IX WARNING COLORATION AND MIMICRY 265 



3. That the imitators are always less numerous in in- 



dividuals. 



4. That the imitators differ from the bulk of their allies. 



5. That the imitation, however minute, is external and 



visible only, never extending to internal characters or 

 to such as do not affect the external appearance. 



These five characteristic features of mimicry show us that 

 it is really an exceptional form of protective resemblance. 

 Different species in the same group of organisms may obtain 

 protection in different ways : some by a general resemblance 

 to their environment ; some by more exactly imitating the 

 objects that surround them — bark, or leaf, or flower ; while 

 others again gain an equal protection by resembling some 

 species which, from Avhatever cause, is almost as free from 

 attack as if it were a leaf or a flower. This immunity may 

 depend on its being uneatable, or dangerous, or merely strong ; 

 and it is the resemblance to such creatures for the purpose 

 of sharing in their safety that constitutes mimicry. 



Condiiding RenmrJcs on IFarning Colours and Miniicry. 



Colours which have been acquired for the purpose of serv- 

 ing as a warning of inedibility, or of the possession of 

 dangerous offensive weapons, are probably more numerous than 

 have been hitherto supposed ; and, if so, we shall be able to 

 explain a considerable amount of colour in nature for which 

 no use has hitherto been conjectured. The brilliant and 

 varied colours of sea-anemones and of many coral animals 

 will probably come under this head, since we know that 

 many of them possess the power of ejecting stinging threads 

 from various parts of their bodies which render them quite 

 uneatal)le to most animals. Mr. Gosse describes how, on 

 putting an Anthea into a tank containing a half -grown 

 bullhead (Cottus bubalis) which had not been fed for some 

 time, the fish opened his mouth and sucked in the morsel, 

 but instantly shot it out again. He then seized it a second 

 time, and after rolling it about in his mouth for a moment 

 shot it out again, and then darted away to hide himself 

 in a hole. Some tropical fishes, however, of the genera 

 Tetrodon, Pseudoscarus, Astracion, and a few others, seem 



