32 



S-MITHSONIAX MISCELLANEOUS COLLECTION: 



\0L. 94 



and a ventral sinus, or perineural cavity (VS). Each of the dia- 

 phragms differs much in the degree of its development in different 

 insects. The dorsal diaphragm is almost always present in some form, 

 but the ventral diaphragm is frequently absent ; the first is confined 

 principally to the abdomen, the second may extend into the thorax. 

 Probably each diaphragm consists of a double peritoneal membrane, 

 the layers of which are reflected from the walls of the body cavity ; but 

 the membranes enclose between them the dorsal and ventral transverse 

 muscles, and the muscles become the more important elements of the 



DTrc 



m^ 



Tra 



'^^^;- 



A 



Fig. 



Ht tra C 



[5. — The dorsal blood vessel and diaphragms of Dissostcira Carolina. 



A, ventral view of anterior part of dorsal diaphragm extending to lobes of third 

 phragma {sPh) , showing segmental groups of transverse muscles (/</), and 

 dorsal blood vessel along median line above the diaphragm. B, posterior part 

 of dorsal diaphragm and dorsal blood vessel in segments /7//, IX, and A'. C, 

 dorsal view of part of ventral diaphragm, attached on lateral parts of sterna. 



diaphragms, which by the vibratory contractions of the muscles serve 

 as important adjuncts to the heart in the circulation of the blood. 



The dorsal diaphragm of Acrididae extends from the anterior end 

 of the first abdominal segment to the posterior part of the ninth seg- 

 ment, and is continued into the metathorax as a narrow membranous 

 fringe along each side of the aorta. In the first abdominal segment the 

 broad anterior margin of the diaphragm is attached to the posterior 

 faces of the lobes of the third phragma (fig. 15 A) ; the lateral edges 

 in this segment are free and deeply emarginate. In the following seg- 

 ments the limits of the dorsal diaphragm are difficult to define in a 

 ventral dissection, except bv the muscle attachments, for the lower 



