Russia.
I have seen four specimens of the caterpillar in
Dr. Staudinger's collection, three of which are
certainly in the last ontogenetic stage. The
ground-colour appears ash-grey, ash-brown, or
blackish with whitish granulations. A broad
white subdorsal line extends to the base of the
black caudal horn, this line in one specimen
appearing at first sight not to possess a trace of
spot rudiments (Fig. 50). On closer investiga-
tion, however, there could be observed, in the
same position where the ring-spots stand in the
other species of Deilephila, small black crescents
above and below the subdorsal line. In other
specimens the white subdorsal line had also
become expanded in these positions into distinct
spots ; indeed, in one individual light white
mirror-spots, bordered above and below by black
crescents, stood on the subdorsal line (Fig. 50 A).
It is thus in this distinguishing character that
the caterpillar is extremely variable, and we may
2 1 8 Studies in the Theory of Descent.
suppose either that this species is now in a state
of transition to a higher stage of phyletic develop-
ment, or else that the ring-spots were formerly more
strongly developed, and are now degenerating.
The developmental history of the larva could alone
decide which of these two views is correct. There
would be no difficulty in procuring materials for
this purpose if one of the numerous and zealous
Russian naturalists would take up the subject.
DEILEPHILA HIPPOPHAES, ESPER.
This is the only representative of the fifth and
oldest group known to me. The moth resembles
D. Euphorbia to the extent of being sometimes
confounded with it, a circumstance which is made
the more remarkable by the fact that the cater-
pillars are so completely different.
The adult larva of this local moth has been
made known by the figures, more or less exact, in
the works of Htibner, Boisduval, and Duponchel.
Wilde also gives a description of it, although from
a foreign source. I will not here delay myself by
criticizing the different descriptions and figures ;
they are partly correct, partly inexact, and some-
times altogether erroneous ; they were of no avail
for the question which here primarily concerns us,
and new observation had to be undertaken.
I have been able to compare altogether about
forty caterpillars, thirty-five of which were living.
All these specimens possessed nearly the same
The Origin of the Markings of Caterpillars. 219
greyish-green ground-colour, and most of them had
exactly the simple marking as represented, for
instance, in Hubner's figure, i. e., a rather broad
greenish-white subdorsal line, somewhat faded at
the edges, and without a trace of spots on any of
the segments with the exception of the eleventh,
on which there was a yellowish, black-bordered
mirror-spot, with a broad, diffused, vivid orange-
red nucleus. Specimens also occur, and by no
means uncommonly, in which no other markings
are to be seen than those mentioned ; there were
nine among twenty-eight examples compared from
this point of view.
In many other individuals of this species small
red spots appear on the subdorsal line, exactly in
the positions where the ring-spots are situated in
the other species of the genus (Fig. 60), so that
these spots are thus repetitions of the single ring-
spot — a fact which must appear of the greatest
interest in connection with the development of the
markings throughout the whole genus. But this
is not all, for again in other specimens, these red
spots stand on a large yellow " mirror," and in one
individual (Fig. 59), they had become developed
into well-formed ring-spots through the addition of
a black border. We have thus presented to us in
one and the same stage of a species, the complete
development of ring-spots from a subdorsal line.
These facts acquire a still greater interest, as show-
ing how new elements of marking are produced.
220 St^t,dies in the Theory of Descent.
The spots on the subdorsal line decrease from the
posterior to the anterior segments, so that they
must undoubtedly be regarded as a repetition or
transference of the ring- spot previously developed
on the eleventh segment. I will now proceed to
furnish proofs in support of this statement.
I have never met with any specimens having
ring-spots on all the segments — in the most promi-
nent instances these spots were present on seg-
ments 10 — 5. This was the case in three out of
the twenty-eight caterpillars minutely examined.
On all these segments, however, the ring-spots
were not equally developed, but increased in per-
fection from the posterior towards the anterior
segments. In the larva represented in Fig. 59 for
example, there is a completely developed ring-spot
on segment 10, which, although possessing but a
feeble black " ground-area," is still distinctly bor-
dered ; on segment 9 this border is less sharp,
and not so dark, and it is still less sharp and
much lighter on segments 8 and 7, whilst
it has completely disappeared from segment 6,
the yellow " mirror " having at the same time lost
in size. On segment 5, only two small con-
tiguous reddish spots, the first rudiments of the
nucleus,25 can be recognized on close inspection.
Specimens in which the spots extend from the
eleventh to the seventh segment are of more
25 The fading of the red anteriorly has not been represented
in the figure.
The Origin of the Markings of Caterpillars. 221
frequent occurrence, five having been found among
the twenty-eight. In these the spots diminish
anteriorly in size, perfection, and intensity of colour.
Still more frequently (in eleven specimens) are the
ring-spots or their rudiments restricted to the
tenth and ninth segments, the spot on the latter
being without exception less developed than that
on the former segment.
An anteriorly progressing formation of ring-
spots thus undoubtedly occurs, the spots generally
diminishing in perfection very suddenly towards
the front segments ; and specimens, such as that
represented in Fig. 60, PI. VII., in which traces of
ring-spots are to be seen on all the segments
from the tenth to the fifth, are of rare occurrence.
From what elements of marking are these
secondary ring-spots resulting from transference
developed ? They do not, as in the case of the
primary eye-spots of the Cheer ocampincz, originate
in the separation of one portion of the subdorsal
line, and the subsequent formation of this detached
spot into a " mirror ;" but they arise from the for-
mation of a nucleus, first one and then two of the
shagreen-dots on the subdorsal line acquiring a
yellowish or reddish colour (Fig. 61, PL VII., seg-
ments 6 and 7). The ground on which these two
spots are situated then becomes yellow (Fig. 61,
PL VII., segment 8), and a more or less distinct
black border, having the forrn of two small crescents,
is afterwards formed. At a later period these two
222 Studies in the Theory of Descent.
crescents and also the two primary nuclei coalesce,
producing a ring-spot which, as in Fig. 61, PL VI I.,
segment 9, can be distinctly resolved into two
portions.
It certainly cannot be denied that these facts
may also be theoretically interpreted in a reverse
sense. We might interpret the phenomena in this
case, as also in that of D. Zygophylli, as a gradual
disappearance from the front towards the hind
segments of ring-spots formerly present, a view
which could only be refuted by the ontogeny of
the species. I have not been fortunate enough to
procure eggs of D. Hippophaes, so that the younger
stages are unknown to me. Among my cater-
pillars, however, there were two in the fourth
stage of development, but these did not show
ring-spots on all the segments, as we should expect
on the above view ; on the contrary, no trace of
such spots could be seen on any of the segments
with the exception of the eleventh, on which
there was a ring-spot less perfectly developed than
in the last stage.
In this fourth stage the larva of D. Hippophaes
is of a lighter green (Fig. 58), the subdorsal
yellowish with sharp boundaries, and the infra-
spiracular line pure white, as in the next stage.
The shagreening is present, but none of the
shagreen-dots are red or reddish, and no trace of
a ring-spot can be detected on the subdorsal line
with the exception of that on the eleventh segment.
The Origin of the Markings of Caterpillars. 223
In this last position this line is somewhat widened,
and a long, diffused, rose-red spot can there be
recognized upon it (Fig. 58 A). The black "ground-
area " present in the fifth stage is as yet absent,
and the spot is not so sharply separated ante-
riorly from the subdorsal line as it becomes later.
From these observations we might venture to
expect that in the third stage of Hippophaes, the
subdorsal line would also be free from this spot
on the eleventh segment, and it is possible that in
the second stage this line is itself absent.
THE GENUS DEILEPHILA : SUMMARY OF FACTS AND
CONCLUSIONS.
Regarding only the adult larvae of the species
of Deilephila, these represent in their five groups,
five stages in the phyletic development of the
genus ; but if we also take into consideration the
developmental history, two more stages must be
added, viz., that in which the caterpillar possesses
no particular marking, as was found to be the case
in the first stage of the development of D. Euphor-
bia and D. Dahlii ; and a second stage with a sub-
dorsal line, but without any ring-spot formations.
Seven stages of phyletic development must there-
fore be distinguished.
Stage i. — No species with entire absence of
marking in the adult form now occurs.
Stage 2. — A subdorsal, accompanied by a spira-
cular line, extends from the caudal horn to the
224 Studies in the Theory of Descent.
first segment. This also no longer forms the final
stage of the ontogeny, but is, however, undoubt-
edly retained in the second stage of several
species (D. Vespertilio, Livornica^ Lineata, and
perhaps also Galii}.
Stage 3. — The subdorsal line bears a ring-spot
on the penultimate segment ; the other markings
as in the last stage. D. Hippophaes only belongs
to this stage, a small number of specimens, how-
ever, showing a transition to the following stage
by the transference of ring-spots from the posterior
to the anterior segments.
Stage 4. — Open ring-spots appear on the sub-
dorsal line on all the segments from the eleventh
to the first. D. Zygophylli and the North
American D. Lineata belong here.
Stage 5. — Closed ring-spots are situated on the
subdorsal line. Of the known species, only D.
Livornica concludes its development at this phy-
letic stage.
Stage 6. — A single row of ring-spots replaces
the subdorsal line. D. Galii, Vespertilio, and
Mauritania represent this stage at the conclusion
of their ontogeny.26
Stage 7. — A double row of ring-spots. Only
D. Dahlii, Euphorbice, and Niccea attain to this
highest stage of Deilephila marking, the two first
26 [The caterpillar of Deilephila Euphorbiarum, figured by
Burmeister (Ldp. Re'p. Arg., PI. XVI, Fig. i) belongs to this
stage. R.M.]
The Origin of the Markings of Caterpillars. 225
species in the fourth stage, and Niccza in the
third stage of its ontogeny.
Although our knowledge of the history of the
development of the individual species is still so
fragmentary, we may conclude with certainty that
the development of the markings has been uniform
throughout — that it has proceeded in the same
manner in all species. All the species appear to
be making for the same goal, and the question
thus arises whether there may not be an innate
force urging their phyletic development. The
rigorous examination of this conception must be
reserved for a later section. Here, as we are only
occupied essentially in establishing facts, it must
be remarked that retrogression has never been
observed. The young larval forms of a species
never show the markings of a later phyletic stage
than the older larval forms ; the development takes
the same course in all species, only making a
greater advance in the same direction in some
than in others.
Thus, Niccza and Euphorbia have advanced to
the seventh phyletic stage, Zygophylli and Hippo-
phaes only to the third, and some specimens of
Zygophylli to the fourth. But at whatever
phyletic stage the ontogeny of a species may
terminate, the young larval stages always display
the older phyletic stages. Thus, Galii in its last
ontogenetic stage reaches the sixth phyletic stage ;
in its penultimate stage it reaches the fifth
Q
226 Studies in the Theory of Descent.
phyletic stage ; and in its third stage ; the fourth
phyletic stage is represented, so that little imagina-
tion is required to anticipate that in the second
stage the third or second phyletic stage would be
pictured.
If we tabulate the development of the various
species, indicating the ontogenetic stages by
Arabic numerals, and the stages of the phylogeny
which are reached in each stage of the ontogeny
by Roman numerals, we obtain a useful synopsis
of the series of developments, and, at the same
time, it shows how many gaps still remain to be
filled up in order to complete our knowledge even
of this small group of species.
TABLE OF DEVELOPMENT OF THE SPECIES OF DEILEPHILA.
Deilephila.
Ontogeny
Stage i.
Ontogeny
Stage 2.
Ontogeny
Stage 3.
Ontogeny
Stage 4.
Ontogeny
Stage 5.
i. Hippophaes
?
?
?
III.
III.— IV.
2. Zygophylli
?
?
?
?
m.__iv.
3. Lineata
?
?
?'
?
IV.
4. Livornica
?
?
?
IV.
V.
5. Galii
?
?
IV.
V.
VI.
6. Vespertilio
?
II. (?)
IV.
V.
VI.
7. Mauritanica
?
?
?
?
VI.
8. Dahlii
I.
?
VI.
VII.
VII.
9. Euphorbise
I.
V.
VI.
VII.
VII. .
10. Nicaea
?
?
VII.
VII.
VII.
The Origin of the Markings of Caterpillars. 227
From this very incomplete table we perceive
that, in certain instances, the stages can be repre-
sented as a continuous series of phyletic steps, as
in the case of D. Galii ; that in others certain steps
may be omitted, as with D. Euphorbia, in which
grade I. of stage i is immediately followed by
grade V. in stage 2. In reality the gap caused
by this omission is still greater than would appear,
as grade V. is only indicated, and not actually
reached, the subdorsal not being present as a
sharply-defined line, but only as a faint stripe.
The suppression of phyletic steps increases with
the advancement in phyletic development. The
higher the step to which a species finally attains,
the greater is the tendency of the initial stages to
be compressed, or omitted altogether.
From what has thus far been seen with respect
to the development of D. Hippophaes, there may
be drawn what to me appears to be a very
important conclusion, viz. that the ring-spots
of Deilephila first originated on the segment
bearing the caudal horn, and were then gradually
transferred as secondary spots to the preceding
segments. Complete certainty would be given to
this conclusion by a knowledge of the young
forms of other phyletically retarded species, espe-
cially those of the American D. Lineata, and
perhaps also those of Zygophylli and Livornica.
The few observations on the development of
D. Galii already recorded give support to this
Q 2
228 Studies in the Theory of Descent.
view, since the absence of ring-spots on the three
front segments in the young caterpillar (one
instance), or their less perfect formation on these
segments (second instance), indicates a forward
transference of the spots.
If the foregoing view be accepted, there follows
from it a fundamental difference between the
development of the genera Chczrocampa and
Deilephila. In the former the formation of the
eye-spots proceeds from a subdorsal line, but they
first appear on two of the front segments, and are
then transferred to the posterior segments. In
Deilephila, on the other hand, a single ring-spot
is formed on the penultimate segment bearing the
caudal horn, and this is repeated on the anterior
segments by secondary transference. With respect
to the origination of the ring-spot also, there is a
distinction between thiu genus and Chcerocampa,
inasmuch as t'he first step towards the eye-
formation in the latter consists in the separation of
a curved portion of the subdorsal line, whilst in
Deilephila the nuclear spot first seems to originate
and the separation of the mirror-spot from the
subdorsal line appears to occur secondarily. It is
difficult here to draw further conclusions, since the
first appearance of the primary ring-spot has not
yet been observed, and no more certain inference
respecting the history of the formation of the
primary ring-spots can be drawn from the manner
in which the secondary ring-spots are formed.
The Origin of the Markings of Caterpillars. 229
Because in Hippophaes the formation of the
secondary ring-spots begins with the red colora-
tion of one or two shagreen-dots, it does not follow
that the primary spot on the eleventh segment also
originated in this manner ; and this is not without
importance when we are concerned with the causes
which underlie the formation of ring-spots. In
Ch&rocampa also, the formation of the primary
eye-spots appears to differ from that of the
secondary — in the latter the black " ground-area"
first appearing, and in the former the " mirror-
spot." The secondary eye-spots certainly remain
rudimentary in this last genus, so that the
evidence in support of this conclusion is thus much
weakened ; but it must be admitted that we are
here on ground still too uncertain to admit of
wider conclusions being based thereon.
As a final result of the investigation, we may
advance the opinion that the existing species of
the genus Deilephila have reached five different
phyletic stages, and that their very different
external appearance is explained by their different
phyletic ages ; the appearance from these cater-
pillars of moths so extremely similar, can other-
wise be scarcely understood.
It may appear almost unnecessary to bring
forward additional proofs in support of this inter-
pretation of the facts, but in a field where the
data are so scanty, no argument which can be
drawn from them should be considered as super-
230 Studies in the Theory of Descent.
fluous. The variations which occasionally occur
in the larvae, however, to a certain extent furnish
a proof of the correctness of the theoretical inter-
pretation offered.
When, in the ontogeny of these species, we
actually see before us a series of stages of phyletic
development, we must admit that ordinary rever-
sion may occur, causing an adult caterpillar to
show the characters of the young. Forms
reverting to an earlier phyletic stage must, on the
whole, occur but seldom, as this stage is removed
further back in the ontogeny. Thus, indications
of the subdorsal line must occur but rarely in the
adult larvae of Euphorbia, and still less frequently
in Nic&a, whilst they must be expected to be of
more common occurrence in Vespertilio, and also,
as has already been seen, in Dahlii. In this last
species, as also in Vespertilio, the completely-
developed subdorsal line is still present in the
third stage, whilst it is possessed by Euphorbia
only in the second stage, and then in a rudimentary
condition.
The state of affairs may in fact be thus de-
scribed : Among several hundred adult larvse of
Dahlii found in Sardinia by Dr. Staudinger, there
were some which did not actually possess a dis-
tinct subdorsal line, but in place thereof, and as its
last indication, a feeble light stripe. One of Dr.
Staudinger's caterpillars showed also a distinct
line between the closed eye-spots. In the last
The Origin of the Markings of Caterpillars. 231
stage of Vespertilio this line appears still more
frequently, whilst in Euphorbia it is extremely
rare, and when present it only appears as a faint
indication. This is the case with one of the
specimens figured in Hiibner's work as an " aber-
ration," and also with one in Dr. Staudinger's
collection. Of Niccea I have at most seen only
eight specimens, none of which showed any trace
of the long-vanished subdorsal line.
It must be expected that any ontogenetic stage
would most readily revert to the preceding phyletic
stage, so that characters present in the preceding
stage are consequently those which would most
commonly arise by reversion. This postulate of
the theory also finds confirmation in the facts.
Caterpillars which, when full grown, belong to the
seventh phyletic stage, e.g. D. Euphorbia ', not
unfrequently show variations corresponding to the
sixth stage, i. e. only one instead of two rows of
ring-spots — the upper and first-appearing series.
On the other hand, forms reverting to the fifth
phyletic stage (ring-spots with connecting sub-
dorsal line) occur but very rarely. I have never
met with such cases in adult living caterpillars of
D. Euphorbia, although in one instance such a
larva was found in the fourth ontogenetic stage ;
but the strikingly dark, brownish subdorsal line
which connected the otherwise perfectly developed
ring-spots, completely disappeared in the fifth stage
of the ontogeny. Those larvae which, in the adult
232 Studies in the Theory of Descent.
state, belong to the sixth phyletic stage, not
unfrequently show the characters of they£/M stage
more or less developed, as, for example, D. Vesper-
HKo*
THE GENUS SMERINTHUS, LATREILLE.
The caterpillars of this genus are very similar
in appearance, and all possess extremely simple
27 [In concluding this account of the Chcerocampincz I may
call attention to the following species, which have since been
figured by Burmeister : — Pachylia Ficus, Linn. (loc. cit. PI. XIV,,
Figs, i and 2) ; during the three first stages the larva is uni-
formly green, with a yellow subdorsal line, and below this ten
oblique yellow stripes slanting away from the head ; after the
third moult the colour completely changes, the whole area of
the body being divided into two distinct portions by the sub-
dorsal line, above which the colour is red, and underneath of
a pale green ; the oblique stripes have almost disappeared ; no
occelli nor annuli are present. Pachylia Syces, Hiibn. (loc. cit.
Fig- 3) j very similar to the last species in its young stages
(figured also by Merian, Surin. pi. 33). Philampelus Vitis,
Linn. (loc. cit. Figs. 4 and 5) ; two stages represented ; between
first and second moults green, with oblique paler stripes slant-
ing in same direction as in Pachylia, and each one containing
a red streak surrounding the spiracle. When adult, the
ground-colour is yellow above and green beneath, the whole
surface being mottled with deep black and red transverse
markings ; the oblique stripes whitish, bordered with black at
their lower extremities (figured also by Me'rian, pis. 9 and 39).
Philampelus Anchemolus, Cram. (loc. cit. PI. XV., Fig. i ; Merian,
pl- 47) j green when young, with seven oblique red stripes ;
when adult, uniformly brown, with seven pale yellow lateral
markings, the first four of which are spots, and the remainder
broad oblique stripes slanting forwards. Philampelus Labrusae,
(see note 13, p. 195). R.M.]
The Origin of the Markings of Caterpillars. 233
markings, The occurrence of numerous stages of
development of these markings is thus excluded,
and the study of the ontogeny therefore promised
to furnish less information concerning the phyletic
development of the genus than in the case of the
preceding genera. This investigation has never-
theless also yielded interesting results, and the
facts here recorded will be found of value in like-
wise throwing light on the causes which have
produced the markings of caterpillars.
I shall commence, as in former cases, with the
developmental history. I have easily been able to
obtain fertile eggs of all the species of Smerinthus
known to me. Impregnated females laid large
numbers of eggs in confinement, and also bred
females of the commoner species can readily be
made to copulate, when pinned, and exposed in a
suitable place in the open air. A male soon
appears under these circumstances, and copulation
is effected as readily as though the insect were not
fastened in the way indicated.
SMERINTHUS TILLE, LiNN.28
The light green eggs are nearly spherical, and
28 [Mimas Tilicz of Butler's revision. The author states that
this genus is " easily distinguished from Laothoe by the form
of the wings, the outer margin of secondaries deeply excavated
below the apex, and the secondaries narrow and not denticu-
lated." Here again we have a clashing of the results arrived
at by a study of the ontogeny of the larvae, on the one hand,
and the founding of genera on the characters of the imagines
234 Studies in the Theory of Descent.
after fourteen days (beginning of July) the young
larvae emerge. These are also of a light green
colour, and are conspicuous for the great length
of the caudal horn, which is nearly half as long as
the body. This horn is likewise of a light green
at first, but becomes dark violet in the course of
an hour. No trace of any markings can be
detected at this stage.
As soon as the caterpillars are hatched they
commence to nibble the empty egg shells ; then
they run about with great activity, and after
several hours take up their position on the largest
vein on the under side of the lime leaves, where
they remain for a long period. In this situation
they have the same form and colour as the leaf-
vein, and are very difficult to discover, which
would not be the case if they reposed obliquely or
transversely to the vein. In about 4 — 5 days
the caterpillars undergo their first moult, and
enter upon the second stage. On each side of
the segments n — 4, there now appear seven
oblique whitish stripes on a somewhat darker
only, on the other. Of the three species discussed by Dr.
Weismann, Mr. Butler, following other authors, refers Tilia to
the genus Afimas, Populi to Laothoe, and Ocellatus to Smerin-
thus. It is to be hoped that when our knowledge of the
developmental history of larvae is more complete in all groups,
a reconciliation between the results of the biological investi-
gator and the pure systematist will be brought about, so that
a genus may not, as at present, have such very different values
when regarded from these two points of view. R.M.]
The Origin of the Markings of Caterpillars. 235
green ground ; these slope in the direction of the
caudal horn. Owing to the transparency of the
skin, a dark green dorsal line appears in the posi-
tion of the underlying dorsal vessel, the green
contents of the alimentary canal being distinctly
visible through the absence of adipose matter in
the tissues. The larvae possess also a fine whitish
subdorsal line, which extends from the horn to the
head. The horn at this stage becomes black with
a yellowish red base.
In the third stage, which occurs after six or seven
days, the oblique stripes appear darker, and the
subdorsal line disappears.
Fourth Stage.
After another period of 4 — 5 days the third
moult takes place, and there now commences
a dimorphism which will perhaps be better desig-
nated as variability, since the two extremes are
connected by transitional forms. The majority of
the larvae have, as in the preceding stage, pure
white oblique stripes, but many of them possess a
blood-red spot on the anterior side of the stripes,
this spot showing all gradations in size and depth
of colour between maximum development and a
mere trace. Special interest attaches to these
spots, as they are the first rudiments of the coloured
border of the oblique stripes which occurs in so
many Sphinx caterpillars.
In the fifth stage — the last of the larval de-
236 St^tdies in the Theory of Descent.
velopment — the red spots become more strongly
pronounced. Among eighty caterpillars from one
brood there were about twenty without any red
whilst the remainder were ornamented with more
or less vivid blood-red spots, often large and irre-
gular in form. In some specimens the spots had
become drawn out into lines,29 forming a coloured
edge to the oblique white stripes, similar to that
possessed by the larva of Sphinx Ligustri. The
caterpillar is thus represented in many figures, but
generally the coloured stripe is made too regular,
as in reality it is always irregularly defined above,
and never so sharp and even as in Sphinx
Ligustri. The character is here obviously not yet
perfected, but is still in a state of development.
SMERINTHUS POPULI, LINN.
From green spherical eggs there emerged larvae
6.5 millimeters in length without any markings.
They were of a light greenish-white, the large head
and long caudal horn being of the same colour.
The posterior boundary of the segments appears
as a light shining ring (PL VI. Fig. 55).
The characteristic markings of the genus appear
on the following day without the occurrence of any
moult : seven oblique white stripes arise from near
the dorsal line, and extend along the sides in a
direction parallel to that of the horn. On the
three front segments they are represented only by
*J The caterpillar is thus figured by Rosel.
The Origin of the Markings of Caterpillars. 237
three small white spots (Fig. 56). The cater-
pillar likewise possesses a marking of which the
adult species of the genus retain only a trace,
viz., a well-developed, pure white subdorsal line,
which is crossed by the six anterior oblique stripes,
and uniting with the upper part of the seventh
extends to the caudal horn.
I long believed that the markings described were
first acquired in the second stage, as I was possessed
with the generally accepted idea that the changes
of form and colour in insects could only occur at
the period of ecdysis. I at first thought that the
moult had escaped my notice, and I was only
undeceived by close observation of individual
specimens.
Second Stage.
The first moult took place after five days, the
larvae being 1.4 centimeters in length. Only un-
important changes of marking are connected there-
with. The subdorsal line loses much in thickness
and definition, and the first and last of the oblique
stripes become considerably broader than the
intermediate ones (Fig. 57). The green ground
colour and also the stripes acquire a yellowish
hue.
On the other hand, there occur changes in form.
The head, which was at first rounded, becomes of
the characteristic triangular shape, with the apex
upwards, common to all the species of the genus,
238 Studies in the Theory of Descent.
and at the same time acquires two white lines,
which unite above at the apex of the angle. The
shagreening of the skin now also takes place,
and the red spot at the base of the horn is formed.
There appears to be at this stage a general
tendency for the suffusion of red, the thoracic legs
also becoming of this colour.
Third Stage.
The second moult occurs after six or eight days,
the marking only changing to the extent of the
subdorsal line becoming still more indistinct. This
line can now only be distinctly recognized on the
three front segments in a few individuals, whilst
in the majority it is completely absent. Some-
times the ferruginous red spots on the oblique
stripes now appear, but this character is not com-
pletely developed till the fifth stage. Out -of about
ninety bred specimens in which I followed the
entire development, only one possessed such spots,
and these were situated on both sides of the sixth
segment.
Fourth Stage.
The third moult, which takes place after another
period of six days, is not associated with any change
of marking.
In this stage also I observed in one specimen
(not the one just mentioned) the ferruginous spots,
and again only on the sixth segment. On account
of the theoretical conclusions which may be drawn
The Origin of the Markings of Caterpillars. 239
from this localization of the spots — supposing it to
be of general occurrence — it becomes of importance
to institute observations with different broods, so
as to investigate their first appearance, frequency,
and local limitation. It appears to me very pro-
bable that, with respect to frequency and time of
appearance, there would be great differences, since,
in the last stage, it is just this character which shows
a great variability. It would be more remarkable
if it should be established that the first appearance
of the spots was always limited to a certain seg-
ment ; and there would then be a great analogy
with the first appearance of the eye-spots in
Chcerocampa and the ring-spots in Deilephila.
Fifth Stage.
The adult caterpillar does not differ in marking
to any considerable extent from the preceding
stages. The first and last stripes do not appear
larger than the intermediate ones, as the latter
now increase in size. Many specimens were
entirely without red spots ; in others they were
present, but were small and inconspicuous, whilst
in others again there were two spots, one above
the other, of a vivid ferruginous red, these
coalescing in some cases, and thus forming one
spot of a considerable size. I have never seen
these spots formed into a regular, linear, coloured
border to the white oblique stripes — as occasionally
happens in TY/z^-^-either in living specimens,
blown larvae, or in figures.
240 Studies in the Theory of Descent.
SMERINTHUS OCELLATUS, LINN.
The green eggs much resemble those o
as also do the newly hatched caterpillars, which, as
in the case of this last species, are entirely without
markings. As with Populi, the markings are
formed in the course of the first stage, and are
distinctly visible before the first moult. The long
caudal horn is of a red colour.
After two to three days the caterpillars moult,
their length then being one centimeter ; the seven
beautiful oblique white stripes, and the fine white
subdorsal line, are more strongly pronounced, the
latter becoming broader in front. They differ
from Populi in having the oblique stripes united
in the dorsal line.
The second moult occurs after another three
days, and brings no important change ; only the
fine subdorsal line becoming somewhat fainter.
Neither is the third moult, which takes place four
days later, associated with the appearance of any
essentially new character. The oblique stripes
remain as before, but their upper portions now
stand on a somewhat darker green ground colour,
whilst the subdorsal line vanishes, leaving distinct
traces only on the three or four front segments.
The fourth moult follows after a period of seven
days, and my bred larvae underwent scarcely any
alteration in marking. Only small differences in
coloration became perceptible in the head and
The Origin of the Markings of Caterpillars. 24 i
horn, these changing to bluish. Specimens occur,
although but rarely, which show in this last stage
red spots in the vicinity of the oblique stripes, just
in the same manner as with Populi> in which
species, however, they occur more commonly. I
only once found an adult larva of Ocellatus
possessing reddish-brown spots above and below
the oblique stripes,30 exactly as in one of the
specimens figured by Rosel/
31
80 [In 1879 Mr. E. Boscher found about thirty full-grown
caterpillars of this species in the neighbourhood of Twickenham,
ten to twelve of which were feeding on Salix viminalis, and
the remainder, from a locality not far distant, on Salix triandra.
The whole of the specimens taken on the plant first named,
had the red-brown spots above and below the oblique stripes
more or less completely developed, as I myself had an oppor-
tunity of observing. In these spotted specimens the ground-
colour was bright yellowish-green, and in the others this
colour was dull whitish-green above, passing into bluish-green
below. Should these observations receive wider confirmation,
it would be fair to conclude that this species is now in two
states of phyletic development, the more advanced stage being
represented by the brighter spotted variety. (See also Proc.
Ent. Soc. 1879, P- xliv.). Mr. Peter Cameron has recently
suggested (Trans. Ent Soc. 1880, p. 69) that the reddish-
brown spots on the Smerinthus caterpillars may serve for pur-
poses of disguise, as they closely resemble, both in colour
and form, certain galls (Phytoptus) of the food-plants of these
species. If this view be admitted, these spots must be
considered as a new character, now being developed by
natural selection. The variation in the ground-colour of the
two forms of S. Ocellatus may possibly be phytophagic, but
this can only be decisively settled by a< series of carefully con-
ducted experiments. R. M.]
31 " Insekten-Belustigungen," Suppl. PL 38, Fig. 40.
R
242 Studies in the Theory of Descent.
In this stage also there remains almost always
on the three to six front segments, a more or
less distinct residue of the subdorsal, which ex-
tends backwards from the head as a whitish line
intersecting the foremost oblique stripes. (Fig.
70, PI. VII.)
RESULTS OF THE DEVELOPMENTAL HISTORY OF SMERINTHUS
TlLIJE, POPULI AND OCELLATUS.
From the meagre materials furnished by these
three obviously nearly related species, we may at
least conclude that, with respect to marking, three
stages of development can be distinguished : —
(1) Simple (green) coloration without marking ;
(2) subdorsal lines crossed by seven pairs of oblique
stripes ; (3) more or less complete absence of the
subdorsal lines, the oblique stripes remaining, and
showing a tendency to become edged with a
red border.
Which of the three species is the oldest I will
not attempt to decide. If we might venture to
form any conclusion from the frequency of the
red spots, Tilia would be the youngest, /. e., the
species which has made the farthest advance. But
this does not agree with the fact that the oblique
stripes appear somewhat later in this species.
Both these distinctions are, however, too unim-
portant to enable us to build certain conclusions
on them. Neither does a comparison of the adult
The Origin of the Markings of Caterpillars. 243
larvae with other species of Smerinthus furnish any
further information of importance.
Of the genus Smerinthus, Latr., thirty species
were catalogued by Gray,52 of which I am only ac-
quainted with the larvae of eight (five European,
and three North American). None of these in the
last stage possess a complete subdorsal line toge-
ther with oblique stripes. Neither, on the other
hand, do any of them show a more advanced
stage of development in having the red spots con-
stantly formed into coloured border-stripes. We
must therefore admit that they have all reached
nearly the same stage of phyletic development.
On turning to the doubtfully placed genus Calym-
nia, Boisduval, which is represented in Gray by
only one species, figured by Westwood 33 as a
Smerinthus, we first meet with an older stage of
development of the genus.
The adult caterpillar of C. Panopus, from the
East Indies, possesses, in addition to the oblique
stripes, a completely developed subdorsal line,
34
32 " Catalogue of Lepidop." British Museum. [Butler
divides the subfamily Smerinthince into 17 genera, containing
79 species, viz. Metamimas, 2 ; Mimas ; 4 ; Polyptychus, 7 ;
Lophostethus, i ; Sphingonapiopsis, i ; Langia, 2 ; Triptogon, 23 ;
Laothoe, 2 • Cressonia, 3 ; Paom'as, 2 ; Calasymbolus, 5 ;
Smerinthus^ 5 ; Pseudosmerinthus, 2 ; Daphnusa, 4 ; Leuco-
phhbia, 5 ; Basiana, 10 ; Ccequosa, i. R.M.]
83 " Cabinet Orient. Entom.," p. 13, PL VI., Fig. 2. [Butler
places this species doubtfully among, the Sphingince. R.M.]
84 "Catalogue of the Lepidop. Insects of the E.I. Co.," by
Horsfield and Moore. PL VIII., Fig. 6.
R 2
244 Stiidies in the Theory of Descent.
and thus corresponds to the first stage of S. Populi.
This species may possibly retain in its ontogeny
a stage in which the oblique stripes are also absent,
whilst the subdorsal line is present. From the early
disappearance of the subdorsal line in the species
of Smerinthus, we may venture to conclude that
this character appeared at an early stage of the
phylogeny, whilst the oblique stripes represent
a secondary form of marking, as shall be further
established subsequently.35
85 [The larvae of four other species of this subfamily have since
been made known through Mr. Butler's figures. Smerinthus
Tatarinovii, Menetries (loc. cit. PI. XC., Fig. 16), from Japan,
is " pale sea-green, tuberculated with white, with seven lateral,
oblique, crimson-edged white stripes." There is no trace of
the subdorsal line shown in the figure, so that this species
thus appears to be in the third phyletic stage of development.
Smerinthus Planus, Walker, from China (loc. cit. PI. XCIL,
Fig. n), is "pale green, with white or yellow lateral stripes."
A trace of the subdorsal line remains on the front segments,
thus showing that the species is in the second phyletic stage
of development. Triptogon Roseipennis, Butler, from Hakodadi
(loc. cit. PI. XCL, Fig. 6), is represented as yellow, with seven
oblique white stripes, with large irregular triangular red spots
extending from the anterior edge of the stripes, nearly across
each segment. It is probably in the third phyletic stage.
The Indian Polyptychus Dentatus, Cramer (loc. cit. PL XCL,
Fig. 10), is "bluish-green at the sides, with oblique purple
stripes, with a broad, dorsal, longitudinal, golden-green band,
bordered by subtriangular purple spots, one above each stripe."
The dorsal band is bordered by coloured stripes, which maybe
the subdorsal lines ; but the position in which it is figured, and
its very different mode of coloration, make it very difficult to
compare satisfactorily with the foregoing species. The genus
Ambulyx is closely allied to the SmerintJimce, and the two
The Origin of the Markings of Caterpillars. 245
THE GENUS MACROGLOSSA, OCHSENHEIMER.
The adult larvae of five species are known, and
to these I can now add a sixth. In Gray the
genus contains twenty-six species.36 I cannot find
any figures or descriptions of the young stages of
these caterpillars, and I have myself only observed
the complete ontogeny of one species.
By placing a captured female M. Stellatarum in
a capacious breeding-cage, in the open air, I was
enabled to procure eggs. The moth hovered
about over the flowers, and laid its small, grass-
green, spherical eggs (partly when on the wing),
singly, on the leaves, buds, and stalks of Galium
Mollugo. Altogether 130 were obtained in three
days.37
following species may be here mentioned : A. Gannascus,
Stall, figured by Burmeister (foe. tit. PI. XIII., Fig. 5), is
green, with a yellow subdorsal line, and seven oblique white
lateral stripes, edged with red. A. Liturata, Butl. (loc. cit.
PL XCL, Fig. 2), is yellowish-green above, passing into
bluish-green below. The subdorsal is present on the three
front segments, and is followed by a row of white, elongated
patches, one on each segment, these being the upper portions
of a row of lateral oblique stripes. The thickened upper
extremities of the latter are edged with red, and their arrange-
ment is very suggestive of their having arisen from the breaking
up of a subdorsal line. R.M.]
36 [Butler catalogues 43 species of this genus. R.M.]
3T The deposition of eggs was accomplished by the insect
laying hold of the point of a twig with its legs during flight,
and curving its abdomen upwards against a leaf, the wings
being kept vibrating. The egg is instantaneously fastened to
the leaf. This operation is repeated from twice to four times
246 Studies in the Theory of Descent.
First Stage.
After about eight days the caterpillars emerge.
They are only two millimeters in length, and are at
first yellowish, but soon become green, set with small
single bristles, and they possess a short greenish
caudal horn, which afterwards becomes black.
The head is greenish-yellow. The young larvae
are entirely destitute of marking. (PL III.,
Fig. i).
Second Stage.
The first moult takes place after four days, the
caterpillar now acquiring the marking which it
essentially retains to pupation.
Fine white subdorsal and spiracular lines ap-
pear, and at the same time a dark green dorsal
line, which, however, does not arise from the de-
position of pigment, as is generally the case, but
from a division in the folds of the fatty tissue along
this position. (Fig. 2, PL III.)
The colour is now dirty green in all specimens,
the skin being finely shagreened.
Third Stage.
The second moult, occurring after another
period of four days, does not bring any change of
successively, the moth then hovering over and sucking at the
flowers for some time. The eggs exactly resemble in colour
the young green buds of Galium.
The Origin of the Markings of Caterpillars. 247
marking, the colour only becoming somewhat
darker. Length, twelve millimeters.
Fourth Stage.
The third moult (after another four days) like-
wise brings only a change of colouring, which is of
such a nature that the caterpillar becomes dimor-
phic. At the same time that peculiar roughening
of the skin takes place which, in the case of Chcero-
campa, was designated as " shagreening.'' The
colour is now light grass-green in some specimens,
and dark green in others ; in these last the sub-
dorsal line is edged above with dark brown, and
the spiracles are also of this colour. Length,
seventeen millimeters.
Fifth Stage.
Four days later, after the fourth ecdysis, the
dimorphism becomes a polymorphism. Five chief
types can be distinguished : —
Variety I. — Light green (Fig. 7, PI. III.); dorsal
line, blackish-green, strongly marked ; subdorsal
line broad, pure white, edged above with dark
green ; spiracular line, chrome-yellow ; horn,
black, with yellow tip and blue sides. Spiracles,
blackish-brown, with narrow yellow border ; legs,
and extremities of prolegs, vermilion-red.
Variety //.—Blackish-brown (Fig. 6, PI. III.) ;
head and prothorax, yellowish-brown ; markings
the same as above.
248 Studies in the Theory of Descent.
Variety III. — Blackish-green or greenish-black
(Figs. 10 and n, PI. III.); subdorsal line with
blackish-green border above, gradually passing into
a light green ground-colour; spiracular line,chrome
yellow ; head and prothorax, greenish-yellow.
Variety IV. — Light green (Figs. 4 and 12, PI.
III.) ; dorsal line quite feeble ; subdorsal broad,
only faintly edged with dark green ; subspira-
cular line, faint yellowish ; head and prothorax,
green.
Variety F.— Brownish-violet (Fig. 8, PI. III.) ;
the black dorsal line on a reddish ground either
narrow or broad.
From these five varieties we see that the dif-
ferent types do not stand immediately next to'
one another ; they are, in fact, connected by
numerous transitional forms, the ground-colour
varying greatly, being dark or light, yellowish or
bluish. (Compare Figs. 4, 5, 7, and 12.) The
markings remain the same in all, but may be of
very different intensities. The dorsal line is often
only very feebly indicated, and the subdorsal line
is frequently but faintly edged ; the latter is also
sometimes deep black above and bordered rather
darkly beneath, the sides then being of a dark
green, often with blackish dots on the yellow
spiracular line (Fig. 5, PI. III.), this likewise
being frequently edged with black. Only the
horn and legs are alike in all forms. The green
ground-colour passes into blackish-green, greenish
The Origin of the Markings of Caterpillars. 249
or brownish-black, and again, from reddish-brown
to lilac (Fig. 3), this last being the rarest
colour.
The designation " polymorphism JJ may here
appear very inapplicable, since we have no sharply
distinct forms, but five very variable ground-
colours connected by numerous intermediate modes
of coloration. Should, however, the term " vari-
ability" be suggested, I am in possession of an
observation which tends to show that the dif-
ferent colours have to a certain extent become
fixed. I found a brown caterpillar, the five front
segments of which were light green on the left
side, and the fifth segment brown and green
mixed (Fig. 9, PI. III.). Such parti-coloration can
evidently only appear where we have contending
characters which cannot become combined ; just as
in the case of hermaphrodite bees, where one half
of a segment is male and the other half female,
the two characters never becoming fused so as to
produce a truly intermediate form.38 From this
observation, I conclude that some of the chief
38 [Figures of a remarkable case of gynandromorphism in
a butterfly (Cirrochroa Aoris, Doubl.) have recently been
published by Prof. Westwood (Trans. Ent. Soc. 1880, p. 113).
On the right fore and hind- wings of a male specimen there are
patches of female colouring, thus bearing out in a very striking
manner the above views concerning the non-fusibility of
characters (in this case sexual) which have been long fixed.
Complete (/. e. half-and-half) gynandromorphism is not un-
common in butterflies. R.M.]
250 Studies in the Theory of Descent.
varieties of Stellatarum have already become
so far removed from one another that they must
be regarded as intermediate fixed forms, the colours
of which no longer become fused together when
they occur in one individual, but are developed
in adjacent regions. Other facts agree with this
conclusion. Thus, among the 140 adult larvae
which I bred from the batch of eggs above
mentioned, the transition forms were much in
the minority. There were forty-nine green and
sixty-three brown caterpillars, whilst only twenty-
eight were more or less transitional.
On these grounds I designate the phenomenon
as " polymorphism," although it may not yet have
reached, as such, its sharpest limits. This would
be brought about by the elimination of the inter-
mediate forms.39
89 [I have long held the opinion that the di- and trimorphism
displayed by certain butterflies has originated through poly-
morphism from ordinary variability. I will not here enter into
details, but will only cite a few instances indicating the general
direction of the arguments. The phenomenon to which I
refer is that so ably treated of by Mr. A. R. Wallace (see Part I.,
p. 32, note 1 8) and others. One male has often two or more
distinctly coloured females, and in such cases one form of the
female generally resembles the male in colour. Cases of
polymorphic mimetic females may for the present be excluded,
in order to reduce the argument to its greatest simplicity. Thus,
in the case of native species, Colias Edusa has two females, one
having the orange ground-colour of the male, and the other
the well-known light form, var. Hdice. So, also, Argynnis
Paphia has a normal female and the dark melanic form
var. Valezina. Numerous other cases might be mentioned
The Origin of the Markings of Caterpillars. 2 5 1
Immediately before pupation, all the caterpillars,
both green and brown, acquire a lilac coloration.
The fifth stage lasts seven days, and the whole
larval development twenty-three days, the period
from the deposition of the eggs to the appearance
of the moth being only thirty-one days.
I have treated of the polymorphism of Stella-
tamm in detail, not only because it has hitherto
remained unknown, and an analysis of such cases
has been completely ignored,40 but more particu-
larly because, it appears to me, that important
conclusions can be drawn therefrom. Moreover,
among exotic species ; and, looking at the phenomenon as a
whole, it is seen to be one of gradation. For instance, our
common " Blues" (Plebeius Icarus, P. Thetis, &c.) have females
showing a complete gradation between the ordinary blue male and
the brown female coloration. In a large number of specimens of
Callosune Eupompe in my cabinet, collected in Arabia by the late
J. K. Lord, there is a completely graduated series of females, vary-
ing from individuals having the scarlet tips of the fore-wings as
strongly developed as in the males, to specimens without a trace
of such colouring : and the same is the case with other species of
this and allied genera. In such instances it is only necessary
for the intermediate female forms to become extinct, in order to
have true cases of dimorphism. It is significant that in 1877,
when Colias Edusa appeared in this country in such extra-
ordinary profusion, large numbers of intermediate forms were
captured, these forming an uninterrupted series connecting
the normal female and the var. Helice. R.M.]
40 [Many of our best describers of caterpillars, such as the
late Edward Newman, Messrs. Hellins and Buckler, &c., have
described the various forms of nurrierous polymorphic species,
but not from the point of view of the comparative morphology
and ontogeny of the markings. R.M.]
252 Stiidies in the Theory of Descent.
such an extreme multiplicity of forms is interesting,
since, so far as I know, polymorphism to this
extent has not been observed in any insect.
The theoretical bearing of this polymorphism
will be treated of subsequently. It is not in any
way connected with a more advanced development
of the markings, since M. Stellatarum shows in
this respect a very low state of development. This
species displays only two stages : — (i), complete
absence of all markings; and (2), a simple subdorsal,
with dorsal and spiracular lines. We must there-
fore admit that the phyletic development of the
markings has for a long time remained at a stand-
still, or, what expresses the same thing, that the
marking which the adult larva now possesses is
extremely old.
In order to complete my observations on M.
Stellatarum, I now add some remarks on the
pupa, the colour variations of which it appeared of
importance to investigate, owing to the extraordi-
nary variability of the caterpillar, The pupa varies
but very slightly ; the ochreous yellow ground-
colour sometimes passes into reddish, and some-
times into greenish ; the rather complicated black-
ish-brown marking of streaky lines is very con-
stant, [especially on the wing portions, being at
most only more or less strongly pronounced. The
minute colour variations of the pupa therefore have
no connection with the colour of the caterpillar,
both green and brown larvae furnishing sometimes
The Origin of the Markings of Caterpillars. 253
reddish-yellow and sometimes greenish-yellow
pupae.
The comparison of M. Stellatarum with the
other known species of the genus, brings scarcely
any addition to our knowledge of the phyletic
development. Thus, the two European species of
which the caterpillars are known, viz. M. Fucifor-
mis and Bombyliformis^ show essentially the same
markings as Stellatarum, the chief element being
a well-developed subdorsal line. The Indian M.
Gilia, Herrich-Schaf., possesses also this line,42 and,
togetherwith the East Indian M. Cory thus, Walk.,43
has oblique stripes in addition ; the stripes do not,
however, cross this line, but commence underneath
it, and probably originated at a later period than the
subdorsal line. Should this be the case, we must
regard M. Corythus as representing a later phyletic
stage. According to Duponchel's figures, in both
M. Fuciformis and Bombyliformis small oblique
stripes (red) occur near the spiracles, but these
have nothing to do with the oblique stripes of M.
Gilia just mentioned, as they run in a contrary
direction. Of the two European species, I have
41 [In Butler's revision both these species are placed in the
genus Hemaris. R.M.]
42 [This species is figured also by Butler (loc. cit. PI. XC.,
Fig. 9), who represents it with seven oblique green lines
between the spiracles and below the subdorsal line. R.M.]
43 "Cat. E. Ind. Co. Mus.," PI., VIII., Fig. 2. [Walker,
Lepidop. Heter. VIII., p. 92, No. 14, 1856; this species is
strictly confined to Java. R.M.J
254 Studies in the Theory of Descent.
only seen the living caterpillar of F^i,c^formis, and
this possessed no oblique stripes.
To these five species I am now enabled to add
a sixth, viz. Macroglossa Croatica^ a species
inhabiting Asia Minor and Eastern Europe, of
which a specimen and notice were kindly forwarded
to me by Dr. Staudinger. The adult caterpillar
much resembles that of M. Stellatarum in form and
marking, but the subdorsal line appears much
less distinctly defined, and the dorsal and spiracular
lines seem to be entirely absent. The colour is
generally green, but varies to red, and the sub-
dorsal is more distinct and sharper in the young
than in the adult larva. The markings of this
species do not therefore in any way surpass those
of Stellatarum, but are, on the contrary, much
simpler.45
44 [Eng. ed. The caterpillar is described and figured by
Milliere, " Iconographie des Chenilles et Le'pidopteres inedits,"
tome iii., Paris, 1869 ; also in the Annales, Soc. Linn, de
Lyon, 1871 and 1873.] [This sp. = Hemaris Croatica,
Esper., of Butler's revision. R.M.]
45 [The following additional species of the subfamily Macro-
glosshuz have been figured by Butler \-Lophura Hyas, Walk.
(loc. cit. PI. XC, Figs, i and 2), Hong-Kong, Silhet, and Java.
The larva is apparently figured in two stages, the younger being
red-brown with oblique white stripes, and the head and three front
segments green. The larger specimen is green, mottled with
red-brown, and no oblique stripes. In both figures the sub-
dorsal line is indicated. The whole colouring is very suggestive
of protective resemblance. Hemaris Hylas, Linn., from China,
Japan, Ceylon, India, Australia, and Africa (loc. cit. PI. XC., Fig.
4). The upper part of the body is light blue, and the lower part
The Origin of the Markings of Caterpillars. 255
THE GENUS PTEROGON, BOISD.48
Although I am acquainted with only a small
portion of the developmental history of a single
species of this genus, I will here proceed to record
this fragment, since, taken in connection with two
other species, it appears to me sufficient to deter-
mine, at least broadly, the direction of develop-
ment which this genus has taken.
green, the two areas being separated by a white subdorsal line
bordered above with brown. The dorsal line is feebly repre-
sented. Macroglossa Belts, Cram., N. India (loc. cit. PL XC., Fig.
6), is figured with the ground-colour deep indigo ; a conspicuous
white subdorsal, and a yellow spiracular line is present; on
the side of each segment, between the two lines mentioned, there
is a large red spot with a yellow nucleus (? eye-spots), the spots
decreasing in size towards the head and tail ; these probably
confer upon this species some special protective advantage.
Macroglossa Pyrrhosticta, Butler, China and Japan (loc. cit. PL
XC., Fig. 8), is greenish-white with dorsal andsubdorsal lines, and
seven dark oblique stripes along the sides, below the subdorsal
line. Of the foregoing species Hemaris Hyas appears to be in
the same phyletic stage as M. Stellatarum and M. Croatica,
&c., whilst M. Pyrrhosticta is probably, together with M. Cory,
thus and M. Gilia, in another and more advanced stage, which
is also passed through by Lophura Hyas in the course of its
ontogenetic development. This last species (adult) and M.
Belts may represent phyletic stages still further advanced.
Caliomma Pluto, Walk., of which the caterpillar is figured by
Burmeister (loc. cit. PL XIII., Fig. i), appears to be a case of
special protective resemblance to a twig or branch of its food-
plant. Figured also by Chavannes ; Bull. Soc. Vadoise des
Sci. Nat, Dec. 6th 1854. R.M.].
46 [Genus Pterogon, Boisd., = Proserpinus and Lophura
(part). Butler, loc. cit. p. 632. The species above treated of
= Proserpinus (Enothera, Fabr. R.M.]
256 Studies in the Theory of Descent.
PTEROGON CENOTHER^E, FABR.
The adult larva, as made known by many, and
for the most part good figures, has very complicated
markings, which do not seem derivable from any
of the elements of marking in the Sphingidce
hitherto considered. I was therefore much sur-
prised at finding a young caterpillar of this
species, only twelve millimeters in length, of
a light green colour, without any trace of the
subsequent latticed marking, and with a broad
white subdorsal line extending along all the twelve
segments. (PI. VII., Fig. 63). Judging from the
size and subsequent development, this caterpillar
was probably in the third stage.
The same colouring and marking remained
during the following (fourth) stage ; but in the
position occupied by the caudal horn in other
Sphingidcz, there could now be observed the rudi-
ment of a future ocellus in the form of a round
yellowish spot (PL VII., Fig. 64). The subdorsal
line disappears suddenly in the fifth stage, when
the larva becomes dark green (rarely) or blackish
brown ; the latticed marking and the small oblique
stripes are also acquired, together with the beauti-
fully developed eye-spots, consisting of a yellow
mirror with black nucleus and ground-area (PL
VII., Fig. 65).
The North American Pterogon Gaurcz and P.
Abboti^ also show markings precisely similar to
47 [These species = Thyreus Abbott and Proserpinus Gaurce
The Origin of the Markings of Caterpillars. 257
those of this European species in the adult state ;
but in the two former the markings are of special
interest as indicating the manner in which the
primary Sphinx-marking has become transformed
into that of the apparently totally different adult
P. GEnotherce. P. Gaurce is green, with a com-
plicated latticed marking, which closer observation
shows to arise from the dorsal line being resolved
into small black dots, whilst the subdorsal line is
broken up into black, white-bordered triangles.
This caterpillar therefore gives fresh support to
the remarkable phenomenon that the animals as
well as the plants of North America are phyleti-
cally older than the European fauna and flora, a
view which also appeared similarly confirmed by
Deilephila Lineata^ the representative form of
D. Livornica. In entire accordance with this is
the fact that the larva of P. Gaiirce is without
the eye-spot on the eleventh segment, and instead
thereof still shows the original although small
caudal horn. The perfect insect also resembles
our P. (Enothera in colour and marking, but not
in the form of the wings.
That the caterpillars of the genus Pterogon
originally possessed the caudal horn we learn
of Butler's revision. Of the former he states :— " Transforma-
tions described, and larva and imago figured, Am. Ent. ii. p.
123, 1870; the larva is also figured by Scudder in Harris's
'Correspondence,' PI. III., Fig. i (1*869), and by Packard in
his ' Guide,' p. 276, Fig. 203." R.M.]
S
258 Studies in the Theory of Descent.
from P. Gorgoniades, Hlibn.,48 a species now
inhabiting south-east Russia, and for a knowledge
of which I am indebted to Dr. Staudinger's collec-
tion. There are in this about eight blown speci-
mens, from 3.710 3.9 centimeters in length, which
show a marking, sometimes on a red and some-
times on a green ground, which unites this species
with the young form of/7. CEnotherce,v\z., abroad
white subdorsal line, extending from the small
caudal horn to the head. In addition to this, how-
ever, the caterpillar possesses an extraordinarily
broad white red-bordered infra-spiracular line, a
fine white dorsal stripe, and a similar line be-
tween the subdorsal and spiracular, i.e. a supra-
spiracular line.
The caterpillars in Staudinger's collection, not-
withstanding their small size, all belong to the last
stage, as the moth itself does not measure more
than 2.6 centimeters in expanse, and is therefore
among the smallest of the known Spkingidce.
This species has therefore in the adult condition a
marking very similar to that of CEnotkera when
young — it bears to CEnothercz the same relationship
that Deilephila Hippophaes does to D. Euphorbia,
only in the present case the interval between the
two species is greater. Gorgoniades is obviously
a phyletically older species, as we perceive from
the marking and from the possession of a horn.
48 \Proserpinus (Sphinx) Gorgon, Esp. R.M.]
The Origin of tha Markings of Caterpillars. 259
We certainly do not yet know whether CEnotherce
possesses a horn in its earliest stages, although in
all probability it does so ; in any case the ancestor
of CEnothera had a horn, since the closely allied
P. Gaurce now possesses one.
We thus see that also in the genus Pterogon
the marking of the caterpillars commences with a
longitudinal line formed from the subdorsal ; an
infra-spiracular or also a supra-spiracular line
(Gorgoniades) being added. A latticed marking is
developed from the linear marking by the breaking
up of the latter into spots or small patches,
which finally (in CEnotherce] become completely
independent, their connection with the linear mark-
ing being no longer directly perceptible.
THE GENUS SPHINX, LINN.
Of this genus (in the narrow sense employed
by Gray) I have only been able, in spite of all
trouble, to obtain fertile eggs of one species.
The females cannot be induced to lay in confine-
ment, and eggs can only be obtained by chance.
I long searched in vain the literature of this
subject for some account of the young stages of
these caterpillars, and at length found, in a note to
Rosel's work, an observation of Kleemann's on the
young forms of Sphinx Ligustri, which, although
far from complete, throws light on certain points.
From a female of S. LigustriYAzvK&xm obtained
400 fertile eggs. The caterpillars on emerging
s 2
260 Studies in the Theory of Descent.
are " at first entirely light yellowish-green, but
become greener after feeding on the fresh leaves ;"
the horn is also at first light green, and then
becomes " darker." The young larvae spin webs,
by which they fasten themselves to the leaves of
their food-plant (this, so far as I know, has not
been observed in any species of Sphingidce).
They moult four times, the border round the head
and the purple stripes appearing after the third
moult, these stripes " having previously been
entirely white." The ecdyses follow at intervals
of about six days, increasing to about ten days
after the fourth moult.49
From this short account we gather that in the
third stage the marking consists of seven oblique
white stripes, which acquire coloured edges in the
fourth stage, a fact which I have myself frequently
observed. On the most important point Klee-
mann's observations unfortunately give no infor-
mation— the presence or absence of a subdorsal
line in the youngest stages. That he does not
mention this character, can in no way be considered
as a proof of its actual absence. I am rather
inclined to believe that it is present in the first, and
perhaps also in the second stage. There occur,
however, species of the genus Sphinx (sensu stric-
tiori) which possess a subdorsal line when young,
as I think may be certainly inferred from the fact
" Rosel, loc. cit. vol. iii., p. 26, note.
77ie Origin of the Markings of Caterpillars. 261
that the remains of such a line are present in the
adult larva of S. Convolvuli.
This conclusion becomes still more certain on
comparing the markings with those of a nearly
allied genus ; without such comparison the separa-
tion of the genus Macrosila, Boisd., from Sphinx is
scarcely justifiable. If to these two genera we
add Dolba, Walk., and Acherontia, Ochs., we must
be principally struck with the great similarity in
the markings, which often reaches to such an
extent that the differences between two species
consist entirely in small shades of colour, while the
divergence of the moths is far greater.
Of the genera mentioned, I am acquainted alto-
gether with fourteen species of caterpillars : —
Macrosila Hasdrubal, Rustica™ and Cingulata ;50
Sphinx Convolvuli, Ligustri, Carolina™ Quin-
quemaculata, 50 Drupiferarum, 50 Kalmitz, 50 and
Gordius ;50 Dolba Hylceus ;60 Acherontia Atropos,
Styx^ and Satanas^ With one exception all
these caterpillars possess oblique stripes of the
nature of those of the Smerinthus larvae, and most of
them are without any trace of a subdorsal line ; one
species— the North American M. Cingulata — has
a completely developed subdorsal ; and the typical
European species, S. Convolvuli, has a rudimentary
*° Figured and described by Abbot and Smith. \_Macrosila
(Sphinx) Cingulata is figured also by Burmeister, loc. tit. PI.
XII., Fig. i. R.M.]
51 Figured in " Cat. Lep. E. Ind. Co/'
^( LIBRARY
262 Studies in the Theory of Descent.
subdorsal line. The ground-colour in most of
these species is of the same green as that of the
leaves of their food-plants ; some are brown, i.e.
earth-coloured, and in these the markings do not
appear so prominently ; others again possess very
striking colours (A. Atropos), the oblique stripes
in these cases being very vivid. Only M. Has-
drubal™ separates itself completely from this
62 See the figure in Sepp's Surinam Lepidoptera, P. 3,
PI. CL, 1848. A specimen in alcohol of the adult caterpillar
is in the Berlin Museum. [The following is the synonymy of
the above mentioned species : — Macrosila Hasdrubal, Walk.=
Pseudosphinx (Sphinx] Tetrio, Linn.; M. Cingulata = Protoparce
(Sphinx) Cingulata, Fabr. ; M. Rustica = Protoparce (Sphinx)
Rustica, Fabr. ; Sphinx Convolviui, Linn. = Protoparce Convol-
vuli ; S> Carolina, Linn. = Pt Carolina; the other species
remain in the genera, as given above. The following additional
species of Sphingincz and Acherontiincz have been figured by
Butler \-Pseudosphinx Cyrtolophia, Butl., from Madras (loc. at.
PI. XCL, Figs, ii and 13); Protoparce Orientalis, Butl., from
India, China, Java, &c. (PL XCL, Fig. 16); Diludia Fates, Butl.
from India, &c. (PL XCL, Fig. 18); Nephele Hespera, Fabr., from
India, Australia, &c. (PL XCL, Fig. 20); Acherontia Morta,
Hiibn., from Java, China, India, &c. (PL XCIL, Fig. 9); and
A. Medusa, Butl,, from nearly the same localities as the last
(PL XCIL, Fig. 10). Most of these species fall under Dr.
Weismann's general remarks, so that it is unnecessary to give
detailed descriptions. The most divergent marking is that of
P. Cyrtolophia, which has a broad white dorsal line bordered
with pink, and two large pink ovals on the back of the four
anterior segments, the hindmost and larger of these being
bisected by the dorsal line. In N. Hespera the subdorsal line is
present on segments 6 to 1 1 only, and it is highly significant
that the oblique stripes are absent from these segments, but
are present on the anterior segments, where the subdorsal line
The Origin of the Markings of Caterpillars. 263
system of classification, since this species is deep
black with narrow yellow rings, the horn and last
segment being red.
The large and most striking caterpillar of M.
Hasdrubal is the same which Wallace has made
use of for his theory of the brilliant colours of
caterpillars. The explanation of the origin of
this widely divergent mode of marking could only
be furnished by the ontogeny, in which one or
another of the older phyletic stages will certainly
have been preserved.
fails. With reference to the larva of A. Atropos, Mr. Mansel
Weale states (Proc. Ent. Soc. 1878, p. v.) that in S. Africa the
ordinary form feeds generally on Solanacea, whilst the darker
and rarer variety is found only on species of Lantana. The
following species of these subfamilies are figured by Burmeister :
Amphonyxjatropha (loc. tit. PI. XL, Fig. i); Protoparce (Diludia)
Florestan, Cram. (Fig. 2); Sphinx Justicicz, Walk. (Fig. 3);
Protoparce (Diludia} Lichenea, Walk. (Fig. 4); Sphinx (Protoparce)
Cingidata, Fabr. (PI. XII., Fig. i); and Sphinx Cestri (Fig. 5).
All these species have the characteristic Sphinx-like markings.
Dilophonota Ello, Linn. (PL XII., Fig. 2), is greenish-brown with
a yellow subdorsal line, and D. Hippothb'on (Fig. 4), yellow with
a whitish subdorsal. Neither of these has oblique stripes.
D. (Enotrus, Cram. (Fig. 3), has neither stripes nor subdorsal,
but is uniform brown above, passing into green beneath.
Protoparce Albiplaga, Walk. (PI. XIIL, Fig. 2, also Merian,
PI. III., and Abbot and Smith, L, PL XXIV.), pale green with
large yellow, black-bordered patches surrounding the spiracles.
Psendosphinx Tetrio, Linn. (PL XIIL, Fig. 3), and P. Scyron
(Fig. 4) are black with broad transverse belts, yellow and white
respectively, encircling the middle of each segment. These
light bands serve very effectively to break up the uniform
surface of the large bodies of these insects. R.M.]
264 Studies in the Theory of Descent.
Strictly speaking the same should be said of
the other species — nevertheless their comparison
with the so similarly marked Smerinthincz, toge-
ther with the circumstance that in certain species
a subdorsal line can be traced, makes it appear
correct to suppose that here also the subdorsal
was the primary marking, this line being subse-
quently entirely replaced by the oblique stripes.
The Sphingina would therefore be a younger
group than the Smerinthince, a conclusion which
is borne out by the fact that in the former the
oblique stripes have reached a higher development,
being always of two, and sometimes even of three
colours (S. Drupiferarum, white, red, black), whilst
in the species of Smerinthus they only occasionally
possess uniformly coloured borders.
THE GENUS ANCERYX, BOISD.
Although this genus is not admitted into most
of the European catalogues — the solitary European
species representing it being referred to the genus
Sphinx, Linn.63 — its separation from Sphinx
appears to me to be justified, not because of the
striking differences presented by the moths, but
because the caterpillars, judging from the little
we know of them, likewise show a similar degree
of difference.
68 [The species referred to is placed by Butler in Hiibner's
genus Hyloicus. R.M.]
The Origin of the Markings of Caterpillars. 265
I have frequently succeeded in obtaining fertile
eggs of Anceryx Pinastri and I will now give the
developmental history of this caterpillar, which has
already been figured with great accuracy in Ratze-
burg's excellent work on forest insects. Rosel
was acquainted with the fact that the " pine moth"
laid its eggs singly on the needles of the pine in
June and July, and he described them as " yellow-
ish, shining, oval, and of the size of a millet seed."
On emerging, the caterpillars are six millimeters
in length, of a light yellow colour, the head shining
black with a yellow clypeus. The caudal horn,
which is forked at the tip, is also at first yellowish,
but soon becomes black. No particular marking
is as yet present, but a reddish stripe extends
along the region of the dorsal vessel, and the
course of the spiracles is also marked by an orange-
red line. (Fig. 53, A & B, PL VI.)
As soon as the young larvae are filled with food
they acquire a greenish streak. The first moult
occurs after four days, and immediately after this
there is still an absence of distinct markings, with
the exception of a greenish-white spiracular line.
In the course of some hours, however, the original
light green ground-colour becomes darker, and at
the same time a sharp, greenish-white subdorsal
line appears, together with a parallel line extend-
ing above the spiracles, which, in Pterogon Gor-
goniades, has already been designated as the
" supra-spiracular." The dorsal line is absent :
265 Studies in the Theory of Descent.
the head is light green, with two narrow blackish
brown lines surrounding the clypeus ; the horn
and thoracic legs are black ; claspers, reddish
green ; length, twelve to thirteen millimeters.
(Fig- 540
Third Stage.
After another period of four days the second
moult occurs, neither colour nor marking being
thereby affected. Only the horn, now no longer
forked, becomes brownish with a black tip. The
young caterpillars are now, as before, admirably
adapted to the pine needles, on which they feed
by day, and from which they can only be distin-
guished with difficulty.
Fourth Stage.
The third moult also brings no essential change.
The ground-colour and marking remain the same,
only the spiracles, which were formerly dull yellow-
ish, are now of a vivid brick-red. The horn be-
comes yellowish-red at the base.
Fifth Stage.
The marking is only completely changed in the
fifth and last stage. A broad reddish-brown dorsal
line replaces the subdorsal, more or less completely.
The supra-spiracular line also becomes broken up
into numerous short lengths, whilst the green
ground-colour in some specimens becomes more or
The Origin of the Markings of Caterpillars. 267
less replaced by a brownish shade extending from
the back to the sides. Horn, black ; the upper
part of the first segment with a corneous plate,
similar to that of the Deilephila larvae.
This stage is very variable, as shown by the
figures in various works. The variations arise on
the one hand from the struggle between the green
ground-colour and the reddish-brown extending
from above, and, on the other hand, from a more
or less complete disappearance of the associated
longitudinal lines. The latter are sometimes com-
pletely retained, this being the case in a caterpillar
figured by Hiibner (Sphinges, III., Legitimce£,,\>),
where both the subdorsal and supra-spiracular lines
are continuous from segment n to segment i,
an instance which may perhaps be regarded as a
reversion to the primary form.
The entire change of the marking from the
fourth to the fifth stage depends upon the fact that
the young larvae resemble the needles of the pine,
whilst the adults are adapted to the branches. I
shall return to this later.
The ontogeny of A. Pinastri makes us ac-
quainted with three different forms of marking :
(i) simple coloration without marking; (2) a
marking composed of three pairs of parallel
longitudinal lines ; (3) a complicated marking,
arising from the breaking up of the last and the
addition of a darker dorsal line.
Of the fourteen species placed by Gray in the
268 Studies in the, Theory of Descent.
genus Anceryx, I find, in addition to the one
described, notices of only two caterpillars : —
A. Coniferamm^ a North American species,
lives on Pinus Palustris, and was figured by Abbot
and Smith. Colour and marking very similar to
A. Pinastri.
A. Ello, Linn.,55 according to the authority of
Merian, is described by Clemens56 as dark brown,
" with a white dorsal line, and irregular white spots
on the sides." It lives on a " species of Psidium
or Guava"
Most of the species of Anceryx appear to live
on Conifertz, to which they show a general and
decided adaptation. In the absence of decisive
information, I partly infer this from the names, as
Anceryx Juniperi (Africa). It has long been
known that in our A. Pinastri the mixture of
brown and fir-green, interspersed with conspicuous
irregular light yellowish and white spots, causes
the adult larva to present a very perfect adapta-
tion to its environment. Of this caterpillar Rosel
states : — " After eating it remains motionless, and
is then difficult to see, because it is of the same
colour as its food, since its brown dorsal line
has almost the colour of the pine twigs ; and who
14 [= Ellema Coniferarum, of Butler's revision. R.M.]
65 [= Dilophonota Ello of Butler's revision. R.M.]
69 "Synopsis of the North American Sphingides." Philadelphia,
1859.
The Origin of the Markings of Caterpillars. 269
is not familiar with the fact that beneath the green
needles there is also much yellow to be found ? "
This adaptation to the needles and twigs
obviously explains why this caterpillar in the adult
condition is so far removed from those of the
genus Sphinx, while the moths are so nearly
related that they were only separated as a distinct
genus when we became acquainted with a large
number of species.
270 Studies in the Theory of Descent.
II.
CONCLUSIONS FROM PHYLOGENY.
THE considerations previously set forth are entirely
based on Fritz Muller's and Haeckel's view, that
the development of the individual presents the
ancestral history in mice, the ontogeny being a
condensed recapitulation of the phylogeny.
Although this law is generally true — all recent
investigations on development having given it
fresh confirmation — it must not be forgotten that
this " recapitulation " is not only considerably
abbreviated, but may also be " falsified," so that
a searching examination into each particular case
is very desirable.
The question thus arises, in the first place, as
to whether the markings of caterpillars, so dis-
tinct at the different stages of growth, are actu-
ally to be regarded as residual markings inherited
from the parent form ; or whether their differences
do not depend upon the fact that the caterpillar,
in the course of growth, is exposed to different
external conditions of life, to which it has adapted
itself by assuming a different guise.
The former is undoubtedly the case. It can
The Origin of the Markings of Caterpillars. 271
by no means be denied that the conditions of life
in young caterpillars are sometimes different to
those of the adults. It will, in fact, be shown later
on, that in certain cases the assumption of a new
guise at an advanced age actually depends upon
adaptation to new conditions of life ; but as a rule,
the external conditions remain very similar during
the development of the larva, as follows from the
fact that a change of food-plant never takes place.1
We should therefore rather expect a complete
similarity of marking throughout the entire larval
period, instead of the great differences which we
actually observe.
Different circumstances appear to me to show
that the markings of young larvae are only excep-
tionally due to a new adaptation, but that as a
rule they depend upon heredity. In the first
place, there is the fact that closely allied species,
exposed to precisely similar external conditions, as,
for instance, Chcerocampa Elpenor and Porcellus,
possess exactly the same markings when young,
these markings nevertheless appearing at different
stages of growth. Thus, the subdorsal line first
1 [The larvae of many moths which feed on deciduous trees
during the autumn and hibernate, are stated to feed on low-
growing plants in the spring, before the buds of their food-
trees open. On the other hand, low-plant feeders, such as
Triphcena Fimbria, &c., are stated to sometimes feed at night
in early spring on the buds of trees. The habits and ontogeny
of these species are of special interest in connection with the
present researches, and are well worthy of investigation. R.M.]
272 Studies in the Theory of Descent.
appears in Elpenor in the second stage, whilst in
Porcelhis it is present during the first stage. If
this line were acquired by the young larva for
adapting it at this age to special conditions of life,
it should appear in both species at the same
stage. Since this is not the case, we may con-
clude that it is only an inherited character derived
from the adult ancestor of the two species, and
now relegated to the young stages, being (so to
speak), pushed further back in one species than in
the other.
But the strongest, and, as it appears to me, the
most convincing proof of the purely phyletic sig-
nificance of the young larval markings, is to be
found in the striking regularity with which these are
developed in a similar manner in all allied species,
howsoever different may be their external condi-
tions of life. In all the'species of the Chczrocampa
group (the genera Ck&rocampa and Deilephila] the
marking — no matter how different this may be in
later stages — arises from the simple subdorsal line.
This occurs even in species which live on the most
diverse plants, and in which the markings can be
of no biological importance as long as the larvae
are so small as to be only visible through a lens,
and where there can be no possible imitation of
leaf-stalks or veins, the leaves and caterpillars
being so very distinct.
Moreover, when in the Macroglossiita (the
genera Macroglossa, Pterogon, and Thyreus) we
The Origin of the Markings of Caterpillars. 273
see precisely the same simple marking (the sub-
dorsal) line retained throughout all the stages in
two genera, whilst in the Smerinthince this line
vanishes at a very early stage, and in the Sphin-
gincz is only present in traces, we can give but
one explanation of these facts. We have here a
fragmentary series representing the phyletic de-
velopment of the Sphinx-markings, which latter
have arisen from one original plan — the simple
subdorsal line — and have then undergone further
development in various directions. As this sub-
sequent development advanced, the older phyletic
stages would always be relegated to younger onto-
genetic stages, until finally they would be but
feebly represented even in the youngest stage (D.
Euphorbia), or else entirely eliminated (most of the
species of the genus Sphinx). I believe that no
other sufficient explanation of these facts can be
adduced. Granting that the correctness of the
above views can no longer be doubted, we may
now take up the certain position that the onto-
geny of larval markings reveals their phylogeny,
more or less completely, according to the number
of phyletic stages omitted, or, in some exceptional
cases, falsified. In other words, the ontogeny of
larval markings is a more or less condensed and
occasionally falsified recapitulation of the phylo-
geny.
Considering this to be established, we have
next to deal with the uniformity of the develop-
2 74 Sttidies in the Theory of Descent.
mental phenomena, from which we may then
attempt to trace out the inciting causes underlying
this development.
The law, or, perhaps better, the line of direc-
tion followed by the development, is essentially
the following : —
1. The development commences with a state of
simplicity, and advances gradually to one of com-
plexity.
2. New characters first make their appearance
in the last stage of the ontogeny.
3. Such characters then become gradually car-
ried back to the earlier ontogenetic stages, thus
displacing the older characters, until the latter dis-
appear completely.
The first of these laws appears almost self-
evident. Whenever we speak of development,
we conceive a progression from the simple to the
complex. This result therefore does nothing but
confirm the observation, that we have actually
here before us a development in the true sense of
the word, and not simply a succession of different
independent conditions.
The two following laws, on the other hand, lay
claim to a greater importance. They are not now
enunciated for the first time, but were deduced
some years ago by Wlirtemberger 2 from a study
8 " Neuer Beitrag zum geologischen Beweise der Darwin'schen
Theorie." 1873, Nos. i and 2. [This principle, in common
with many others which have only been completely worked out
The Origin of the Markings of Caterpillars. 275
of the ammonites. In this case also the new
characters predominate in the later periods of life,
and are then transferred back to the younger on-
togenetic stages in the course of phyletic develop-
ment. " The change in the character of the shell
in ammonites, first makes itself conspicuous in the
last chamber ; but in the succeeding generations
this change continually recedes towards the be-
ginning of the spiral chambers, until it prevails
throughout the greater part of the convolutions."
In the same sense must also be conceived the
case which Neumayr and Paul have recently made
known respecting certain forms of Melanopsis
from the West Sclavonian Paludina bed. In M.
Recurrens the last convolutions of the shell are
smooth, this being a new character; the small
upper convolutions, however, are delicately ribbed,
as is also the case with the last convolution of
the immediate progenitor. The embryonic con-
of late years, is foreshadowed by Darwin. Thus, he states
when speaking of inheritance at corresponding periods of life :
" I could give a good many cases of variations (taking the
word in the largest sense) which have supervened at an earlier
age in the child than in the parent " (" Origin of Species,"
ist ed., 1860, p. 444). In the case of inherited diseases also :
" It is impossible to ... doubt that there is a strong tendency
to inheritance in disease at corresponding periods of life.
When the rule fails, the disease is apt to come on earlier in
the child than in the parent ; the exceptions in the other
direction being very much rarer." ("Variation of Animals
and Plants under Domestication," ist ed., 1868, vol. ii., p. 83.)
R.M.]
T 2
276 Stiidies in the Theory of Descent.
volutions again are smooth, and the author believes
(on other grounds) that the more remote pro-
genitor possessed a smooth shell.
In this case therefore, and in that of the am-
monites, every shell to a certain extent proclaims
the ancestral history of the species ; in one and the
same shell we find different phyletic stages brought
into proximity. The markings of caterpillars do
not offer similar facilities ; nevertheless I believe
that by their means we are led somewhat further,
and are able to enter more deeply into the causes
underlying the processes of transformation, be-
cause we can here observe the living creature, and
are thus enabled to study its life-history with more
precision than is possible with a fossil species.
When, in 1873, I received Wiirtemberger's
memoir, I was not only struck with the agree-
ment of his chief results with those which I
had arrived at by the study of larval markings,
but I was almost as much astonished at the great
difference in the interpretation of the facts. The
latter indicate the gradual backward transference
of a new character from the latest to the earlier
ontogenetic stages. Without further confirmation
Wiirtemberger assumes that it is to a certain
extent self-evident that the force producing this
backward transference is the same as that which,
according to his view, first called forth the charac-
ter in question in the last stage, viz., natural se-
lection. " Variations acquired at an advanced
The Origin of the Markings of Caterpillars. 277
age of the organism may, when advantageous, be
inherited by the succeeding generations, in such
a manner that they always appear a little earlier
than in the preceding generations."
It is certainly theoretically conceivable that a
newly acquired character, when also advantageous
to the earlier stages, might be gradually transferred
to these stages, since in this case those individuals
in which this character appeared earliest would
have the greatest chance of surviving. In the
case of the development of larval markings, how-
ever, there are facts which appear to me to show
that such backward transference of a new character
is, in a certain measure, independent of the prin-
ciple of utility, and that it must therefore be re-
ferred to another cause — to the innate law of
growth which rules every organism.
When, in the larva of C. Elpenor, we perceive
that the two eye-spots which are first formed on
the fourth and fifth segments appear subsequently
on the other segments as faint traces of no bio-
logical value whatever, we cannot explain this
phenomenon by natural selection. We should
rather say that in segmented animals there is a
tendency for similar characters to be repeated on
all the segments ; and this simply amounts to
the statement, that an innate law of growth is
necessary for the repetition of such newly acquired
characters.
The existence of such a law of growth, acting
278 Studies in the Theory of Descent.
independently of natural selection, may therefore
be considered as established, and indeed cannot be
disputed (Darwin's " correlation of growth''). In
the present case it appears to me that an innate
law of this kind, determining the backward trans-
ference of new characters, is deducible from the
instances already ^quoted in another sense, viz.,
from the fact that in many cases characters which
are decidedly advantageous to the adult are trans-
ferred to the younger stages, where they are at most
of but indifferent value, and can certainly be of no
direct advantage. This is the case with the
oblique stripes of Smerint/ms, which, in the adult
larvae, resemble the leaf ribs, as will be shown
more fully later on, and, in conjunction with the
green coloration, cause these caterpillars to be very
difficult of detection on their food-plants. The
insects are easily overlooked, and can only be dis-
tinctly recognized on close inspection.
Now these oblique stripes appear, in all the Sme-
rinthus caterpillars known to me, in the second, and
sometimes even in the first stage, i. e. in larvae of
from 07 to i centimeter in length. The stripes are
here much closer together than the ribs of any of
the leaves of either willow, poplar, or lime, and can
therefore have no resemblance to these leaves.
The young caterpillars are certainly not rendered
more conspicuous by the oblique stripes, since they
ean only be recognized on close inspection. It is
for this reason that the stripes have not been
eliminated by natural selection.
The Origin of the Markings of Caterpillars. 279
The remarkable phenomenon of the backward
transference of newly acquired characters may
therefore be formulated as follows :— Changes
which have arisen in the later ontogenetic stages
have a tendency to be transferred back to the
younger stages in the course of phyletic develop-
ment.
The facts of development already recorded
furnish numerous proofs that this transference
occurs gradually, and step by step, taking the
same course as that which led to the first esta-
blishment of the new character in the final onto-
genetic stage.
Did this law not obtain, the ontogeny would
lose much of the interest which it now possesses
for us. It would then be no longer possible,
from the ontogenetic course of development of an
organ or of a character, to draw a conclusion as to
its phylogeny. If, for instance, the eye-spots of
the Chcerocampa larvse, which must have been
acquired at a late age, were transferred back to
the younger ontogenetic stages in the course of
phyletic development, as eye-spots already per-
fected, and not showing their rudimentary com-
mencement as indentations of the subdorsal line,
the phenomenon would then give us no informa-
tion as to the manner of their formation.
It is well known to all who have studied the
developmental history of any group of animals,
that no organ, or no character, however complex,
280 Studies in the Theory of Descent.
appears suddenly in the ontogeny ; whereas, on
the other hand, it appears certain that new, or
more advanced, but simpler characters, predo-
minate in the last stage of development. We are
thus led to the following modification of the fore-
going conclusion : — Newly acquired characters
undergo, as a whole, backward transference, by
which means they are to a certain extent dis-
placed from the final ontogenetic stage by charac-
ters which appear later.
This must be a purely mechanical process, de-
pending on that innate law of growth, the action
of which we may observe without being able to
explain fully. Under certain conditions the ope-
ration of this law may be prevented by natural
selection. Thus, fpr instance, if the young cater-
pillars of Anceryx Pinastri have not acquired the
characteristic marking of the adults, it is probably
because they are better protected by their re-
semblance to the green pine-needles than they
would be if they possessed the pattern of the
larger caterpillars in their last stage.
The backward transference of newly acquired
characters may also possibly be accelerated when
these characters are advantageous to the younger
stages ; but this transference takes place quite
independently of any advantage if the characters
are of indifferent value, being then entirely brought
about by innate laws of growth.
That new characters actually predominate in
The Origin of the Markings of Caterpillars. 281
the last stage of the ontogeny, may also be de-
monstrated from the markings of caterpillars. It
is, of course, not hereby implied, that throughout
the whole animal kingdom new characters can
only appear in the last ontogenetic stage. Haeckel
is quite correct in maintaining that the power of
adaptation of an organism. is not restricted to any
particular period. Under certain circumstances
transformations may occur at any period of de-
velopment ; and it is precisely insects undergoing
metamorphosis that prove this point, since their
larvae differ so widely from their imagines that
the earlier stages may be completely disguised.
It is here only signified that, with respect to the
development of caterpillars, new characters first
appear in the adult. The complexity of the mark-
ings, which so frequently increases with the age
of the caterpillar, can scarcely bear any other
interpretation than that the new characters were
always acquired in the last stage of the ontogeny.
In certain cases we are able, although with some
uncertainty, to catch Nature in the act of adding
a new character.
I am disposed to regard the blood-red or rust-
red spots which occur in the last stage of the three
species of Smerinthus larvae in the neighbourhood
of the oblique stripes as a case in point. It has
already been shown that these red spots must be
regarded as the first rudiments of the linear coloured
edges which reach complete development in the
282 Studies in the Theory of Descent.
genus Sphinx. In some specimens of Smerinthus
Tilite the spots coalesce so as to form an irregular
coloured edge to the oblique stripes. In S. Populi
they occur in many individuals, but remain always
in the spot stage ; whilst S. Ocellatus is but seldom,
and S. Quercus appears never to be spotted.
The spots both of S. Tilice and Populi certainly
do not show themselves exclusively in the fifth
(last) stage, but also in the fourth, and sometimes
in Populi even as early as the third stage, from
which we might be disposed to conclude that the
new character did not first appear in the last stage.
But the majority of the spotted individuals first
acquire their spots in the fifth stage, and only a
minority in the fourth ; so that their occasional
earlier appearance must be ascribed to the back-
ward transference of a character acquired in the
fifth stage. Moreover, the fourth and fifth stages
of the caterpillars are closely analogous both in size,
mode of life, and marking, and are therefore ana-
logous with reference to the environment, so that it
is to be expected that new characters, when depend-
ing on adaptation, would be rapidly transferred
from the fifth stage to the fourth.3 We should
8 [If the reddish-brown spots on the larva of S. Populi have
the protective function assigned to them by Mr. Peter Cameron
(Trans. Ent. Soc. 1880, p. 69), it can be readily understood
that they would be of service to the insect in the fourth
stage, and the backward transference of this character might
thus be accelerated by natural selection, in accordance with
the above principles. (See, als.o, note 30, p. 241.) R.M.]
The Origin of the Markings of Caterpillars. 283
thus have a case of the acceleration by natural se-
lection, of processes determined by innate causes.
Why changes should predominate in the last
stage, is a question closely connected with that of
the causes of larval markings in general, and may
therefore be investigated later.
But if we here assume in anticipation that all
new markings depend on adaptation to the con-
ditions of life, and arise through natural selection,
it will not be difficult to draw the conclusion that
such new characters must prevail in the last stage.
There are two conditions favouring this view;
the size of the insect, and the longer duration of
the last stage. As long as the caterpillar is so
small as to be entirely covered by a leaf, it only
requires a good adaptation in colour in order to be
completely hidden ; independently of which, it is
also possible that many of its foes do not consider
it worth attacking at this stage. The last stage,
moreover, is of considerably longer duration than
any of the four preceding ones ; in Deilephila
Euphorbia this stage lasts for ten days, whilst
the remaining stages have a duration of four days ;
in Sphinx Ligustri the last stage also extends
over ten days, and the others over six days.
In its last stage, therefore, a caterpillar is for
a longer period exposed to the danger of being
discovered by its foes ; and since, at the same
time, its enemies become more numerous, and its
increased size makes it more easy of detection, it
284 Studies in the Theory of Descent.
is readily conceivable that a change in the condi-
tions of life, such, for instance, as removal to a
new food-plant, would bring about the adapta-
tion of the adult larva as its chief result.
I shall next proceed to show how far the as-
sumption here made — that all markings depend
on natural selection — is correct.
The Origin of the Markings of Caterpillars. 285
III.
BIOLOGICAL VALUE OF MARKING IN GENERAL.
HAVING now described the development of larval
markings, so far as possible from their external
phenomena, and having traced therefrom the
underlying law of development, I may next pro-
ceed to the main problem — the attempt to discover
those deeper inciting causes which have produced
marking in general.
The same two contingencies here present
themselves as those which relate to organic life as
a whole ; either the remarkably complex and ap-
parently incomprehensible characters to which we
give the name of markings owe their origin to
the direct and indirect gradual action of the chang-
ing conditions of life, or else they arise from
causes entirely innate in the organism itself, i. e.
from a phyletic vital force. I have already stated
in the Introduction why the markings of cater-
pillars appear to me such particularly favourable
characters for deciding this question, or, more
precisely, why these characters, above any others,
appear to me to render such decision more easily
286 Studies in the Theory of Descent.
possible; repetition is here therefore unneces-
sary.
The whole of the present investigation had
not been planned when I joined with those who,
from the first, admitted the omnipotence of natu-
ral selection as an article of faith or scientific
axiom. A question which can only be solved by
the inductive method cannot possibly be regarded
as settled, nor can further evidence be considered
unnecessary, because the first proofs favour the
principle. The admission of a mysteriously work-
ing phyletic power appears very unsatisfactory
to those who are striving after knowledge ; the
existence of this power, however, is not to be
considered as disproved, because hundreds of
characters can be referred to the action of natural
selection, and many others to that of the direct
action of the conditions of life. If the develop-
ment of the organic world is to be considered as
absolutely dependent on the influence of the en-
vironment, not only should we be able here and
there to select at pleasure characters which ap-
peared the most accessible for elucidating this
point, but it becomes in the first place necessary
to attempt to completely refer all characters be-
longing to any particular group of phenomena,
however small this group might be, to known
transforming factors. We should then see whether
this were possible, or whether there would remain
residual phenomena not explicable by known
The Origin of the Markings of Caterpillars. 287
principles and compelling us to admit the exist-
ence of a force of development innate in the
organism. In any case the " phyletic vital force "
can only be got rid of by a process of elimination
—by proving that all the characters generally oc-
curring throughout the group of phenomena in
question, must be attributed to other causes, and
that consequently nothing remains for the action
of the supposed phyletic vital force, which
would in this manner be negatived, since we
cannot infer the presence of a force if the latter
exerts no action whatever.
I shall here attempt such an investigation of the
group of phenomena displayed by larval markings,
with special reference to those of the Spkingidte.
The alternatives upon which we have to decide
are the following : — Are the markings of cater-
pillars purely morphological characters, produced
entirely by internal causes ? or, are they simply
the response of the organism to external influ-
ences ?
The solution of these questions will be arrived at
by seeking to refer all the markings present to
one of the known transforming factors, and the
success or failure of this attempt will give the re-
quired decision. The first question to be attacked
is obviously this, — whether the Sphinx-mark-
ings are actually, as they appear at first sight,
purely morphological characters. If it can be
shown that all these markings were originally of
288 Studies in the Theory of Descent.
biological value, they must be attributed to the
action of natural selection.
Did I here at once proceed to establish the
biological value of larval markings- — and especially
of those of the Sphingidce — so as to arrive in this
manner at a conclusion as to their dependence upon
natural selection, it would be impossible to avoid the
consideration of the total coloration of the cater-
pillars, since the marking frequently consists only
of a local strengthening of the colour, and cannot
be comprehended without coming to this under-
standing. The action of the markings also often
appears to be opposed to that of the colouring,
making the caterpillar again conspicuous ; so that
the two factors must necessarily be considered to-
gether. I shall therefore commence the investi-
gation with colour in general, and then proceed to
treat of marking.
The Origin of the Markings of Caterpillars. 289
IV.
BIOLOGICAL VALUE OF COLOUR.
THE general prevalence of protective colouring
among caterpillars has already been so frequently
treated of that it is not here my intention to
recall particular instances. In order to judge of
the effect of marking, however, it will be well to
bear in mind that these insects, being generally
defenceless and thus requiring protection, have
acquired the most diverse means of rendering
themselves in some measure secure from their
foes.
The sharp spines which occur on the cater-
pillars of many butterflies (Vanessa, Melitcea,
Argynnis), and the hairs on those of many moths,
serve for protective purposes. Among other
means of protection — although in a different sense
— we have in all the species of the great family of
the Papiliomda the strikingly coloured (yellowish
red) odour-emitting tentacles concealed near the
head, and suddenly protruded for terrifying foes ;
and likewise the forked horn at the tail of the
caterpillars of the genus of moths Harpy ia, the
u
290 Studies in the Theory of Descent.
tentacles of which can be suddenly protruded in
a similar manner. Adaptive colours and forms
combined with certain habits 1 are, however, much
1 [For cases of correlation of habit with protective resem-
blance in larvae, see a paper in " Ann. and Mag. of Nat. Hist.,"
Feb., 1878, pp. 159, 1 60. Also Fritz Miiller on a Brazilian
Cochliopod larva, Trans. Ent. Soc. 1878, p. 223. Mr. Mansel
Weale states, with reference to S. African Sphingidtz (Proc.
Ent. Soc. 1878, p. vi.), that many species when seized "have
a habit of doubling up the body, and then jumping a consider-
able distance with a spring-like action. This is especially the
case with species having eye-like markings ; and it is probable
that if attacked by birds in a hesitating manner, such species
might effect their escape amid the grass or foliage." Many of
the defensive weapons and habits of larvae are doubtless means
of protection from ichneumons and other parasitic foes. In
the case of saw-flies, Mr. Peter Cameron has shown (Trans.
Ent. Soc. 1878, p. 196) that the lashing about of the posterior
part of the body may actually frighten away such enemies.
The grotesque attitude and spider-like appearance and move-
ments of the caterpillar of Stauropus Fagi are considered by
Hermann Miiller (" Kosmos," Nov., 1879, p. 123) to be means
of protection from ichneumons. Among the most remarkable
means of defence possessed by larvae is that of secreting a liquid,
which Mr. W. H. Edwards has shown, in the case of certain
North American Lycanidd (" Canadian Entomologist." vol. x.,
1878, pp. 3 — 9 and 131 — 136), to be attractive to ants, who
regularly attend these caterpillars, in the same manner and for
the same purpose as they do our aphides. The mutual advan-
tage derived by the ants and larvae was discovered in the case
of Lyccena Pseudargiolus. Mr. Edwards states that the mature
larva of this species is singularly free from Hymenopterous and
Dipterous parasites : — " Why this species, and doubtless many
other Lyccence, are thus favoured will, perhaps, in some degree
appear from a little incident to be related. On 2oth June, in
the woods, I saw a mature larva on its food-plant ; and on its
back, facing towards the tail of the larva, stood motionless one
The Origin of the Markings of Caterpillars. 291
more common than defensive weapons. Thus,
the caterpillars of the Noctuce belonging to the
genus Catocala and its allies, feed only at night on
the green leaves of various forest-trees ; by day
they rest in crevices of the bark on the tree trunk,
which they resemble so perfectly in the colour of
their peculiar glossy dull grey or brownish skin
beset with small humps, that only sharp eyes can
of the larger ants. ... At less than two inches behind the larva,
on the stem, was a large ichneumon-fly, watching its chance to
thrust its ovipositor into the larva. I bent down the stem, and
held it horizontally before me, without alarming either of the
parties. The fly crawled a little nearer and rested, and again
nearer, the ant making no sign. At length, after several
advances, the fly turned its abdomen under and forward, thrust
out its ovipositor, and strained itself to the utmost to reach
its prey. The sting was just about to touch the extreme end
of the larva, when the ant made a dash at the fly, which flew
away, and so long as I watched — at least five minutes —
did not return. The larva had been quiet all this time, its
tubes out of sight, and head buried in a flower-bud, but the
moment the ant rushed and the fly fled, it seemed to become
aware of the danger, and thrashed about the end of its body
repeatedly in great alarm. But the tubes were not protruded,
as I was clearly able to see with my lens. The ant saved the
larva, and it is probable that ichneumons would in no case get
an opportunity to sting so long as such vigilant guards were
about. It strikes me that the larvae know their protectors,
and are able and willing to reward them. The advantage is
mutual, and the association is friendly always." Those who
are familiar with Mr. Belt's description of the standing armies
of ants kept by the "bull's-horn thorn" ("Naturalist in
Nicaragua," pp. 218 — 222) and by certain Cecropice and Mela-
stomtz, will be struck with the analogy between these and the
foregoing case. R.M.]
U 2
292 Studies in the Theory of Descent.
detect them, even when we are familiar with their
habits.2
The striking resemblance of many moths to
splinters of wood is well known, and to this is
added a habit which helps their disguise, viz., that
of remaining stiff and motionless on the approach
of danger, just like a splinter projecting from the
branch.3 Among the moths coming under this
category may be mentioned Cucullia Verbasci, and
particularly those of the genus Xylina^ which, when
at rest, closely resemble a broken splinter of wood
in the colour and marking of their fore wings, and
when touched, have a habit of drawing in their
legs and falling without opening their wings as
though dead.
That simple adaptive colouring prevails widely
2 [The adaptive resemblance is considerably enhanced in
Catocala and in Lasiocampa Querdfolia by the row of fleshy
protuberances along the sides of these caterpillars, which enables
them to rest on the tree trunks by day without casting a sharp
shadow. The hairs along the sides of the caterpillar of Pacilo-
campa Populi doubtless serve the same purpose. (See a paper
by Sir John Lubbock, Trans. Ent. Soc. 1878, p. 242; also
Peter Cameron, ibid., 1880, p. 75.) It is well known to col-
lectors that one of the best methods of finding the caterpillars
of the Catocala is to fee! for them by day on the barks of their
respective food-trees, or to beat for them at night. R.M.]
3 [See Wallace's " Contributions to the Theory of Natural
Selection," ist ed., p. 62. Also a paper in "Ann. Mag. Nat.
Hist." Feb. 1878, p. 159, for cases in point. Rosel in 1746
mentioned this habit in Calocampa Exoleta. Hermann Miiller
has recorded many other similar instances on the authority of
Dr. Speyer ; see " Kosmos," Nov., 1879, p. 114. R.M.]
The Origin of the Alar kings of Caterpillars. 293
among caterpillars is shown by the large number
of green species.4 It may be fairly said that all
caterpillars which possess no other means of pro-
tection or defence are adaptively coloured. These
facts are now well known ; so also is the explana-
tion of the varied and striking colours of many
caterpillars given by Wallace.6 There is, how-
4 [Andrew Murray called attention to this fact in 1859
("Edinburgh New Philos. Journ.," Jan., 1860, p. 9). This
view is also corroborated by the fact that no internal feeders
are green; see note 2, p. 310 and Proc. Zoo. Soc. 1873, P-
159. R.M.]
5 [Proc. Ent. Soc. March 4th, 1867; and "Contributions to
the Theory of Natural Selection," ist ed., pp. 117^—122; also
Darwin's " Descent of Man," 2nd ed., p. 325. Among the
most important recent additions to the subject of the colours,
spines, and odours of caterpillars, I may call attention to a
paper by Fritz MUller (" Kosmos," Dec., 1877), the following
abstract of which I communicated to the Entomological
Society (Proc. 1878, pp. vi, vii) : — "The larvae of Dione Juno
and Acraa Thalia live gregariously, and are brown in colour ;
they are covered with spines, but, being of dull colours,
their spiny protection (which in the case of D, Juno is very
imperfect) would not preserve them unless they were dis-
tinguished as inedible at the right time, and not after being
seized, in accordance with the principles laid down by
Mr. Wallace. It is suggested that the social habits of the
larvae, which lead them to congregate in large numbers, make
up for their want of colour, since their offensive odour then
gives timely warning to an approaching enemy. The cater-
pillars of Col&nis Julia and Dione Vanilla are equally wanting
in bright colours, but are solitary in their habits, and these
species rest on the under side of the leaf when feeding. On
the other hand, the caterpillars of Heliconius Eucrate^ Colcenis
Dido, and C. Isabella, which are of solitary habits, and which
freely expose themselves, are very gaudily coloured, and there-
294 Studies in the Theory of Descent.
ever, novelty in the proof contained in the fore-
going descriptions of larval development, as to
fore most conspicuous. As examples of nearly allied larvae,
of which some species are gregarious and others solitary, Fritz
Miiller mentions Morpho and Brassolis^ which are gregarious ;
while Opsiphanes and Caligo are solitary. The larva of Papilio
Pompeius also is gregarious, and those of P. Nephalion, P.
Polydamas, and P. Thoas are solitary Fritz Miiller
sums up his observations by remarking that those caterpillars
which live alone, and lack the bright colouring as a sign of
offensiveness, must hide themselves ; as those of C. Julia and
D. Vanilla. The spiny covering is much less a protection
against birds than against smaller enemies ; and they may, by
the protective habit of living together, diffuse around themselves
an offensive atmosphere, even to man, and thus gradually be-
coming shorter (as with D. Juno], the spines of these cater-
pillars become useless, and finally are altogether dropped."
See also Sir John Lubbock's " Note on the Colours of British
Caterpillars," Trans. Ent. Soc. 1878, p. 239. Mr. Peter
Cameron finds (Trans. Ent. Soc. 1880, pp. 71 and 75) that
these remarks are also applicable to the larvae of certain saw-
flies. In 1877 Mr. J. W. Slater published a paper "On the
Food of gaily- coloured Caterpillars" (Trans. Ent. Soc. 1877,
p. 205), in which he suggested that such caterpillars might
derive their distasteful qualities from feeding on plants con-
taining poisonous or otherwise noxious principles. A much
larger number of observations will be required, however,
before this view can be accepted as of general application.
A beautiful illustration of the theory of warning colours is
given by Belt in his "Naturalist in Nicaragua," p. 321. All
the frogs found in the woods round St. Domingo are, with one
exception, protectively coloured ; they are of nocturnal habits,
and are devoured by snakes and birds. The exception was a
species of bright red and blue colours, which hopped about
by day and made no attempt at concealment. From these
facts Mr. Belt concluded that this species was inedible, and on
trying the experiment with ducks and fowls this was found to
be the case. R.M.]
The Origin of the Markings of Caterpillars. 295
the manner in which the di- and polymorphism
of caterpillars can be explained from the external
phenomena which they present, these phenomena
being well adapted for showing the great impor-
tance of protective colouring to the larvae. We
have here presented a double adaptation, although
not quite of the nature of that which I formerly
admitted on hypothetical grounds.6 In the first
place, from the developmental history there results
the conclusion that all Sphinx-larvae which, in the
adult state, are di- or polymorphic, are unicolorous
when young. Thus, the caterpillars of Chtzro-
campa Elpenor all remain green till the fourth
stage, when they mostly become light or dark
brown, and only very seldom retain their green
colour. Chcerocampa Porcellus behaves in a
precisely similar manner ; as also does Pterogon
(Enotherce, which inhabits the same localities, and
is found on the same food-plant, but is not very
closely related to the Chczrocampa. In this
species also (P. (Enothercs) the brown is more
common than the green form in the adult state,
both varieties showing a complicated marking.
The young larvae possess only a light green
colour, and a pure white subdorsal line as the only
marking ; they are so well adapted to the leaves
of their food-plants, Epilobium Hirsutum, and E.
Rosmarinifolium, that they can only be detected
• See the essay " Uber den Einfluss der Isolirung auf die
Artbilding." Leipzig, »i 8 7 2, p. 22.
296 Studies in the Theory of Descent.
with great difficulty. After the third moult they
become brown, and can be easily seen when at
rest on their food-plant.
Now in all known caterpillars brown colours are
adaptive, sometimes causing a resemblance to the
soil, and at others to dead leaves or branches. As
soon, therefore, as the caterpillars have attained
a considerable size, they remain concealed by day.7
The truth of this observation not only appears
from various entomological notes, but I have
frequently convinced myself of its accuracy. I
well remember from the earliest times that C.
Elpenor, especially when the larva is adult, always
rests by day among the dead branches and leaves
of its shrub-like food-plant, Epilobium Hirsutum ;
and even when this species lives on the low-grow-
ing Epilobium Parviflorum, it conceals itself by day
on the ground, among the tangled leaves and
branches. I have observed that Sphinx Con-
volvuli has a precisely similar habit, for which
reason it is difficult to obtain, even in localities
where it occurs very commonly.
In the neighbourhood of Basle I once found at
mid-day a brown caterpillar of Pterogon CEnotherce
on an isolated dead branch of Epilobium Rosmari-
nifolium, and I was informed by H err Riggenbach-
Stahelina — collector of great experience who
accompanied me — that these caterpillars always
rest (by day) on withered plants as soon as they
7 [See also preceding note 5, p. 294. R.M.]
The Origin of the Markings of Caterpillars. 297
become brown, but before this change they are
only to be found on green plants.
Thus, it cannot well be doubted that the change
of colour is associated with a change in the habits
of life, and the question arises as to which has been
the primary change.
If the view here entertained, that the later
brown coloration is adaptive, be correct, the species
must have first acquired the habit of concealing
itself by day on the ground and among dead
herbage, before the original green colour could
have been changed into brown by natural selec-
tion. This must represent the actual facts of the
case.
Nearly allied species which at an advanced age
are not dimorphic, but are darkly coloured in all
individuals, are especially calculated to throw some
light on this point. For instance, the caterpillar
of Deilephila Vespertilio, which comes under this
denomination, is light green when young, and rests
both by day and night on the leaves of the plant
on which it feeds. As soon as it acquires its dark
colour — after the third moult — it changes its habits,
concealing itself by day on the ground and feeding
only by night. For this reason collectors prefer
seeking for it in the evening, or with a lantern by
night.
The most instructive case, however, is that of
Deilephila Hippophaes, in which no change of
colour is associated with age, the caterpillar,
298 Studies in the Theory of Descent.
throughout its whole life, remaining of a greyish
green, which exactly matches the colour of the
leaves of its food-plant, Hippophae Rhamnoides.
Nevertheless this species also possesses the habit
of feeding only at night as soon as it has attained
to a considerable size, hiding itself by day at the
root of its food-plant. Collectors expressly state
that this larva can scarcely be found by day, and
recommend that it should be sought for at night
with a lantern.
From the foregoing facts and considerations it
may fairly be concluded, that the habit of hiding
by day, possessed by these and other allied cater-
pillars, was acquired when they resembled the
leaves in colour, and that the adaptation to the
colour of the soil, or dead foliage and withered
branches, ensued as a secondary consequence.
But why have these caterpillars acquired such a
habit, since they appear to be perfectly protected
by their resemblance in colour to the green leaves ?
The answer to this question is easily given when
we consider in which species this habit generally
occurs.
Does the habit prevail only among the species
of the one genus Deilephila, and in all the species
of this genus ? This is by no means the case,
since, on the one hand, many species of Deilephila^
such as D. Euphorbia, Galii, Niccea, and Dahlii,
do not possess the habit, and, on the other hand, it
occurs in species of other genera, such as Macro-
The Origin of the Markings of Caterpillars. 299
glossa Steilatarum, Sphinx Convolvuli, and Ache-
rontia Atropos.
The habit in question must therefore be the
result of certain external conditions of life common
to all those species which rest by day. The mode
of life common to them all is that they do not live
on trees with large leaves or with thick foliage,
but on low plants or small-leaved shrubs, such as
the Sea Buckthorn. 8 I believe I do not err when
I attribute the habit possessed by the adult larvae,
of concealing themselves by day, to the fact that
the green colour is protective only so long as they
are small — or, more precisely speaking, as long as
their size does not considerably exceed that of a
leaf or twig of their food-plant. When they
become considerably larger, they must become
conspicuous in spite of their adaptive colour, so
that it would then be advantageous for them to
conceal themselves by day, and to feed only by
night. This habit they have acquired, and still
observe, even when the secondary adaptation to
the colour of the soil, &c., has not been brought
about. We learn this from D. Hippophaes, which
8 [Eng. ed. The habit of hiding by day occurs also in those
caterpillars which resemble the bark of their food-trees. Thus
Catocala Sponsa and Promissa conceal themselves by day in
crevices of the bark, and are, under these circumstances, only
found with difficulty. Dr. Fritz Miiller also writes to me that
in Brazil the caterpillars of Papilio Evander rest in this manner
in large numbers, crowded together into dense masses, on the
trunks of the orange-trees, which they resemble in colour.]
300 Studies in the Theory of Descent.
remains green throughout its whole larval exist-
ence ; and no less from the green forms of the adult
larvae of Sphinx Convolvuli, Chcerocampa Elpenor,
and Force ilus, all of which conceal themselves by
day in the same manner as their brown allies.
It may be objected that there are Sphinx-larvae
— instances of which I have myself adduced —
which live on low small-leaved plants, and which
nevertheless do not hide themselves by day. This
is the case with the spurge-feeding D. Euphorbia,
so common in many parts of Germany. This
caterpillar must, however, be classed with those
which, on account of their distastefulness, or for
other reasons to be subsequently considered, are
rejected by birds and other larger foes, and which,
as Wallace has shown, derive advantage from
being coloured as vividly as possible. I shall
return to this subject later, when treating of the
biological value of special markings.
On the other hand, it is readily conceivable that,
from the conditions of life of caterpillars living on
trees or shrubs with dense foliage, the habit of
resting by day and descending from the tree for
concealment would not have been acquired. Such
larvae are sufficiently protected by their green
colour among the large and numerous leaves ; and
I shall have occasion to show subsequently that
their markings increase this protective resem-
blance.
The di- or polymorphism of the larvae of the
The Origin oj the Markings of Caterpillars. 301
Spkingidce does not therefore depend upon a con-
temporaneous double adaptation, but upon the
replacement of an old protective colour by a new
and better one, and therefore upon a successive
double adaptation. The adult caterpillars of C.
Elpenor are not sometimes brown and sometimes
green because some individuals have become
adapted to leaves and others to the soil, but because
the anciently inherited green has not yet been
completely replaced by the newly acquired brown
coloration, some individuals still retaining the old
green colour.
When, in another place,9 I formerly stated
" that a species can become adapted in this or that
manner to given conditions of life, and that by no
means can only one best adapted form be allowed
for each species," this statement is theoretically
correct speaking generally, but not in its applica-
tion to the present class of cases. A comparison
with one another of those caterpillars which repose
by day, distinctly shows that they all possess a
tendency to abandon the green and assume a dull
colour, but that this process of replacement has
advanced further in some species than in others.
It will not be without interest to follow this
operation in some detailed cases, since we may
thus obtain an insight into the processes by which
polymorphism has arisen, as well as into the con-
' " Uber den Einfluss der Isolirung auf die Artbildung."
Leipzig, 1872, p. 21.
302 Studies in the Theory of Descent.
nection between this phenomenon and simple
variability.
In D. Hippophaes the process has either not yet
commenced, or is as yet in its first rudiments. If
we may trust the statements of authors, together
with the ordinary green form there occurs, rarely,
a silver-grey variety, which may be regarded as the
beginning of a process of colour substitution.
Among thirty-five living specimens of this scarce
species which I was able to procure, the grey
form did not occur, neither have I found it in
collections.
In Macroglossa Stellatarum we see the trans-
forming process in full operation. A large number
of individuals (about thirty-five per cent.) are still
green ; the number of dark-coloured individuals
reaches forty-six per cent., these, therefore,
preponderating ; whilst between the two extremes
there are about nineteen per cent, of transition
forms, showing all possible shades between light
green and dark blackish-brown or brownish-
violet, and even, in solitary individuals, pure violet
(See Figs. 3 — 12, PL III.). The relatively small
number of the intermediate forms, taken in con-
nection with the fact that all the 140 specimens
employed in my investigation were obtained from
one female, leads to the conclusion that these
forms owe their existence to cross-breeding. It
would be superfluous to attempt to prove this last
conclusion with reference to the before-mentioned
l he Origin of the Markings of Caterpillars. 303
case, in which a caterpillar was streaked with brown
and green (Fig. 9, PL III.).
The process of transformation, as already
mentioned, advances in such a manner that the
intermediate forms diminish relatively to the dark
individuals. This is found to be the case with
Sphinx Convolvuli, and almost to the same extent
with Chcerocampa Elpenor, in both of which species
the green caterpillars are the rarest.10 Forms truly
intermediate in colour between green and brown
no longer occur, but apparently only different
shades of light and dark brown, passing into
brownish-black.
The process has again made a further advance
in CJuwocampa Porcellus and Celerio as well as in
Pterogon CEnothera. In all these species the
green form occurs,11 but so rarely that very few
collectors have seen it. The brown form has
therefore in these cases nearly become the
predominant type, and the solitary green specimens
which occasionally occur, may be regarded as
reversions to an older phyletic stage.
Deilephila Livornica appears to have reached a
similar stage, but the caterpillar of this species
has been so imperfectly observed, that it is
10 I am unfortunately not able to give exact numbers show-
ing the relative proportions of the different forms, since I have
never bred S. Convolvuli from eggs, nor C. Elpenor in sufficient
numbers.
11 [With reference to C. Porcellus, see note 2, p. 188. R.M.]
304 Studies in the Theory of Descent.
difficult to determine, even approximately, the
relative proportion of the brown to the green
individuals. I have only seen one of the latter
in Dr. Staudinger's collection (Compare Fig. 62,
PL VII.).
In Deilephila Vesper tilio, Euphorbia, Dahlii,
Mauritanica^ Nic&a, and Galii^ the green form
has completely disappeared. The blackish olive-
green colour shown by many caterpillars of the
two last species, can be considered as a faint
retention of the light green colour which they
formerly possessed, and which they both show at
the present time in their young stages.
Beginning with the appearance of single darker
individuals, we pass on in the first place to a
greater variability of colouring, and from this, by
the greater diminution of the intermediate forms,
to polymorphism ; the complete extermination of
these forms ending in dimorphism. The whole
process of transformation has been thus effected : —
As the new colouring always prevailed over the old,
the latter was at length completely displaced, and
the caterpillars, which were at first simply variable,
became polymorphic and then dimorphic, finally
returning to monomorphism.
We thus see the process of transformation still
going on, and no doubt can arise as to its
inciting causes. When a character can with
certainty be ascribed to adaptation, we can explain
its origin in no other way than by the action of
The Origin of the Markings of Caterpillars. 305
natural selection. If, as I believe, it can and has
been shown, not only that caterpillars in general
possess adaptive colours, but that these colours
can change during the lifetime of one and the
same species, in correspondence with external
conditions, we must certainly gain a very high
conception of the power which natural selection
exerts on this group of living forms.12
12 [In the class of cases treated of in the foregoing portions
of this essay, the external conditions remain unaltered during
the lifetime of the caterpillar, but change of habit, and in some
cases of colour, occurs when the insect has attained a size
sufficient to make it conspicuous. Cases are, however con-
ceivable a priori, and are realized by observation, in which the
environment itself may undergo change during the lifetime of
the individual caterpillar. Thus, in the case of hibernating
species, the colour which is adaptive to the autumnal colours
of the foliage of their food-trees would not assimilate to that
of the newly-opened leaves in the spring. I have already
quoted (Proc. Zoo. Soc. 1873, p. 155) as instances of what may
be called " seasonal adaptation," the larvae of Geometra Papilio-
naria, Addalia Degeneraria, and Gnophos Obscurata, and many
more could be named. These species undergo a change of
colour before or after hibernation, the change being always
adaptive to the environment.
It has long been known that caterpillars which feed on
flowers or on plants of variously-coloured foliage, in some cases
partake of the colour of their food. See, for instance, Dr. L.
Holler's memoir, " Die Abhangigkeit der Inseckten von ihrer
Umgebung," 1867, and B. D.Walsh " On Phytophagic Varieties
and Phytophagic Species," Proc. Ent. Soc. Philadelph., vol.
iii., p. 403. In 1869 Mr. R. McLachlan published a paper
entitled " Observations on some remarkable varieties of Sterrha
Sacraria, Linn., with general notes, on variation in Lepi-
doptera" (Trans. Ent. Soc. 1865, p. 453), in which he gave
many illustrations of this phenomenon. The larva of Hdiotlm
X
306 Studies in the Theory of Descent.
Peltiger, according to Mr. Reading's description (Newman's
" British Moths," p. 438), is another case in point. In
1874 a number of instances were published by Mr. Thomas
G. Gentry in a paper entitled " Remarkable Variations in
Coloration, Ornamentation, &c., of certain Crepuscular and
Nocturnal Lepidopterous Larvae " (" Canadian Entomologist,"
vol. vi., p. 85. See also W. H. Edwards' description of the
summer and autumnal larvae of Lyc&na Pseudargiolus ; Ibid.y
vol. x., pp. 12, 13).
The caterpillars of the Sphingidce appear also in some cases
to vary in a manner very suggestive of phytophagic influences.
The observations upon S. Ocellatus recorded in the previous
note (p. 241) may perhaps be interpreted in this sense. In
order to get experimental evidence upon this subject, I may
add that Mr. E. Boscher was good enough at my request to
repeat his observations, and conduct some breeding experiments
during the present year (1880). In the same locality as that
previously mentioned, seven larvae were found feeding on Salix
viminalisy all of which were the bright green spotted variety ;
and in the same osier-bed six more were found on another
species of Satz'x, two of these being the bluish-green variety,
and the other four the bright green form. Unless we have
here a local race, these observations, in connection with those of
last year, tend to show that the light green form is associated
with Salix viminalis. When found in the natural state feeding
on apple, the caterpillar of this species is generally, perhaps
invariably, the bluish-green form. In order to try the effect of
breeding the larvae ab ovo on distinct food-plants, a large number
of eggs laid by a female Ocellatus in July were divided into
three batches, one being supplied with Salix triandra, another
with S. viminalis, and the third lot with apple. The experi-
ment unfortunately failed in great part, owing to most of the
larvae dying off, three from .. the third lot only surviving ; but
these were all of the bluish-green form, which colour was
shown by all the caterpillars of this batch from their earliest
stage. The observation is thus so far successful, as it goes
to support the view that the variety mentioned is associated
with apple (and S. triandra .?) My friend Mr. W. J. Argent
informs me that he had a number of specimens of Sphinx
The Origin of the Markings of Caterpillars. 307
Ligustri in his possession this autumn, some of which had been
found on lilac and others on laurestinus, and he states that all
those on the latter plant had the ground-colour distinctly darker
than in those feeding on lilac. I learn also from Mr. W. Davis,
of Dartford, that he found a number of these larvae this year
feeding on ash, and that they were all differently coloured to
those found on lilac or privet, being of a more greyish-green.
Another case of colour-variation in larvae is that Emmelesia
Unifasdata, specimens of which I have recently had an oppor-
tunity of examining, through the courtesy of Mr. W. Davis.
This species feeds on the seeds of a species of Bartsia when
the capsules are in various stages of growth, and (omitting
details of marking) those caterpillars found on the green cap-
sules were green, whilst those on the brown capsules were of a
corresponding colour.
On the whole I am inclined to believe that sufficient import-
ance has not hitherto been given to phytophagic variability as
a factor in determining larval coloration, fcand a large field
for experimental investigation here lies open for future work.
The obscure chemico-physiological processes which may
perhaps be shown by such researches to lead to phytophagic
variation, cannot, I am persuaded, produce any great divergence
of character if unaided \ but when such causes of variability play
into the hands of natural selection variations of direct pro-
tective advantage to the species, we can easily see that this all-
important agency would seize upon and perpetuate such a
power of adaptability to a variable environment. (See Proc.
Zoo. Soc. 1873, p, 158, and "Nature," vol. xiv., pp. 329 and
330. R.M.]
X 2
308 Studies in the Theory of Descent.
V.
BIOLOGICAL VALUE OF SPECIAL MARKINGS.
THE following questions now present them-
selves : Have the markings of caterpillars any
biological value, or are they in a measure only
sports of nature ? Can they be considered as
partially or entirely the result of natural selection,
or has this agency had no share in their produc-
tion ?
The problem here offers itself more distinctly
than in any other group of living forms, because
it presents an alternative without a third possi-
bility. In other words, if it is not possible to
show that larval markings have a distinct biological
significance, there remains only for their explana-
tion the assumption of a phyletic force, since the
direct action of the environment is insufficient
to account for such regularity of development
throughout a series of forms. The explanation by
sexual selection is excluded ad initio, since we are
here concerned with larvae, and not with reproduc-
tive forms.1
1 [In 1879 Mr. George Francis, of Adelaide, forwarded from
the latter place a number of moths (a species of Anapaa)
The Origin of the Markings of Caterpillars. 309
The biological significance of marking — if such
significance it possess — will be most easily inves-
tigated by examining whether species with similar
markings have any conditions of life in common
which would permit of any possible inference as
to the significance of the markings.
Among the Sphingidcz we find four chief forms
of marking ; (i) complete absence of all marking ;
(2) longitudinal stripes ; either a simple subdorsal
or this together with a spiracular and dorsal line ;
(3) oblique stripes; (4) eye-spots and ring-spots,
single, paired, or in complete rows.
Now if we consider in which species these four
kinds of marking are of general occurrence, not
together with their larvae (in alcohol) and cocoons (Proc. Ent.
Soc. 1879, p. xvi),and in an accompanying note he stated that
the male larva when living is ,of " a bright emerald green, with
red and pink markings on the back, and yellow, black, and
white streaks on the sides." The male larva is described as
being smaller than the female, and as possessing all the
brilliant colours, the latter "having no red markings, but only
white, yellow, and green, with a little black." I was at first
disposed to think that we might be dealing here with two dis-
tinct species having differently marked larvae ; but Mr. Francis
this present year (1880) forwarded a large number of the living
cocoons of this species, which I separated according to size,
and, on the emergence of the moths (August), I found that all
those from the small cocoons were males, and those from the
larger cocoons females. There can be no doubt, therefore,
that we have but one species in this case, the larva of which
presents the remarkable phenomenon of sexual difference of
coloration. As an analogous fact I may here mention the
well-known case of Orgyia Antiqua^ the larva of which differs
in the colour of the tufts of hair according to sex. R.M.]
3io Studies in the Theory of Descent.
only in the small group of the Sphingidce but in
the whole order Lepidoptera, we shall arrive at
the following results : —
i. Complete absence of marking, so common m
the larvae of other insects, such as the Coleoptera,
is but seldom found among Lepidopterous cater-
pillars.
To this category belong all the species of Sesiidcz
(the genera Sesza, Trochilia, Sciapteron, Bembecia,
&c.), the larvae of which, without exception, are of
a whitish or yellowish colour, and live partly in the
wood of trees and shrubs and partly in the shoots
of herbaceous plants. Subterranean larvae also,
living at the roots of plants, such as Hepialus
Humuli at the roots of hop, and H. Lupulinus at
those of Triticum Repens, possess neither colour
nor marking. These, like the foregoing, are
yellowish-white, evidently because they are de-
prived of the influence of light. 2 The larvae of
1 [I have already given reasons for suspecting that the colour
of green caterpillars may be due to the presence of chlorophyll
(or some derivative thereof) in their tissues (see Proc. Zoo.
Soc. 1873, p. 159). This substance appears to be one of great
chemical stability, and, according to Chautard, who has detected
it in an unaltered state in the tissues of certain leaf-feeding
insects by means of its absorption spectrum (" Comp. Rend."
Jan. 1 3th, 1873), it resists the animal digestive processes
(Ann. Ch. Phys. [5], hi., i — 56). If this view should be
established by future observations, we must regard the green
colour of caterpillars as having been produced, when protective,
from phytophagic variability by the action of natural selection ;
and the absence of colour in internal feeders, above referred to,
The Origin of the Markings of Caterpillars. 311
certain small moths, such as Tortrix Arbutana
and Ponwnana, which live in fruit, and many case-
bearing Tineina, are likewise without marking and
devoid of bright colour, being generally whitish.
Many of the small caterpillars which feed ex-
teriorly are also — so far as my experience extends —
without definite markings, these being among the
most minute, such as the greenish leaf-mining
species of Nepticula. It is among the larger
species that we first meet with longitudinal and
oblique stripes. Eye-spots do not occur in any of
these larvae, a circumstance of the greatest impor-
tance for the biological significance of this character,
as will be shown subsequently. The small size of
the caterpillars cannot be the sole cause of the
absence of such eye-spots, since in young Smerin-
thus caterpillars one centimeter long, the oblique
stripes are beautifully developed, and the larvae of
many of the smaller moths considerably exceed
this size. The surface of these caterpillars there-
fore, /.£., the field on which markings are displayed,
is not absolutely too small for the development of
such a character,
is only secondarily due to the exclusion of light, and depends
primarily on the absence of chlorophyll in their food. In con-
nection with this I may adduce the fact, that some few species
of Nepticula {N. Oxyacanthella, N, Viscerella, &c.) are green,
although they live in leaf-galleries where this colour can hardly
be of use as a protection ; but their food (hawthorn and elm)
contains chlorophyll. See also note 2, p. 293. Further inves-
tigations in this direction are much needed. R.M.]
3 1 2 Studies in the Theory of Descent.
Besides the larvae of the Micro-lepidoptera and
of those species living in the dark, there is also a
complete absence of marking in the young stages
of many caterpillars. Thus, all the Sphingidce of
which I have been able to observe the develop-
ment, show no markings immediately after emer-
gence from the egg ; in many they appear very
soon, even before the first moult, and, in other
species, after this period.
2. The second category of markings, longitudinal
stripes, is very widely distributed among the most
diverse families. This character is found among
the larvae of butterflies, Sphingidcz, Noctucz} Micro-
lepidoptera, &c., but in all these groups it is absent
in many species. This last fact is opposed to the
view that this character is purely morphological,
and leads to the supposition that it may have a
biological value, being of service for the preserva-
tion of the individual, and therefore of the
species.
I find that such marking is of service, stripes
extending longitudinally along the upper surface
of the caterpillar generally making the latter less
conspicuous. This, of course, does not hold good
under all circumstances, since there are many
species with very striking colours which possesss
longitudinal stripes. Let us consider, however, a
case of adaptive colouring, such as a green cater-
pillar, which, on this account only, is difficult to
see, since it accords with the colour of the plant
The Origin of the Markings of Caterpillars. 313
on which it lives. If it is a small caterpillar, i.e.,
if its length and thickness do not considerably
exceed that of the parts of its food-plant, it
can scarcely be better concealed — stripes would
hardly confer any special advantage unless the
parts of the plant were also striped. But the case
is quite different if the caterpillar is considerably
larger than the parts of the plant (leaves, stalks,
&c.). The most perfect adaptive colouring would
not now prevent it from standing out con-
spicuously as a larger body, among the surround-
ing parts of the plants. It must be distinctly ad-
vantageous therefore to such a caterpillar to be
striped, since these markings to a certain extent
divide the large body into several longitudinal
portions — they no longer permit it to be seen as
a whole, and thus act more effectively than mere
assimilative colouring in causing it to escape detec-
tion. This protection would be the more effica-
cious if the stripes resembled the parts of the plant
in colour and size, such, for instance, as the lines
of light and shadow produced by stalks or by long
and sharp-edged leaves,
If this view be correct, we should expect longi-
tudinal stripes to be absent in the smallest cater-
pillars, and to be present more especially in those
species which live on plants with their parts
similarly disposed, i. e., on plants with numerous
thin, closely-growing stalks and grass-like leaves,
or on plants with needle-shaped leaves.
3 1 4 Studies in the Theory of Descent.
It has already been mentioned that the smallest
species are devoid of longitudinal striping. The
larvae of the Micro-lepidoptera show no such
marking, even when they do not live in the dark,
but feed either on the surface or in superficial
galleries of the leaves (Nepticula, &c.), in which
they must be exposed to almost as much light as
when living on the surface. The fact that the
subdorsal line sometimes appears in very young
Sphinx-larvae is explained, as has already been
shown, by the gradual backward transference of
adaptational characters acquired in the last stage
of development.
It can easily be demonstrated that longitudinally
striped caterpillars mostly live on plants, of which
the general appearance gives the impression of a
striped arrangement. We have only to consider
in connection with their mode of life, any large
group of adaptively coloured species marked in
this manner. Thus, among the butterflies, nearly
all the Satyrincz possess larvae conspicuously
striped — a fact which is readily explicable, because
all these caterpillars live on grasses. This is the
case with the genera Melanargia, Erebia^ Satyrus,
Pararge, Epinephele, and Ccenonympha, no species
of which, so far as the larvae are known, is without
longitudinal stripes, and all of which feed on
grasses. It is interesting that here also, as in
certain Sphingida, some species are brown, i. e.,
adapted to the soil, whilst the majority are green,
The Origin of the Markings of Caterpillars. 315
and are therefore adapted to living grass. Just
as in the case of the Spkingidce also, the brown
species conceal themselves by day on the earth,
whilst some of the green species have likewise
acquired this habit. I have already shown how
this habit originates from the increasing size of
the growing larva, which would otherwise become
too conspicuous, in spite of adaptive colour and
marking, A beautiful confirmation of this view is
found in the circumstance that only the largest
species of Satyr us, such as S. Proserpinus, Her-
mione, Phczdrus, &c., possess brown caterpillars.
I should not be surprised if a more exact investi-
gation of these species, which have hitherto been
but seldom observed, revealed in some cases a
dimorphism similar to that of the Sphingidcz ; and
I believe that I may venture to predict that the
young stages of all these brown larvae — at present
quite unknown — are, as in the last-named group,
green.
Besides the Satyrince, most of the larvae of the
Pierince and Hesperidce possess longitudinal stripes,
which are generally less strongly pronounced than
in the former subfamily. Some of the Pierince
live on Cruciferce, of which the narrow leaves and
thin leaf- and flower-stalks present nothing but a
linear arrangement ; other species of this group,
however, feed on Leguminosce (Lathyrus, Lotus,
Coronilla, Vicia), and some few on broad-leaved
bushes (Rhamnus). This last fact may appear to be
3 1 6 Studies in the Theory of Descent.
opposed to the theory ; but light lateral stripes, such
for example, as those possessed by Gonepteryx
Rhamni, can never be disadvantageous, and may
be of use, even on large leaves, so that if we
consider them as an inherited character, there is
no reason for natural selection to eliminate them.
In the case of caterpillars living on vetch, clover,
and other Leguminosce, it must not be forgotten
that, although their food-plants do not present any
longitudinal arrangement of parts, they always
grow among grasses, the species feeding on such
plants always resting between grass stems, and
very frequently on the grass itself, so that they
can have no better protective marking than
longitudinal stripes. The striping of the Hesperidce
larvae, which partly feed on grasses but mostly on
species of Leguminosay can be explained in a
similar manner.
It is not here my intention to go through all
the groups of Lepidoptera in this manner. The
instances adduced are quite sufficient to prove
that longitudinal stripes occur wherever we should
expect to find them, and that they really possess
the biological significance which I have ascribed to
them. That these markings are occasionally con-
verted into an adaptive imitation of certain special
parts of a plant, is shown by the larvae of many
moths, such for example as Chesias Spartiata,
which lives on broom (Spartium Scoparium),
The Origin of the Markings of Caterpillars. 317
its longitudinal stripes deceptively resembling the
sharp edges of the stems of this plant.3
3. Oblique striping. Can the lilac and white
oblique stripes on the sides of a large green
caterpillar, such as those of Sphinx Ligustri ; or
the red and white, or white, black, and red stripes
of Smerinthus Tilicz and Sphinx Drupiferarum
respectively, be of any possible use ? Have we
not here just one of those cases which clearly
prove that such a character is purely morpho-
logical, and worthless for the preservation of the
individual ? Does not Nature occasionally sport
with purposeless forms and colours ; or, as it has
often been poetically expressed, does she not here
give play to the wealth of her phantasy ?
At first sight this indeed appears to be the
case. We might almost doubt the adaptive
importance of the green ground-colour on finding
coloured stripes added thereto, and thus — as one
might suppose — abolishing the beneficial action
of this ground-colour, by making the insect
strikingly conspicuous. But this view would be
decidedly incorrect, since oblique stripes are of
8 [The same applies to Pseudoterpna Cytisaria, also feeding
on broom at the same time of the year. The most striking
cases of adaptive resemblance brought about by longitudinal
stripes are to be found among fir and pine feeders, species
belonging to the most diverse families (Hyloicus Pinastri,
Trachea Piniperda, Fidonia Piniaria, &c., &c.) all being most
admirably concealed among the needle-shaped leaves. R.M.]
318 Studies in the Theory of Descent.
just the same importance as longitudinal stripes.
The former serve to render the caterpillar diffi-
cult of detection, by making it resemble, as far as
possible, a leaf ; they are imitations of the leaf-veins.
Nobody who is in the habit of searching for
caterpillars will doubt that, in cases where the
oblique stripes are simply white or greenish-white,
it is extremely difficult to see the insect on its
food-plant, e.g. S. Ocellatus on Saiix ; not only
because it possesses the colour of the leaves, but
no less because its large body does not present
an unbroken green surface, which would bring it
into strong contrast with the leaves, and thus
arrest the attention. In the case of the species
named, the coloured area of the body is divided
by oblique parallel stripes, just in the same
manner as a willow leaf. In such instances of
course we have not presented to us any special
imitation of a leaf with all its details — there is not
a perfect resemblance of the insect to a leaf, but
only an arrangement of lines and interspaces which
does not greatly differ from the division of a leaf
by its ribs.
That this view is correct is shown by the occur-
rence of this form of marking. It is on the whole
rare, being found, besides in many Sphingidcz, in
isolated cases in various families, but is always con-
fined to those larvae which live on ribbed leaves, and
never occurring in species which feed on grasses
or on trees with needle-shaped leaves. This has
The Origin of the Markings of Caterpillars. 3 1 9
already been shown with respect to the Sphingidce,
in which the oblique stripes are only completely
developed in the subfamilies Smerinthince and
Sphingince. The species of Smerinthus all live
on trees such as willows, poplars, lime, oak, &c.,
and all possess oblique stripes. The genus
Anceryx also belongs to the Sphingince, and these
caterpillars, as far as known, live on trees with
needle-shaped leaves. The moths of this last
genus are very closely allied to the species of
Sphinx, not only in form and colour, but also in
many details of marking. The larvae are how-
ever different, this distinction arising entirely from
their adaptation to needle-shaped leaves, the
Sphinx caterpillars being adapted to ordinary
foliage. The species of Anceryx, as has been
already shown, are brown mixed with green, and
never possess even a trace of the oblique stripes,
but have a latticed marking, consisting of many
interrupted lines, which very effectively serves to
conceal them among the needles and brown bark
of the Coniferce.
Of the Sphingince living on plants with ordinary
foliage, not a single species is without oblique
stripes. I am acquainted with ten species of
caterpillars and their respective food-plants, viz.
Sphinx Carolina, Convolvuli, Qidnquemaculata,
Prini,Drupiferarum, Ligustri; Macrosila Rnstica
and Cingulata ; Dolba Hylceus and Acherontia
Atropos.
320 Studies in the Theory of Descent.
Besides among the Sphingince, oblique stripes
occur in the larvae of certain butterflies, viz.
Apatura Iris, Ilia, and Clytie, all of which live on
forest trees (aspen and willows), and are excellently
adapted to the leaves by their green colour. In
addition to these, I am acquainted with the larvae
of some few moths, viz. of Aglia Tau and
Endromis Versicolora, both of which also live on
forest trees.
Oblique stripes also occasionally occur in the
smaller caterpillars of Notice, Geometry, and
even in those of certain Pyrales, in all of which
they are shorter and differently arranged. In
these cases also, my theory of adaptation holds
good, but it would take us too far if I attempted
to go more closely into them. I will here only
mention the extraordinary adaptation shown by
the caterpillar of Eriopus Pteridis. This little
Noctuid lives on Pteris Aqiiilina ; it possesses
the same green colour as this fern, and has double
oblique white stripes crossing at a sharp angle on
each segment, these resembling the lines of sort of
the fern-frond so closely, that the insect is very
difficult to perceive.
After all these illustrations it can no longer
remain doubtful that the oblique stripes of the
Spkingida are adaptive. But how are the
coloured edges bordering these stripes in so many
species to be explained ?
I must confess that I long doubted the possi-
The Origin of the Markings of Caterpillars. 321
bility of being able to ascribe any biological value
to this character, which appeared to me only
conspicuous, and not protective. Cases may actually
occur in which the brightly coloured edges of the
oblique stripes make the caterpillar conspicuous —
just in the same manner as any marking may bring
about a conspicuous appearance by presenting a
striking contrast of colour. I am acquainted with
no such instance, however. As a rule, in all well-
adapted caterpillars, considering their colour in
its totality, this is certainly not the case. The
coloured edges, on the contrary, enhance the
deceptive appearance by representing the oblique
shadows cast by the ribs on the under-side of the
leaf ; all these caterpillars rest underneath the
leaves, and never on the upper surface.
This explanation may, perhaps, at first sight
appear far-fetched, but if the experiment be made
of observing a caterpillar of Sphinx Ligustri on
its food-plant, not immediately before one's eyes
in a room, but at a distance as under natural con-
ditions, it will be found that the violet edges do not
stand out brightly, but show a colour very similar to
that of the shadows playing about the leaves. The
coloured edges, in fact, produce a more effective
breaking up of the large green surface of the
caterpillar's body, than whitish stripes alone. Of
course if the insect was placed on a bare twig in
the sun, it would be easily visible at a distance ; the
larva never rests in such a position, however,
Y
322 Studies in the Theory, of Descent.
but always in the deep shadow of the leaves, in
which situation the coloured edges produce their
peculiar effect. It may be objected that the
oblique white stripes, standing simply on a dark-
green ground-colour, would produce the same
effect, and that my explanation therefore leaves
the bright colouring of these edges still unaccounted
for. I certainly cannot say why in Sphinx
Ligustri these edges are lilac, and in ,5*. Drupife-
rarum, S. Print, and Dolba Hylceus red, nor why
they are black and green in Macrosila Rustica, and
blue in Acherontia Atropos. If we knew exactly
on what plants these caterpillars fed originally, we
might perhaps indulge in comparing with an
artistic eye the shadows playing about their
leaves, seeing in one case more red, and in an-
other more blue or violet. The coloured stripes
of the Sphingidce must be regarded as the
single strokes of a great master on the countenance
of a human portrait. Looked into closely, we
see red, blue, or even green spots and strokes ;
but all these colours, conspicuous when close, dis-
appear on retreating, a general effect of colour
being then produced, which cannot be precisely
described by words.
Quite in accordance with this explanation, we
see caterpillars with the brightest coloured stripes
concealing themselves in the earth by day, and
betaking themselves to their food-plants only in
the dusk of the evening or dawn of morning and
The Origin of the Markings of Caterpillars. 323
even during the night ; i.e. in a light so faint that
feeble colours would produce scarcely any effect.
The bright blue of A cherontia A tropos, for example,
would give the impression of oblique shadows
without any distinctive colour.
It is precisely the case of this last caterpillar,
which formerly appeared to me to present insur-
mountable difficulties to the explanation of the
coloured stripes by adaptation, and I believed
that this insect would have to be classed with
those species which are brightly coloured because
they are distasteful, and are avoided by birds.
But although we have no experiments on this
point, I must reject this view. Unfortunately, we
know scarcely anything of the ontogeny of this
caterpillar ; but we know at least that the young
larvae (stage four) are greener than the more
purely yellow ones of the fifth stage (which, how-
ever, are also frequently green), and we know
further that some adults are of a dark brownish
grey, without any striking colours. From analogy
with the dimorphism of the species of Charocampa
and Sphinx, fully considered previously, it must
therefore be concluded that in this case also, a
new process of adaptation has commenced — that the
caterpillar is becoming adapted to the soil in and on
which it conceals itself by day.4 An insect which
4 The geographical distribution of the dark form indicates
that in the case of this species also, the form referred to is
replacing the yellow (green) variety. Whilst in the middle of
Y 2
324 Studies in the Theory of Descent.
acquires undoubted protective colours cannot,
however, be classed with those which possess an
immunity from hostile attacks.
That the coloured edges are correctly explained
as imitations of the oblique shadows of the leaf-
ribs, may also be proved from another point of
view. Let us assume, for the sake of argument,
that these coloured stripes are not adaptive, and
that they have not been produced by natural
Europe (Germany, France, Hungary) the dark form is extremely
rare, in the south of Spain this variety, as I learn from Dr. Noll,
is almost as common as the yellow one. I hear also from
Dr. Staudinger that in South Africa (Port Natal) the dark form
is somewhat the commoner, although the golden-yellow and,
more rarely, the green varieties, occur there. I have seen a
caterpillar and several moths from Port Natal, and these all
agree exactly with ours. The displacement of the green (yellow)
form by the dark soil-adapted variety, appears therefore to
proceed more rapidly in a warm than in a temperate climate.
[Eng. ed. Dr. Noll writes to me from Frankfort that the
caterpillar of Acherontia Atropos in the south of Spain does
not, as with us, conceal itself by day in the earth, but on the
stems underneath the leaves. "At Cadiz, on the hot, sandy
shore, Solatium violaceum grows to a height of three feet, and
on a single plant I often found more than a dozen Atropos
larvae resting with the head retracted, It can easily be under-
stood why the lateral stripes are blue when one has seen the
south European Solanea} on which this larva is at home.
Solanum violaceum is scarcely green : violet tints alternate with
brown, green, and yellow over the whole plant, and between
these appear the yellow-anthered flowers, and golden-yellow
berries of the size of a greengage. Thus it happens that the
numerous thorns, an inch long, between which the caterpillar
rests on the stem, pass from violet into shades of blue, red,
green, and yellow."]
The Origin of the Markings of Caterpillars. 325
selection, but by a hypothetical phyletic force.
We should then expect to see them appear at some
period in the course of the phyletic develop-
ment— perhaps at first only in solitary individuals,
then in several, and finally in all ; but we certainly
could not expect that at first single, irregular,
coloured spots should arise in the neighbourhood of
the oblique white stripes — that these spots should
then multiply, and fusing together, should adhere
to the white stripes, so as to form an irregular
spot-like edge, which finally becomes formed into
a straight, uniformly broad stripe. The phyletic
development of the coloured edges takes place,
however, in such a manner, the species of Smerin-
thus, as has already been established, showing
this with particular distinctness. In S. Tilice the
course of development can be followed till the
somewhat irregular red border is formed. In the
species of Sphinx this border has become com-
pletely linear. It is very possible that the ontogeny
of 6*. Ligustri or Drupiferarum would reveal the
whole process, although it may also be possible
that owing to the contraction of the development,
much of the phylogeny is already lost.
I have now arrived at the consideration of the
last kind of marking which occurs in the Sphin-
gid(z> viz. : —
4. Eye-spots and Ring-spots. — These markings,
besides among the Sphingidce, are found only in a
very few caterpillars, such as certain tropical
326 Studies in the Theory of Descent.
Papilionidtz and Noctucz. I know nothing of the
conditions of life and habits of these species, how-
ever, and without such knowledge it is impossible
to arrive at a complete explanation.
With Darwin, I take an eye-spot to be " a spot
within a ring of another colour, like the pupil
within the iris," but to this central spot " concen-
tric zones " may be added. In the Chcerocampa
larvae and in Pterogon (Enotherce, in which com-
plete ocelli occur, there are alway three zones —
a central spot, the pupil, or, as I have called it,
the " nucleus ;" then a light zone, the " mirror ;"
and, surrounding this again, a dark zone (generally
black), the " ground-area."
As ring-spots I will consider those ocelli which
are without the nucleus (pupil), and which are not
therefore, strictly speaking, deceptive imitations
of an eye, but present a conspicuous light spot sur-
rounded by a dark zone.
Between these two kinds of markings there is,
however, no sharp boundary, and morphologically
they can scarcely be separated. Species with
ring-spots sometimes have nuclei, and ocellated
larvae in some cases possess only a pale spot instead
of a dark pupil. I deal here writh the two kinds
separately, because it happens that they appear in
two distinct genera, in each of which they have
their special developmental history. Ring-spots
originate in a different position, and in another
manner than eye-spots ; but it must not, on this
The Origin of the Markings of Caterpillars. 327
account, be assumed without further inquiry, that
they are called into existence by the same causes ;
they must rather be investigated separately, from
their origin.
Eye-spots are possessed by the genera Chczro-
campa and Pterogon ; ring-spots by the genus
Deilephila. In accordance with the data furnished
by the above-given developmental histories, the
origination of these markings in the two genera
may be thus represented : —
In the genera named, eye-spots and ring-spots
are formed by the transformation of single portions
of the subdorsal line.
In Chcerocampa the primary ocelli originate on
the fourth and fifth segments by the detachment
of a curved portion of the subdorsal, this fragment
becoming the " mirror," and acquiring a dark
encircling zone ("ground-area"). The nucleus
(pupil) is added subsequently.
In Deilephila we learn from the development of
D. Hippophaes, that the primary annulus arises on
the segment bearing the caudal horn (the eleventh)
by the deposition of a red spot on the white
subdorsal line, which is somewhat enlarged in this
region. The formation of a dark " ground-area "
subsequently occurs, and with this, at first the par-
tial, and then the complete, detachment of the
mirror-spot from the subdorsal line takes place.
In both genera the spots arise at first locally on
one or two segments, from which they are trans-
328 Studies in the Theory of Descent.
ferred to the others as a secondary character. In
Chcerocampa this transference is chiefly backwards,
n Deilephila invariably forwards.
We have now to inquire whether complete
eye-spots — such as those of the Chczrocampa
larvae — have any significance at all, and whether
they are of biological importance. It is clear at
starting, that these spots do not belong to that
class of markings which make their possessors
more difficult of detection ; they have rather the
opposite effect.
We might thus be disposed to class ocellated
caterpillars with those " brightly coloured " species
which, like the Heliconince and Danaina among
butterflies, possess a disgusting taste, and which
to a certain extent bear the signal of their distaste-
fulness in their brilliant colours. But even if I
had not found by experiment that our native
Chcerocampa larvae were devoured by birds and
lizards, and that they are not therefore distasteful
to these insect persecutors, from the circumstance
that these caterpillars are all protectively coloured,
it could have been inferred that they do not belong
to this category. It has been found that all
adaptively coloured caterpillars are eaten, and one
and the same species cannot possibly be at the
same time inconspicuously (adaptively) and con-
spicuously coloured ; the one condition excludes
the other.
What other significance can eye-spots possess
The Origin of the Markings of Caterpillars. 329
than that of making the insects conspicuous ?
Had we to deal with sexually mature forms, we
should, in the first place, think of the action of
sexual selection, and should regard these spots as
objects of taste, like the ocelli on the feathers of
the peacock and argus-pheasant. But we are
here concerned with larvae, and sexual selection
is thus excluded.
The eye-spots must therefore possess some
other significance, or else they are of no import-
ance at all to the life of the insect, and are purely
" morphological characters ; " in which case, sup-
posing this could be proved, they would owe their
existence exclusively to forces innate in the organ-
ism itself — a view which very closely approaches
the admission of a phyletic vital force.
I am of opinion, however, that eye-spots certainly
possess a biological value as a means of terrifying
— they belong to that numerous class of characters
which occur in the most diverse groups of animals,
and which serve the purpose of making their
possessors appear as alarming as possible.
The caterpillars of the Sphingidcz are known
to behave themselves in different manners when
attacked. Some species, such, for instance, as
Sphinx Ligustri and Smerinthus Ocellat^(,sy on the
approach of danger assume the so-called Sphinx
attitude ; if they are then actually seized, they dash
themselves madly to right and left, by this means
not only attempting to get free, but also to terrify
33° Studies in the Theory of Descent.
their persecutor. This habit frequently succeeds
with men, and more especially with women and
children ; perhaps more easily in these cases than
with their experienced foes, birds.
The ocellated CJkzr&campa larvae behave differ-
ently. They remain quiet on being attacked,
and do not put on a Sphinx-like attitude, but only
withdraw the head and three small front seg-
ments into the large fourth segment, which thus
becomes much swollen, and is on this account
taken for the head of the insect by the inex-
perienced.5 Now the large eye-spots are situated
on the fourth segment, and it does not require
much imagination to see in such a caterpillar an
alarming monster with fiery eyes, especially if we
consider the size which it must appear to an enemy
such as a lizard or small bird. Fig. 28 represents
the larva of C. Porcellus in an attitude of defence,
although but imperfectly, since the front segments
can be still more withdrawn.
These facts and considerations do not, however,
amount to scientific demonstration, and I therefore
made a series of experiments, in order to determine
whether these caterpillars did actually frighten
small birds. The first experiment proved but little
satisfactory. A jay, which had been domesticated
for years, to which I threw a caterpillar of CJuero-
6 [For Mr. J. P. Mansel Weale's remarks on the habits of
certain ocellated S. African Sphinx-larvae see note i, p. 290.
R.M.]
The Origin of the Markings of Caterpillars. 331
campa Elpenor, did not give the insect any time
for manoeuvring1, but killed it immediately by a
strong blow with its bill. This bird had been
tame for years, and was in the habit of pecking at
everything thrown to him. Perhaps a wild jay
(Garrulus Glandariiis) would have treated the
insect differently, but it is hardly possible that such
a large and courageous bird would have much
respect for our native caterpillars. I now turned
to wild birds. A large brown Elpenor larva was
placed in the food- trough of an open fowl -house
from which the fowls had been removed. A flock
of sparrows and chaffinches (Fringilla Domes tica
and Calebs) soon flew down from the neighbouring
trees, and alighted near the trough to pick up
stray food in their usual manner. One bird soon
flew on to the edge of the trough, and was just
about to hop into it when it caught sight of the
caterpillar, and stood jerking its head from side
to side, but did not venture to enter. Another bird
soon came, and behaved in a precisely similar
manner ; then a third, and a fourth ; others settled
on the perch over the trough, and a flock of ten
or twelve were finally perched around. They all
stretched their heads and looked into the trough,
but none flew into it.
I now made the reverse experiment, by remov-
ing the caterpillar and allowing the birds again
to assemble, when they hopped briskly into the
trough.
332 Studies in the Theory of Descent.
I often repeated this experiment, and always
with the same result. Once it could be plainly
seen that it was really fear and not mere curiosity
that the birds showed towards the caterpillar.
The latter was outside the trough amongst
scattered grains of food, so that from one side it
was concealed by the trough. A sparrow flew
down obliquely from above, so that at first it could
not see the caterpillar, close to which it alighted.
The instant it caught sight of the insect, however,
it turned in evident fright and flew away.
Of course these experiments do not prove that
the larger insectivorous birds are also afraid of
these caterpillars. Although I have not been able
to experiment with such birds, I can certainly
prove that even fowls have a strong dislike to
these insects. I frequently placed a large Elpenor
larva in the poultry yard, where it was soon dis-
covered, and a fowl would run hastily towards it,
but would draw back its head just when about to
give a blow with the bill, as soon as it saw the
caterpillar closely. The bird would now run round
the larva irresolutely in a circle — the insect in the
meantime assuming its terrifying attitude — and
stretching out its head would make ten or twenty
attempts to deal a blow with its bill, drawing back
again each time. All the cocks and hens acted in
a similar manner, and it was often five or ten
minutes before one particularly courageous bird
would give the first peck, which would soon be
The Origin of the Markings of Caterpillars. 333
followed by a second and third, till the cater-
pillar, appearing palatable, would finally be
swallowed.
These experiments were always made in the
presence of several persons, in order to guard
myself against too subjective an interpretation of
the phenomena ; but they all invariably considered
the conduct of the birds to be as I have here
represented it.6
If it be admitted that the ocelli of caterpillars
are thus means of exciting terror, the difficulty of
their occurring in protectively coloured species at
once vanishes. They do not diminish the advan-
tage of the adaptive colouring, because they do not
make the caterpillars conspicuous, or at least any
more easily visible at a distance, excepting when
the insects have assumed their attitude of alarm.
But these markings are of use when, in spite of
protective colouring, the larva is attacked by an
enemy. The eye-spots accordingly serve the
caterpillar as a second means of defence, which
is resorted to when the protective colouring has
failed.
By this it must not be understood that the ocelli
of the Chcerocampa larvae invariably possess only
this, and no other significance for the life of the
insect. Every pattern can be conceived to render
• [Some experiments with the caterpillar of C. Elpenor, con-
firming these results, have been made by Lady Verney. See
" Good Words," Dec. 1877, p. 838. R.M.]
334 Studies in the Theory of Descent.
its possessor in the highest degree conspicuous by
strongly contrasted and brilliant colouring, so that
it might be anticipated that perfect eye-spots in
certain unpalatable species would lose their original
meaning, and instead of serving for terrifying be-
come mere signals of distastefulness. This is
perhaps the case with Chcerocampa Tersa (Fig. 35),
the numerous eye-spots of which make the insect
easily visible. Without experimenting on this
point, however, no certain conclusion can be
ventured upon, and it may be equally possible that
in this case the variegated ocelli with bright red
nuclei resemble the blossoms of the food-plant
(Spermacoce Hyssopifolia).7 I here mention this
possibility only in order to show how an inherited
form of marking, even when as well-defined and
complicated as in the present case, may, under cer-
tain circumstances, be turned in quite another
direction by natural selection, for the benefit of its
possessor. Just in the same manner one and the
same organ, such, for instance, as the limb of a
crustacean, may, in the course of phyletic develop-
ment, perform very different functions — first serv-
ing for locomotion, then for respiration, then for
reproduction or oviposition, and finally for the
acquisition of food.
7 [The eye-spots on Ch. Nerii have thus been supposed by
some observers to be imitations of the flowers of the periwinkle,
one of its food-plants. See, for instance, Sir John Lubbock's
"Scientific Lectures," p. 51. R.M.]
The Origin of the Markings of Caterpillars. 335
I now proceed to the consideration of the bio-
logical value of incomplete eye-spots, or, as I have
termed them, ring-spots. Are these also means
of terrifying, or are they only signals of distasteful-
ness ?
I must at the outset acknowledge that on this
point I am able to offer but a very undecided
explanation. The decision is only to be arrived
at by experiments conducted with each separate
species upon which one desires to pronounce
judgment. It is not here legitimate to draw
analogical inferences, and to apply one case to all,
since it is not only possible, but very probable, that
the biological significance of ring-spots changes in
different species. Nothing but a large series of
experiments could completely establish this. Un-
fortunately I have hitherto failed in obtaining
materials for this purpose, I would have deferred
the publication of this .essay for a year, could I have
foreseen with certainty that such materials would
have been forthcoming in sufficient quantity during
the following summer ; but this unfortunately de-
pends very much upon chance, and I believed that
a preliminary conclusion would be preferable to
uncertainty. Perhaps some entomologist to whom
materials are more easily accessible, may, by
continuing these experiments, accomplish this
object.
The experiments hitherto made by other ob-
servers, are not sufficient for deciding the question
336 Studies in the Theory of Descent.
under consideration. Weir,8 as is well known,
showed that certain brightly coloured and con-
spicuous larvae were refused by insectivorous birds ;
and Butler 9 proved the same for lizards and frogs.
These experiments are unfortunately so briefly
described, that in no case is the species experi-
mented with mentioned by name, so that we do
not know whether there were any Sphinx cater-
pillars among them.10 I have likewise experimented
in this direction with lizards, in order to convince
myself of the truth of the statement that (i) there
are caterpillars which are not eaten on account of
their taste, and (2) that such larvae possess bright
colours. I obtained positive, and on the whole,
very decided results. Thus, the common orange
and blue striped caterpillars of Bombyx Neiistria
enjoyed complete immunity from the attacks of
lizards, whilst those of the nearly allied Eriogaster
Lanestris and Z. Pini were devoured, although not
exactly relished. That the hairiness is not the
cause of their being unpalatable, is shown by the
fact that L. Pini is much more hairy than B.
Neustria. The very conspicuous yellow and black
ringed caterpillar of Euchelia Jacobcece gave also
most decided results. I frequently placed this
8 " On Insects and Insectivorous Birds," Trans. Ent. Soc.
1869, p. 21.
9 Ibid., p. 27.
10 [Messrs. Weir and Butler inform me that they have not
experimented with Sphinx-larvae. R.M.]
The Origin of the Markings of Caterpillars. 337
insect in a cage with Lacerta Viridis, but they
would never even notice them, and I often saw the
caterpillars crawl over the body, or even the head
of the lizards, without being snapped at. On every
occasion the larvae remained for several days with
the lizards without one being ever missed. The
reptiles behaved in a precisely similar manner with
respect to the moth of E. Jacobtzcz, not one of
which was ever touched by them. The yellow
and black longitudinally striped caterpillars of
Pyg&ra Bucephala were also avoided, and so were
the brightly coloured larvae of the large cabbage
white (Pieris Brassicce), which when crushed give
a disagreeable odour. This last property clearly
shows why lizards reject this species as distasteful.
Both caterpillar and butterfly possess a blood of a
strong yellow colour and oily consistency, in
which, however, I could not detect such a decided
smell as is emitted by that of the Heliconince and
Danaince.11
I next made the experiment of placing before
a lizard a caterpillar as much as possible like that
of E. Jacobcza. Half grown larvae of Bombyx
Rubi likewise possess golden yellow (but narrower)
II [It appears that the nauseous character of these last
butterflies is to a certain extent retained after death, as I
found that in an old collection which had been destroyed by
mites, the least mutilated specimens were species of Danais
and Euplaa, genera which are known ' to be distasteful when
living, and to serve as models for mimicry. See Proc. Ent
Soc. 1877, p. xii. R.M.]
z
338 Studies in the Theory of Descent.
transverse rings on a dark ground, and they are
much more hairy than those of E. Jacobcecz. The
lizard first applied its tongue to this caterpillar and
then withdrew it, so that I believed it would also
be avoided ; nevertheless it was subsequently
eaten. The caterpillars of Saturnia Carpini were
similarly devoured in spite of their bristly hairs,
and likewise cuspidate larvae (Dicranura Vinuld),
notwithstanding their extraordinary appearance and
their forked caudal horn.12 These lizards were by
no means epicures, but consumed large numbers of
earth-worms, slugs, and great caterpillars, and once
a specimen of the large and powerfully biting Or-
thopteron, Decticus Verucivorus. Creatures which
possessed a strongly repugnant odour were, how-
ever, always rejected, this being the case with the
strongly smelling beetle, Chrysomela Populi.-ds also
with the stinking centipede, lulus Terrestris^
whilst the inodorous Lithobius Forficatus was
greedily eaten. I will call particular attention to
these last facts, because they favour the supposition
that with rejected caterpillars a disgusting odour —
although perhaps not always perceptible by us —
is the cause of their being unpalatable.
Striking colours are of course only signals of
distastefulness, and the experiment with Bombyx
12 [This bears out the view expressed in a previous note i,
p. 290, that the grotesque attitude and caudal tentacles are more
for protection against ichneumons than against larger foes.
R.M.]
The Origin of the Markings of Caterpillars. 339
Rubi shows that the lizards were from the first
prejudiced against such larvae, the prejudice only
being overcome on actually trying the specimen
offered. A subsequent observation which I made
after arriving at this conclusion, is most note-
worthy. After the lizard had learnt by experience
that there might be not only distasteful caterpillars
(E. Jacob&ce), but also palatable ones banded with
black and yellow (B. Rubi), it sometimes tasted
the Jacobcece larvae, as if to convince itself that the
insect was actually as it appeared to be, viz., un-
palatable !
A striking appearance combined with a very
perceptible and penetrating odour is occasionally
to be met with, as in the caterpillar of the common
Swallow-tail, Papilio Machaon. I have never seen
a lizard make the slighest attempt to ' attack this
species. I once placed two large specimens of
this caterpillar in the lizard vivarium, where they
remained for five days, and finally pupated un-
harmed on the side of the case.
I have recorded these experiments, although
they do not thus far relate to Sphinx-caterpillars,
with the markings of which we are here primarily
concerned, because it appeared to me in the first
place necessary to establish by my own experi-
ments that signals of distastefulness did occur in
caterpillars.
I now come to my unfortunately very meagre
experience with Deilephila larvae, with only two
z 2
340 Studies in the Theory of Descent.
species of which have I been able to experiment,
viz., jD. Galii and Euphorbia,
The first of these was constantly rejected. Two
large caterpillars, one of the black and the other
of the yellow variety, were left for twelve hours in
the lizard vivarium, without being either examined
or touched. It thus appears that D. Galii is a
distasteful morsel to lizards ; and the habits of the
caterpillar are quite in accordance with this, since
it does not conceal itself, but rests fully exposed
by day on a stem, so that it can scarcely escape
being detected. It is almost as conspicuous as
D. Euphorbia.
I was much surprised to find, however, that this
last species was not rejected by lizards. On placing
a large caterpillar, six to seven centimeters long,
in the vivarium, the lizard immediately commenced
to watch it, and as soon as it began to crawl
about, seized it by the head, and, after shaking it
violently, commenced to swallow it. In spite of
its vigorous twisting and turning, the insect
gradually began to disappear, amidst repeated
shakings ; and in less than five minutes was
completely swallowed.13 With regard to lizards,
therefore, the prominent ring-spots of this larva
are not effective as a means of alarm, nor are they
considered as a sign of distastefulness.
18 These experiments, as already mentioned above, were not
made with the common German lizard (Lacerta Stirpium\ but
with the large South European Lacerta Viridis.
The Origin of the Markings of Caterpillars. 341
Unfortunately I have not hitherto been able to
make any experiments with birds. It would be
rash to conclude from the experience with lizards
that ring-spots were of no biological value. There
is scarcely any one means of protection which
can render its possessor secure against #// its foes.
The venom of the most poisonous snakes does
not protect them from the attack of the secretary
bird (Serpentarius Secretariats) and serpent eagle
(Spilornis Cheeld) ; and the adder, as is well known,
is devoured by hedgehogs without hesitation. It
must therefore be admitted that many species
which are protected by distastefulness, may possess
certain foes against which this quality is of no
avail. Thus, it cannot be said that brightly
coloured caterpillars, which are not eaten by birds
and lizards, are also spared by ichneumons. It is
readily conceivable therefore, that the larva of
D. Euphorbia may not be unpalatable to lizards,
because they swallow it whole ; whilst it is perhaps
distasteful to birds, because they must hack and
tear in order to swallow it.
From these considerations it still appears most
probable to me that D. Euphorbia, and the nearly
allied D. Dakliiasid Mauritania, bear conspicuous
ring-spots as signs of their being unpalatable to
the majority of their foes. The fact that these
species feed on poisonous Euphorbiace<%> combined
with their habit of exposing themselves openly by
day, so as to be easily seen at a distance, may
342 Studies in the Theory of Descent.
perhaps give support to this view. As these
insects are not protectively coloured, this habit
would long ago have led to their extermination ;
instead of this, however, we find that in all
situations favourable to their conditions of life
they are among the commonest of the Sphingidcz.
Thus, D. Euphorbia occurs in large numbers
both in South and North Germany (Berlin) ; and
Dr. Staudinger informs me that in Sardinia the
larvae of D. Dahlii were brought to him by
baskets full,
But if the conspicuous ring-spots (combined of
course with the other bright colours) may be
regarded as signals of distastefulness in many
species of Deilephila, this by no means excludes
the possibility that in some species these markings
play another part, and are effective as a means
of alarm. It even appears conceivable to me
that in one and the same caterpillar they may
play both parts against different foes, and it
would certainly be of interest to confirm or refute
this supposition by experiment.
In the light yellow variety of the caterpillar
of D. Galii the ring-spots may serve as means of
alarm, and still more so in that of D . Niccza, the
resemblance of which to a snake has struck earlier
observers.14
14 Thus, Boisduval states of this caterpillar, which in Provence
lives on Euphorbia esula and allied species : — " Its resem-
blance to a serpent, and its brilliant colour, permit of its being
The Origin of the Markings of Caterpillars. 343
In those species of Deilephila which conceal
themselves by day, the ring-spots cannot be con-
sidered as signals of distastefulness, and they
must therefore have some other meaning. As
examples of this class may be mentioned D.
Vespertilio, which is protectively coloured both in
the young and in the adult stages ; and likewise
D. Hippophaes, in which this habit of concealment
is associated with adaptive colouring. In the
case of the first-named species, it appears possible
that the numerous large ring-spots may serve to
alarm small foes, but the truth of this supposition
could only be decided by experiment. In D. Hippo-
phaes, on the other hand, such an interpretation
must be at once rejected, since most individuals
possess but a single ring-spot, which shows no
resemblance whatever to an eye.
I long sought in vain for the meaning of this
ring-spot, the discovery of which would in this
particular case be of the greatest value, because
we have here obviously the commencement of the
whole development of ring-spots before us — the
initial stage from which the marking of all the
other species of Deilephila has proceeded.
I believe that I have now found the correct
answer to this riddle, but unfortunately at a period
of the year when I am unable to prove it
easily discovered." This was written in 1843, long before
natural selection was thought of.
344 Studies in the Theory of Descent.
experimentally. I consider that the ring-spots
are crude imitations of the berries of the food-
plant. The latter are orange-red, and exactly of
the same colour as the spots ; the agreement in
colour between the latter and the berries is quite
as close as that between the leaves and the
general colouring of the caterpillar. I know of
no species which more closely resembles the
colour of the leaves of its food-plant, the dark
upper side and light under side corresponding in
the leaves and caterpillars. The colour of the
Hippophae is not an ordinary green, but a grey-
green, which shade also occurs, although certainly
but rarely, in the larvae. I may expressly state that
I have repeatedly shown to people as many as six
to eight of the large caterpillars on one buckthorn
branch, without their being able at once to detect
them. It is not therefore mere supposition, but a
fact, that this species is protected by its general
colouring. At first the orange-red spots appear
rather to diminish this protection — at least when
the insects are placed on young shoots bearing no
berries. But since at the same time when the
berries become red (end of July and the beginning
of August) the caterpillars are in their last stage
of development (z. e. possess red-spots), it appears
extremely probable that these spots are vague
representations of the berries. For the same
reason that these caterpillars have acquired the
habit of feeding only at dusk and during the
The Origin of the Markings of Caterpillars. 345
morning twilight, or at night, and of concealing
themselves by day, it must be advantageous for
them to have the surface of their large bodies not
only divided by white stripes, but also interrupted
in yet another manner. How could this be better
effected than by two .spots which, in colour and
position, represent the grouping of the red berries
on the branches ? When feeding, the insect
always rests with the hind segments on a branch,
the front segments only being more or less raised
and held parallel to the leaves ; the red spots thus
always appear on the stem, where the berries are
likewise situated. It might indeed be almost
supposed that the small progress which the
formation of secondary ring-spots on the other
segments has made up to the present time, is
explicable by the fact that such berry-like spots
on other portions of the caterpillar would be rather
injurious than useful.
It may, however, be asked how an imitation of
red berries, which are eaten by birds just as much
as other berries, can be advantageous to a cater-
pillar, since by this means it would rather attract
the attention of its enemies ?
Two answers can be given to this. In the
first place, the berries are so numerous on every
plant that there is but a very small chance of the
smaller and less conspicuous berry-spots catching
the eye of a bird before the true berries ; and,
secondly, the latter, although beginning to turn
346 Studies in the Theory of Descent.
red when the caterpillars are feeding, do not
completely ripen till the autumn, when the leaves
are shed, and the yellowish-red clusters of berries
can be seen at a distance. The caterpillar, how-
ever, pupates long before this time.
I have considered this case in such detail be-
cause it appears to me of special importance. It
is the only instance which teaches us that the rows
of ring-spots of the Deilephila larvae proceed from
one original pair — the only instance which permits
of the whole course of development being traced
to its origin. Were it possible to arrive at the
causes of the formation of these spots, their
original or primary significance would thereby be
made clear.
I will now briefly summarise the results of the
investigation of the biological value of the Deile-
phila ring-spots.
In the known species of the genus now existing
these spots have different meanings.
In some species (certainly in Galii, and pro-
bably in Euphorbia and Mauritanica) the con-
spicuous ring-spots serve as signals of distasteful-
ness for certain enemies (not for all).
In a second group of species they serve as a
means of alarm, like the eye-spots of the Chczro-
campa larvae (Niccea ? light form of GaliiT).
Finally, in a third group, of which I can at
present only cite Hippophaes, they act as an
adaptive resemblance to a portion of a plant,
The Origin of the Markings of Caterpillars. 347
and enhance the efficacy of the protective colour-
ing.
5 . Subordinate Markings. — I f, from the foregoing
considerations, it appears that the three chief ele-
ments of the Sphinx-markings — longitudinal and
oblique stripes, and spot formations — are not purely
morphological characters, but have a very decided
significance with respect to their possessors, there
should be no difficulty in referring the whole of
the markings of the Sphingidce to the action of
natural selection, supposing that these three kinds
of marking were the only ones which actually
occurred.
In various species, however, there appear other
patterns, which I have comprised under the term
"subordinate markings," some of which I will
select, for the purpose of showing the reasons which
permit of their being thus designated.
I ascribe to this category, for example, that fine
network of dark longitudinal streaks which often
extends over the whole upper side of the cater-
pillar, and which is termed the "reticulation.''
This character is found chiefly in the adult larvae
of Chczrocampa, being most strongly pronounced
in the brown varieties : it occurs also in Deilephila
Vespertilio, Pterogon (Enothera, and Sphinx Con-
volvuli. As far as I know, it is only associated
with adaptive colours, and indeed occurs only in
those caterpillars which rest periodically at the
348 Studies in the Theory of Descent.
base of their food-plants among the dead leaves
and branches. I do not consider this reticulation
to be a distinct imitation, but only as one of the
various means of breaking up the large uniform
surface of the caterpillar so as to make it present
inequalities, and thus render it less conspicuous.
There can be no doubt as to the dependence of
this character upon natural selection.
There is, however, a second group of markings,
which must be referred to another origin. To
this group, for instance, belong those light dots
in Cheer ocampa Porcellus and Elpenor which have
been termed " dorsal spots." I know of no other
explanation for these than that they are the neces-
sary results of other new formations, and depend
on correlation (Darwin), or, as I may express it,
they are the result of the action of the law govern-
ing the organization of these species.
As long as we are confined to the mere sup-
position that the character in question may be
the outward expression of an innate law of growth,
it is permissible to attempt to show that a quite
similar formation in another species depends upon
such a law.
Many of the dark specimens of Sphinx Convol-
vuli show whitish dots on segments six to eleven,
one being situated on the front edge of each of
these segments, at the height of the completely
vanished subdorsal line (Fig. 52). These spots
vary much in size, lightness, and sharpness of
The Origin of the Markings of Caterpillars. 349
definition. Now it might be difficult to attribute
any biological significance to this character, but its
origin becomes clear on examining light specimens
in which the oblique white stripes are distinct on
the sides and the subdorsal line is retained at
least on the five or six anterior segments. It can
then be seen that the spots are located at the
points of intersection of the subdorsal and the
oblique stripes (Fig. 16, PL III.), and they can
accordingly be explained by the tendency to the
deposition of light pigment being twice as great
in these positions as in other portions of the two
systems of light lines. Light spots are thus
formed when the lines which cross at these points
are partially or completely extinct throughout
their remaining course.
A marking is therefore produced in this case by
a purely innate law of growth — by the superposi-
tion of two ancient characters now rudimentary.
Many other unimportant details of marking must
be regarded as having been produced in a similar
manner, although it may not be possible to prove
this with respect to every minute spot and stripe.
The majority of " subordinate markings " depend
on the commingling of inherited, but now mean-
ingless, characters with newly acquired ones.
It would be quite erroneous to attribute to
natural selection only those characters which can
be demonstrated to still possess a biological value
in the species possessing them. They may be
35° Studied in the Theory of Descent.
equally due to heredity. Thus, it is quite possible
that the faint and inconspicuous ring-spots of Deile-
phila Vespertilio are now valueless to the life of
the species — they may be derived from an ances-
tral form, and have not been eliminated by natural
selection simply because they are harmless. I
only mention this as a hypothetical case.
In the case of markings of the second class,
i.e. oblique stripes, a transference to later phyletic
stages can be demonstrated, although the stripes
thereby lose their original biological value. Thus,
the Chcerocampa larvae, when they were green
throughout their whole life and adapted to the
leaves, appear to have all possessed light oblique
stripes in imitation of the leaf-ribs. All the species
of the older type of colouring and marking, such
as Chcerocampa Syriaca (Fig. 29) and Darapsa
Chcerilus (Fig. 34), and also the light green young
forms of C. Elpenor (Fig. 20), and Porcellus
(Figs. 25 and 26), show these oblique stripes. In
these last species the foliage imitation is abandoned
at a later stage, and a dark brown, or blackish
brown, ground-colour acquired. Nevertheless the
oblique stripes do not disappear, but show them-
selves— in the fourth stage especially, and sometimes
in the fifth — as distinct dirty yellow stripes, although
not so sharply defined as in the earlier stages.
These persistent stripes, in accordance with their
small biological value, are very variable, since
they are only useful in so far as they help to break
The Origin of the Markings of Caterpillars. 351
up the large surface presented by the caterpillar,
and are of no value as imitations of surrounding
objects.
The oblique stripes of Sphinx Convolvuli offer
a precisely similar case ; and it may be safely pre-
dicted that the young forms of this species would
possess sharply defined light oblique stripes, since
more or less distinct remnants of these markings
occur in all the adult larvae, and especially in the
green form. The entire pattern of this caterpillar
depends essentially on the commingling of charac-
ters persisting from an earlier period, i.e. of residues
of the subdorsal and oblique stripes, both these
markings being extraordinarily variable. The
black reticulation was added to the ground-
colour as a new means of adaptation, this charac-
ter appearing only in the phyletically younger
brown form, and being entirely absent, or only
faintly indicated, in the older green variety.
352
VI.
OBJECTIONS TO A PHYLETIC VITAL FORCE.
IT has been shown in the previous section that the
three elements composing the markings of the
Sphinx-larvae originally possessed a distinct sig-
nificance with respect to the life of the species, and
that they were by this means called into existence.
It has likewise been shown, that in most of the
species which possess these characters at the pre-
sent time they still have a decided, although some-
times a different use, for their possessors, so that
from this point of view no objection can be raised
to their being considered as having arisen by
natural selection.
On looking at the phenomenon as a whole,
however, certain instances occur which appear
quite irreconcilable with this view.
The most formidable objection is offered by the
genus Deilephila. The row of ring-spots which
nearly all the existing species have more or less
developed, has arisen from a simple subdorsal line.
It would not, therefore, be surprising if a species
were discovered which possessed this line without
The Origin of the Markings of Caterpillars. 353
any ring-spots as its only marking. If D. Hippo-
phaes were thus marked, there would be no objec-
tion to the theoretica lassumption that this * was the
ancestor of the other species. It would then be
said that ring-spots were first developed in a later
species by natural selection, and that they had been
transmitted to all succeeding and younger species.
Certain individuals of D. Hippophaes, however,
possess small ring-spots, some of which are well
developed on several segments. In this species
the row of ring-spots is therefore comprised in the
development. The remaining species, which are
much younger phyletically than Hippophaes, could
not have inherited their ring-spots from the latter,
since this species itself only possesses them occa-
sionally, and, so to speak, in a tentative manner.
The spots would therefore appear to have arisen
spontaneously in this species, and independently
of those in the other species. But if this were the
case, how should we be able to prove that in the
other species also the ring-spots did not arise
independently ; and if, moreover, a large number
of species showed the same character without its
being referable to inheritance from a common
ancestor, how could this be otherwise explained
than as the result of a force innate in these species
and producing similar variations ? But this is
nothing bnt Askenasy's " fixed direction of varia-
tion"— i.e., a phyletic vital force.
1 Or some other extinct analogously-marked species.
A a
354 Studies in the Theory of Descent.
The only escape from this difficulty is perhaps
to be found in proving that D. Hippophaes for-
merly possessed ring-spots, and that these have been
subsequently either partially or completely lost, so
that their occasional appearance in this species
would therefore depend upon reversion. The
ontogeny, however, teaches us that this is not the
case, since the young caterpillar does not possess
a greater number of more distinct ring-spots, but
wants them altogether with the exception of a red
spot on the eleventh segment, which is, however,
much fainter than in the last stage.
This last-mentioned fact contains the solution
of the problem. The premises from which this
reasoning set out were all incorrect — the one red
spot on the eleventh segment is likewise a ring-
spot, and indeed the most important one of all,
being primary, or the first to come into existence.
Now all specimens, without exception, possess this
first ring-spot, which is useful, and has therefore
been called forth by natural selection ; it is not
inherited, but newly acquired by this species ; at
least, if the explanation of these spots which I
have previously offered is correct.
The primary pair of spots may have been trans-
ferred from this to later species by heredity ; and
since, in all segmented animals there is a tendency
for the peculiarities of one segment to be repeated
on the others, this repetition must have occurred
with greater frequency and more completely in
The Origin of the Markings of Caterpillars. 355
the later species — the more so if the process were
favoured by natural selection, i.e. if the row of
ring-spots which originated in this manner could
in any way be turned to the use of the species.
\i\Hippophaes itself there must also be a ten-
dency to the formation of secondary ring-spots,
and indeed in a number of specimens we actually
see series of such ring-spots, the latter being pre-
sent in varying numbers, and in very different
states of development. The fact that the ring-
spots have not become a constant and well-
developed character, is simply explained by the
circumstance that as such they would have endan-
gered the existence of the species.
In this case there is therefore no necessity for
assuming a phyletic vital force. The ring-spots
of the genus Deilephila rather furnish us with an
excellent explanation of a fact which might other-
wise have been adduced in support of a phyletic
vital force, viz., the strict uniformity in the develop-
ment of larval markings.
Before I had been led to the discovery, by the
study of the marking and development of Hippo-
pha'e's, that the spots of the genus Deilephila origin-
ated on one segment only, from which they were
transferred secondarily to the others, this astonish-
ing regularity appeared to me an incomprehensible
problem, which could only be solved by assuming
a phyletic vital force. If it be attempted, for the
ten species here considered, to construct a gqnea-
A a 2
356 Studies in the Theory of Descent.
logical tree based on the supposition that it is the
rows of spots which have been inherited in cases
where they occur, and not the mere tendency to
their production by the transference of the one
originally inherited primary spot to the remaining
segments, the attempt will fail. The greater
number of the species would have to be arranged
in one row, since one species always bears a per-
fected form of marking, which appears in the young
stages of the following species. But it is very
improbable that nine different species, derived
directly the one from the other, would contempora-
neously survive.2 One species, D. Vespertilio,
could not be inserted at all in the genealogical
tree, since it wants one character which occurs in
all the other species, viz., the caudal horn, which
is absent even in the third stage, and must there-
fore have been lost at a very early period of the
phyletic development, so that we may consider it
to be on this account genetically allied to the
oldest known form. But the markings of this
larva pass through precisely the same stages of
development as do those of the other species.
Now if the ring-spots were inherited as such, the
existence of a hornless species with ring-spots
would be an insoluble riddle, and would favour the
admission of parallel developmental series, which
* [See Darwin's remarks on the struggle for life being most
severe between individuals and varieties of the same species
" Origin of Species," 6th ed. p, 59. R.M.]
77ie Origin of the Markings of Caterpillar:. 357
again could be scarcely otherwise explained than
by a " fixed direction of variation." We have here
one of that class of cases which the supporters
of a phyletic vital force have already so often made
use of in support of their view.
The explanation of such a case— i.e. its refer-
ence to known causes of species transformation —
is never easy, and is indeed impossible without a
precise knowledge of the ontogeny of many species,
as well as of the original significance of the charac-
ters in question. In the case of the Deilephila
larvae, however, such knowledge is still wanting.
It is true that they present us with parallel develop-
mental series, but these do not depend on an
unknown phyletic force — the parallelism can be
referred to the action of the imperfectly known
laws of growth innate in segmented organisms.
Because the characters of one segment have a
tendency to repeat themselves on the others, from
one parent-form possessing ring-spots on one seg-
ment only, there may have proceeded several
developmental series, all of which developed rows
of such spots independently of each other.
From these considerations we may venture to
construct the following genealogical tree : —
358 Studies in the Theory of Descent.
POSSIBLE GENEALOGICAL-TREE OF THE GENUS DEILEPHILA.
The circles indicate the phyletic stages IV. — VIII. ; the eighth
is only reached by Niccza, and is distinguished from the seventh
chiefly by the ontogeny, in the third stage of which the seventh
phyletic stage is reached, whilst in RufihorbicE and Dahlii this
stage is reached in the fourth ontogenetic stage. The phyletic
stages indicated by queries are extinct, and only known through the
ontogeny of existing species. It must be understood that this
pedigree expresses only the ideal and not the actual relations of
the species to one another. Thus, it is possible that Hippophaes
is not the parent-form, but an unknown or extinct species, which
must, however, have possessed the same marking, and so on.
The Origin of the Markings of Caterpillars. 359
Four parallel series here proceed from the
parent-form Hippophaes ; there may have been
five, or possibly only three, but the incomplete
state of our knowledge of the ontogeny does not
permit of any certain conclusion. For the point
under consideration this is, however, quite imma-
terial. The distance from the central point (the
parent-form) indicates the grade of phyletic de-
velopment which the respective species have at
present reached.
There is another case which is no less instruc-
tive, because it reveals, although in a somewhat
different manner, the action of a law of growth
innate in the organism itself, but which can never-
theless by no means be regarded as equivalent to
a phyletic vital force. I refer to the coloured
edges of the oblique stripes which occur in most
of the species of the genus Sphinx. It has already
been insisted upon in a previous section, that the
mode in which this character originates negatives
the assumption of a phyletic force, because these
coloured edges are gradually built up out of irre-
gularly scattered spots. There is no occasion for
a " developmental force "to grope in the dark;
if such a power exists, we should expect that it
would add new characters to old ones with the
precision of a master workman.
If, however, the coloured edges certainly depend
on natural selection, this agency causing .the
scattered spots to coalesce and become linear, we
360 St^ld^es in the Theory of Descent.
have here the proof that such spots first arose in a
precisely similar manner in several species, quite in-
dependently of one another — that, in fact, a " nxed
direction of variation " in a certain sense exists.
In three species of Smerinthus~\a,rv<£\ red spots
appear towards the end of the ontogeny ; in S.
Populi and Ocellatus in only a minority of indi-
viduals, and always separate (not coalescent),
and in £. Tilicz in a majority of specimens,
the spots frequently becoming fused into one
large, single, longish marking. These three
species cannot have inherited the spots from a
common ancestor, since they are absent in the
younger ontogenetic stages, or occur only excep-
tionally, becoming larger and more numerous in
the last stage ; they obviously form a character
which must be considered as a case of " anticipated
development."
How is it then that three species vary inde-
pendently of each other in an analogous manner ?
I know of no other answer to this question than
that similar variations must necessarily arise from
similar physical constitutions — or, otherwise ex-
pressed, the three species have inherited from an
unknown parent species, devoid of spots, not this
last character itself, but a physical constitution,
having a tendency to the formation of red spots
on the skin.3 The case offers many analogies to
3 [Compare this with Darwin's remarks on "analogous
variations," "Origin of Species," 6th ed., p. 125. R.M.]
The Origin of the Markings of Caterpillars. 361
that of the colour varieties of Lacerta Muralis, to
which Eimer 4 briefly calls attention in his interest-
ing communications on the blue lizard of the
Faraglioni Rocks at Capri. The South Italian
lizards, although having differently formed skulls,
show the same brilliantly coloured varieties as
those of North Italy ; and Eimer believes that
these parallel variations in widely separated
localities, some of which have long been isolated,
must be referred to a tendency towards fixed
directions of variation innate in the constitution
of the species.
I long ago insisted 5 that it should not be for-
gotten that natural selection is, in the first place,
dependent upon the variations which an organism
offers to this agency, and that, although the number
of possible variations may be very great for each
species, yet this number is by no means to be
considered as literally infinite. For every species
there may be impossible variations. For this
reason I am of opinion that the physical nature
of each species is of no less importance in the
4 " Zoologische Studien auf Capri. II. Lacerta muralis
caerula, ein Beitrag zur Darwin'schen Lehre." Leipzig, 1874.
[The subject of colour-variation in lizards has been much
discussed in " Nature " since the publication of the above-
mentioned essay; see vol. xix., pp. 4, 53, 97, and 122, and
vol. xx., pp. 290 and 480. R M.]
6 " Uber die Berechtigung der Darwin'schen Theorie."
Leipzig, 1868. See also the previous essay "On the Seasonal
Dimorphism of Butterflies," pp. 1 1 2 — 1 16.
362 Studies in the Theory of Descent.
production of new characters than natural selection,
which must always, in the first place, operate upon
the results of this physical nature, i.e. upon the
variations presented, and can thus call new ones
into existence.
It requires but a slight alteration of the defini-
tion to make out of this " restricted " or " limited
variability," which is the necessary consequence of
the physical nature of each species, a " fixed
direction of variation " in the sense of a phyletic
vital force. Instead of — the SmerintkusAarvat
show a tendency to produce red spots on the
skin, it is only necessary to say — these larvae tend
to produce red borders to the oblique stripes.
The latter statement would, however, be incorrect,
since the red borders first arose by the coalescence
of red spots through the action of natural selec-
tion. It is not even correct to say that all the
species of Smerinthiis show this tendency to
produce spots, since this character does not seem
to occur either in S. Quercus or S. Tremulce.
The distinction between the two modes of con-
ception will become clear if we ask, as an example,
whether those Cheer ocampaA'd^v^ which do not at
present possess eye-spots will subsequently acquire
these markings, supposing that they maintain their
existence on the earth for a sufficient period ?
The supporters of a " fixed direction of varia-
tion " would answer this question in the affirmative.
Ocelli constitute a character which occurs in nearly
The Origin of the Markings of Caterpillars. 363
all the species of the group — they are the goal
towards which the phyletic force is urging, and
which must sooner or later be reached by each
member of the group. On the other hand, I
cannot express so decidedly my own opinion, viz.,
that such complicated characters as the many-
coloured oblique stripes or eye-spots are never
the results of purely internal forces, but always
arise by the action of natural selection, /. e. by the
combination of such minute and simple variations
as may present themselves. It may be replied
that the formation of eye-spots in those species
which are at present devoid of them, cannot indeed
be considered impossible, but that they would
only appear if the constitution of these species
had a tendency to give rise to the production of
darker spots on the edge of the subdorsal line,
and if, at the same time, the possession of eye-
spots would be of use to the caterpillar under its
special conditions of life.
The condition of affairs would be quite different
if we were simply concerned with the transference
of a character from one segment on which it was
already present, to the remaining segments. The
transference would, in this case, result from causes
purely innate in the organism — from the action of
laws of equilibration or of growth (correlation), and
the external conditions of life would play only a ne-
gative part, since they might prevent tire complete
reproduction of a character such, for example, as
364 Studies in the Theory of Descent.
eye-spots, on all the segments, in cases where it was
disadvantageous to the species. The fact that our
species of Charocamp.a have only faint indications,
and not a completely-developed eye-spot, on the
remaining segments, may perhaps be explained in
this manner. It is conceivable that the two pairs
of ocelli on the front segments are more effective as
a means of alarm than if the insects were provided
with two long rows of such markings ; but nothing
can be stated with certainty on this point until
experiments have been made with caterpillars
having rows of eye-spots.
The question raised above — whether the species
of Charocampa at present devoid of eye-spots are
to be expected to acquire this character in the
course of their further phyletic development-
brings with it another point, which cannot be here
passed over.
If the iitility of the four kinds of markings in
their perfected form is demonstrated, their origina-
tion through natural selection is not, strictly
speaking, thereby proved. It must also be shown
that the first rudiments of these characters were
also of use to their possessors. The question as
to the utility of the " initial stages " of useful
characters must here be set at rest.
In the case of markings such as longitudinal
and oblique stripes, it is quite evident that the
initial stages of these simple characters do not
differ greatly from the perfected marking, but
The Origin of the Markings of Caterpillars. 365
this is certainly not the case with eye- and ring-
spots. The most light is thrown upon this question
by the latter, because a species which has remained
at the initial stage of the formation of ring-spots
here presents itself for examination, viz. Deilephila
Hippophaes.
I have attempted to show that the orange-red
spots, which, as a rule, adorn only the eleventh
segment, enhance the adaptive colouring of this
caterpillar by their resemblance to the berries of the
sea-buckthorn, whilst the general surface resembles
the leaves in colour. If this be admitted, the
origination of these spots by natural selection
offers no difficulty, since a smaller spot, or one of
a fainter red, must also be of some use to its
possessor.
This case is of importance, as showing that a
" change of function " may occur in markings, just
as it does in certain organs among the most
diverse species of animals, in the course of phyletic
development. The spots which in Hippophaes
are imitations of red berries, in species which have
further advanced phyletically play quite another
part — they serve as means of alarm, or signals of
distastefulness.
It appears to me very improbable, however,
that the perfect ocelli of the Cktzrocampa-lzrvaz
have also undergone such a "functional change"
(Dohrn). I rather believe that the first rudiments
of these markings produced the same effect as that
366 Stiidies in the Theory of Descent.
which they now exercise, viz., terror. We are
certainly not so favourably circumstanced in this
case in knowing a species which shows the initial
steps of this character in its last stage of life ; but
in the initial steps which the second stage of certain
species present, we see preserved the form under
which the eye-spots first appeared in the phylogeny,
and from this we are enabled to judge with some
certainty of the effect which they must have
produced at the time.
In the ontogeny of C. Elpenor and Porcellus
we see that a small curvature of the subdorsal
line first arises, the concavity of which becomes
filled with darker green, and soon afterwards with
black ; the upwardly curved piece of the subdorsal
then becomes detached and more completely
surrounded by black. The white fragment of the
subdorsal which has become separated, in the next
place broadens, and a black (dark) pupil appears
in its centre.
Now the first rudiments of the eye-spot certainly
appear very insignificant in a caterpillar two
centimeters long, but we must not forget that in
the ancestors of the existing Ch<zrocampa-\2xv^
this character appeared in the adult state. If we
conceive the curvature of the white subdorsal with
the underlying dark pigment to be correspondingly
magnified, its importance as a means of alarm can
scarcely be denied, particularly when we consider
that this marking stands on the enlarged fourth seg-
The Origin of the Markings of Caterpillars. 367
ment, which alone invests the caterpillar with a sin-
gular, and, to smaller foes, an alarming appearance.
We know that in the case of those Ch&rocampa-
larvse which possess no eye-spots, the distension of
this segment is employed against hostile attacks.
(See the illustration of Darapsa Chcerilus, PL IV.,
Fig. 34.) Those markings which even only re-
motely resembled an eye must, in such a posi-
tion, have increased the terrifying action. On
these grounds I believe that it may be safely
admitted, that this kind of marking possessed the
same significance in its initial stages as it now
does when fully perfected. No functional change
has here taken place.
Among all the facts brought together in the
first section I only know of one group of
phenomena which at least permit of an attempt to
refer them to a phyletic vital force. This is the
occurrence of dark ground-colours in adult larvae
which are of light colours in their young condi-
tion. I have already attempted to show that in the
Chcerocampa-\dxv&, this change of colour depends
on a double adaptation, the young caterpillars
being adapted to the green colour of the plant
and the adults to the soil and dead leaves. This
interpretation appears the more correct when we
find the same process, viz. the gradual replacement
of the original green by brown colours, among
species of widely different genera, which, with
the dark colouring, possess the necessarily
368 Studies in the Theory of Descent.
correlated habit of hiding themselves by day
when in the adult condition. This is the case
with Sphinx Convolvuli, Deilephila Vespertilio,
and Acherontia Atropos.
Thus far all has been easily explicable by natural
selection ; but when we also see a u tendency" to
acquire a dark colour in the course of develop-
ment, in those species which neither conceal
themselves nor are adaptively coloured, but are
very conspicuously marked — and if, further, it can
be shown that these species, such for instance as
Deilephila Galii, actually possess immunity from
the attacks of foes, — how can this tendency to the
formation of a dark colour be otherwise explained
than by the admission of a phyletic vital force
urging the variations in this direction ?
Nevertheless I believe that also on this point
an appeal to unknown forces can be dispensed
with. In the first place, dark ground-colours can
be of use to a species otherwise than as means of
adaptation. In D. Galii, as well as in D. Euphor-
bia, the light ring-spots appear rather at their
brightest on the pitchy-black ground ; and if this
caterpillar must ( sit venia verbo /) become con-
spicuous, this purpose would be best attained by
acquiring a dark ground-colour, such as that of
D. Euphorbia.
The tendency, apparently common to all these
Sphingidce, to acquire a dark colour with increasing
age, depends therefore on two quite distinct adap-
The Origin of the Markings of Caterpillars. 369
tations — first, in species sought by enemies, on an
adaptation to the colour of the soil ; and secondly,
in species rejected by foes, on the endeavour to
produce the greatest possible contrast of colour.
Moreover, the supposition from which this last
plea for a vital force set out is not universally
correct, since there are species, such for instance
as D. Niccea, which never acquire a dark colour ;
and in D. Galii also, although all the individuals
abandon the protective green of the young stages,
they by no means all acquire a dark hue in ex-
change for this colour ; many individuals in their
light ochreous-yellow colouring rather strikingly
resemble the snake-like caterpillar of D. Niccza.
B b
370
VII.
PHYLETIC DEVELOPMENT OF THE MARKINGS OF
THE SPHINGID^E : SUMMARY AND CONCLUSION.
IF, from the form possessed by many of the cater-
pillars of the Sphingida on their emergence from
the egg, we may venture to draw a conclusion
concerning the oldest phyletic stage, these larvae
were originally completely destitute of marking.
The characteristic caudal horn must be older
than the existing markings, since it is present in
the younger stages (except in cases where it is
altogether wanting), and is generally even larger
than at a later age.
There is, however, further evidence that there
were once Sphinx-larvae without any markings.
Such a species now exists. I do not mean the
boring caterpillars of the Sesiidce^ which live in the
dark, and are therefore colourless, but I refer to a
1 [Mr. A. G. Butler has recently advanced the view that
this family is not allied to the Sphingidcz, but is related on the
one side to the Py rates, and on the other to the Gelechiidce.
See his paper " On the Natural Affinities of the Lepidopterous
Family JEgcriidte," Trans. Ent. Soc. 1878, p. 121. R.M.]
The Origin of the Markings of Caterpillars. 371
large larva (over six centimeters long) preserved in
spirit in the Berlin Museum,2 which, from its form,
belongs to the Smerinthus group, it possesses a
caudal horn, and on the whole upper surface is
covered with short and sparsely scattered bristles,
such as occur in the Sesiida. The colour of this
unknown insect appears to have been light green,
although it now shows only a yellowish shade.
Every trace of marking is absent, and it thus
corresponds exactly with the youngest stages of
the majority of the existing Sphinx-larvae — even
to the short bristles sparsely scattered over the
whole upper surface of its body. We have there-
fore, so to speak, a living fossil before us, and it
would be of great interest to ascertain its history.
All the data furnished by the developmental
history go to show that of the three kinds of
markings which occur in the Sphingidce> viz.,
longitudinal and oblique stripes and spots, the
first is the oldest. Among the species which are
ornamented with oblique stripes or spots there are
many which are longitudinally striped in their
young stages, but the reverse case never occurs —
young larvae never show spots or oblique stripes
when the adult is only striped longitudinally.
The first and oldest marking of the caterpillars
of the Sphingida was therefore the longitudinal
striping, or, more precisely speaking, the subdorsal,
2 I am indebted to my esteemed colleague, Prof. Gestacker,
for the knowledge of this specimen.
B b 2
372 Studies in the Theory of Descent.
to which dorsal and spiracular lines may have
been added. That this second stage of phyletic
development has also been preserved in existing
species has already been sufficiently shown ; the
greater portion of one group, the Macroglos since,
has indeed remained at this stage of develop-
ment.
From the biological value which must be attri-
buted to this kind of marking, its origination by
natural selection presents no difficulty. The first
rudiments of striping must have been useful, since
they must have broken up the large surface of the
body of the caterpillar into several portions, and
would thus have rendered it less conspicuous to its
enemies.
Thus it is not difficult to perceive how a whole
group of genera could have made shift with this
low grade of marking up to the present time.
Colour and marking are not the only means of
offence and defence possessed by these insects ; and
it is just such simply-marked larvae as those of the
Macroglossincz which have the protective habit of
feeding only at night, and of concealing themselves
by day. Moreover, under certain conditions of
life the longitudinal stripes may be a better means
of protection, even for a Sphinx-larva, than any
other marking ; and all those species in which this
pattern is retained at the present time live either
among grasses or on Conifers.
It cannot be properly said that the second form
The Origin of the Markings of Caterpillars. 373
of marking — the oblique stripes — has been de-
veloped out of the first. If these had arisen by
the transformation of the longitudinal stripes, the
two forms could not exist side by side. This is
the case, however, both in certain species in the
adult state (Calymnia Panopus*), as well as in
others during their young stages (most beautifully
seen in Smerinthus Populi, Fig. 56). Various facts
tend to show that the oblique stripes appeared in
the phyletic development later than the longi-
tudinal lines. In the first place they appear later
than the latter in the ontogeny of certain species.
This is the case with Charocdmpa Elpenor and
Porcellus, in which, however, they certainly do
not reach a high state of development. Then
again, the longitudinal lines disappear completely
in the course of the ontogeny, whilst the oblique
stripes alone maintain their ground. Thus, the
subdorsal line vanishes at a very early stage, with
the exception of a small residue,4 in all native
species of Smerinthus. I have already attempted
to show that new characters are only acquired in
the last stage, and that if still newer ones are then
added, the former disappear from the last stage,
and are transferred back to a younger one.
Characters vanish therefore from a stage in the
same order as they were acquired.
2 Cat. Lep. East India Co., PL VIII.
4 Such a residue is distinctly visible in S. Ocellatus ; see
Fig. 70, PL VII.
374 Studies in the Theory of Descent.
Finally, among the genera with longitudinal
stripes (e.g. Macroglossa) we know certain species
which, when at an advanced age, possess oblique
stripes (M. Fuciformis], although these slant in a
direction opposite to those of most of the other
larvae of the Sphingidce. These are, however,
always species which differ from their allies in their
mode of life, not feeding on grasses or low plants,
but on large-leaved shrubs. If we were able to
ascertain the ontogeny of these species, we should
find that the oblique stripes appeared late in life,
as has already been shown in the case of Pterogon
CEnotherce.
If it be asked why the longitudinal lines were
first formed, and then the oblique stripes, it may
be replied that the physical constitution of these
caterpillars would be more easily able to give rise
to simple longitudinal lines than to complicated
oblique stripes crossing their segments.5 It may
6 [The question here also suggests itself as to why the dorsal
line should not have been the primary longitudinal stripe,
seeing that such a marking is almost naturally produced in
many caterpillars by the food in the alimentary canal ; or, in
other words, why has not natural selection taken advantage of
such an obvious means of producing a stripe in cases where it
would have been advantageous? In answer to this I may
state, that in large numbers of species the dorsal line has thus
become utilized ; but in the case of large caterpillars resting
among foliage, it can be easily seen that light lateral (i.e. sub-
dorsal) stripes, are more effective in breaking the homogeneity
of the body than a dorsal line only slightly darker than the
general ground-colour. Lateral lines are in fact visible from
The Origin of the Markings of Caterpillars. 375
perhaps also be suggested that the oldest Sphingidce
lived entirely on low plants among grasses, and in
the course of time gradually took to shrubs and
trees. At the present time the majority of the
Sphinx-larvae still live on low plants, and but few
on trees, such caterpillars generally belonging to
certain special genera.
The character of oblique stripes becomes per-
fected by the addition of coloured edges, the
latter, as is self-evident, having been added subse-
sequently.
The third chief constituent of the Sphinx-mark-
ings, i.e. the spots — whether perfect ocelli or only
ring-spots — in two of the special genera here con-
sidered, arise on the subdorsal, where they are
either deposited (Deilephila), or built up from a
fragment of this line (Chcerocampa). That these
markings can, however, also originate independ-
ently of the subdorsal, is shown by the ocellus of
Pterogon CEnotherce, situated on the segment
bearing the caudal horn. In this case, however,
the ontogeny teaches us that the spot also succeeds
the subdorsal, so that we can state generally that
all these spot-markings are of later origin than the
longitudinal striping.
two directions of space. If a caterpillar thus marked be placed
on a twig, these lines are visible when we look at the creature's
back or at either side. That the subdorsal are therefore the
primary lines, as shown by Dr. Weismann's observations of the
ontogeny of many of the Sphingida^ is quite in harmony with the
view of their having been produced by natural selection. R.M.]
376 Studies in the Theory of Descent.
The question as to the relative ages of the
oblique stripes and the spot-marking does not
admit of a general answer. In some cases (C.
Elpenor and Porcellus] the oblique stripes disap-
pear when the ocelli reach complete development,
and we may therefore venture to conclude that in
these cases the former appeared earlier in the
phylogeny. But it is very probable that oblique
stripes arose independently at different periods,
just as longitudinal lines occur irregularly in quite
distinct families. It would be a great error if we
were to ascribe the possession of oblique stripes
solely to descent from a common ancestor. The
oblique markings found on certain species of
Macroglossa (M. Cory thus from India) have not
been inherited from a remote period, but have been
independently acquired by this or by some recent
ancestral species. They have nothing to do
genetically with the oblique stripes which occur in
some species of Chcerocampa (e.g. in C. Nessus,
from India), or with those of the species of
Smerinthus and Sphinx. They depend simply
on analogous adaptation (Seidlitz 6), i.e. on adapta-
tion to an analogous environment.
The case is similar with the spot-markings. I
have already shown that under certain conditions
ring-spots may assume the exact appearance of
6 " Die Darwin'sche Theorie. Elf Vorlesungen iiber die
Entstehung der Thiere und Pflanzen durch Naturziichtung."
2nded., Leipzig, 1875, p. 195.
The Origin of the Markings of Caterpillars. 377
eye-spots by the formation of a nucleus in the
" mirror," such as occurs occasionally in Deilephila
Euphorbia (Fig. 43), more frequently in I}. Galii,
and as a rule in D. Vespertilio. Nevertheless,
these markings arise in quite another manner to
the eye-spots of the Cheer ocampincz, with which
they conseqently have no genetic relation ; the two
genera became separated at a time when they
neither possessed spot-markings. Further, in
Pterogon (Enotherce we find a third kind of spot-
marking, which is most closely allied to the ocelli
of the Ch&rocampa-\&rv&,> but is situated in quite
another position, and must have originated in
another manner, and consequently quite inde-
pendently of these eye-spots.
It can also be readily understood why the first
and second elements of the markings of the Sphin-
gidce should be mutually exclusive, and not the
second and third or the first and third.
A light longitudinal line cutting the oblique
stripes, considerably diminishes that resemblance
to a leaf towards which the latter have a tendency,
and it is therefore only found in cases where an
adaptive marking can be of no effect on account of
the small size of the caterpillar, i.e. in quite young
stages. (See, for instance, Fig. 56, the first stage
of S. Populi.} At a later period of life the old
marking must give way to the new, and we accord-
ingly find that the subdorsal Jine vanishes from all
the segments on which oblique stripes are situated,
378 Studies in the Theory of Descent.
and is only retained on the anterior segments
where the latter are wanting. In some few cases
both elements of marking certainly occur together,
such as in Calymnia Panopus and Macroglossa
Corythus ; but the oblique stripes are, under these
circumstances, shorter, and do not extend above
the subdorsal line, and in Darapsa Ckcerilus even
become fused into the latter.7
In certain cases there may also be a special leaf
structure imitated by the longitudinal lines, but
on the whole the latter diminish the effect of the
oblique stripes ; and we accordingly find that not
only has the subdorsal disappeared from those
segments with oblique stripes, but that most larvae
with this last character are also without the other-
wise broad spiracular and dorsal lines. This is
the case with all the species of SmerintJms 8 known
7 [In the following species, already mentioned in previous
notes, the oblique stripes are bounded at their upper extremities
by a conspicuous subdorsal line : — Acosmeryx Ancens, Cram. ;
Sphinx Cingulata, Fabr. ; Pachylia Fiats, Linn. ; P. Syces, Hubn.
In Pseudosphinx Cyrtolophia, But!., the oblique white stripes,
beautifully shaded with pink, run into the white pink -bordered
dorsal line, so that when seen from above the markings
present the appearance of the midrib and lateral veins of a
leaf, and are probably specially adapted for this purpose.
R.M.]
8 [The dorsal line as well as the oblique stripes is present
in the caterpillar of Smerinthus Tartarinovii, Menet.; and in
Ambulyx Gannascus, Stoll., the oblique stripes are bounded
above by a subdorsal line, as in the species named in the
preceding note. R.M.]
The Origin of the Markings, of Caterpillars. 3 79
to me, as well as with all the species of the genera
Sphinx, Dolba, and Acherontia.
Oblique stripes and spot-markings are not,
however, necessarily mutually exclusive in their
action, and we also find these in certain cases
united in the same larva, although certainly never
in an equal state of perfection. Thus, Ctuzrocampa
Nessus 9 possesses strongly marked oblique stripes,
but feebly developed ocelli; and, on the other
hand, Chcerocampa Elpenor shows strongly de-
veloped eye-spots, but the earlier oblique stripes
are at most only present as faint traces. This is
easily explained by the mode of life. These cater-
pillars— at least such of them as are perfectly
known — do not live on plants with large, strongly-
ribbed leaves, and are even in the majority of
individuals adapted to the colour of the soil ; the
oblique stripes have therefore in these cases
only the significance of rudimentary formations.
That the first and third forms of markings also
are not always mutually prejudicial in their action
is shown by the case of Chcerocampa Tersa, in
which the eye-spots certainly appear to possess
some other significance than as a means of causing
terror. In most of the Ck<zrocampa-\axvzz the
subdorsal line disappears in the course of the
phylogeny, and it can be understood that the
illusive appearance of the eye-spots would be
9 Cat. Lep. East India Co., PI. XI.
380 Studies in the Theory of Descent.
more perfect if they did not stand upon a white
line.
If we consider the small number of facts with
which I have here been able to deal, the result
of these investigations will not be deemed unsatis-
factory. It has been possible to show that each
of the three chief elements of the markings of the
Sphingidce have a biological significance, and their
origin by means of natural selection has thus been
made to appear probable. It has further been
possible to show that the first rudiments of these
markings must also have been of use ; and it thus
appears to me that their origin by means of natural
selection has been proved to demonstration.
Moreover, it has not been difficult to understand
the displacement of the primary elements of the
markings by secondary characters added at a later
period, as likewise an essential effect of natural
selection. Finally, it has been possible to explain
also the subordinate or accessory elements of the
markings, partly by the action of natural selection,
and partly as the result of markings formerly
present acting by correlation.
From the origin and gradual evolution of the
markings of the Sphingida we may accordingly
sketch the following picture : —
The oldest Sphinx-larvae were without markings ;
they were probably protected only by adaptive
colouring, and a large caudal horn, and by being
armed with short bristles.
The Origin of the Markings of Caterpillars. 381
Their successors, through natural selection, be-
came longitudinally striped ; they acquired a sub-
dorsal line extending from the horn to the head, as
well as a spiracular, and sometimes also a dorsal,
line. The caterpillars thus marked must have
been best hidden on those plants in which an
arrangement of parallel linear parts predominated ;
and we may venture to suppose that at this period
most of the larvae of the Sphingidce lived on or
among such plants (grasses).
At a later period oblique stripes were added to
the longitudinal lines, the former (almost always)
slanting across the seven hindmost segments from
the back towards the feet in the direction of the
caudal horn. Whether these stripes all arose
simultaneously, or, as is more probable, whether
only one at first appeared, which was then trans-
ferred to the other segments by correlation
assisted by natural selection, cannot, at least
from the facts available, at present be determined.
On the whole, as the oblique stripes became
lengthened towards the back, the longitudinal lines
disappeared, since they injured the deceptive effect
of the stripes. In many species also there were
formed dark or variegated coloured edges to the
oblique stripes, in imitation of the shadow lines cast
by the leaf-ribs.
Whilst one group toiSpkirigida (Sphinx, Smerin-
thus) were thus striving to 'make their external
appearance approximate more and more to that of
382 Studies in the Theory of Descent.
a ribbed leaf, others of the longitudinally striped
species became developed in another manner.
Some of the latter lived indeed on bush-like
leaved plants, but no oblique stripes were de-
veloped, because these would have been useless
among the dense, narrow, and feebly-ribbed leaves
of the food-plants. These caterpillars, from the
earlier markings, simply retained the longitudinal
lines, which, combined with a very close resem-
blance to the colour of the leaves, afforded them a
high degree of protection against discovery. This
protection would also have been enhanced if other
parts of the food-plant, such as the berries (Hip-
pophaes), were imitated in colour and position in
such a manner that the large body of the caterpillar
contrasted still less with its environment. In this
way the first ring-spot probably arose in some
species on only one — the penultimate segment.
As soon as this first pair of ring-spots had be-
come an established character of the species, they
had a tendency to become repeated on the other
segments, advancing from the hind segments
towards the front ones. Under certain conditions
this repetition of the ring-spots might have been of
great disadvantage to the species, and would there-
fore have been as far as possible prevented by
natural selection (HippophaZs) ; in other cases, how-
ever, no disadvantage would have resulted — the
caterpillar, well adapted to the colour of its food-
plant, would not have been made more conspicuous
The Origin of the Markings of Caterpillars. 383
by the small ring-spots, which might thus have
become repeated on all the segments (Zygophylli] .
In cases like the two latter, striking colours must
have been eliminated when inherited from an im-
mediate ancestor; but on this point nothing can
as yet be said with certainty.
In other cases the repetition of the ring-spots
with strongly contrasted colours was neither pre-
judicial nor indifferent, but could be turned to the
further advantage of the species. If a caterpillar
fed on plants containing acrid juices (Euphorbiacece)
which, by permeating its alimentary system, ren-
dered it repulsive to other animals, the ring-spots
commencing to appear (by repetition) would fur-
nish an easy means for natural selection to adorn
the species with brilliant colours, which would
protect it from attack by acting as signals of dis-
tastefulness.
But if the dark spots stood on a light ground
{Nicczd), they would present the appearance of
eyes, and cause their possessors to appear alarming
to smaller foes.
From the developmental histories and biological
data at present before us, it cannot with certainty
be said which of these two functions of the ring-
spots was first acquired in the phylogeny, but we
may perhaps suppose that their significance as a
means of causing alarm was arrived at finally.
It may also be easily conceived that as the ring-
spots became more and more complicated, they
384 Stiidies in the Theory of Descent.
would occasionally have played other parts, being
fashioned once again in these stages into imitations
of portions of plants, such as a row of berries or
flower-buds. For this, however, there is as yet no
positive evidence.
As the ring-spots became detached from the
subdorsal line out of which they had arisen, the
latter disappeared more and more completely
from the last ontogenetic stage, and receded
to wards the younger stages of life of the caterpillar
— it became historical. This disappearance of the
subdorsal may also be explained by the fact that
the original longitudinal stripe imitating the linear
arrangement of leaves would become meaningless,
even if it did not always diminish the effect of the
ring-spots. But characters which have become
worthless are known in the course of time to
become rudimentary, and finally to disappear
altogether. I do not believe that disuse alone
causes such characters to vanish, although in the
case of active organs it may have a large share in
this suppression. With markings it cannot, how-
ever, be a question of use or disuse — nevertheless
they gradually disappear as soon as they become
meaningless. I consider this to be the effect of
the arrest of the controlling action of natural
selection upon these characters (suspension of the
so-called " conservative adaptation," Seidlitz).
Any variations may become of value if the charac-
ter concerned is met with in the necessary state of
The Origin of the Markings of Caterpillars. 385
fluctuation. That this process of extinction does
not proceed rapidly, but rather with extreme
slowness, is seen in the ontogeny of several species
of Deilephila, which retain the now meaningless
subdorsal line through a whole series of stages of
life.
In another group of Sphinx-larvae with longitu-
dinal stripes, an eye-spot became developed inde-
pendently of the subdorsal line, in the position of
the caudal horn, which has here vanished with the
exception of a small knob-like swelling. This
character — -which we now see perfected in Ptero-
gon (Enotherce — undoubtedly serves as a means
of causing terror ; but whether the incipient stages
possessed the same significance, cannot be decided
in the isolated case offered by the one species of
the genus Pterogon possessing this marking.
In a third group of longitudinally striped cater-
pillars, the younger genus Chcerocampa, eye-spots
were developed directly from portions of the
subdorsal line, at first only on the fourth and fifth
segments. It can be here positively asserted that
this character served as a means of alarm from its
very commencement. It is certainly for this reason
that we see the subdorsal line in the immediate
neighbourhood of the spots disappear at an early
stage, whilst it is retained on the other segments
for a longer period. A portion of the younger
(tropical) species of this group then developed
similar, or nearly similar, ocelli on the remaining
c c
386 Studies in the Theory of Descent.
segments by correlation ; and it may now have
occurred that in solitary cases the eye-spots
acquired another significance (C. Tersa ?), becom-
ing of use as a disguise by resembling berries or
flower-buds. It is also conceivable that the eye-
spots may in other cases have been converted
into a warning sign of distastefulness.
In all those larvae which possessed purely terrify-
ing markings, however, not only was the original
protective colouring preserved, but in most of them
this colour gradually became replaced by a better
one (adaptation of the adult larva to the soil).
The oblique stripes imitating the leaf-ribs also are
by no means lost, but are almost always present,
although but feebly developed, and often only
temporarily.
The pattern formed by the oblique stripes may
also be retained, even with perfect adaptation to
the soil, and may be converted to a new use by
losing its sharpness, and, instead of imitating defi-
nite parts of plants, may become transformed into
an irregular and confused marking, and thus best
serve to represent the complicated lights and
shadows, stripes, spots, &c., cast on the ground
under low-growing plants from between the stems
and dead leaves.
Just as in the case of ocellated species where cater-
pillars without eye-spots may retain and newly
utilize their older markings, so larvae havingoblique
stripes with, the most diversely coloured edges may
The Origin of the Markings of Caterpillars. 387
show the same markings in allied (younger?)
species, both in a rudimentary and in a transformed
condition. These markings may thus contribute
to the formation of a latticed or reticulated pattern.
Even the oldest marking, the subdorsal line, may
still play a part, since its remnants cause certain
portions of the complicated pattern to appear more
strongly marked (S. Convolvuli). Finally, when
an adaptation to a changing environment in-
tersected by lights and shadows is required, new
markings may be here added as in other cases,
viz., dark streaks extending over the light surface
of the whole caterpillar.
In concluding this essay, I may remark that,
with respect to the wide and generally important
question which gave rise to these investigations,
a clearer and simpler result has been obtained than
could have been expected, considering the com-
plexity of the characters requiring to be traced
to their causes, as well as our still highly imperfect
knowledge of ontogenetic and biological facts.
For a long time I believed that it was not
possible to trace all the forms of marking and their
combinations to those causes which are known to
produce transformation ; I expected that there
would be an inexplicable residue.
But this is not the case. Although it cannot
yet be stated at first sight with certainty in every
single instance how far any particular element of
marking may have a biological value in the species
c c 2
388 Studies in the Theory of Descent.
possessing it, nevertheless it has been established
that each of the elements of marking occurring in
the larvae of the Sphingidcz originally possessed a
decided biological significance, which was produced
by natural selection.
In the case of the three chief elements of the
markings of the Sphingidcz, it can be further
shown that not only the initial stages but also their
ultimate perfection — the highest stages of their
development, are of decided advantage to their
possessors, and have a distinct biological value, so
that the gradual development and improvement of
these characters can be traced to the action of
natural selection.
But although natural selection is the factor
which has called into existence and perfected the
three chief forms and certain of the subsidiary
markings, in the repetition of the local character
on the other segments, as well as in the formation
of new elements of marking at the points of inter-
section of older characters now rudimentary, we
can recognize a second factor which must be
entirely innate in the organism, and which governs
the uniformity of the bodily structure in such a
manner that no part can become changed without
exerting a certain action on the other parts — an
innate law of growth (Darwin's " correlation ").
Only once during the whole course of the in-
vestigations was it for an instant doubtful whether
a phyletic vital force did not make itself apparent,
The Origin of the Markings of Caterpillars. 389
viz., in the red spots accompanying the oblique
stripes in several Smerinthus-\dxv&. Closer
analysis, however, enabled us to perceive most
distinctly the wide gulf that separates " analogous
variation " from the mystic phyletic vital force.
Nothing further remains therefore for the action
of this force in respect to the marking and colour-
ing of the Sphingida, since several even of the
subordinate markings can be traced to their
causes, only the " dorsal spots " of our two native
species of Charocampa having been referred to cor-
relation without decided proof. From the tem-
porary inability to explain satisfactorily such an
insignificant detail, no one will, however, infer
the existence of such a cumbrous power as a
phyletic vital force.
The final result to which these investigations
have led us is therefore the following : — The
action of a phyletic vital force cannot be recognized
in the marking and colouring of the Sphingidce ;
the origination and perfection of these characters
depend entirely on the known factors of natural
selection and correlation.
3QO Studies in the Theory of Descent.
n.
ON PHYLETIC PARALLELISM IN METAMORPHIC
SPECIES.
INTRODUCTION.
IN the previous essay I attempted to trace a
whole group of apparently " purely morpho-
logical " characters to the action of known factors
of transformation, to explain them completely by
these factors, and in this manner I endeavoured
to exclude the operation of an internal power
inciting change (phyletic vital force).
In this second study I have attempted to solve
the problem as to whether such an innate inciting
power can be shown to exist by comparing the
forms of the two chief stages of metamorphic
species, or whether such a force can be dispensed
with.
Nobody has as yet apparently entertained the
idea of testing this question by those species which
appear in the two forms of larva and imago
(insects), or, expressed in more general terms, by
those species the individuals of which successively
possess quite different forms (metamorphosis), or
Phyletic Parallelism in Metamorphic Species. 391
in which the different forms that occur are dis-
tributed among different individuals alternating
with and proceeding from one another (alternation
of generation). Nevertheless, it is precisely here
that quite distinct form-relationships would be
expected according as the development of the
organic world depended on a phyletic vital force,
or was simply the response of the specific organism
to the action of the environment.
Assuming the first to be the case, there must
have occurred, and must still occur, what I desig-
nate " phyletic parallelism," i. e. the two stages of
metamorphic species must have undergone a pre-
cisely parallel development — every change in the
butterfly must have been accompanied or followed
by a change in the caterpillar, and the systematic
groups of the butterflies must be also found in a
precisely corresponding manner in a systematic
grouping of the caterpillars. If species are able
to fashion themselves into new forms by an innate
power causing periodic change, this re-moulding
cannot possibly affect only one single stage of
development — such as the larva only — but would
rather extend, either contemporaneously or suc-
cessively, to all stages — larva, pupa, and imago :
each stage would acquire a new form, and it might
even be expected that each would change to the
same extent. At least, it cannot be perceived
why a purely internal force should influence the
development of one stage more than that of
39 2 Studies in the Theory of Descent.
another. The larvae and imagines of two species
must differ from one another to the same extent,
and the same must hold good for the larvae and
imagines of two genera, families, and so forth. In
brief, a larval system must completely coincide
with the system based entirely on imaginal cha-
racters, or, what amounts to the same thing,
the form-relationships of the larvae must corre-
spond exactly with the form-relationships of the
imagines.
On the other hand, the condition of affairs must
be quite different if an internal power causing
phyletic remodelling does not exist, the transforma-
tion of species depending entirely on the action of
the environment. In this case dissimilarities in
the phyletic development of the different stages of
life must be expected, since the temporary, and
often widely deviating, conditions of life in the
two stages can and must frequently influence the
one stage whilst leaving the other unacted upon —
the former can therefore undergo remodelling
while the latter remains unchanged.1
1 [Compare this with Darwin's " Origin of Species " (ist.
ed. p. 440), where it is stated that when an animal, during any
part of its embryonic career, is active, and has to provide for
itself, " the period of activity may come on earlier or later in
life ; but whenever it comes on, the adaptation of the larva to
its conditions of life is just as perfect and beautiful as in the
adult animal. From such special adaptations the similarity of
the larvae or active embryos of allied animals is sometimes
much obscured." R.M.]
Phyletic Parallelism in Metamorphic Species. 393
By this means there would arise an unequal
difference between the two stages of two species.
Thus, the butterflies, supposing these to have
become changed, would bear a more remote form-
relationship to each other than the caterpillars,
and the differences between the former (imagines)
would always be greater than that between the
larvae if the butterflies were, at several successive
periods, affected by changing influences whilst the
larvae continued under the same conditions and
accordingly remained unaltered. The two stages
would not coincide in their phyletic development — -
the latter could not be expressed by parallel lines,
and we should accordingly expect to find that
there was by no means a complete congruity
between the systems founded on the larval and
imaginal characters respectively, but rather that
the caterpillars frequently formed different sys-
tematic groups to the butterflies.2
Accordingly, the problem to be investigated
was whether in those species which develope by
means of metamorphosis, and of which the indi-
vidual stages exist under very different conditions
of life, a complete phyletic parallelism was to be
found or not. This cannot be decided directly
since we cannot see the phyletic development
unfolded under our observation, but it can be
* [For Fritz Miiller's application of this principle to the case
of certain groups of Brazilian butterflies see Appendix II. to this
Part. R.M.]
394 Stztdies in the Theory of Descent.
established indirectly by examining and comparing
with each other the form-relationships of the
two separate stages — by confronting the larval
and imaginal systematic groups. If the phyletic
development has been parallel and perfectly equal,
so also must its end-results — the forms at present
existing — stand at equal distances from one
another ; larval and imaginal systems must coin-
cide and be congruent. If the course of the
phyletic development has not been parallel, there
must appear inequalities — incongruences between
the two systems.
I am certain that systematists of the old school
will read these lines with dismay. Do we not
regard it as a considerable advance in taxonomy
that we have generally ceased to classify species
simply according to one or to some few characters,
and that we now take into consideration not
merely the last stage of the development (the
imago), but likewise the widely divergent young
stages (larva and pupa) ? And now shall it not
be investigated whether caterpillars and butterflies
do not form quite distinct systems ? In the case
of new species of butterflies of doubtful systematic
position was not always the first question : — what
is the nature of the caterpillars ? and did not this
frequently throw light upon the relationships of the
imago ? Assuredly ; and without any doubt we
have been quite correct in taking the larval struc-
ture into consideration. But in so doing we
Phyletic Parallelism in Metamorphic Species. 395
should always keep in mind that there are two
kinds of relationship — form- and blood-relation-
ship— which might possibly not always coincide.
It has hitherto been tacitly assumed that the
degree of relationship between the imagines is
always the same as that between the larvae, and if
blood-relationship is spoken of this must naturally
be the case, since the larva and the imago are the
same individual. In all groups of animals we have
not always the means of deciding strictly between
form- and blood-relationship, and must accordingly
frequently content ourselves by taking simply the
form-relationship as the basis of our systems,
although the latter may not always express the
blood-relationship. But it is exactly in the
case of metamorphic species that there is no
necessity for, nor ought we to remain satisfied with,
this mode of procedure, since we have here two
kinds of form-relationship, that of the larvae and
that of the imagines, and, as I have just attempted
to show, it is by no means self-evident that these
always agree ; there are indeed already a sufficient
number of instances to show that such agreement
does not generally exist.
This want of coincidence is strikingly shown in
a group of animals widely remote from the Insecta,
viz. the Hydromedusae, the systematic arrange-
ment of which is quite different according as this
is based on the polypoid or on the medusoid gene-
ration. Thus, the medusoid family of the oceanic
396 Studies in the Theory of Descent.
Hydrozoa springs from polypites belonging to
quite different families, and in each of these poly-
poid families there are species which produce
Medusa of another family.
Similarly, the larvae of the Ophiuroidea (Pluteus-
form) among the Echinodermata are not the most
closely related in form to those of the ordinary
star-fishes, but rather to the larvae of quite a
distinct order, the sea-urchins.
I will not assert that in these two cases the
dissimilarity in the form-relationship, or, as I may
designate it, the incongruence of the morphological
systems, must depend on an unequal rate of phyletic
development in the two stages or generations, or
that this incongruence can be completely explained
by the admission of such an unequal rate of de-
velopment : indeed it appears to me probable that,
at least in the Ophiurece, quite another factor is
concerned — that the form-relationship to the larvae
of the sea-urchins does not depend upon blood-
relationship, but on convergence (Oscar Schmidt),
i. e. on adaptation to similar conditions of life.
These two cases, however, show that unequal
form-relationship of two stages may occur.
From such instances we certainly cannot infer
off-hand that a phyletic force does not exist ; it
must first be investigated whether and to what
extent such dissimilarities can be referred to unequal
phyletic development and, should this be the case,
whether deviations from a strict congruence of the
Phyletic Parallelism in Metamorphic Species. 397
morphological systems are not compatible with
the admission of an internal transforming power.
That a certain amount of influence is exerted by
the environment on the course of the processes of
development of the organic world, will however be
acceded to by the defenders of the phyletic vital
force. It must therefore be demonstrated that
deviations from complete congruence occur, which,
from their nature or magnitude, are incompatible
with the admission of innate powers, and, on the
other hand, it must likewise be attempted to show
that the departures from this congruence as well
as the congruence itself can be explained without
admitting a phyletic vital force.
In the following pages I shall attempt to solve
this question for the order Lepidoptera, with the
occasional assistance of two other orders of insects.
Neither the Echinodermata nor the Hydromedusse
are at present adapted to such a critical examin-
ation ; the number of species in these groups
of which the development has been established
with certainty is still too small, and their biological
conditions are still to a great extent unknown.
In both these respects they are far surpassed by
the Lepidoptera. In this group we know a large
number of species in the two chief stages of their
development and likewise more or less exactly the
conditions under which they exist during each of
these phases. We are thus able to judge, at least
to a certain extent, what changes in the conditions
398 Studies in the Theory of Descent.
of life produce changes of structure. Neither in
the number of known species of larvae, nor in the
intimate knowledge of their mode of life, can any
of the remaining orders of insects compete with the
Lepidoptera. There is no Dipterous or Hymenop-
terous genus in which ten or more species are so
intimately known in the larval stage that they can
be employed for the purposes of morphological
comparison. Who is able to define the distinctions
between the life-conditions of the larvae of twenty
different species of Culex or of Tipula f The
caterpillars of closely allied species of Lepidoptera,
on the other hand, frequently live on different
plants, from which circumstance alone a certain
difference in the life-conditions is brought about.
The chief question which the research had to
reply to was the following : — Does there exist a
complete phyletic parallelism among Lepidoptera
or not ? or, more precisely speaking : — Can we
infer, from the form-relationships which at pre-
sent exist between larvae on the one hand and
imagines on the other, an exactly parallel course
of phyletic development in both stages ; or do
incongruences of form-relationship exist which
point to unequal development ?
Before I proceed to the solution of this question
it is indispensable that one point should be cleared
up which has not been hitherto touched upon,
but which must be settled before the problem
can be formally stated in general terms. Before
Phyletic Parallelism in Metamorphic Species. 399
it can be asked whether larvae and imagines have
undergone a precisely parallel development, we
must know whether unequal development is pos-
sible— whether there does not exist such an
intimate structural relationship between the two
stages that every change in one of these must
bring about a change in the other. Were this the
case, every change in the butterfly would cause a
correlative change in the caterpillar, and vice versa,
so that an inequality of form-relationship between
the larvae on one hand and the imagines on
the other would be inconceivable — systems based
on the characters of the caterpillars would com-
pletely coincide with those based on the characters
of the butterflies and we should arrive at a false
conclusion if we attributed the phyletically parallel
development of the two stages to the existence
of an internal phyletic force, whilst it was only
the known factor, correlation, which caused the
equality of the course of development.
For these reasons it must first be established
that the larva and imago are not respectively fixed
in form, and the whole of the first section will there-
fore be devoted to proving that the two stages
change independently of one another. Conclusions
as to the causes of change will then be drawn, and
these will corroborate from another side a subse-
quent inquiry as to the presence or absence of com-
plete congruence in the two morphological systems.
The two questions the answers to which will be
400 Studies in the Theory of Descent.
successively attempted are by no means identical,
although closely related, since it is quite con-
ceivable that the first may be answered by there
being no precise correlation of form, or only an
extremely small correlation, between the caterpillar
and the imago, whilst, at the same time, it would
not be thereby decided whether the phyletic
development of the two stages had kept pace
uniformly or not. A perfect congruence of mor-
phological relationships could only take place if
transformations resulted from an internal power
instead of external influences. The question : —
Does there exist a fixed correlation of form
between the two stages ? must therefore be
followed by another : — Do the form-relationships
of the two stages coincide or not — has their
phyletic development been uniform or not ?
WEISKANN, AUGUST
Studies in the
theory of descent.
QH
366
v.l
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