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 Keaurnur in the 

 A 



CJ 



5 



FIG. 375. Libellula deprensa, opened 

 from the back, showing the nervous cord 

 (by->> 3 , thoracic, 7t 1 -/i T , abdominal, gan- 

 glia), also the furrow-like ventral sinus 

 closed by a muscular diaphragm. 



FIG. 377. Diagrammatic section of the ab- 

 domen of Aoridium lartarioum, showing 

 the ventral septum (*', p, I) contracted, and 

 (i, k, I) stretched out ; oh, rib-like lateral 

 processes of the urite ; /, ganglia ; ft, heart, 

 with its suspensorium (a) ; o, fat tissue in 

 the pericardial tissue sinus ; d, dorsal sep- 

 tum or diaphragm contracted, q, extended ; 

 g, fat-body ; e, muscular part of diaphragm ; 

 no, expiration, hm, inspiration, muscle. 

 This and Figs. 375, 376, after Graber. 



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

 lula deprexsa more highly magnified : a, a sternal 

 plate (urite) ; c, the septum stretched over it, at s in 

 a relaxed or collapsed state ; b and d, the wing-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 (Acrydiidue). 

 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.) 



