74 Colouration in Animals and Plants. 



Butterflies (Rhopalocera) are grouped into four sub-families, as 

 under : — 



1. Nymphalido3, having the fore-legs rudimentary, and the pupae 



suspended from the base of the abdomen. 



2. Erycinidce, in which the males only have rudimentary fore- 



legs. 



3. Lycamida, in which the fore-legs of the males are smaller 



than those of the females, and terminate in a simple hook. 



4. Papilionidai, which have six perfect pans of legs, and in which 



the pupae assume an upright posture, with a cincture round 

 the middle. 



It may, at first sight, appear curious that the imperfect-legged 

 Nymphalidaz should be placed at the head of the list, but this is based 

 upon sound reasoning. The larva consists of thirteen segments, 

 and, in passing to the mature stage, the second segment alone 

 diminishes in size, and it is to this segment that the first pair of legs 

 is attached. Looking now to the aerial habits of butterflies, we can 

 understand how, in the process of evolution towards perfect aerial 

 structure, the legs, used only for walking, would first become modi- 

 fied ; and, naturally, those attached to the segment which decreases 

 with development would be the first affected. When this is found 

 to be combined with an almost aerial position of the pupae, we see at 

 once how such insects approach nearest to an ideal flying insect. 

 It is a general law that suppression of parts takes place as organisms 

 become specialized. Thus, in the mammalia, the greatest number of 

 toes and teeth are found in the lowest forms and in the oldest, 

 simplest fossil species. 



A butterfly is, indeed, little more than a beautiful flying machine ; 

 for the expanse of wing, compared with the size of the body, is 

 enormous. 



