in 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 algae. 



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 Tapiriba, 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 



