26 ILLINOIS BIOLOGICAL MONOGRAPHS [26 



denly appears at the first molt on all the segments of Hepialus and on the 

 mesothorax and metathorax of Frenatae. Another late arrival is omega, 

 situated between nu and tau on the abdomen. Whether it is present 

 in the first stage on the thorax, I do not know, but in the mature larva 

 it is on the ventral surface of the thoracic as well as of the abdominal 

 segments. 



The mature larva of Hepialus humuli may then be described as 

 follows : 



Prothorax (Fig. 5) . Six setae are located above the spiracle and three 

 in front of it. All of these are placed on the cervical shield, which ex- 

 tends ventrad to the level of the middle of the spiracle. Along the ceph- 

 alic border of the shield are five setae the upper three of which are alpha, 

 gamma, and epsilon, as described on the first-stage larva. The lower two, 

 kappa and eta, in front of the dorsal margin of the spiracle, are lateral 

 in position and belong to the Kappa group. On the caudal margin of the 

 shield is a group of three setae, beta, delta, and rho, arranged in a curved 

 line directly above the spiracle. Slightly separated from these is another, 

 ventrad of the lower end of this line. The latter is theta, the third 

 member of the Kappa group, and is always associated with kappa 

 and eta. 



Near the coxa of the leg is a chitinized plate bearing two setae, pi 

 and nu, representing the constant and important Pi group. In front 

 of the leg are certain small setae, usually two in number, with a third 

 sometimes added. These I call the Tau group, for they are extremely 

 variable and it is difficult to homologize the individual setae. They are, 

 however, not related to each other in the same sense as the members of 

 the Kappa group, Pi group, etc. The one closest to Pi may be called 

 omega, and the others, tau and phi. Behind the coxa, as in all cater- 

 pillars, sigma is present near the ventromeson. 



Mesothorax and Metathorax (Fig. 5). These segments are each 

 divided into three annulets, marked distinctly on the dorsal half of the 

 segment but partially lost on the ventral. On the first of these is found 

 a group of three minute setae, which must represent gamma or a struc- 

 ture developed in its place. As it is in the position of gamma it is most 

 convenient to give it that name altho the evidence is not conclusive. The 

 middle annulet bears two setae, one near the dorsomeson, the other 

 directly caudad of the prothoraeic spiracle. These, as in the first stage, 

 are clearly homologous with alpha and epsilon. Assuming that the 

 homology suggested in regard to the first annulet is correct, we now 

 have the entire row, alpha, gamma and epsilon, accounted for. 



The third annulet bears three subdorsal setae and two lateral ones. 

 The three subdorsal are plainly beta, delta, and rho, as on the pro- 



