VII 



MOLLUSGA—THE BODY CAVITY 



213 



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

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

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



The Cephalopoda may with advantage be considered in connection with the 

 Aiiiphinrura. In Nautilus and the Becapoda {e.g. Sepia, Fig. 177) a spacious 

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

 pletely divided by a projecting dorsal septum into two cavities, one lying above the 

 other ; 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 the upper holds the stomach and the genital glands. This double cavity, 



Fig. 177.— Diagram sliowiag tlie 

 secondary "body cavity of Sepia (after 

 GroblDen). Median longitudinal section 

 ihrough the body, in which, however, some 

 organs are represented which, being paired 

 and -syniinetrieal, 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) ; 4«, anterior 

 venous appendage of the renal system ; 6, 

 aperture (funnel) of the kidney into the 

 ccelom ; 7, outer or pallial 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 ; 14i, 

 posterior venous appendage of the renal 

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

 completely dividing the coelom 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; d, dorsal; v, ventral; a, 

 anterior ; j), posterior. 



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

 covers the organs within 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, 

 whose apertures lie- close to the renal apertures. 



While the coelom in Nautilus and the 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 Nautilus and the Decapoda lie in the ccelom, viz. 

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

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



