56 ILLINOIS BIOLOGICAL MONOGRAPHS (298 



in an active condition. In order to present more clearly the relations shown 

 in the data collected, it has been divided into two sections, the first of which 

 includes only those species hibernating as larvae on or beneath the ground, 

 the second section embracing those not passing the winter in this stage. 

 If we compare two equally subterranean species, one of which hibernates in 

 the soil as a larvae, the other as a pupa, we note that the former is very 

 much more resistant to water. Feltia subgothica and A grot is ypsilon or 

 Nephelodes emmedonia and Phytomelra hrassicae afford examples of this 

 point. It is evident, then, that we should confine our comparisons of the 

 resistance to submergence of species, with reference to their habitats, to 

 those which fall in the same section. By so doing the factor of the stage 

 of hibernation is eliminated. 



It has been found that the subterranean species present the greatest 

 resistance. Epizcuxis luhricalis, because of its exceptional mode of life, 

 cannot properly be compared to other species in this section. Altho never 

 entering the soil, it remains in wet weather in or beneath water-soaked 

 pieces of decaying wood on the ground, dead-wood furnishing the food for 

 this biologically specialized species. Consequently, it presents a high 

 resistance, altho non-subterranean. The relative development of the 

 power to resist water in species of the subterranean-, field-, and tree-strata 

 is indicated in Section 2, in spite of the insufficiency of the data. Most 

 resistant is the fairly subterranean Lycophotia margaritosa, next the non- 

 subterranean cabbage looper, Phylomctra hrassicae, of the field-stratum, 

 and least so the arboreal forest-species, Homoptera lunata. 



EPICRANIAL INDEX AND SUBTERRANEAN HABIT 



This investigation of the resistance to submergence in water leads us to 

 conclude that this factor is an index to the extent of the development of the 

 subterranean mode of life, altho hibernating larvae cannot be directly 

 compared in this respect with those not passing the winter in this stage. 

 We have now established two criteria for determining the relative "sub- 

 terraneanness" of species, namely, the readiness with which the larvae 

 enter the soil and their resistance to water. The latter, since it is capable of 

 numerical expression much more accurately than the former, is far more 

 significant as a guide to the extent of the development of this habit. 



It has been stated previously that the epicranial index is correlated 

 with the subterranean habit, those species presenting the most marked 

 underground mode of life having the shortest epicranial stem. Having 

 necessarily disgressed from our principal line of thought, in order to 

 establish the relative "subterraneanness" of various species, we are now 

 prepared to continue our consideration of this suture. We have already 

 shown that the short epicranial stem or large epicranial index isan excep- 

 tional condition in lepidopterous larvae, associated with a specialized feed- 



