6 BULLETIN 128, UNITED STATES NATIONAL MUSEUM. 



individuals who in remote or recent time diverged in method to a 

 common end (in the case in point to a form without uncus). To 

 lump all such groups of species into a single genus because no one 

 single consistent and inflexible character can be found to separate 

 each of them from all the others is to beg the issue. Not only con- 

 venience but fidelity to the truth, as we know it, demands some ar- 

 rangement and separation of the specific groups that will link the 

 species in their natural order and separate them according to their 

 different lines of development. These groupings we call genera. 

 Their definitions we must frame in a synthesis of characters so as 

 to include within the genus those species which are obviously close 

 and to exclude all obviously different. 



On the other hand, to unite forms that agree on one or two struc- 

 tural details — whatever they may be — or to classify upon one set of 

 characters, venational, genitalic, vestigial, or secondary sexual, is to 

 commit the absurd, bringing together species of widely different 

 origin and separating others that by their very habitus must be spe- 

 cifically close. For example, the stalking or fusion of veins 7 and 8 

 of the fore wing, the uniting of 3 and 4 of hind wing, the loss of 

 uncus or socii from the genitalia, the presence of raised scales or an 

 antennal notch may and do occur each in several places. It is that 

 synthesis of several characters considered in the manner of their 

 development which must be considered significant. 



The comparative chart will illustrate more clearly than any possible 

 description the tendencies working to separate groups and how far 

 each has progressed in the several groups, and should show at once 

 the necessity of some arrangements expressing this progression and 

 the difiiculty of defining it in terms of " yes or no," " with or without," 

 since its real significance is the total of results plus direction. 



The general tendencies in the Eucosminae may be enumerated as 

 follows : 



1. In wing shape : from a form with rather broad f orewings with a 

 costal fold and convex termen tending to narrower winged forms, 

 with termen straight and slanting, evenly concave with apex rounded 

 or distinctly falcate, or with termen deeply notched between veins 

 4 and 5, the costal fold disappearing and frequently lost. 



2. In f orewing venation : from a primitive form with 2 straight, 3, 

 4, and 5 well separated at termen, 11 arising from cell well before 

 middle, with upper internal vein of ceU branching off between 10 

 and 11 and with apical end of cell unconstricted ; the tendencies are 

 for the apical end of the cell to become constricted, for the internal 

 vein to move forward till it branches off between 9 and 10, for 11 to 

 move forward till it arises from the middle or somewhat beyond the 

 middle of the cell, for 3, 4, and 5 to crowd together at the termen 



