Dec. 12, 1872] 
: MIMICRY IN THE COLOURS OF INSECTS* 
-HAvinG observed that in treating of the interesting pheno- 
“mena of mimicry, writers have used indiscriminately very diffe- 
rent factors, I shall try to give some preliminary ideas which I do 
not find published, and which I believe will be useful in explain- 
ing this interesting subject. 
_ It will be best to consider the colour and pattern separately. 
here are three different kinds of colours: viz., colours pro- 
duced by interference of light, colours of the epidermis, and 
colours of the hypodermis. All three may either be wanting, or 
all three or two of them may occur together in the same place. 
Colours produced by interference are produced in two different 
ways: first by thin superposed lamellz, as in the wings of 
Diptera, Neuroptera, &c., without any other colour, as in 
hyaline wings, or connected with other colours as in the 
scales of Entimus and others. 
There must be at least two superposed lamellze to bring out 
colours by interference, and there cannot be more than four, as 
both wings and scales consist only of four layers, two internal 
belonging to the hypodermis, two external belonging to the 
epidermis. In fact, if scales taken from dry specimens of Enti- 
mus are observed under the microscope, many partly injured can 
be found, which give different colours according to the layers of 
the lamellze which remain. é 
Secondly, colours by interference are produced by many very 
fine lines or strize in very near juxtaposition, as in Apatura and 
other colour-changing insects. Colours by interference may per- 
haps be sometimes also produced in the same way as in the 
feathers of the dove’s neck by very small impressions situated 
near together. 
_ The colours produced by the interference of light are only 
optical phenomena, differing in this respect from the other 
_ colours of the body, the epidermal and hypodermal colours. 
The epidermal colours belong to the pigment deposited in the 
cells of the chitinised external skin, the epidermis. These 
_ colours are mostly metallic blue, green, bronze, golden, silver, 
black, brown, and perhaps more rarely red. The epidermal 
_ colours are very easily recognised, because they are persistent, 
never becoming obliterated or changed after death, 
__ The hypodermal colours are situated in the non-chitinised and 
soft layer, called hypodermis by Weismann. They are mostly 
‘brighter and lighter, light blue or green, yellow, milk white, 
orange, and all the shades between. The hypodermal colours 
in the body of the insect fade or change, or are obliterated after 
the death of the insect. A fresh or living insect when opened 
may easily be deprived of the hypodermal colours simply by the 
action of alittle brush. I said hypodermal colours in the body, 
because there are hypodermal colours which are better protected, 
_ being encased nearly air-tight, and therefore are more easily pre- 
_ served even after the death of the insect. I refer to the colours 
in the elytra and wings, and in their appendages, the scales, 
The elytra and the wings are, as is well known, at first open sacs 
in communication with the body, of which they are only the ex- 
tension ; of course they are formed of the epidermis and hypo- 
‘dermis, which become so strongly glued together after the 
transformation into the imago ‘state that a maceration of years 
tried by me showed no effect at all on such wings. This fact is 
very interesting, as it explains how wings, and even coloured 
wings, can be found in paleontological layers in good preser- 
-yation. The destruction of insects, which is so peculiar to the 
secondary strata in England, proves, as I believe, that the bodies 
of the insects must have floated a very long time before they 
were deposited. It is quite a rarity to find well-preserved 
‘insects there, although many well-preserved wings, even of lace- 
winged flies, have been described. 
There is an interval after the transformation, before the mem- 
branes of the wings become inseparably glued together ; it is at 
this time that the finishing of the colours takes place. For in- 
stance in an Asschna, a Lidellula depressa or trimaculata, if the 
wing is cut off at the base, the two layers can be easily sepa- 
_rated by manipulation under water, and the wing can be inflated 
‘with a little tube by separating the borders with a knife. I can 
show specimens so prepared. But this is only possible as long 
as the wings possess the appearance of having been dipped into 
mucilage, an appearance which is well known in young 
Odonata. 
__ The scales have just the same development as the wings. At 
‘first they are little open sacs, communicating with the hollow of 
~ * Reprinted from the American Naturalist for July 1872. 
NATURE 
113 
the wing and the whole body, and at a later period are glued 
together like the wings themselves. 
In the wings and in the scales the hypodermal colours are 
formed and finished before the wings stick together, and by this 
means they are well preserved and safely encased. They have 
no more communication in the glued parts with the interior of 
the animal, and are preserved in the same way, as if hermetically 
inclosed in a glass tube There are even here in the wings and 
scales many epidermal colours, chiefly ithe metallic ones ; but all 
the brighter colours (for instance the somewhat transparent spots 
in the elytra of the Lampyridee, Cicindelidz, &c., and in the 
greater number of Lepidoptera) are, as I believe, hypodermal 
colours. 
Finally there sometimes occurs outside of the animal, that is, 
on the epidermis, a kind of colour which I consider as hypoder- 
mal colour, such as the pale blue on the abdomen of many 
Odonata, the white on the outside of many Hemiptera, the pale 
grey on elytra and thorax of the Goliathus beetle, the powder 
on Lixus and others. Some of these colours are very easily re- 
solved in ether, and are apparently a kind of wax. I believe 
that these colours are produced by the hypodermis, and are 
exuded through the little channels of the pores. 
The hypodermal colours are very often different in males and 
females of the same species, the epidermal colours rarely differ 
so far as I know; but there are genera with prominent epider- 
mal colours which are nearly always different in different sexes, 
viz., Calopteryx, Lestes, some Hymenoptera, &c. 
It would be interesting to know the different colours of the 
epidermis in such cases. So far as I know, the change seems to 
be between related, and not between complementary colours. 
But my observations are far from having any conclusive im- 
portance. The same investigation would be necessary for the 
hypodermal colours, 
The hypodermal colours may change or be altered in some 
male or female during its lifetime, by sexual or other influences, 
The epidermal colours never change. By sexual influences 
yellow is changed into orange, brown into red, and even some- 
times more changed. By other influences, for instance by cold 
in hibernation, pale yellow is changed into red (Chrysopa). 
The hypodermal colours may be changed even by a voluntary 
act of the animal, and the new colours disappear again 
(Cassida), The hypodermal colours are the only ones on which 
the animal has any influence, either involuntarily by the action 
of the nutritive fluid, or voluntarily. The epidermal cells are 
placed entirely outside of any influences of the animal, when 
once established. It will perhaps be possible to prove that the 
so-called mimetic colours are all hypodermal colours, 
The hypodermal colours seem to be produced by a photo- 
graphic process (I know no better expression), the epidermal 
colours by a chemical process of combustion or oxidation. 
Would it be possible to prove that by a photographic process 
even the colours of the surrounding world could be transmitted, 
a great step towards an understanding of the phenomena would 
be gained. The fact, of course, is very probable, at least, in 
some instances. 
In observing the mimicry, the pattern of an insect must be 
clearly separated from the colour. In fact, the pattern is not 
the product of an accidental circumstance, but apparently the 
product of a certain law, or rather the consequence of certain 
actions or events in the interior of the animal and in its develop- 
ment. The proof is very easily afforded by the regularity of the 
pattern in a genus or a family of insects. If studied carefully 
and comparatively, the pattern in a genus is the same, or is only 
more or less elaborated. The number of such families is so 
exceeding great that some example will readily occur to every 
one. 
Moreover a certain and constant pattern can be found for the 
head, a different pattern for the segments of the thorax, and a 
different pattern for the segments of the abdomen, This 
pattern is in the different segments of the abdomen (Hymenop- 
tera, Diptera, Neuroptera, Orthoptera) always the same, only 
more or less elabora:ed, and less finished in the first and last 
segments, In some way the same is true for the thoracic 
segments, 
In some few instances I was able to observe how the pattern 
is produced. Inthe Odonata (Dragon-flies) at the moment of 
transformation the thorax is transparent, and shows no colours 
at all. At this time the muscles are without importance, and 
in process of formation. The thoracic muscles, as is well known, 
are, in the Odonata, very powerful, and also very extraordinary 
