HOW TO KNOW THE BUTTERFLIES 



These studies have shown that all winged in- 

 sects have doubtless descended from a common 

 winged ancestor. And although we do not know 

 the exact form of this primitive winged insect, 

 which lived during the Silurian age, we may infer 

 that those structural features that are common to 

 the generalized members of the different orders 

 of winged insects have been inherited from this 

 common ancestor. 



The features of the wing-venation which are 

 commonly present with the generalized members 

 of the different orders of winged insects, and 

 which we therefore infer were possessed by the 

 primitive winged insect, are represented in Figure 

 5. From this hypothetical primitive type of 

 wing-venation there can be derived, by methods 

 of modification of which we have many illustra- 

 tions among living insects, all the forms of vena- 

 tion of insect wings known. 



The venation of the wings of butterflies is one 

 of the more specialized types of wing-venation, 

 and one which can not be understood by the study 

 of the wings of butterflies alone. It is necessary, 

 therefore, to lead up to the explanation of this 

 type by describing more simple or less modified 

 types. We will describe first the hypothetical 

 primitive type and then point out the ways in 



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