48 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 30. 



of the segment from one pleural suture to the other. This was then 

 divided by sutures into a sternal sclerite, an episternal sclerite, a 

 trochantin, and a large plate lying between the sternum and the 

 episternum, which Crampton calls the "laterale." Finally, this 

 is supposed to have differentiated into an "episternal laterale" ad- 

 joining the episternum (fig. 7, Peps) and into a "sternal laterale" (x) 

 adjoining the sternum. A study of adult insects furnishes plenty of 

 facts for illustrating such a theory, and it certainly looks reasonable, 

 but the writer would not urge it without knowing whether there are 

 any facts of development that would contradict it. Since neither of 

 the plates in question (Pe2:)S and x) occur in the Hymenoptera, 

 however, a decision on their nature or origin is immaterial to the 

 present paper. 



Venter. — The under surface of any segment, of any part, or of the 

 entire body. 



Sternum (S). — The chitinous parts of the venter of any segment, 

 wliich, however, may extend upward in the latera, thereby encroach- 

 ing upon the territory of the pleura. 



The determination of the homologies of the stermites — that is, the 

 sclerites of each sternum — is the most unsatisfactory subject con- 

 nected with a study of the thorax. In the higher orders the sternum 

 very commonly consists of a single ventral sclerite often continu- 

 ously fused with the pleura. But in many of the lower orders there 

 is a multiplicity of sternal sclerites, and it is often a difficult matter 

 to determine corresponding parts in different forms. MacLeay 

 (1830) first surmised that there are four stermites corresponding with 

 the four parts of the tergum, and he named them the "praesternum," 

 "sternum," "sternellum," and "poststernellum." Comstock and 

 Koclii (1902) adopted the same nomenclature. Crampton (1909), 

 however, has made a more carefid study of the sternal anatomy, and, 

 while he discovers four transverse parts, he names them the "prsester- 

 num," " basis ternum," "furcisternum," and "spinisternum," because, 

 as he says, only the first coincides with, the divisions recognized under 

 the earlier set of names. Crampton's system eliminates the incon- 

 venience of calling both the entire ventral chitinization and its 

 principal subdivision the "sternum." The writer, however, would 

 prefer to substitute the word eusternum for the second subdivision 

 (as given in the table, page 42) so as to retain the original names 

 even though with an altered significance as to the limits of the 

 sclerites to wliich they are applied. 



Each thoracic sternum almost invariably has a forked apodeme 

 projecting upward from its inner surface. This is commonly known 

 as the furca or "entosternum." The furca, according to Crampton, is 

 carried by the tliird sternite, the "frucis ternum" of his nomenclature. 



