PROTECTIVE AND AGGRESSIVE RESEMBLANCE 337 



remember standing with my gun in the midst of a dense patch 

 of scrub in Australia and hearing the pademelons 1 hopping about 

 all around me. For a long time, however, I could see nothing 

 but the trees. My native guide pointed out where I was to aim, 

 but I only fired at a log from the side of which a pademelon 

 hopped away. Again he pointed, and this time at a small white 

 spot which I could just distinguish amongst the trees. I fired 

 once more, aiming at the white spot, and sure enough a pademelon 

 rolled over. It appeared that I had aimed at the white fur which 

 occurs on the breast of the animal and which to the experienced 

 eye of the native told all that he needed to 

 know. It is often supposed that conspicuous 

 patches of this kind serve as recognition marks 

 between individuals of the same species, but it 

 may be questioned how far the advantage of 

 being recognized by a friend compensates for a 

 disturbance of the colour harmony which reveals 

 an animal to its enemies. 



The type of colouration which aids in the 

 concealment of an animal is termed, by Pro- 

 fessor Poulton, cryptic. It belongs, of course, 

 to the apatetic group. Concealment may be 

 desirable either as a means of escape from 

 enemies or for the purpose of ambuscading 

 prey, or possibly for both. In the former case 

 we may speak of it as protective resemblance 

 (procryptic colouration), in the latter as aggres- 

 sive resemblance (anticryptic colouration). 



Protective resernbjance is often of a very highly 

 specialized character, and may be due as much to adaptation 

 in actual form as to adaptation in colour ; frequently these two 

 factors unite in producing the result, and a third may be added, 

 viz., adaptation in habit or instinct. In the common stick 

 caterpillars of the geometer moths we see all three factors 

 co-operating. In colour and shape these caterpillars precisely 

 resemble small twigs. They move about with a characteristic 

 looping action amongst the leaves or branches of the bushes 

 which they frequent, but when at rest they stiffen themselves up 

 and stand out from the branch at the exact angle of a twig, and 



FIG. 169. Larva 

 of the Brim- 

 stone Moth 

 (Rnmia cratae- 

 yata) resting 

 upon a Haw- 

 thorn twig ; 

 nat.size. (From 

 Poulton.) 



A small species of kangaroo. 



