F. CEPHALOPODA. 391 



which has the shape of a ring with wing-like processes. The 

 otocysts lie in the ventral arch of the ring. Two pits opening 

 "behind the eye are regarded as olfactory, while Nautilus has, 

 "besides osphradia, two pairs of ciliated optic tentacles. 



Most noticeable of the circulatory structures is the presence of 

 two kinds of hearts (fig. 390). The systemic heart consists of two 

 (four in Nautilus) auricles receiving the blood from the gills, and 

 a median ventricle from which arise anterior and posterior aortse. 

 Then there is a branchial heart at the base of each ctenidium 

 which receives the blood from the vena cava and pumps it into the 

 gill. Of venae cavse there are an anterior unpaired and two pos- 

 terior paired trunks, the former dividing and sending a branch to 



FIG. 392. Male sexual organs of Sepia offlcinalis. (After Grobben.) ft, coelomic sac 

 passing to the left and above into the pericardium ; c, coalomic canal to the 

 vas deferens ; d, vas deferens ; d', its opening to coelom ; /, portions of coelom ; ?i, 

 Needham's pocket ; n', its mouth ; p', p 2 , prostates ; t, testis ; t ', its opening to 

 coelom. 



each branchial heart. These trunks are of importance in con- 

 nexion with the nephridia. The nephridial openings (p. 386) lead 

 to two spacious sacs through which the veins pass obliquely, this 

 part of the blood vessels being enclosed by diverticula of the 

 lumen, covered with epithelial excretory cells. Near its mouth each 

 nephridial sac communicates by a nephrostome with the usually 

 large coelom (pericardium, gonads, etc.). 



In the Octopoda the coelom is reduced to the gonads and narrow 

 canals leading from the nephrostome to the gonads and branchial 

 hearts, but elsewhere there is a well-developed system of connected cavi- 

 ties (in Nautilus opening by two pores into the mantle cavity), consisting 



