202 



THE CANADIAN ENTOMOLOGIST 



the relationship of Theisoa and Helice. For earher references to these genera 

 see Dyar's List, Nos. 5592, 6130, 6182. 



In Theisoa constrictella, males (Fig. 24-a) in the fore wing, veins 7 and 9 

 are out of 6, with 8 absent; here the transverse vein is much nearer to 10 than 

 to 9. In the female (Fig. 24-b)8 is present, and 9 separates from the stalk of 

 6, 7, 8 and 9 sooner than in the male, thus showing a less specialized condition. 

 In the hind wing of the male (Fig. 24-c) the vein apparently forming the upper 

 margin of the cell reaches the margin of the wing just heloiv the apex; if followed 

 toward base, it is seen to curve downward, being more or less distinctly con- 

 nected with lower margin of cell near the middle of the wing by a very short 

 discal vein, from thence to base it is obsolescent. In one specimen, the hind 

 wing on one side (Fig. 24-d) shows an additional vein lying costalward of this;it is 

 indistinct from base to middle, where it makes a scarcely noticeable bend toward 

 the discal vein, and reaches the costa at about two-thirds the wing length. 

 I consider this vein 7 and its presence in this instance an atavistic character. 

 In the hind wing of the female (Fig. 24-e) the upper margin of the cell extends 

 almost straight from base, reaching the costa almost at apex; it is rather in- 

 distinct in its basal half. Its course in the basal half is exactly that of the 

 ^'additional vein" in one male wing, above mentioned; in its apical half its 

 course is such as to lead to the inference that it is formed by the coalescence 

 of the vein, which normally in the male forms the upper margin of the cell 

 with the '''additional vein." There is no indication of a discal vein in the female. 

 From these observations I conclude that the venation of the hind wing in this 

 species was derived from a type in which both veins, 6 and 7, were present and 

 separate; in the process of evolution, the male and female show a divergence, 

 in direction of development to the extent that in the male vein 7 has disap- 

 peared completely by obsolescence leaving vein 6 to form the upper margin of 

 the cell, while in the female, 6 has coalesced completel'y with 7, the oni(y evidence 

 of the process remaining being the costal ending of the apical vein as contrasted 

 with its terminal ending in the male. 



a 



In order to determine whether the same difference in venation exists be- 

 tween the sexes of Theisoa permolestella, an examination of a series of specimen, 

 was made; this examination revealed that all the specimens of T. permolestella 



