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COLOURATION
IN
ANIMALS AND PLANTS.
BY THE LATE
ALFRED TYLOR, F.G.S.
_Edited by_
SYDNEY B. J. SKERTCHLY, F.G.S.,
LATE OF H.M. GEOLOGICAL SURVEY.
LONDON:
PRINTED BY ALABASTER, PASSMORE, AND SONS,
FANN STREET, ALDERSGATE STREET, E.C.
1886.
IN MEMORY
OF A FRIENDSHIP OF MANY YEARS,
THIS BOOK
IS
Affectionately Inscribed
TO
THE RIGHT HON. GEORGE YOUNG, P.C.
1885.
PREFACE.
This little book is only a sketch of what its Author desired it to be,
and he never saw the completed manuscript. Beginning with the
fundamental idea that decoration is based upon structure, he saw that
this was due to the fact that in the lower, transparent, animals, colour
is applied directly to the organs, and that the decoration of opaque
animals is carried out on the same principle--the primitive idea being
maintained. Where function changes the pattern alters, where function is
localized colour is concentrated: and thus the law of emphasis was
evolved. Symmetry was a necessary consequence, for like parts were
decorated alike, and this symmetry was carried out in detail apparently
for the sake of beauty, as in the spiracular markings of many larvæ.
Hence the reason for recognizing the law of repetition.
With the developing of these ideas the necessity for recognizing some
sort of consciousness even in the lowest forms of life was forced upon
the Author, until inherited memory formed part of his scientific faith.
This he saw dimly years ago, but only clearly when Mr. S. Butler's
remarkable "Life and Habit" appeared, and he was gratified and
strengthened when he found Mr. Romanes adopting that theory in his
"Mental Evolution."
The opening chapters are designedly elementary; for the Author had a
wise dread of locking intellectual treasures in those unpickable
scientific safes of which "the learned" alone hold keys.
Only a very small portion of the vast array of facts accumulated has
been made use of, and the Author was steadily working through the
animal kingdom, seeking exceptions to his laws, but finding none, when
death closed his patient and far-seeing eyes. A few days before the end
he begged me to finish this abstract, for I had been at his side through
all his labours.
The work contains his views as clearly as I could express them, though
on every page I feel they suffer from want of amplification. But I
feared the work might become the expression of my own thoughts, though
want of leisure would probably have prevented that unhappy result. Now
it is finished, I would fain write it all over again, for methinks
between the lines can be seen gleams of brighter light.
SYDNEY B. J. SKERTCHLY.
CARSHALTON,
_July 17th, 1886_.
The coloured illustrations were drawn by Mrs. Skertchly chiefly from
nature, and very carefully printed by Messrs. Alabaster, Passmore, and
Sons.
[Illustration]
CONTENTS.
CHAPTER PAGE
I. INTRODUCTORY 1
II. INHERITED MEMORY 8
III. INTRODUCTORY SKETCH 16
IV. COLOUR, ITS NATURE AND RECOGNITION 25
V. THE COLOUR SENSE 32
VI. SPOTS AND STRIPES 39
VII. COLOURATION IN THE INVERTEBRATA 49
VIII. DETAILS OF PROTOZOA 56
IX. DETAILS OF COELENTERATA 59
X. THE COLOURATION OF INSECTS 68
XI. THE COLOURATION OF INSECTS 75
XII. ARACHNIDA 82
XIII. COLOURATION OF INVERTEBRATA 85
XIV. COLOURATION OF VERTEBRATA 88
XV. THE COLOURATION OF PLANTS 95
XVI. CONCLUSIONS 97
LIST OF WOODCUTS.
Fig. 1. Part of Secondary Feather of Argus Pheasant.
Fig. 2. Ditto Wing-feather of ditto.
Fig. 3. Diagram of Butterfly's Wing.
Fig. 4. Python.
Fig. 5. Tiger's Skin.
Fig. 6. Ditto.
Fig. 7. Tiger's Head, side view.
Fig. 8. Ditto, crown.
Fig. 9. Leopard's Skin.
Fig. 10. Ditto.
Fig. 11. Leopard's Head, side view.
Fig. 12. Ditto, crown.
Fig. 13. Lynx' Skin.
Fig. 14. Ditto.
Fig. 15. Ocelot.
Fig. 16. Badger.
Fig. 17. Begonia Leaf.
DESCRIPTION OF PLATES.
PLATE I. _Kallima Inachus_, the Indian Leaf Butterfly.
_p._ 28. Fig. 1. With wings expanded.
Fig. 2. Two Butterflies at rest, showing their exact
resemblance to dead leaves.
This insect affords one of the best examples of
protective resemblance.
PLATE II. Illustration of mimicry in butterflies.
_p._ 30. Fig. 1. Male of _Papilio merope_.
Fig. 2. Female of ditto mimicking Fig. 3.
Fig. 3. _Danais niavius._
On the African continent both species occur, but in
Madagascar _D. niavius_ is wanting, and the female
_P. merope_ is coloured like the male.
PLATE III. Fig. 1. _Gonepteryx Cleopatra._
_p._ 40. Fig. 2. _Gonepteryx rhamni_, male.
_Note._--The orange spot in Fig. 2 has
spread over the wing in Fig. 1.
Fig. 3. _Vanessa Antiopa._
Fig. 4. _Panopoea hirta._
Fig. 5. _Acrea gea._
These two last belong to widely different genera, but
are admirable examples of mimicry.
PLATE IV. Fig. 1. _Leucophasia Sinapis._
_p._ 42. Fig. 2. Ditto, var. _diniensis_.
Fig. 3. _Anthocaris cardamines_, male.
Fig. 4. Ditto, female.
Fig. 5. _Anthocaris belemia._
Fig. 6. _Anthocaris belia._
Fig. 7. Ditto, var. _simplonia_.
Fig. 8. _Anthocaris eupheno_, female.
Fig. 9. Ditto, male.
Fig. 10. _Anthocaris euphemoides._
Fig. 11. _Papilio machaon._
Fig. 12. _Papilio podalirius._
Fig. 13. _Pieris napi_, summer form.
Fig. 14. Ditto, winter form.
Fig. 15. Ditto, var. _bryoniæ_ (alpine form).
Fig. 16. Ditto, summer form, underside.
Fig. 17. Ditto, winter form, underside.
Fig. 18. Ditto, var. _bryoniæ_, underside.
Figs. 13-18 illustrate admirably the variations of the
yellow and black in the same species.
PLATE V. Fig. 1. _Araschnia prorsa_, male.
_p._ 44. Fig. 2. Ditto, female.
Fig. 3. _Araschnia levana_, female.
Fig. 4. Ditto, male.
Fig. 5. _Paragra ægeria._
Fig. 6. _Araschnia porima._
Fig. 7. Ditto, var. _meione_.
Fig. 8. _Grapta interrogationis._
Fig. 9. Ditto.
Fig. 10. Ditto.
Fig. 11. _Papilio Ajax_, var. _Walshii_.
Fig. 12. Ditto, var. _telamonides_.
Fig. 13. Ditto, var. _Marcellus_.
Figs. 1-5 are all one species; _levana_ being the winter form,
_prorsa_ the summer form, and _porima_ intermediate. Similarly
6-7 are the same species, _meione_ being the southern form. So
with 8-9 and 11-13, which are only seasonal varieties. Here we
can actually trace the way in which varieties are formed.
_See_ Weismann's work, cited in the text.
PLATE VI. _Syncoryne pulchella_, magnified. After Professor Allman.
_p._ 62. Gymnoblastic or Tubularian Hydroids. Ray Soc., 1871,
pl. vi., figs. 1 and 3.
Fig. 1. A planoblast as seen passively floating in the water
after liberation.
Fig. 2. The entire hydrosoma of syncoryne.
_a._ The spadix.
_b._ The medusæ or planoblasts in various stages of
development.
PLATE VII.
_p._ 80. Fig. 1. _Deilephila galii_, immature.
Fig. 2. Ditto brown variety, adult.
Fig. 3. _Deilephila euphorbiæ._
Fig. 4. _Sphinx ligustri._
Fig. 5. _Deilephila euphorbiæ_, dorsal view.
Fig. 6. _Orgyia antiqua._
Fig. 7. _Abraxas grossulariata._
Fig. 8. _Bombyx neustria._
Fig. 9. _Callimorpha dominula._
Fig. 10. _Euchelia jacobæa._
Fig. 11. _Papilio machaon._
SPIDERS.
PLATE VIII. Fig. 1. _Segestria senoculata_, female.
_p._ 84. Fig. 2. _Sparassus smaragdulus_, male.
Fig. 3. _Lycosa piscatoria_, female.
Fig. 4. ---- _andrenivora_, male.
Fig. 5. ---- ---- female.
Fig. 6. ---- _allodroma_, male.
Fig. 7. ---- _agretyca_, male.
Fig. 8. ---- _allodroma_, female.
Fig. 9. Diagram of _Lycosa_, showing form and position of
vessels. After Gegenbaur.
Fig. 10. _Lycosa campestris_, female.
Fig. 11. _Thomisus luctuosus_, male.
Fig. 12. _Salticus scenicus_, female.
Fig. 13. _Lycosa rapax_, female.
Fig. 14. ---- _latitans_, female.
Fig. 15. _Theridion pictum_, female.
Fig. 16. _Lycosa picta_, female.
Fig. 17. ---- ---- male.
All the above are British species, and copied from Blackwell's
"Spiders of Great Britain and Ireland." Ray Soc., 1862.
FISHES.
PLATE IX. Fig. 1. Windermere Char. _Salmo Willughbii._ A species
_p._ 88. peculiar to our North of England lakes.
Fig. 2. Perch, _Perca fluviatilis_, showing the modified
rib-like markings.
SUNBIRDS.
PLATE X. Fig. 1. _Nectarinea chloropygia._
_p._ 90. Fig. 2. _Nectarinea christinæ._
These birds illustrate regional colouration well.
LEAVES.
PLATE XI. Fig. 1. Horse Chestnut, _Æschulus hippocastanum_, decaying.
_p._ 95. Fig. 2. _Coleus._
Fig. 3. _Begonia rex._
Fig. 4. _Begonia_.
Fig. 5. _Caladium bicolor._
Fig. 6. _Anoechtochilus xanthophyllus._
FLOWERS.
PLATE XII. Fig. 1. _Gloxinia_, with 5 petals, showing uneven
_p._ 96. colouring.
Fig. 2. _Gloxinia_, with 6 petals, showing regular
colouring.
Figs. 3 and 4. Pelargoniums, showing the variation of the
dark markings with the different sized petals.
[Illustration]
COLOURATION IN ANIMALS AND PLANTS.
CHAPTER I.
INTRODUCTION.
Before Darwin published his remarkable and memorable work on the Origin
of Species, the decoration of animals and plants was a mystery as much
hidden to the majority as the beauty of the rainbow ere Newton analysed
the light. That the world teemed with beauty in form and colour was all
we knew; and the only guess that could be made as to its uses was the
vague and unsatisfactory suggestion that it was appointed for the
delight of man.
Why, if such was the case, so many flowers were "born to blush unseen,"
so many insects hidden in untrodden forests, so many bright-robed
creatures buried in the depths of the sea, no man could tell. It seemed
but a poor display of creative intelligence to lavish for thousands of
years upon heedless savage eyes such glories as are displayed by the
forests of Brazil; and the mind recoiled from the suggestion that such
could ever have been the prime intention.
But with the dawn of the new scientific faith, light began to shine upon
these and kindred questions; nature ceased to appear a mass of useless,
unconnected facts, and ornamentation appeared in its true guise as of
extreme importance to the beings possessing it. It was the theory of
descent with modification that threw this light upon nature.
This theory, reduced to its simplest terms, is that species, past and
present, have arisen from the accumulation by inheritance of minute
differences of form, structure, colour, or habit, giving to the
individual a better chance, in the struggle for existence, of obtaining
food or avoiding danger. It is based on a few well-known and universally
admitted facts or laws of nature: namely, the law of multiplication in
geometrical progression causing the birth of many more individuals than
can survive, leading necessarily to the struggle for existence; the law
of heredity, in virtue of which the offspring resembles its parents; the
law of variation, in virtue of which the offspring has an individual
character slightly differing from its parents.
To illustrate these laws roughly we will take the case of a bird, say,
the thrush. The female lays on the average five eggs, and if all these
are hatched, and the young survive, thrushes would be as seven to two
times as numerous in the next year. Let two of these be females, and
bring up each five young; in the second year we shall have seventeen
thrushes, in the third thirty-seven, in the fourth seventy-seven, and so
on. Now common experience tells us not merely that such a vast increase
of individuals does not take place, but can never do so, as in a very
few years the numbers would be so enormously increased that food would
be exhausted.
On the other hand, we know that the numbers of individuals remain
practically the same. It follows, then, that of every five eggs four
fail to arrive at maturity; and this rigorous destruction of individuals
is what is known as the struggle for existence. If, instead of a bird,
we took an insect, laying hundreds of eggs, a fish, laying thousands, or
a plant, producing still greater quantities of seed, we should find the
extermination just as rigorous, and the numbers of individuals destroyed
incomparably greater. Darwin has calculated that from a single pair of
elephants nearly nineteen millions would be alive in 750 years if each
elephant born arrived at maturity, lived a hundred years, and produced
six young--and the elephant is the slowest breeder of all animals.
The struggle for existence, then, is a real and potent fact, and it
follows that if, from any cause whatever, a being possesses any power or
peculiarity that will give it a better chance of survival over its
fellows--be that power ever so slight--it will have a very decided
advantage.
Now it can be shown that no two individuals are exactly alike, in other
words, that variation is constantly taking place, and that no animal or
plant preserves its characters unmodified. This we might have expected
if we attentively consider how impossible it is for any two individuals
to be subjected to exactly the same conditions of life and habit. But
for the proofs of variability we have not to rely upon theoretical
reasoning. No one can study, even superficially, any class or species
without daily experiencing the conviction that no two individuals are
alike, and that variation takes place in almost every conceivable
direction.
Granted then the existence of the struggle for existence and the
variability of individuals, and granting also that if any variation
gives its possessor a firmer hold upon life, it follows as a necessity
that the most favoured individuals will have the best chance of
surviving and leaving descendants, and by the law of heredity, we know
these offspring will tend to inherit the characters of their parents.
This action is often spoken of as the preservation of favoured races,
and as the survival of the fittest.
The gradual accumulation of beneficial characters will give rise in time
to new varieties and species; and in this way primarily has arisen the
wonderful diversity of life that now exists. Such, in barest outline, is
the theory of descent with modification.
Let us now see in what way this theory has been applied to colouration.
The colours, or, more strictly, the arrangement of colours, in patterns
is of several kinds, viz.:--
1. _General Colouration_, or such as appears to have no very special
function _as_ colour. We find this most frequently in the vegetable
kingdom, as, for instance, the green hue of leaves, which, though it has
a most valuable function chemically has no particular use as colour, so
far as we can see.
2. _Distinctive Colouration_, or the arrangement of colours in different
patterns or tints corresponding to each species. This is the most usual
style of colouring, and the three following kinds are modifications of
it. It is this which gives each species its own design, whether in
animals or plants.
3. _Protective Resemblance_, or the system of colouring which conceals
the animal from its prey, or hides the prey from its foe. Of this class
are the green hues of many caterpillars, the brown tints of desert
birds, and the more remarkable resemblances of insects to sticks and
leaves.
4. _Mimetic Colouration_, or the resemblance of one animal to another.
It is always the resemblance of a rare species, which is the favourite
food of some creature, to a common species nauseous to the mimicker's
foe. Of this character are many butterflies.
5. _Warning Colours_, or distinctive markings and tints rendering an
animal conspicuous, and, as it were, proclaiming _noli me tangere_ to
its would-be attackers.
6. _Sexual Colours_, or particular modifications of colour in the two
sexes, generally taking the form of brilliancy in the male, as in the
peacock and birds of paradise.
Under one or other of these headings most schemes of colouration will be
found to arrange themselves.
At the outset, and confining ourselves to the animal kingdom for the
present, bearing in mind the fierce intensity of the struggle for life,
it would seem that any scheme of colour that would enable its possessor
to elude its foes or conceal itself from its prey, would be of vital
importance. Hence we might infer that protective colouring would be a
very usual phenomenon; and such we find to be the case. In the sea we
have innumerable instances of protective colouring. Fishes that lie upon
the sandy bottom are sand-coloured, like soles and plaice, in other
orders we find the same hues in shrimps and crabs, and a common species
on our shores (_Carcinus mænas_) has, just behind the eyes, a little
light irregular patch, so like the shell fragments around that when it
hides in the sand, with eyes and light spot alone showing, it is
impossible to distinguish it.
The land teems with protective colours. The sombre tints of so many
insects, birds and animals are cases in point, as are the golden coat of
the spider that lurks in the buttercup, and the green mottlings of the
underwings of the orange-tip butterfly. Where absolute hiding is
impossible, as on the African desert, we find every bird and insect,
without exception, assimilating the colour of the sand.
But if protective colour is thus abundant, it is no less true that
colour of the most vivid description has arisen for the sole purpose of
attracting notice. We observe this in the hues of many butterflies, in
the gem-like humming birds, in sun-birds, birds of paradise, peacocks
and pheasants. To see the shining metallic blue of a Brazilian Morpho
flashing in the sun, as it lazily floats along the forest glades, is to
be sure that in such cases the object of the insect is to attract
notice.
These brilliant hues, when studied, appear to fall into two classes,
having very diverse functions, namely Sexual and Warning Colours.
Protection is ensured in many ways, and among insects one of the
commonest has been the acquisition of a nauseous flavour. This is often
apparent even to our grosser senses; and the young naturalist who
captures his first crimson-and-green Burnet Moth or Scarlet Tiger,
becomes at once aware of the existence of a fetid greasy secretion. This
the insectivorous birds know so well that not one will ever eat such
insects. But unless there were some outward and visible sign of this
inward and sickening taste, it would little avail the insect to be first
killed and then rejected. Hence these warning colours--they as
effectively signal danger as the red and green lamps on our railways.
It may here be remarked that wherever mimickry occurs in insects, the
species mimicked is always an uneatable one, and the mimicker a
palatable morsel. It is nature's way of writing "poison" on her
jam-pots.
The other class of prominent colours--the Sexual--have given rise to two
important theories, the one by Darwin, the counter-theory by Wallace.
Darwin's theory of Sexual Selection is briefly this:--He points out in
much detail how the male is generally the most powerful, the most
aggressive, the most ardent, and therefore the wooer, while the female
is, as a rule, gentler, smaller, and is wooed or courted. He brings
forward an enormous mass of well-weighed facts to show, for example, how
often the males display their plumes and beauties before their loves in
the pairing season, and his work is a long exposition of the truth that
Tennyson proclaimed when he wrote:--
"In the spring a fuller crimson comes upon the robin's breast,
In the spring the wanton lapwing gets himself another crest,
In the spring a livelier iris changes on the burnished dove,
In the spring the young man's fancy lightly turns to thoughts of love."
That birds are eminently capable of appreciating beauty is certain, and
numerous illustrations are familiar to everyone. Suffice it here to
notice the pretty Bower Birds of Australia, that adorn their love
arbours with bright shells and flowers, and show as unmistakable a
delight in them as the connoisseur among his art treasures.
From these and kindred facts Darwin draws the conclusion that the
females are most charmed with, and select the most brilliant males, and
that by continued selection of this character, the sexual hues have been
gradually evolved.
To this theory Wallace takes exception. Admitting, as all must, the fact
of sexually distinct ornamentation, he demurs to the conclusion that
they have been produced by sexual selection.
In the first place, he insists upon the absence of all proof that the
least attractive males fail to obtain partners, without which the theory
must fail. Next he tells us that it was the case of the Argus pheasant,
so admirably worked out by Darwin, that first shook his faith in sexual
selection. Is it possible, he asks, that those exquisite eye-spots,
shaded "like balls lying loose within sockets" (objects of which the
birds could have had no possible experience) should have been produced
... "through thousands and tens of thousands of female birds, all
preferring those males whose markings varied slightly in this one
direction, this uniformity of choice continuing through thousands and
tens of thousands of generations"?[1]
As an alternative explanation, he would advance no new theory, but
simply apply the known laws of evolution. He points out, and dwells
upon, the high importance of protection to the female while sitting on
the nest. In this way he accounts for the more sombre hues of the
female; and finds strong support in the fact that in those birds in
which the male undertakes the household duties, he is of a domestic dun
colour, and his gad-about-spouse is bedizened like a country-girl at
fair time.
With regard to the brilliant hues themselves, he draws attention to the
fact that depth and intensity of colour are a sign of vigour and
health--that the pairing time is one of intense excitement, and that we
should naturally expect to find the brightest hues then displayed.
Moreover, he shows--and this is most important to us--that "the most
highly-coloured and most richly varied markings occur on those parts
which have undergone the greatest modification, or have acquired the
most abnormal development."[2]
It is not our object to discuss these rival views; but they are here
laid down in skeleton, that the nature of the problem of the principles
of colouration may be easily understood.
Seeing, then, how infinitely varied is colouration, and how potently
selection has modified it, the question may be asked, "Is it possible
to find any general system or law which has determined the main plan of
decoration, any system which underlies natural selection, and through
which it works"? We venture to think there is; and the object of this
work is to develop the laws we have arrived at after several years of
study.
[Illustration]
[1] Wallace, Tropical Nature, p. 206.
[2] _Op. cit._, p. 206.