

350 Annals Entomological Society of A mei tea [Vol. XII, 



Micropterygid^e and the generalized Trichoptera,* and a pupa 

 resembling that of the Microptergyidae. The venation of the 

 Nepticulidas (Braun, '17) shows highly specialized features. 

 It resembles most closely the venation of some of the Hydropti- 

 lidas, but shows extreme anastomosis of main veins and absence 

 of cross-veins. It differs from that of Hydroptilidfe chiefly 

 in the few points in which the Nepticulidas approach the usual 

 type of venation in the frenate Microlepidoptera with reduced 

 venation. The existence of this group, which shows undoubted 

 trichopterous affinities, further complicates the question of the 

 true relationship existing between the Trichoptera, the Microp- 

 terygidae, the Nepticulidce, the Hepialidae, and the frenate 

 Lepidoptera. 



The discovery of another family, the Prototheoridae (Mey- 

 rick, Annals South African Museum, XVII, 17, 1917), with 

 characters intermediate between the Micropterygidas and the 

 Hepialidae, would seem to make it impossible to place the 

 Micropterygidas and Hepialidae in different orders. 



In two related groups, any adaptation for a particular 

 function may have been handed down from the common ancestor 

 of the two, or it may be a similar modification of an homologous 

 structure arising independently in each group, because of the 

 same inherent tendencies in each, or the adaptations serving 

 the same purpose may be developments of entirely different 

 structures in the two groups. The two former conditions 

 indicate community of descent and closeness of relationship; 

 the third the phylogenetic divergence of the two groups. The 

 same principles may be applied in the analysis of the entire 

 structure of the groups whose true relationship is to be deter- 

 mined. If it can be shown, that the more primitive members of 

 one group having many characteristics in common with the 

 primitive members of another group and thus appearing more 

 closely related to them than to any other group, show the 

 beginning of divergence in structure from that other group, and 

 these modifications can be consistently traced in the same 

 direction through the more specialized members of the first 

 group, in my opinion the point where the two groups begin 

 to diverge, that is, the point where the distinctive characteristics 

 of a group originate, is the logical place to make a taxonomic 



* The term Trichoptera is used in this paper in its commonly accepted sense, 

 not including the Micropterygidae. 



