THE PULSATING VENTRAL SINUS 



403 



The supra-spinal vessel. - - In many insects there is a ventral heart 

 acting on the heart's blood as an aspirator, or more correctly a 



ventral sinus lying on the nervous cord, 

 and closed by a pulsating diaphragm. 

 This was discovered by Reaumur in the 



B f 



FIG. 375. Lihelluln depresita, opened 



from the back, showing the nervous cord 

 (''i-''3, thoracic. /'i-/' 7 . abdominal, tran- 

 <rlia). also the furrow-like ventral sinus 

 closed by a muscular diaphragm. 



FIG. 377. Diagrammatic section of the ab- 

 domen of AI'I ill i n 111 tu rtn rii'iini, showing 

 the ventral septum (/. ji. /) contracted, ami 

 (i, k, h stretched out; ok., rib-like lateral 

 proee*se> ,it' the urite ; ./", panplia ; />, heart, 

 with its suspeiisoriimi an: <. tilt tissue in 

 the pericardia! tissue sinus: d, dorsal sep- 

 tum or diaphrairm contracted, if, extended ; 

 (t, fat-body ; t. muscular part of diaphragm ; 

 >ni. expiration, hrn, inspiration, muscle. 

 This and Figs. 375, 376, after Graber. 



b 



FIG. 376. A, part of the ventral furrow of LHnl- 

 ?ti!<i dtpreiwa more highly inairiiihYd : <i. a sternal 

 plate (urite}; c, the septum stretched over it, at . * in 

 a relaxed or collapsed state ; li and //. tin- winjr-like, 

 sternal processes from which the muscular bundles of 

 the diaphragm arise. B, same in Acridium. 



larva of a fly, and by Graber in the 

 dragon-fly and locusts (Acrydiidie). 

 A glance at Figs. 375 and 376 will 

 save a long description. The ventral 

 wall forms a furrow, and between its 

 borders (Fig. 377, e) extends the dia- 

 phragm. During the contraction of 

 the muscles and this, here, acts 

 from before backwards the mem- 

 brane rises up and makes a cavity 

 for the blood, which passes back- 

 wards over the nervous cord. The 

 dorsal and ventral sinuses together 

 thus bring about a closed circulation. 

 It thus appears that the insects are 

 well provided with the means of 

 distribution of their nutritive fluid, 

 and that the blood is kept continu- 

 ally fresh and rich in oxygen. 

 (Graber.) 



