r. CEPHALOPODA. 



391 



wliich has the shajie of a ring with wing-Hke prf)fesses. The 

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

 behind the eye are regarded as olfactory, while Xantilus has, 

 besides osphradia, two pairs of ciliated optic tentacles. 



Most noticeable of the circulatory structures is the presence of 

 two kinds of hearts (fig. 300). The systemic heart consists of two 

 (four in Na/tdilus) auricles receiving the blood from the gills, and 

 a median ventricle from which arise anterior and posterior aortas. 

 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 vense cavje there are an anterior unpaired and two pos- 

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



Fig. 393.— Male sexual oreans of ^epia nfflvinalis. (After Grobben.) ft, ooelomio sac 

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

 vas deferens ; (/, vas deferens ; it\ its opening to ccelom ; /, portions of ctelom ; ii, 

 Needham's pocket; ti', its mouth; p', p'\ prostates; (, testis; I', its opening to 

 coelom. 



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

 nexion with the nephridia. The nephridial openings (p. 3<Sij) lead 

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

 jiart of the blood vesscils Ijeing enclosed by diverticula of the 

 lumen, covered with ei^itliclial excretory cells. Near its mouth each 

 neijhridial sac communicates by a nephrostome with the usitally 

 large coelom (pericardium, gonads, etc.). 



In the Octopoda llie cwlom 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 cavityj, consisting 



