224 



COMPARATIVE ANATOMY 



CHAP. 



contact with the epithelium of tlie renal sacs. The same is the ca.se with all organs 

 which, like the stomach, the gastric crecum, and tlie 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 l)ody 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-jiericardial apertures. This fact was 



X)<\S 



Fig. 186.— Diagram showing the posterior paired renal sacs of Sepia oflacinalis, and the vein 

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

 Vena cava ; nw, rigl't ueiibridial aperture ; i/j, left reiio-pericarJial aperture, the outline.s of the 

 secondary body cavity are indicated by a dotted line ; vg, vena genitalis ; rrc, riglit brancli of the 

 vena cava ; vpd, right pallia! vein ; I'tt, right vena abdoniinalis ; vha, vein of the ink-bag ; ims, left 

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

 surrounds the brancliial heart ch, and the appendage of the same (pericardial gland) x; vps, left 

 pallial vein; Ivc, left branch of the vena cava cephalica; vm, left vena genitalis; rpc, secondary 

 liody cavity (viscero-pericardial sac) ; ,'/, 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 Dihranchia. 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 

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

 It gains no support from the (Jhitonida:, where, in spite of large numbers of pairs of 

 gills, only two auricles occur, and where no relation e.xists between the number of the 

 shell plates and that of the gills. 



