70 ILLINOIS BIOLOGICAL MONOGRAPHS [312 



also present considerable difference according to the instar. The stipuiar 

 setae frequently increase in relative size during larval life (Figs. 40, 43, 44), 

 altho they may remain about the same (Figs. 33, 38). A striking decrease 

 in relative size is always undergone by the two sensoria of the palpiger and 

 by the pair of smaller ones on the proximal semicircular sclerite of the 

 spinneret (Figs. 29-32, 33-36, 38, 40, 41, 43-45). As previously mentioned 

 the same situation is presented by those of the head, altho not so marked. 

 This appears to be a non-recapitulative change due to the mechanics of 

 growth. The pronounced decrease in the relative size of the ocellarae 

 already discussed offers an apparently parallel situation. It seems evident 

 that the modified hypodermis of sensory organs, whether of visual or of 

 chemical sense, grows more slowly than the ordinary hypodermis. 



In the first instar of some species the proximal sclerite of the spinneret 

 is continuous between the sensoria, forming a complete ring instead of a 

 semicircle, as it sometimes does in the older noctuid larvae (Figs. 33-38). 

 The fact that the former condition is of quite frequent occurrence thruout 

 the order suggests that it may be the primitive one, in which case this 

 change is to be regarded as a recapitulation, the semicircular sclerite of the 

 noctuid larva representing the remnant of a complete ring. The first instars 

 of PoUa renigera and of Agrolh ypsilon, on the other hand, exhibit the 

 condition typical of fully grown noctuid larvae with respect to this point 

 (Figs. 29-40). In the former species, however, a secondary chitinization 

 appears in the last instar, connecting the two ends of the semicircle (Figs. 

 31-32). 



The palpi undergo changes in form and in the shape and relative size 

 of their setae. A comparison of Figures 30 and 31, 33 and 38, and 40 and 

 44 reveals the fact that both segments of the palpus become relatively 

 longer and narrower during development. Since there appears to be no 

 evidence indicating whether or not the ancestral palpus was shorter and 

 broader than the typical one of existing forms, we cannot attempt to 

 classify this change. The significance of the striking reduction of the seta 

 of the proximal segment during larval growth is also problematical. 

 Usually, altho not always, the terminal seta of the distal segment becomes 

 much more slender and relatively shorter in the later stadia. Lycophotia 

 margarilosa appears to present an exceptional situation in the development 

 of all of the setae of this region. Those of the stipula fail to increase in 

 relative size as they usually do and the terminal one of the palpus becomes 

 relatively larger in the course of growth, whereas the reverse is typically 

 true. The reduction of the terminal seta commonly found in the Noctuidae 

 is paralleled in certain leaf-miners figured by Tragardh. ^Moreover, the 

 terminal setae of the antennae and maxillae of caterpillars are frequently 

 short and stout in the first instar, becoming normal in form during develop- 

 ment. The significance of these changes cannot be definitely determined in 



