NO. II LEGS OF PRIMITIVE ARTHROPODS EWING 37 



9. The so-called intersegmental region of certain thysanurans 

 shovild not be regarded either as a distinct segment or as an interseg- 

 mental structure but each region as an integral part of the segment 

 bearing the adjoining posterior sternite. 



10. The primitive thoracic tergal plates are simple structures with- 

 out condyles or apodemes and did not completely cover the dorsal 

 surface of the segments on which they were situated. 



1 1 . The primitive thoracic sterna of an insect were probably trans- 

 versely divided into two sternal plates, the posterior of which articu- 

 lated laterally with the inner condyles of the coxae. 



12. In general, all vestiges of pleural plates are wanting in those 

 arthropods which have a cylindrical and functional subcoxa. As the 

 subcoxa becomes reduced and its inner (ventral) walls obliterated, 

 two outer crescentic plates persist as body sclerites. They appear to 

 have resulted from the development of a pseudosegmentation of the 

 subcoxa. The distal one of these two sclerites becomes the trochantin 

 of generalized insects and the proximal one the eupleuron, or 

 " mother " pleural plate from which certain others were later derived 

 by " fragmentation." 



13. The subcoxal theory of the origin of the pleural plates of in- 

 sects is sound, and receives further support because of this investi- 

 gation. 



REFERENCES TO LITERATURE 



Barrows, W. M. 



1925. Modification and Development of the Arachnid Palpal Claw, with 



Especial Reference to Spiders. Ann. Ent. Soc. Amer., Vol. xviii, 

 pp. 483-516, pis. xxxv-xliii. 

 Berlese, a. 



1910. Monografia d. Myrientomata. Redia, Vol. vi, Ease, i, pp. 1-182, 

 pis. i-xvii. 

 Bernard, H. M. 



i8g6. The Comparative Morphology of the Galeodidae. Trans. Linn. Soc. 

 Lend., 2d Ser., Vol. vi, Pt. 4, pp. 305-417, pis. xxvii-xxxiv. 

 BORNER, C. 



1903. Kritische Bemerkungen iiber einige vergleichend-morphologische 

 Untersuchungen K. W. Verhoefif's. Zool. Anz., Bd. xxvi, pp. 290- 

 315, figs. I-II. 

 1921. Die Gliedmassen der Arthropoden. Lang's Handb. Morph. d. wir- 

 bellosen Tiere, Bd. 4, Arthropoda, pp. 649-694. figs. 1-57. 



BORRADAILE, L. A. 



1926. Notes upon Crustacean Limbs. Ann. & Mag. Nat. Hist., Ser. 9, 



Vol. xvii, pp. 193-213, pis. vii-x. 

 Carpenter, G. H. 



1916. The Apterygota of the Seychelles. Proc. Roy. Irish Acad., Vol. 

 xxxiii. Sect. B, No. i, pp. 1-70, pis. i-xviii. 



