24 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8S 



Heymons' ( 1895) assertion that the eleventh segment of the embryo 

 in GyyUotalpa and other Orthoptera is lost during development, regard 

 the supra-anal plate of pterygote insects as belonging to the twelfth 

 segment. On the other hand, Wheeler's (1893) observations on the 

 development of Xiphidiuin are fully convincing that the cercus-bear- 

 ing eleventh segment persists in the Orthoptera, and, though it be- 

 comes reduced, forms the terminal parts of the adult abdomen asso- 

 ciated with the cerci. Wheeler's idea that the rudimentary appendages 

 of the tenth segment become the inner valvulae of the ovipositor in 

 the female does not conform with the evident facts of comparative 

 anatomy, but this detail of interpretation does not afifect his exposition 

 of the segmentation. 



When we compare the usual circumanal structures of pterygote in- 

 sects with the ]mrts of the eleventh segment in the Odonata (fig. 12 A, 



An A 



-XApd 

 Cer 



Fig. g. — Posterior segments and appendage rudiments of embryos of Xiphi- 

 (iium. (Outlines from drawings by Wheeler, 1893. showing segmentation and 

 appendages, but with other details omitted.) 



A, male embryo. B, female embryo, each with cereal appendages (Ccr) on 

 eleventh segment. C, female embryo in later stage, showing retention of eleventh 

 segment structures (XI). 



Eppt, Ccr, Papt), in which Heymons himself has shown that the 

 twelfth segment (Prpt) is present though rudimentary, we can 

 scarcely question the identity of the parts in all cases. In other words, 

 the epiproct, the cerci, and the paraprocts, which in larval Odonata 

 clearly belong to the eleventh segment, must be eleventh segment 

 structures in all Pterygota, as they are in Thysanura. Heymons' 

 (1904) claim that the appendages of the eleventh segment in the 

 Odonata are not trvie cerci, and that the latter are represented in the 

 apparent paraprocts finds no support in comparative anatomy, and 

 has been generally rejected on the ground that it would set the Odonata 

 apart from all other insects. 



The writer would, therefore, agree with Crami)ton ( 1918) that the 

 epiproct is in all insects the tergum of the ele\'enth segment ( lig. 6, 



