Evolution and Taxonomy 



73 



iir. 



Let us see how the facts regarding the changes of media can 

 be used in taxonomic work. 



First, the presence of the main trunk of media is an indica- 

 tion of a generalized condition. This at once throws light on 

 the position of the Megalopygidse, the Ps}'chidse, the Cossidae, 

 the Limacodidse, and certain of the Zj-gaenina. These fami- 

 lies are evidently much nearer the stem form of the Lepidop- 

 tera than are those families in which media has been lost. 



It does not follow that these families should be classed to- 

 o-ether. For each one may represent a distinct line of devel- 

 opment. The presence 

 or the absence of the 

 base of media is a char- 

 acter that merely indi- 

 cates the degree of di- 

 vergence from a primi- 

 tive type (see p. 43). 

 The divergence in each 

 case may be along a dis- 

 tinct line. It ma)' be 

 worth while to state in 

 this connection that the 

 families named above 

 are nearly all of those of 

 the Macrofrenatse i n 

 which three anal veins 

 are preserved in the hind 

 wings, another character 

 indicating a compara- 

 tivel}' slight degree of 

 divergence from the primitive type. 



Correlated with the abortion of the base of media is the 

 coalescence of its branches with the adjacent veins. It fol- 

 lows from this that the extent to which this coalescence has 

 gone is an indication of the degree of departure of a form 

 from the primitive type. Compare, for example, the hind 

 wings oi Packardia (Fig. 16) with the hind wings of Adoneta 

 (Fig. 17), two genera of the family Ivimacodidse. In Packar- 



VIII 



Fig. 17. — Adoneta. 



