Vol. 1.] 



WoodwortJi. — Wing Veins of Insects. 



145 



only to that extent, shall we find the venations comparable. 

 The nomenclature of venation in each group may be to that 

 extent independent. Thus, in the Odonata we may be able to 

 use with entire propriety the term primary vein at the same 

 time that we use it in the Diptera, but it will not do to apply 

 the term triangle, or basal cell, to structures in the two groups' 

 interchangeably. This principle has never been clearly recog- 

 nized by those who would establish a uniform nomenclature. 

 There must be a distinct nomenclature for each group, with 

 only such terms in common as are clearly homologous. How 

 far homologies can be carried will doubtless be for a long 



Neoptera 



Elytropte 



^Corrodenlia 



ertdcc 



meridi 



axa. 



'rct/donatA 



Subuli 



FIG. 101. Diagram illustrating the phylogeny of insects. Extinct 

 groups are omitted, unless definitely leading to existing groups; those 

 given are in italics. 



time a disputed point. My own conviction is that strict 

 homology (that is, the use of terras for veins completely com-, 

 parable) is not possible throughout the whole series of insects, 

 in the case of any vein, not even the primary, because cross 

 veins and independents become, to all intents and purposes, 

 branches of the other veins, and it is not unlikely that true 

 branches often become disconnected, and would then be indis- 

 tinguishable from independents. It is possible, however, to 

 use terms in a more elastic sense and to speak of the primary 

 with the knowledge that in one case it has branches not 

 strictly comparable with those in the other. The marginal, 

 the primary, the anterior, and the posteriors can, I think, in 

 this sense be used in all the orders of insects, as has been done 

 in the preceding pages. The independents and most of the 

 10~v 



