81 



the digestive gland, lying immediately under the 

 epithelium, passes ventrally and slightly forwards to the 

 anterior end of the renal organ, where it enters the dorsal 

 sinus. Branches join it from the digestive gland and 

 stomach. 



A sinus-like plexus of vessels between the muscle and 

 the visceral mass passes blood from the gonads and 

 intestine to the sinuses communicating with the renal 

 organs. The blood from the adductor passes along ill- 

 defined paths in that muscle to enter these sinuses, thus 

 completing the circuit. 



The greater part of the blood from the visceral mass 

 and alimentary canal passes by very conspicuous veins on 

 the surface of the gonads (fig. 18, F. v.) to the sides of the 

 renal organ, where they communicate with the numerous 

 small vessels of the latter. 



Thus all the blood is brought to the renal organs, with 

 the exception of that which proceeds by the pallial arteries 

 to the mantle. This will be considered later. 



The blood returning to the heart leaves the renal 

 organ by a series of fine vessels in the outer wall which 

 open into a wide passage, the entrance to the afferent 

 branchial vessel (fig. 16, Bi\ aff.]. This soon contracts in 

 size, and the vessel runs along the ctenidial axis proximal 

 to the accompanying efferent vessel. It communicates 

 with a vessel or cavity on each of the respiratory 

 expansions of the principal filaments, but no connections 

 with any of the other gill filaments can be seen. 



The blood is brought from the gills, after aeration, 

 to the heart, by means of the efferent branchial vessels, 

 which, cohiing from the ctenidial axes, ]wss between the 

 digestive gland and the adductor, and open into the 

 narrow ends of the auricles, after receiving, at about the 

 level of the dorsal extremity of the glandular part of the 



