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67. THE COLOURS OF ANIMALS: Their Meaning and Use. By EDWABD

BAGNALL POULTON, F. R.8.










MIMICRY IN SOUTH AFRICAN BUTTERFLIES.

KlGCRKS 1, 4, AND 5, THK FEMALES OF A SoUTH AFRICAN PafiKo, TOTALLY UNLIKE THE MAI
(FlGHHB iX BltT MIMICKING RESPECTIVELY THREE SPECIF.S OF THE UNPALATABLE GENUS, DdnaiS (FlGURl

3*,- 4a, AND sa) THE FEMALE (FIGURE 2) OF A NEARLY ALUHD Papilla, IN MADAGASCAR, is NOT MIMETI

AND RKSEMHLES THE HALE.



DESCBIPTION OF PLATE



THE figures have been copied, by kind permission of the author, and
the council of the Linnean Society, from the plates accompany-
ing Mr. Koland Trimen's paper, ' On some Remarkable Mimetic
Analogies among African Butterflies.' ('Linn. Soc. Trans.' vol.
xxvi. pp. 497, et seqq.)

All figures are represented one-half of their natural size. The
appearance of the under side of the wings is shown on the left hand
of the four upper figures.

Figure 1. The male of Papilio merope (now called P. cenea ; the
name P. merope being restricted to the West African form), from
Knysna, Cape Colony. A closely allied butterfly (P. meriones),
with a very similar male, is found in Madagascar.
Figure 2. The female of Papilio meriones, from Madagascar. The
male is almost exactly like Figure 1. The black bar on the costal
margin of the fore wing of the female probably represents the
beginning of the darkening which has been carried so far in the
females of the African P. merope and P. cenea.
Figure 3. First or cenea-torm of female of Papilio merope (now
called P. cenea), from Knysna, Cape Colony. The female is totally
unlike the male of the same species (Figure 1), but closely mimics
an unpalatable butterfly, Danais echeria, prevalent in its locality.
The appearance of the latter is shown in Figure Ba. The mimetic
resemblance is seen to be very striking on both upper and under
sides of the wings. A local variety of the Danais is also
mimicked by a corresponding variety of the Papilio.
Figure 4. Second or hippocoon-form of female of Papilio merope
(now called P. cenea), from Graham's Town, Cape Colony. This
variety mimics the southern form of the unpalatable Danais
niavius, shown in Figure 4a.

Figure 5. - Third or tropJionius-tona. of female of Papilio merope
(now called P. cenea), from Knysna, Cape Colony. This variety
mimics the abundant and unpalatable Danais chrysippus shown
in Figure 5a.

In a closely allied species of Papilio from West Africa (the true
Papilio merope) the male closely resembles Figure 1, while there are
two mimetic varieties of female. The hippocoon-iorm is like Figure 4,
except that it is larger and the white patch on the hind wing
is smaller ; corresponding in both these respects to the West African
variety of Danais niavius. The trophonitis-torm resembles Figure 5.
There is no cenea-torm of this species. For further details see
pp. 234-38.



THE INTERNATIONAL SCIENTIFIC SERIES



THE



COLOURS OF ANIMALS



THEIR MEANING AND USE, ESPECIALLY CONSIDERED
IN THE CASE OF INSECTS



BY

EDWARD BAGNALL POULTON, M.A., F.R.S.



WITH CHROMOLITHOGRAPHS FRONTISPIECE
AND SIXTY-SIX FIGURES IN TEXT



NEW YORK
D. APPLETON AND COMPANY

1890

son



Qu



PEEFACB



I HAVE adopted a general title, 'The Colours of
Animals,' in order to indicate the contents of this
volume, although the vast majority of the examples
are taken from insects, and indeed almost invariably
from a single order, the Lepidoptera. The examples
are, however, employed merely to illustrate principles
which are of wide appli cation.

I have purposely abstained from multiplying in-
stances when a little observation or even reflection
will supply them in large numbers. For example,
the ordinary Protective Resemblances of mammals
and birds are barely alluded to, on this account. On
the other hand, more difficult problems, such as the
change of colour in arctic mammals, or the meaning
of the colours of birds' eggs, are treated at far greater
length. My object in both cases is the same : to
stimulate observation in a subject which will amply
repay investigation, from the scientific value of the
results, and the never-failing interest and charm of
the inquiry.



viii THE COLOURS OF ANIMALS

Variable Protective Eesemblance in insects is
treated in considerable detail, for the reasons given
above, and because much of the work is so recent
that no complete account can be found outside the
original memoirs.

My chief object has been to demonstrate the
utility of colour and marking in animals. In many
cases I have attempted to prove that Natural Selection
has sufficed to accouDt for the results achieved ; and
I fully believe that further knowledge will prove that
this principle explains the origin of all appearances
except those which are due to the subordinate prin-
ciple of Sexual Selection, and a few comparatively
unimportant instances which are due to Isolation or
to Correlation of Growth.

In support of these views I have endeavoured to
bring together a large amount of experimental evi-
dence in favour of the theories as to the various uses of
colour. 'Further experiments are still greatly needed.

In the chapters on ' Sexual Selection ' I have
argued in favour of Darwin's views, and have
attempted to defend them against recently published
attacks.

At the conclusion of the volume I have brought
forward a detailed classification of the various uses
of colour, in which new, and, I believe, more con-
venient terms are suggested. Definitions and exam-
ples are also given in the classification, which is, in
fact, a brief abstract of the whole book.



PEEFACE IX

I have to thank the Councils of various scientific
societies for the courteous permission to copy figures
from their respective publications. The figures in
the coloured plate are copied from the plates accom-
panying Mr. Eoland Trimen's paper in the ' Trans-
actions of the Linnean Society,' vol. xxvi. pp.
497-522. Figures 18, 19, 20, 21, and 22 are copied
from the plate accompanying Mr. E. Bowdler Sharpe's
paper in the ' Proceedings of the Zoological Society,'
1873, pp. 414 et seqq. Figures 3, 4, 5, 6, 7, 8, 11,
14, 58, 60, 61, 62 are copied from the plates and
woodcuts accompanying my papers in the ' Transac-
tions of the Entomological Society,' 1884, 1885, 1887,
and 1888. Figures 25, 26, and 27 are copied from
the plate accompanying Mrs. Barber's paper in the
' Transactions of the Entomological Society,' 1874,
pp. 519 et seqq. Figures 29 and 30 are copied from
the plate and woodcuts accompanying my paper in
the ' Philosophical Transactions of the Eoyal Society,'
vol. 178 (1887), B, pp. 311-441. Figures 15, 16, 53,
54, 63, 64, 65, 66 are copied from the woodcuts and
plates accompanying G. W. and E. G. Peckham's
paper in the ' Occasional Papers of the Natural
History Society of Wisconsin,' vol. i. (1889), Milwaukee.
Figures 55 and 56 are copied from the plates accom-
panying Professor Weismann's ' Studies in the Theory
of Descent,' translated by Professor Meldola. Figure
10 is copied from one of the plates accompanying Dr.
Wilhelm Midler's ' Siidamerikanische Nymphaliden-



X THE COLOURS OF ANIMALS

raupen' (' Zoologische Jahrbiicher,' J. W. Spengel,
Jena, 1886). Figure 42 is copied from Vogt (' The
Natural History of Animals ' : English translation :
Blackie and Son). Figures 44 and 45 are copied
from the plates accompanying Curtis's 'British
Lepidoptera.' The remaining figures are original.
Figure 17 was kindly lent me by Dr. A. K. Wallace,
to whom it had been sent by Mr. Wood-Mason. In
preparing the drawings of the original figures I have
been greatly assisted by my wife, my sister Miss L. S.
Poulton, Miss Herman Fisher, Mr. Alfred Sich,
Mr. Alfred Robinson, and especially by Miss Cundell.
I have almost invariably referred to original
papers from which facts or conclusions have been
adopted; so that any reader having access to a
scientific library may easily gain possession of further
details. Not wishing to overburden the book with
such notes, I have abstained from referring constantly
to my own papers, although most of the examples are
taken from them. A list of my papers which deal
with the colours of insects is therefore printed below.

Transactions Entomological Society,' London, 1884, pp. 27-60

1885, 281-329

1886, 137-179

1887, 281-321

* .. >. 1888, 515-606

Philos. Trans. Royal Society,' vol. 178 (1887), B, pp. 311-441
Abstract of the above in 'Proceedings Royal Society,' 1887, vol. xlii.

pp. 94-108
' Proceedings Royal Society,' 1885, vol. xxxviii. pp. 269-315

1886, vol. xl. pp. 135-173
' Proceedings Zoological Society,' 1887, pp. 191-274



PEEFACE Xi

Short papers or notes (exclusive of those which
are mere abstracts of the above) :

' Proceedings Entomological Society,' London, 1887, pp. 1-li

1887, Ixi-lxii
1888, p. v

> > > > PP- viii x

xxvii-xxviii

1889 xxxvii-xl
' Journal of the Victoria Institute,' 1888, vol. xxii., ' On Mimicry.'

It is my pleasant duty to thank many friends for
their kind assistance. I owe to Professor Meldola
more than I can possibly express : his writings first
induced me to enter upon this line of investigation,
and I have had the benefit of his great experience
and wise advice during the whole of the time that I
have been at work. Nearly every subject touched
upon in this volume has been discussed with him.

Professor Westwood has always been most kind
in helping me with the literature of the subject, with
which he has so intimate an acquaintance, and in
giving me the free use of the Hope collection at
Oxford. Professor E. Eay Lankester has read the
proof-sheets dealing with the classifications of the
uses of colour, and has offered valuable suggestions.
Several beautiful examples were suggested to me by
Professor C. Stewart. Dr. Giinther, Mr. Eoland
Trimen, Mr. Oldfield Thomas, Mr. E. Bowdler Sharpe,
Mr. F. E. Beddard, Mr. W. W. Fowler, and Mr. A.
H. Cocks have been very kind in answering questions
upon their special subjects. Sir John Conroy has



xii THE COLOURS OF ANIMALS

kindly helped me in explaining the physical questions
involved in the first chapter. I am especially pleased
to speak of the help received from my former pupils
Mr. W. Garstangand Mr. E. C. L. Perkins, who have
supplied many valuable instances, which are specified
in the volume, where other kind assistance is also duly
acknowledged.

Although I have ventured to disagree with my
friend Dr. A. R. Wallace upon the subject of ' Sexual
Selection,' I wish to acknowledge how very much I
owe to his writings, which I have very frequently
quoted. I have also made great use of the late
Thomas Belt's extremely interesting and suggestive
' Naturalist in Nicaragua.'

Among recent papers I wish especially to mention
that by G. W. and E. G. Peckham, of Milwaukee,
U.S.A. The minute observation of these authors
upon the courtship of spiders of the family Attidce is
a model for investigation in a subject which has never
before been attacked systematically.

Above all, I should wish to acknowledge, although
I can never fully express, the depth of my indebted-
ness to the principles which first made Biology a
science, the principles enunciated by Charles Darwin.
It is common enough nowadays to hear of new
hypotheses which are believed (by their inventors) to
explain the fact of evolution. These hypotheses are
as destructive of one another as they are supposed to
be of Natural Selection, which remains as the one



PREFACE xiii

solid foundation upon which evolution rests. I have
wished to express this conviction because my name
has been used as part of the support for an opposite
opinion, by an anonymous writer in the ' Edinburgh
Eeview.' 1 In an article in which unfairness is as
conspicuous as the prejudice to which it is due, I am
classed as one of those ' industrious young observers '
who ' are accumulating facts telling with more or less
force against pure Darwinism.' 2 On the strength of
this and other almost equally strange evidence, the
Eeviewer triumphantly exclaims, ' Darwin, the thanes
fly from thee ! ' In view of this public mention of my
name, I may perhaps be excused for making the per-
sonal statement that any scientific work which I have
had the opportunity of doing has been inspired by
one firm purpose the desire to support, in however
small a degree, and to illustrate by new examples,
those great principles which we owe to the life and
writings of Charles Darwin, and especially the pre-
eminent principle of Natural Selection.

E. B. P.
OXFORD : Dec. 28, 1889.



1 Edinburgh Review. Article V. April 1888, pp. 407-47.

* p. 443. The bias of the writer appears in a most singular
manner upon this page. In the short space of seventeen lines the
following adjectives are divided between five writers and their works
industrious, illustrious, gifted, well-read, acute, intelligent, brilliant,
thoughtful. I need hardly say that all five writers are believed by
the Reviewer to oppose the theory of Natural Selection.



CONTENTS



CHAPTER PAGE

I. THE PHYSICAL CAUSE OF AKIMAL COLOURS ... 1

II. THE USES OF COLOUR 12

III. PROTECTIVE KESEMBLANCES IN LEPIDOPTEBA ... 24

IV. PROTECTIVE RESEMBLANCES IN LEPIDOPTERA (continued)

DIMORPHISM, ETC 42

V. PROTECTIVE RESEMBLANCES IN VERTEBRATA, ETC. . . 60

VI. AGGRESSIVE RESEMBLANCES ADVENTITIOUS PROTECTION 72
VII. VARIABLE PROTECTIVE RESEMBLANCE IN VERTEBRATA,

ETC 81

VIII. VARIABLE PROTECTIVE RESEMBLANCE IN INSECTS . . 110
IX. VARIABLE PROTECTIVE RESEMBLANCE m INSECTS (con-
tinued) 133

X. WARNING COLOURS 159

XI. WARNING COLOURS (continued) 189

XII. PROTECTIVE MIMICRY 216

XIII. PROTECTIVE AND AGGRESSIVE MIMICRY .... 245

XIV. THE COMBINATION OF MANY METHODS OF DEFENCE . 269
XV. COLOURS PRODUCED BY COURTSHIP . . . . 284

XVI. OTHER THEORIES OF SEXUAL COLOURING . . . 314

XVII. SUMMARY AND CLASSIFICATION 336



THE

COLOURS OP ANIMALS

CHAPTER I
THE PHYSICAL CAUSE OF ANIMAL COLOUBS

Colours due to absorption

THE colours of animals are produced in various ways.
By far the commonest method is the absorption of
certain elements of light by means of special sub-
stances which are called pigments, or colouring matters.
The colour of each pigment is due to those elements
of the light which it does not absorb, and which can
therefore emerge and affect the eye of the spectator.
Black is, of course, caused by the absorption of all
the constituents of light, so that nothing reaches the
eye. The colour of red pigment, like that of red
glass, depends upon the fact that red is less absorbed
than any other element of the light which passes
through. If a sheet of red glass be placed upon
white paper, the light traverses the glass, is reflected



2 THE COLOUKS OF ANIMALS

from the surface of the paper, re-traverses the glass,
and emerges. Similarly, in painting, bright effects
are produced by covering a surface of Chinese white
with the desired colour. The light passing twice
through the thickness of the colour, absorption is
far more complete than when only one thickness is
traversed, as in a piece of red glass held up to the
light. Absorption being more complete, the red colour
is deeper. Animal pigments are nearly always twice
traversed by the light, and therefore a very thin layer
produces a considerable effect.

Animal colours are therefore generally due to
precisely the same optical principle which causes the
colour of a wall-paper, a carpet, or a picture. Certain
transparent animals are, however, for the most part
coloured by light which passes but once through them,
upon the same principle as the colours of a stained-
glass window. The beautiful transparent blue of
many pelagic animals, such as the Portuguese Man-
of-war (Physalia), is caused in this way.

It would be out of place to discuss the details of
the causes of colour by absorption. I may, however,
mention that vibrations of very different rates are
started in the luminiferous ether by the sun, the
electric light, &c. A certain series of these vibrations
causes the effect of white light when it falls on our
retina; but there are vibrations above and below
this visible series vibrations which we cannot see.
We can, however, prove their existence in other ways ;



THE PHYSICAL CAUSE OF ANIMAL COLOURS 3

and it is certain that some animals can see vibrations
which do not affect our eyes. 1 The slowest vibrations


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