299] NOCTUID LARVAE— RIPLEY 57 



ing habit. The data confirms not only that this condition in the Noctuidae 

 is confined to subterranean larvae, but that the extent of the development 

 of this habit is correlated very definitely with the relative length of the 

 epicranial stem. We have ample reason, therefore, for stating that the 

 short epicranial stem is a specialized condition in noctuid larvae, associated 

 with a specialized mode of life, the subterranean one. 



Our understanding of the mechanics of this correlation is by no means 

 complete. Subterranean larvae are characterized in general by an extensive 

 chitinization of the pronotum, beneath which the caudal part of the head is 

 retracted most of the time. The mouth-parts tend to become directed 

 cephalad instead of ventrad in such larvae. A parallel, but more extreme 

 condition is exhibited by the lepidopterous leaf-miners, where we find the 

 greatest reduction of the epicranial stem correlated with mouth-parts 

 directed cephalad, the caudal portion of the head remaining beneath the 

 chitinized pronotum. It seems evident that mandibles in this position are 

 better adapted for burrowing than those directed ventrad, and that this 

 change in the position of the head has induced a shortening of the epicranial 

 suture, a point which has been discussed in the morphological section of this 

 paper. When we consider the profound specialization in the heads of 

 beetles, which has been brought about in correlation with the change in the 

 position of the mouth-parts from a ventral to a cephalic direction, it seems 

 quite reasonable to suppose that a less marked specialization in the position 

 of the head, such as we find in subterranean noctuid larvae, would be 

 accompanied by proportionately less pronounced modifications of the 

 head-capsule. 



Our knowledge of this relation between the epicranial stem and the 

 feeding habit should be of some value to the economic entomologist. 

 Cut-worms attacking well-cultivated crops, such as corn or tobacco, must 

 be able to enter the soil in order to protect themselves from the heat of the 

 sun. The larvae of those species which do not burrow must depend upon 

 an abundance of grass or weeds, among the bases of which they can with- 

 draw during the brighter part of the day. Noctuid larvae with a long 

 epicranial stem, such as the bronzed cutworm, Nephelodes emmedonia, or 

 the members of the genus Cirphis, to which the army-worm belongs, are 

 unable to enter the soil and are therefore seldom found attacking well 

 cultivated crops. When such crops are attacked by army-worms, it is 

 during migratory outbreaks, when their reactions are abnormal. It is a 

 significant fact that all of the fourteen species dealt with by Crumb in his 

 key to tobacco cutworms are of the short-stemmed type. The army-worm's 

 abstinence from tobacco is not a matter of appetite, since this author has 

 found them to eat it as readily as grass, but it is rather because of the 

 inability of this species to burrow into the earth and thus escape the rays 

 of the sun. Hence an examination of the length of the epicranial stem of an 



