PROTECTIVE MIMICRY. 213 



that which is seen between various other unpalatable animals. 

 Stress has been very justly laid upon the prevalence of such 

 strongly contrasted colours as yellow and black among un- 

 eatable caterpillars, which are, moreover, disposed in more than 

 one form in alternate rings. This tends to the advantage of 

 the insects, for their enemies have to learn fewer colours and 

 patterns, and thus are less likely to make mistakes, than if the 

 lesson to be learnt were an excessively complicated one. 



It is just possible that this principle may be also applied to 

 the mimicking Pierids. The general belief appears to be that 

 these insects are sweet and palatable : but I find in Scudder's 

 " Butterflies of New England " the observation quoted that the 

 females of two genera of Pierids viz., Melite and Gallidryas 

 have similar organs to those of the Heliconida? which secrete 

 a strongly odorous substance. Even Leptalis, one of the 

 mimicking genera of Pierids, gives off an odour which, ac- 

 cording to Miiller, " is disagreeable to human noses." It may 

 be that the primary object of these to us disagreeably smelling 

 substances is to attract the opposite sex; but the same sugges- 

 tion might, of course, be offered as explanatory of the scent 01 

 the Heliconida>. Mr. Poulton has expressed the opinion that 

 no hard-and-fast line can be drawn between sexual and warn- 

 ing colours : the same brilliancy which delights the female 

 insect or bird may, it is thought, warn off an enemy. Perhaps 

 the same idea may be extended to embrace sexual attraction 

 due to the secretion of strongly smelling substances; these may 

 also serve the same double purpose. 



Butterflies more attacked by Birds in the Tropics than in 



Temperate Regions. 



In this country butterflies are not greatly persecuted by 

 birds ; moths are when they are to be found ; but a moth has 



