WARNING COLOURS AND MIMICRY 153 



those who share the popular belief that one butterfly is 

 very much the same as any other butterfly. Many thou- 

 sands of distinct butterfly forms exist, and these fall 

 naturally into families, each of which is characterised by 

 structural differences as marked as those which separate 

 dogs from horses, or cassowaries from sparrows. We 

 have seen that whole families of butterflies are rendered 

 unfit for food because of the pungent juices which per- 

 meate their tissues. Other groups, such as that to which 

 our common white butterflies belong, comprise species 

 which are perfectly edible and much sought after by 

 insectivorous creatures. 



Plate XXIII represents some South American butter- 

 flies. The species called Dismorphia prcumnoe, of which 

 both sexes are shown, is the mimic. Why there are two 

 models will be explained subsequently. For the moment 

 we will focus our attention upon the female Dismoiphia. 

 A casual observer, misled by colour and shape, would pro- 

 bably fall into Bates's initial error and class the insect along 

 with its models. But a detailed examination brings to light 

 certain racial traits — more especially the arrangement of 

 the nervures, or " veins," of the wings and the development 

 of the legs — which inform the systematic naturalist that the 

 species belongs to the family of typically black-and-white 

 butterflies called the Picridce ; while in the case of the 

 male, a remnant of this early character — the whiteness of 

 the wing — is actually retained on that part of the hind- 

 wing which is not seen during flight. It is to this family 

 that our " cabbage whites ' belong, while many of its 

 South American representatives differ little from their 

 kindred of the Eastern Hemisphere. Others, like Dis- 

 morphia praxinoc, exhibit a wonderful mimetic likeness to 

 distasteful types with which they have no real affinity. 



We may well ask by what process this insect has come 



