224 



COMPARATIVE ANATOMY 



CHAP. 



contact with the epithelium of the renal sacs. The same is the case with all organs 

 which, like the stomach, the gastric ccecum, and the efferent ducts of the digestive 

 glands in the Decapoda (Sepia), apparently lie inside the spacious renal sacs. These 

 organs really lie outside of them, being only suspended into them, like the intestine 

 of an Annelid, which apparently lies within the body cavity, but is entirely separated 

 from it by the peritoneal endothelium. 



It has been already mentioned that only one of the two pairs of renal sacs of 

 Nautilus, viz. the upper pair, has reno-pericardial apertures. This fact was 



arvo 



FIG. 186. Diagram showing the posterior paired renal sacs of Sepia officinalis, and the vein 

 running along its anterior wall with its venous appendages, from behind (after Vigelius). vc, 

 Vena cava ; r.o, right nephridial aperture ; i/j, left reno-pericardial aperture, the outlines of the 

 secondary body cavity are indicated by a dotted line ; nj, vena genitalis ; rvc, right branch of the 

 vena cava ; fpil, right pallial vein ; m, right vena abdominalis ; rim, ruin nf the ink-bag ; vns, left 

 vena abdominalis ; cv, section of the secondary body cavity (capsule of the branchial heart), which 

 surrounds the branchial heart cl>, and the appendage of the same (pericardial gland) x; vps, left 

 pallial vein; Ire, left branch of the vena cava cephalica ; rm, left vena genitalis; rpr, secondary 

 body cavity (viscero-pericardial sac) ; y, left reno-pericardial aperture (renal funnel) (</. Fig. 174). 



brought forward in support of the view that the two pairs of renal sacs arose by 

 the division of one single pair, corresponding with that of the Dibranchia. Accord- 

 ing to this view, the lower pair of gills, and the two auricles are also to be considered 

 to be new acquisitions. Indeed, the whole question of the original metamerism of the 

 Molluscan body, which has so often been asserted, rests on very weak foundations. 

 It gains no support from the Chitonidc?, where, in spite of large numbers of pairs of 

 gills, only two auricles occur, and where no relation exists between the number of the 

 shell plates and that of the gills. 



