I PROTECTIVE RESEMBLANCES AMONG ANIMALS 41 
protective tint would be useless to them, and they accordingly 
retain the more usual reptilian hues. 
Fishes present similar instances. Many flat fish, as for 
example the flounder and the skate, are exactly the colour of 
the gravel or sand on which they habitually rest. Among 
the marine flower gardens of an Eastern coral reef the fishes 
present every variety of gorgeous colour, while the river fish 
even of the tropics rarely if ever have gay or conspicuous 
markings. A very curious case of this kind of adaptation 
occurs in the sea-horses (Hippocampus) of Australia, some of 
which bear long foliaceous appendages resembling seaweed, 
and are of a brilliant red colour; and they are known to live 
among seaweed of the same hue, so that when at rest they 
must be quite invisible. There are now in the aquarium of 
the Zoological Society some slender green pipe-fish which 
‘fasten themselves to any object at the bottom by their 
prehensile tails, and float about with the current, looking 
exactly like some simple cylindrical alge. 
It is, however, in the insect world that this principle of 
the adaptation of animals to their environment is most fully 
and strikingly developed. In order to understand how 
general this is, it is necessary to enter somewhat into details, 
as we shall thereby be better able to appreciate the signifi- 
cance of the still more remarkable phenomena we shall 
presently have to discuss. It seems to be in proportion to 
their sluggish motions or the absence of other means of 
defence, that insects possess the protective colouring. In the 
tropics there are thousands of species of insects which rest 
during the day clinging to the bark of dead or fallen trees ; 
and the greater portion of these are delicately mottled with 
gray and brown tints, which, though symmetrically disposed 
and infinitely varied, yet blend so completely with the usual 
colours of the bark, that at two or three feet distance they 
are quite undistinguishable. In some cases a species is 
known to frequent only one species of tree. This is the case 
with the common South American long-horned beetle 
(Onychocerus scorpio), which, Mr. Bates informed me, is 
found only on a rough-barked tree, called Tapiribd, on the 
Amazon. It is very abundant, but so exactly does it resemble 
the bark in colour and rugosity, and so closely does it cling 
