398 ENTOMOLOGICAL NEWS. [Nov., '17 



A Phylogenetic Study of the Lateral Head, Neck and 



Prothoracic Regions in Some Apterygota 



and Lower Pterygota."^' 



By G. C. Crampton, Ph.D. 



(Plate XXVIL) 



Of the eight groups of lower Pterygotan insects here dis- 

 cussed, the Plecoptera are structurally the most similar to the 

 Lepismids, and have apparently departed much less than the 

 typical Blattids have from the ancestral condition of the Ptery- 

 gota in general. Together with the Ephemerids, the Plecoptera 

 are undoubtedly the lowest living winged insects, and, since the 

 Lepismids (i. e. such forms as Lcpisma, Nicolctia, etc.) form 

 a sort of "connecting link" between the lower Pterygota and 

 the more primitive Apterygotan forms (such as Campodea, 

 Japyx, etc.) it is preferable to begin a study of the groups in 

 question with a comparison of the conditions found in the Le- 

 pismids and Plecoptera. 



In comparing the heads of the Lepismids (Plate XXVII, 

 Fig. i), the Blattids (Fig. 2), and an immature Plecopteron 

 (Fig, 4), it is at once apparent that the Plecopteron is struct- 

 urally much nearer the Lepismids than the typical Blattids are. 

 Thus, in both Lepismids (Fig. i) and Plecoptera (Fig. 4) the 

 head is markedly prognathous (i. e. mouthparts directed for- 

 ward), while in the typical Blattids (Fig. 2) the head is mark- 

 edly opisthognathous (i. e. mouthparts directed backward). I 

 am not sufficiently familiar with the Blattid group to know 

 what extremes of variation are to be found among these in- 

 sects, but, although some Blattids which I have not seen may 

 also have heads of the prognathous type, it is nevertheless true 

 that the condition depicted in Fig. 2 may be taken as typical 

 for the Blattid group in general, in the following discussion. 



The head contour is essentially similar in both Lepismids and 

 the Plecopteron (Figs, i and 4) ; but the outlines of both heads 

 differ very markedly from that of the Blattids (Fig. 2). Fur- 

 thermore, the nature of the labium, and its mode of attach- 



* Contribution from the Entomological Laboratory of the Massa- 

 chusetts Agricultural College, Amherst, Mass. 



