32 ILLINOIS BIOLOGICAL MONOGRAPHS [32 



in the Saturnioidea. Whether this consists of kappa and eta or eta 

 alone is a disputed point, altho the first instar seems to indicate the 

 correctness of the former view. 



V. Primary and Subprimary Setae 



In the following discussion of the setae, the evidence for each case 

 of homotypy is briefly summarized. The plan followed is that already 

 outlined herein under the title, "Application of the Evidence." Other 

 authors have indicated various conceptions of homotypy in labeling 

 their figures but none have presented proof, except in one case, the brief 

 paper by Quail mentioned in the introduction. As the evidence on all 

 the important points is conclusive, the retention of an unnatural or un- 

 certain nomenclature is no longer defensible. 



Alpha. The position of this seta as given in the descriptions of 

 the groups is so clear that a few words here will suffice. Originally 

 alpha seems to have been farther dorsad as well as farther cephalad 

 than any other seta. This is now true on all the segments of Hepialus, 

 on the abdomen of nearly all Frenatae, and on the prothorax of many 

 Tineidae and Yponomeutidae. The prothorax shows beta nearer the 

 meson than alpha in nearly all the higher Frenatae, but this is clearly 

 a later migration. 



Alpha is always present in the first stage and is therefore primary. 

 It is one of the most persistent setae and usually forms a verruca or 

 scolus in species bearing these structures. Whether it is present or ab- 

 sent on the last two thoracic segments of Frenatae will be discussed 

 under "Beta" on a later page. 



On the ninth abdominal segment of most Frenatae, alpha is located 

 farther laterad than beta, and in the Macrolepidoptera, this condition 

 has gone back into the first instar. But in Hepialus (Fig. 14), Scardia 

 (Fig. 54), Thyris (Fig. 55), and other genera, it is still as close to the 

 dorsomeson as on the other abdominal segments. In Pseudanaphora 

 (Fig. 16) the lateral migration has already begun and in certain Py- 

 ralididae (Fig. 49) it is carried to its greatest extent. In many fami- 

 lies the location of this seta is a character of importance in the classifi- 

 cation of genera (cf. Pyralididae, Tortricidae, etc.. Part Two). The 

 close association with rho in some cases seems to cast doubt on the view 

 that this seta is homologous with alpha ; but the position in generalized 

 larvae, the complete set of intermediate stages connecting it with its 

 other locations, the variation between the original and later positions 

 within limited groups, and the fact that beta, epsilon, and rho are oth- 

 erwise accounted for, show unquestionably that this seta must be alpha. 



Beta. On the prothorax as well as the abdomen beta is always the 

 dorsal seta of the caudal row. Its position varies from that in Hepialus 



