THE INTERNAL ANA TOMY OF INSECTS 163 



from the peristaltic movements of the ahmentary canal. It also 

 supports the heart; and it may play a part in its expansion. 



The dorsal diaphragm is also known as the pericardial diaphragm. 



The ventral diaphragm. — The ventral diaphragm is a very delicate 

 membrane which extends across the abdominal cavity immediately 

 above the ganglia of the central nervous system. It is quite similar 

 in form to the dorsal diaphragm ; it is attached along each side of the 

 body, just laterad of the great ventral muscles, by a series of pro- 

 longations resembling in form the wings of the heart. The position of 

 the ventral diaphragm is illustrated in Figure 182, v. 



This diaphragm has been described as a ventral heart; but I 

 believe that its function is to protect the abdominal ganglia of the 

 central nervous system from the peristaltic movements of the alimen- 

 tary canal. 



The thread-like suspensoria of the viscera. — Under this head may 

 be classed the ligament of the ovary and the ligament of the testis, 

 already described. In addition to these, there is, in some insects at 

 least, a thread-like ligament that is attached to the intestine. 



XVII. SUPPLEMENTARY DEFINITIONS 



There are found in the bodies of insects certain organs not referred 

 to in the foregoing general account of the internal anatomy of insects. 

 These organs, though doubtless very important to the insects in which 

 they occur, are not likely to be studied in an elementary course in 

 entomology and, therefore, a detailed account of them may well be 

 omitted from an introductory text -book. This is especially true as 

 our knowledge of the structure and functions of these organs is so 

 incomplete that an adequate discussion of the conflicting views now 

 held would require more space than can be devoted to it here. The 

 organs in question are the following : 



The cenocytes. — The term oenocytes is applied to certain very large 

 cells, that are found in clusters, often metamerically arranged, and 

 connected with the tracheae and the fat body of insects. The name 

 was suggested by the light yellow color which often characterizes 

 these cells, the color of certain wines; but the name is not a good one, 

 as oenocytes vary greatly in color. Several other names have been 

 applied to them but they are generally known by the name used here. 

 Two types of oenocytes are recognized: first, the larval oenocytes; 

 and second, the imaginal oenocytes. 



