30 ILLINOIS BIOLOGICAL MONOGRAPHS [272 



Agrotinae from a point equidistant to one much nearer to gamma. Epsilon 

 also varies in position in the Hypeninae, being equidistant from gamma 

 and the spiracle in some genera and nearer to the spiracle in others. Some 

 longitudinal variation is offered by epsilon, which may be slightly or con- 

 siderably caudad of kappa according to the genus. Kappa varies slightly 

 but quite constantly in transverse location, ranging from a point distinctly 

 above the spiracle to one a little below it. The relative situation of eta, 

 kappa and the spiracle with reference to one another differs according to 

 the group. Eta is usually distinctly below kappa and slightly caudad of it, 

 being much nearer to kappa than to the spiracle. These setae may, how- 

 ever, be on the same longitudinal line, with kappa so far caudad that it is 

 equidistant from eta and the spiracle. 



As in caterpillars generally the mesothorax and metathorax are very 

 similar to each other, although they exhibit a quite different setal pattern 

 than the prothorax, the arrangement on the former segments resembling 

 rather closely that of the abdominal ones. The mesothorax and metathorax 

 differ from those which follow chiefly in the longitudinal position of alpha 

 and beta and in the situation of the setae occupying the region which bears 

 the spiracle in other segments. One or both of the minute setae xa and xb 

 may be present on the mesothorax, this point representing individual varia- 

 tion. Both are usually present on the metathorax. On the mesothorax 

 beta varies from a position on the transverse line through alpha to one 

 distinctly cephalad of it. The location of beta may be the same on the 

 metathorax as on the mesothorax or it may, as is often the case, be a little 

 further caudad on the metathorax (Fig. 48), the amount of variation in this 

 respect remaining the same for both segments. On both mesothorax and 

 metathorax rho varies longitudinally from a point distinctly cephalad 

 to one a little caudad of epsilon, the latter condition being commonly found 

 in the Agrotinae. A greater difference in position is presented by beta, 

 which on the mesothorax may be either equidistant from alpha and epsilon 

 or very much nearer to alpha as in Catocala. On the metathorax beta 

 is usually further ventrad, varying the same amount as on the mesothorax. 

 The position of a line drawn through rho and epsilon with reference to 

 kappa and theta furnishes one of the best characters on these two segments. 

 The condition in this respect is usually the same on these segments, but 

 may be distinctly different as in Achatodes zeae, showing that there 

 has been some independent variation in the setal position, notwith- 

 standing their very similar organization. In the Agrotinae and 

 Catocalinae examined this line passes nearer to theta than to kappa. 

 It may be distinctly nearer to either one in the Hadeninae, Acronyctinae 

 and Hypeninae according to the genus. In the Phytometrinae it is 

 usually equidistant from the two setae and ranges from a point equi- 

 distant to one much nearer to theta in the Cucullinae. The situation of 



