436 



MOLLUSCA. 



position in the male (Willey). They are innervated by branches 

 of the visceral nerves. 



Vascular system. The heart lies in the viscero-pericardial cavity 

 (except in the Octopoda), and is placed at about the middle of the vis- 

 ceral sac. It consists of a median ventricle and of as many lateral 

 auricles as there are gills (Fig. 351). A large anterior (ventral) 

 aorta passes off from the ventricle, and gives in its course strong 

 branches to the mantle, alimentary canal and funnel, and breaks 

 up in the head into vessels to the cephalic organs. A posteriorly 

 (dorsally) directed visceral artery also leaves the ventricle, supplying 

 the viscera and gonad. The capillary network, which is richly 

 developed in all the organs, passes partly into sinuses, partly into 



veins which are col- 

 lected through lateral 

 veins into a large 

 anterior and a pos- 

 terior vena cava. 

 Each of these bi- 

 furcates into two or 

 four trunks (accord- 

 ing to the number 

 of the gills) which 

 carry the blood 

 through the kidneys 

 to the gills. Im- 

 mediately before 

 their entrance into 

 the gills, the walls 

 of these afferent 

 branchial vessels are 

 (except in Nautilus) 

 especially muscular 

 and rhythmically 

 contractile, and con- 

 stitute the branchial heart*. The glandular appendages of the 

 branchial hearts are the pericardial glands. 



FIG. 351. Circulatory and renal organs of Sepia officinalis 

 from the dorsal (anterior) side (after Hunter), Ao' and Ao" 

 anterior and posterior aorta; Ap appendage of the branchial 

 heart : At, At' auricles ; Br gills ; C ventricle ; Kh branchial 

 heart ; A T renal appendages of the veins ; V lateral vein ; 

 Vbr afferent branchial vessels ; IV, Fc" anterior and 

 posterior vena cava. 



Ill Nautilus the vascular system is largely lacunar, but in Dibranchs capillaries 

 are developed, though these may end in sinuses which open into the veins ; in 

 Octopoda especially there is a large sinus already described, which opens into the 

 anterior vena cava. 



