1909.] 



NATURAL SCIENCES OF PHILADELPHIA. 



23 



previously mentioned shifting forward of the anepimeral region in 

 the Muscidse (fig. 8, EM a ) has displaced the anepisternum (ES a ) in 

 the mesothorax. This phenomenon has led to a great variety of 

 interpretations of these sclerites in the Diptera. Thus Brauer, '82, 

 refers to the anepisternum (fig. 7, ES & ) as the entire episternum, and 

 the katepisternal region (ES^) as the sternum. Lowne, '90, mistakes 

 the anepimeron (fig. 8, EM&) for the entire episternum, and, therefore, 

 terms the anepisternum (ES&) the "lateral plate." Hammond, '81, 

 commits the same error and terms the anepisternum the parapteron. 

 The latter term, however, cannot be used in this connection, as Audouin, 

 '32, made it synonymous with squamula, i.e., the tegula or pterygodum. 

 As first employed by Audouin, '24, the designation parapteron was 

 applied to the anterior margin of the episternum. Audouin himself 

 seems to have had a great deal of trouble in homologizing this region 

 with that of other insects, and finally solved the difficulty by applying 

 the terms hypopteron and parapteron to MacLeay's, '32, squamula — 

 with which they are therefore synonyms, and are so used by most 

 authors. 



On the inner surface of the anepisternum of Chrysopa, Corydalis, 

 and a number of other insects, one can distinguish a lobe-like struc- 

 ture which is apparently formed 

 by the inrolling of the anterior 

 margin of the anepimeron, and 

 serves as an attachment for the 

 muscles extending to the trochan- 

 tin and leg. It is quite easy to 

 follow the modification of this 

 structure in various insects, as it 

 gradually becomes more separated 

 from the anepisternum, assumes 

 a conical form, and is finally 

 connected with the upper portion 

 of the episternum by its apex 

 alone. This plate will be spoken 

 of as the conus. 



The Laterale. — If one compare the mesothorax of a Blattid with that 

 of a Forficulid, it will be seen that the so-called episternum is not the 

 same in both. In order to better understand the relation of the sclerites 

 in these insects a hypothetical type (fig. 20) has been taken as a basis 

 for comparison. In the stage here represented, the epimeron (EM) 

 is indicated as a distinct region, while the remainder of the pleuron 



Fig. S. — Musca. — Lateral view. Head 

 entirely removed; wings, abdomen 

 and legs shortened. A comparison 

 with fig. 7 shows that in the Muscinse 

 there is a shifting forward of the 

 parts, as is indicated by the arrow. 



