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Full text of "Studies in the theory of descent"

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EX LIBRIS 
BERTRAM.C.A 
WINDLE 

D.Sc.M.D 



* W~f*f * 




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 sen 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. Zeller 1 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 same 2 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 elsewhere 7 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. 5562. 



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 IO Q 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 

marking 1 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- 
mation 10 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 hothouse 12 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 
produce 13 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/ut'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. Lubbock 1 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 similar 3 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 i4.9R. ; 
this difference being therefore much more pro- 
nounced than that between the German and 
Sicilian summer, which is only about 3-6R. 
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 

Lubbock 3 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 

[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 
Sars 10 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 Heyden 13 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. 
Botanists 3 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 alw r ays 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 
insisted 6 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 
2 5th 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 Levana y 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 
IIt h (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*5R. 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 2 9 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. Levana y 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- 3 I 3> 
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 the 1 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 Natal 11 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 
(34 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. Celerio y 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- 
colour 22 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. = P t 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 Clemens 56 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, fc and 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 Leguminosa y 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 w r ith 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^(,s y 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 manoeuvring 1 , 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 



34 2 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