Dec, 1916.] Relationships of Apterygotan Insects. 269 



which Handlirsch and his followers unhesitatingly group in the same 

 class — than there is between the Blattidse and Lepismatidse — which 

 they would not group in the same class. In the same way, an imma- 

 ture Plecopteron such as a nymph of Peltoperla, is structually far 

 closer to Lepisma than it is to Pulex, or any of the higher Ptery- 

 gotan insects — and in the last analysis, comparative anatomy 

 (whether it be the comparative anatomy of embryos, or of living or 

 fossil adults) furnishes us with the only reliable material for de- 

 termining relationships ! 



Since the Apterygotan forms, such as Lepisma, etc., are so closely 

 related to the lowest Pterygota (such as the Blattidse, nymphs of 

 Peltoperla, etc.) and since the various Apterygotan groups are 

 intimately bound together by intermediate forms — as is also the case 

 with the Pterygotan groups — the attempt to place the Apterygota in a 

 class, or classes, not included in the class Insecta, is wholly unwar- 

 ranted, and fails to take into consideration the fundamental struc- 

 tural similarities which underlie all groupings based upon relation- 

 ship ! The Apterygota are as much " Insecta " as the Pterygota are, 

 and if the Apterygota are to be split up into several " classes," then 

 the Pterygota also must be split up into several " classes " in order 

 to be consistent. This, however, is neither necessary nor desirable, 

 since the grouping of the class Insecta into two sub-classes, the 

 Apterygota (or Apterygogenea) and Pterygota (or Pterygogenea) 

 is based upon structural similarities, and expresses the actual rela- 

 tionships with sufficient accuracy. 



Prell's division of the Insecta into two subclasses, the Anamercn- 

 toma (Protura) which exhibit a postembryonic increase in the 

 number of abdominal segments, and the Holomerentoma (all other 

 insects), which exhibit no postembryonic increase in the number of 

 abdominal segments, fails to take into consideration the close anato- 

 mical relationship of the Protura to such forms as Tomocerns, etc., 

 which exhibit no such postembryonic increase in the number of 

 abdominal segments; and while Prell's subdivision is very useful from 

 the standpoint of the study of the different types of "metamorphosis," 

 the old subdivisions Apterygota and Pterygota (proposed by Brauer, 

 and modified by Lang) are more useful from the standpoint of the 

 study of relationships. In this connection, it may be further re- 

 marked, that in such Dipterous larvae as Scenopinns, Thereva, Bibio, 



