8 ILLINOIS BIOLOGICAL MONOGRAPHS (250 



general, larval postembryology may reasonably be regarded as the princi- 

 pal source of recapitulative evidence to be applied within families or smaller 

 groups. A study of the later embryonic stages may, on the other hand, be 

 expected to throw light upon the relationships between families and orders. 



Biology, although never serving as a basis for classification, under our 

 present system, quite frequently furnishes evidence of a corroborative 

 nature. For example, the peculiar scattered distribution of Peripatus is 

 regarded as an indication of great phylogenetic antiquity. Physiological 

 life-history in relation to taxonomy has been studied but little. Since vari- 

 ous types of life-history are often found within closely related groups, no 

 marked correlation is generally evident; however, when the evolution of 

 life-history becomes better understood, it seems quite possible that our 

 sources of phylogenetic knowledge will be further supplemented by a study 

 of physiological life-history. 



This consideration of the sources of our taxonomic knowledge with 

 reference to their development in entomology may be summarized thus: 

 the comparative morphology of the immature stages presents a relatively 

 new field of well established systematic value; recapitulation offers a practic- 

 ally unexplored source of information of considerable promise, and biology 

 may yield valuable evidence from the taxonomic point of view. 



In a systematic treatment of an unsatisfactorily classified group all 

 evidence available should be sought. It is to be expected that neglected 

 sources of information will first be called into use in those difficult groups 

 where the morphology of the adults alone has not been sufficient to bring 

 about a satisfactory understanding of relationships. The Noctuidae rep- 

 resent such a group. With its 3500 North American species, its many ill- 

 defined genera, its striking structural uniformity, and its large number of 

 extremely variable species, we are not surprised to find that systematists 

 have had considerable difficulty with this family. A large proportion of 

 the misnamed and unnamed Lepidoptera in collections belong to the 

 Noctuidae. Its general importance is probably not surpassed by that of 

 any other family of insects, containing, as it does, about one-half of the 

 described Lepidoptera of North America. The great economic importance 

 of the Noctuidae needs only to be mentioned. 



It is hoped that the following contribution to the larval postembryology, 

 larval morphology, and general biology of the Noctuidae may not only 

 demonstrate the general value of these more or less neglected sources of 

 phylogenetic evidence, but may also present, in a preliminary manner, 

 their application to the solving of some of the many problems of the evo- 

 lution of structure and habit within the family. 



