Evolution a?id Taxono77iy 43 



the same kind. The former will indicate dichotomous divis- 

 ions of lines of descent ; the latter will merely indicate de- 

 grees of divergence from a primitive type. Thus, to draw an 

 illustration from the following pages, it is shown that there 

 are two distinct ways of uniting the two wings of each side 

 in the I,epidoptera ; they may be united by a frenulum (Fig. 

 22) or the may be united by a jugum (F;g. 27). These are 

 differences in kind oi specialization, and indicate two distinct 

 lines of descent or a dichotomous division of the order. 

 Among those Lepidoptera in which the wings are united by 

 a frenulum great differences occur in the degree to which this 

 organ or a substitute for it is developed ; such differences may 

 merely indicate the degree of divergence from a primitive type 

 and may need to be correlated with other characters to indi- 

 cate dichotomous divisions. 



It is impracticable to indicate degrees of divergence from 

 the primitive type based on the nature of the frenulum at this 

 stage of the discussion ; but another character will serve our 

 purpose well. In the more generalized Lepidoptera the anal 

 areas of one or of both pairs of wings are furnished with three 

 anal veins ; while in more specialized forms the number may 

 be reduced to two or even to one. But the distinctions indi- 

 cated by the presence of three, two, and one anal veins in dif- 

 ferent moths, are merely differences in degree of specialization 

 by reduction of an anal area, and taken alone will not indicate 

 dichotomous divisions. Thus if we group together all the 

 moths that have retained three anal veins in the hind wings, 

 such a group will contain, not merely the Microlepidoptera, 

 as is commonly stated, but also the more generalized members 

 of several distinct divisions of the Macrolepidoptera. 



The fact is, the primitive Lepidoptera evidently possessed at 

 least three anal veins in the hind wings (we will omit the fore 

 wings from the discussion for the time being). In several dis- 

 tinct lines of development within this order the direction of 

 specialization of the anal area of the hind wings has been 

 towards the reduction of the number of veins in this area ; but 

 the extent to which this reduction has gone merel}' indicates 

 the degree of divergence from the primitive type. And so far 



