CONTRIBUTIONS TO THE ANATOMV OF THE HIRUDINEA. 461 



Whitman, following in the steps of Leydig, separates (1) a 

 closed vascular system from (2) a lacunar system (sinuses, 



A. G. B.) 



Ventral Sinus. — This runs the whole length of the body, 

 and contains the nerve-cords, ventral vessel, ovaries, and nephri- 

 dial funnels (woodcut, fig. 3, v.s. ; fig. 64, v.s.). 



Dorsal Sinus. — This runs along the whole length of the 

 body as a special channel, communicating at either extremity 

 with the ventral and the lateral sinuses (woodcut, fig. 3, d.s., 

 and fig. 64, d.s.). 



The great median sinus described by Leydig, containing the 

 dorsal and ventral vessels and alimentary canal, does not exist 

 in Clepsine, nor in any leech throughout the length of the body, 

 but the network of sinuses in this region presents so much 

 blood space and so little parenchymatous tissue that it cannot 

 be a matter of surprise that, basing his observations upon dissec- 

 tions and views of the whole animal as a transparent object, 

 even such an astute observer as Leydig has been misled (see 

 fig. 10, coel, fig. 64, coel). 



Lateral Sinuses (marginal sinus, Whitman). — These run 

 longitudinally along the whole length of the body and commu- 

 nicate very freely with one another and with the dorsal and 

 ventral sinuses at the posterior and anterior extremities (fig. 

 64, and woodcut, fig. 3, Ls.) 



I have been unable to determine the exact arrangement of 

 the sinuses which connect these main trunks, owing to their very 

 extensive nature — owing, in other words, to the slight extent 

 to which the coelom has become split up or has undergone 

 diacoelosis. 



Dorsal Vessel. — This lies in the dorsal sinus (woodcut, 

 fig. 8, and fig. 64 d. v.). Its structure and the arrangement of 

 its branches have been most minutely described by Budge. It 

 presents in the median region a series of fifteen dilatations with 

 specially developed muscular walls, each provided at its posterior 

 extremity with a valve which was correctly described by Leydig 

 as a group of cells. At its anterior extremity the dorsal vessel 

 bifurcates, the branches pass forwards and toward the ventral 



