22 



PROCEEDINGS OP THE ACADEMY OF 



[Jan., 



This sclerite is of a variable nature, being entirely coxal in some insects, 

 while in others it is entirely pleural. The origin and nature of this 

 sclerite will be more fully described in the discussion of the sclerites 

 of the leg. 



The Episternum. — While the division into ana- and kata-epimeron is 

 shown in but few hexapods, a subdivision of the episternum into an 

 upper and lower region is evident in a great number of insects. Among 

 these may be mentioned Sialis, Hepialus, Corydalis, Phassus, Bittacus, 

 Cicada, Tipula, Mantispa, Hemerobius, Raphidia, Chrysopa, Myrmeleon, 

 the Nemoptera, Trichoptera, and a large number of other insects from 

 different families. Beyond a doubt, if enough material could be ex- 

 amined, it would be found that indications of this division occur in 

 some genera of every family. 





Fig. 6. Fig. 7. 



Fig. 6. — Phassus. — Lateral view of right flank. Head completely removed; 



wings, abdomen and two posterior legs shortened. 

 Fig. 7. — Tipula. — Lateral view. Head entirely removed. Wings, abdomen 



and legs shortened. 



The epimeral subdivisions are best shown in Mantispa, but Chrysopa 

 serves the purpose almost as well, and is a much commoner insect. 

 In Chrysopa, the upper region of the episternum — which will be termed 

 the anepisternum (fig. 3, ES a ), is separated from the lower or "katepi- 

 sternum" (ES^), by a narrow strip which may be spoken of as the 

 median region of the episternum (ES m ). In the thorax of Chrysopa 

 this strip is very narrow, but in the thorax of Myrmeleon it is quite 

 broad (fig. 4, ES m ). In the metathorax of the Forficulidse, the upper 

 portion of the anepisternal region is frequently cut off by a white, 

 scar-like softening of the chitin of the episternum. Verhoeff, '03, 

 terms this piece the pteropleure. 6 



While the anepisternum in most insects is in its normal position, the 



•The musculature of the anepisternum clearly shows that it is not to be 

 homologized with the "pteropleure" alone. 



