176 
COLOURS AND COLORATION IN ANIMALS. 
Aug., 1892. 
by the effect on our own eyes, but it is a question how far a 
disguise, which to us, who are so much bigger and have no 
commissariat interest in the matter, seems perfect, would be 
beneficial to a smaller animal, whose chances of forming or 
obtaining a dinner depended on his keenness of eyesight. For 
instance, among the pelagic fauna mentioned above, there are 
small fish so pellucid as to be invisible to our eyes except after 
prolonged watching; as far as human eyes are concerned 
they are well protected. The outer surface of their bodies, 
however, is dotted over with minute specks of pigment. Now 
if these fish were as big as ourselves, the specks would be as 
big as saucers, and would show us the presence of the creatures, 
however transparent the rest of their bodies might be: it is 
fair to conclude that the result would be the same were we as 
small as the fish. 
Again, among insects, it is not at all certain that vision 
goes beyond perception of colour, of light and shade, and of 
movement; appreciation of form seems absent. Such being 
the state of our knowledge, Mr. Beddard seems justified in 
his suggestion that it is “ surely premature to build up 
theories which often demand a sense of vision in invertebrated 
animals precisely similar to that possessed by ourselves.” 
This observation has a considerable bearing on the value 
of protective colouring combined with modification of form ; 
certainly in many cases that deception is intended seems 
obvious, but at the same time it is a question how far insects 
would be affected by it; “there is a tendency,” says our 
author, “ to assume their gullibility without bringing forward 
any proofs.” It seems likely that most insects would be 
indifferent to the appearance of an object, provided that it 
remained motionless, so that in the case of the tree-frog, it 
may not be due so much to its colour that it escapes detec¬ 
tion by insects as to the fact that it remains motionless. 
Various difficulties in the way of the generally received 
theory of protective colouring are brought forward, of which 
we will mention one only. Many caterpillars, which feed on 
grass or low-growing plants among grass, are brown or green, 
with longitudinal stripes; the latter, it is asserted, have 
been developed by natural selection, the caterpillars profiting 
by the resemblance which they are supposed to present to 
blades of grass. The larvae of the Satyridce all have these 
characters, yet they feed by night, when they cannot be seen, 
and hide by day, when, if ever, the coloration would be 
useful. There are other striped larvae to which the resemblance 
is equally useless, since they feed on the pith of reeds, and 
are, therefore, hidden from view. 
