434 



MOLLUSCA. 



In Nautilus the dorsal salivary glands are not present and the liver is less 

 compact and in four lobes, each with its own bile duct. 



The ink sac (Tb), which is absent in Nautilus and Cirroteuthis, 

 is a rectal gland. It is placed on the posterior side of the visceral 

 sac close to the mantle-lining, and opens into the rectum. 



The perivisceral cavity is, as in Gastropods, partly coelomic and 

 partly haemocoelic, but the coelomic portion has a much greater 

 extension than in other Molluscs. 



The haemocoelic part of the body-cavity is best developed in 



Nautilus, where it forms a 

 cavity, in relation with the 

 crop, vena cava and one loop 

 of the intestine ; it occupies 

 the anterior side of the vis- 

 ceral sac, and does not extend 

 to the apex (which is occu- 

 pied by genital coelom). It 

 is traversed by connective- 

 tissue strands, and commu- 

 nicates with the vena cava 

 by numerous foramina in the 

 wall of the latter. In Di- 

 branchs the haemocoele is 

 less developed; in Octopods 

 it has the form of a large 

 sinus surrounding the oeso- 

 phagus, dorsal salivary 

 glands, bile ducts, and ante- 

 rior aorta ; and communicates 

 with the great vena cava. 

 Also the cavity round the 

 buccal mass is a blood space. 



The perivisceral part of the coelom is divided into two parts, which 

 however communicate the so-called viscero-pericardial sac, corre- 

 sponding to the pericardium of other types, and the genital portion. 

 In Nautilus the viscero-pericardial cavity is in relation with the heart 

 and pericardial gland, while the genital portion contains the gonad 

 and has relations with the stomach and intestine. Both open to the 

 exterior, the pericardium by two openings placed respectively just 

 internally to the openings of the posterior nephridia (Fig. 348, Ji), 

 while the genital opens by the single genital duct into the posterior 



FIG. 349. Diagram of the renal and circulatory 

 apparatus of a Decapod, ventral view (after 

 Pelseneer). I ctenidium; II renal sac; III 

 afferent branchial vessel; IV branchial heart; 

 V abdominal vein ; VI ventricle ; VII coelom ; 

 VIII genital gland projecting into the genital 

 part of the coelom, which in front is in relation 

 with the heart as the viscero-pericardial coelom, 

 and opens into the renal sac at XVII; IX 

 posterior aorta ; X auricle ; XI appendage of 

 branchial heart (pericardial gland) ; XII glan- 

 dular tissue of the kidney ; XIII external opening 

 of kidney ; ^7 V vena cava ; XV anterior aorta ; 

 XVI branch of vena cava ; XVII reno-pericardial 

 opening. 



