MOLLUSGA—THE BODY CAVITY 



213 



(2) the genital gland. Certain bands, by means of whieli the three divisions are 

 connected together, have been regarded as the constricted remains of communications 

 between the three divisions of the originally single ccelom (Fig. 176). 



Tlie Cephalopoda may witli advantage be considered in connection with tlie 

 Amphincura. In Nautilus and the Decapoda {e.g. Sepia, Fig. 177) a spacious 

 secondary body cavity is found in the dorsal part of the visceral dome. It is incom- 

 jiletely divided by a jjrojecting dorsal septum into two cavities, one lying above the 

 otlier ; the lower of these contains, as pericardium, the heart with the arteries and 

 veins running out of and into it, the branchial hearts, and the pericardial glands ; 

 while tlie upper holds the stomach and the genital glands. This double cavity, 



Fi<;. IT v.— Diagram showing the 

 secondary body cavity of Sepia (after 

 Grobben). Median longitudinal st'ction 

 ihrongh the body, in which, however, some 

 organs are represented which, being paired 

 and symmetrical, do not properly come 

 into the plane of the section. The outlines 

 of the ccelom are indicated by thicker lines. 

 1, Female germinal body, with eggs (2) pro- 

 jecting into the genital cavity (the ovarial 

 division of the ccelom); 3, shell; 4&, an- 

 terior portion of the renal sac ; 5, pancreatic 

 appendage of the efferent duct (bile duct) 

 of the digestive gland (liver) ; in, anterior 

 venous appendage of the renal system ; 0, 

 aperture (funnel) of the kidney into the 

 cnelom ; 7, outer or jiallial aperture of the 

 kidney ; 8, digestive gland (liver) ; 9, 

 "head" (Kopffuss); 10, funnel; 11, end of 

 the oviduct with female genital aperture ; 

 12, mantle cavity ; 13, mantle ; 14, posterior 

 portion of the renal sac ; 15, intestine; 14], 

 posterior venous appendage of the renal 

 system (pericardial gland); IS, fold, in- 

 completely dividing the ccelom into an 

 upper and a lower portion ; 19, stomach ; 

 20, upper division of the ccelom (principally 

 genital cavity); 21, pigment gland (ink- 

 bag); 22, aperture of the oviduct into the 

 genital cavity; rf, dorsal; c, ventral; n, 

 anterior ; p, posterior. 



which is called the viscero-pericardial cavity, is covered by endothelium, which also 

 covers the organs Avithin it. It is connected by two ciliated funnels with the two 

 renal sacs. In Nautilus it also opens direct into the mantle cavity by two canals, 

 wliose apertures lie close to the renal apertures. 



While the crelom in Nautilus and tlie Decapoda is very spacious, in the Odopoda, 

 on the contrary, it is very much reduced. It consists merely of a narrow system of 

 canals, which, however, have thick walls ; this was formerly called the water vascular 

 system. The organs, which in Nautihis and the Decapoda lie in tlie crelom, viz. 

 tlie arterial heart with its afferent and efferent vessels, the branchial hearts and the 

 stomach, are no longer^found within tlie body cavity, but outside of it, and are 



