34 ILLINOIS BIOLOGICAL MONOGRAPHS [276 



according to the group, altho they provide no convenient characters for 

 use in tables. 



The setae of the anal segment, which probably represents the fused 

 tenth and eleventh abdominal somites, cannot be definitely homodynara- 

 ized with those of other segments. Alpha, beta, and kappa vary a little 

 in relative position according to the genus or in some instances within a 

 genus. Kappa is most commonly equidistant from the other two but may 

 be distinctly nearer to beta or less often slightly nearer to alpha. Both 

 extremes have been found within the genus Phytometra. The position 

 of the setae on the lateral aspect of the anal larvapod is perhaps subject to 

 more striking variation than any other group of setae on the trunk of 

 noctuid larvae. An usually conspicuous sensorium, which Mclndoo has 

 described, also contributes to the taxonomic value of this region, varying 

 considerably in situation relative to the setae. Eta may be nearer either 

 to epsilon or to omega, furnishing a basis for the separation of genera and 

 larger groups, altho occasionally showing specific variation. Scolecocampa 

 liburna presents an exceptional position of the sensorium, which is distad 

 of eta (Fig. 53). In all other species examined it is distinctly proximad of 

 the setae. The sensorium, eta, mu, and tau are frequently arranged so as 

 to form the points of a diamond, which varies considerably in relative length 

 and width, according to larger groups. The line from the sensorium to tau 

 is usually longer than the one from mu to eta, altho the reverse situation is 

 sometimes encountered. Either mu or eta may be nearer to the sensorium, 

 so that the diamond is often out of true. Mu varies in location with refer- 

 ence to the lines epsilon-eta and omega-tau, being nearer to either one. All 

 of these variations appear to apply chiefly to genera. 



LARVAPODS 



The general form of the larvapods of noctuid larvae (Figs. 50-53) is 

 typical for the entire order. As in a number of related families, the crochets 

 are arranged in a mesoseries and are homoideous and uniordinal (Figs. 51, 

 58) representing a supposedly specialized type which Dyar considered to 

 have descended from the circular one found in Hepialus. They are operated 

 by muscles which attach entad of a small usually heavily chitinized spot in 

 the center of the distal end of the uropod. As shown in Figure 59 each 

 crochet lies within a membranous invagination whose mesal edge bears a 

 number of pointed membranous projections. These have not been pre- 

 viously described, so far as known. Their function is problematical. The 

 proximal end of each crochet is pointed and curved mesad, serving for the 

 attachment of muscles. Since the larvapods represent embryonic abdomi- 

 nal appendages which have persisted into postembryonic life, the terms 

 proleg and false leg in general use are inappropriate. 



