Dec, 1917-] Crampton : Abdominal Segments and Appendages. 225 



A PHYLOGENETIC STUDY OF THE TERMINAL 



ABDOMINAL SEGMENTS AND APPENDAGES IN 



SOME FEMALE APTERYGOTAN AND LOWER' 



PTERYGOTAN INSECTS.^ 



By G. C. Crampton, Ph.D., 



Amherst, Mass. 



In a previous paper (Crampton, ipi?^) the insects here discussed 

 were grouped into three superorders whose principal diagnostic char- 

 acters were there given. Strange to say, the neck and thoracic struc- 

 tures furnish far more definite characters for grouping these insects 

 than the terminal abdominal structures of the female do; so that the 

 following brief discussion is intended mainly to serve as the basis 

 for a subsequent more detailed comparison of these parts in the 

 lower orders, and also as the basis of a further study of the modifica- 

 tions met with in the higher insects, from the standpoint of phylogeny. 

 For the material from which the accompanying rough sketches were 

 made, I am indebted to the kindness of Dr. S. C. Ball, Mr. A. N. 

 Caudell, Prof. R. A. Cooley, Mr. C. C. Gowdey, Dr. A. D. Imms, Mr. 

 J. A. Rehn, and Dr. E. M. Walker. 



Handlirsch (Die Fossilen Insekten) does not include the Aptery- 

 gotan insects in the same class with the Pterygotan forms, but, when 

 one makes a careful comparison of the various anatomical structures 

 in the two groups, the fundamental resemblances point to a very close 

 relationship between the Apterygota and lower Pterygota. Indeed, 

 the differences between the lower Pterygota and the higher Pterygota 

 (aside from the presence of wings) is infinitely greater than between 

 the Lepismoid representatives of the Apterygota, and the lower 

 Pterygotan insects. The striking similarity between the head of a 

 Lepismid and that of a nymphal Plecopteron has already been pointed 

 out,- and the similarity between the terminal abdominal segments of 

 a Lepismid and those of a lower Pterygotan insect is no less funda- 

 mental. Thus the suranal plate labeled "11" in fig. 8, of a lower 



1 Contribution from the Entomological Laboratory of the Massachusetts 

 Agricultural College, Amherst, Mass. 



2 Ent. News, for November, p. 398. 



