1909.] NATURAL SCIENCES OF PHILADELPHIA. 19 



This terminology, based upon that of Redtenbacher, '86, is the one 

 usually accepted by modern systematists, and has consequently been 

 here adopted. 



The Pleuron. — The two principal sclerites of the pleuron are the 

 episternum and epimeron of Audouin, '24. The later terms, ante- 

 pleuron (episternum) and postpleuron (epimeron) of Amans, '85, or 

 the coxopleure (episternum) and anopleure (epimeron) of Verhoeff, '03, 

 since they are applied to exactly the same sclerites, must be regarded 

 as superfluous synonyms. The pleurit and subcoxa of Heymons, '99, 

 will be later discussed under the heading Hemiptera. However, it 

 may be remarked of these sclerites — which have given rise to a great 

 deal of discussion — that the pleurit is merely the epimeron, while the 

 greater part of the subcoxa corresponds to the episternum. 



The pleurites of the Blattidae are interesting from the fact that the 

 epimeron and episternum appear to be merely portions of a single 

 plate separated into two regions by a deep pocket-like infolding of the 

 integument. This suggests that the episternum and epimeron may 

 originally have been one piece, but became separated by such an in- 

 folding of the integument — possibly due to muscular tension. In this 

 way there would be formed an external furrow, the so-called pleural 

 suture, and a corresponding hollow ridge, the entopleuron or apodeme. 

 This would account for the fact that the apodemes of insects are hollow 

 processes, and it is conceivable that the apodemes would thus arise as 

 hollow invaginations of the body wall of the embryo, even though 

 the muscular tension which originally developed the apodemes were 

 not strongly operative at this stage. 



There is a greal lack of uniformity in the usage of the terms apodeme 

 and apophysis in referring to the internal or " entothoracic " processes. 

 As here used, the expression apodeme is applied solely to internal 

 processes of the pleuron (i.e., the "entopleura"); while the term 

 apophysis refers only to the internal processes of the sternum — the 

 "entosterna." 



The entopleuron may bear four inward projecting processes as fol- 

 lows: above, a pivot, or articulating process for the wing, which may 

 be termed the alar process of the apodeme; and below this a process 

 serving for muscle attachment (in such insects as Panorpa, etc.), which 

 may be termed the intermedian process. The third is usually quite' 

 a large process. It may or may not extend as far as the furca (or 

 forked apophysis of the sternum), but frequently abuts against the end 

 of the furcal arm, and may even fuse with it. This process will be- 

 referred to as the adfurcal process. The process just below it, which. 



