160 PROTECTIVE COLORING 



This has nothing whatever to do with sex or with 

 food, and Poulton argues that in these eases both 

 colors are protective, and that the species (though 

 in no way either dichromatic form) is advantaged, 

 because when once discovered by an enemy others 

 of the same color would then be more easily found 

 by this enemy (a reason which would appeal to 

 every field entomologist) ; so that while one form 

 might suffer the species would be saved through 

 the escape of the other. Weismann believes that 

 this change has been brought about by natural 

 selection, but Semper urges that selection " could 

 not possibly effect any alteration in the pigment, 

 but could only operate after such a change had 

 actually occurred." Closely allied to this is the 

 well-known fact that, in a number of our cater- 

 pillars and particularly in those of the Papilioninae, 

 an entire change of color takes place just previous 

 to pupation. The period of pupation is probably 

 the most hazardous for an insect, as far as its 

 active external foes are concerned, it being abso- 

 lutely helpless in this period and in a very sensitive 

 state. The time required for the change is nuich 

 greater in any one species than for ordinary ecdysis 

 in the same species ; and whatever the purpose of 

 the change in coloration may be, it will hardly fail 



