390 



MOLLUSCA. 



.yon 



stomach is large and surrounded by the large liver, the ducts of 

 which it receives. The intestine is long and coiled. 



Body-cavity. There is a well-marked perivisceral-cavity in rela- 

 tion with the alimentary canal. Its nature is not certain, for its 



development is not 

 known, and it is not 

 connected with the 

 pericardium. Provi- 

 sionally it may be re- 

 garded as haemocoele. 

 ^ Coelom. The peri- 

 cardial cavity placed 

 at the hind end on 

 the dorsal surface is 

 undoubtedly coelo- 

 mic, for although it 

 has no connection 

 with the gonad, it 

 opens into the 

 nephridia. 



The heart (Fig. 

 308) consists of a 

 median ventricle 

 giving off an anterior 

 -f> c aorta, and of two 



symmetrical auricles, 

 each of which has 

 two openings into 

 the ventricle (in 

 Chiton maynificus it 

 has recently been 

 stated that there are 

 four openings on each 

 side*). The blood 

 flows to the auricles 

 from the gills. 



Excretory organs. There are two kidneys (Fig. 308), each con- 

 sisting of bent tubes of the typical Molluscan type with glandular 

 diverticula. They open into the pericardium on each side, and to the 

 exterior in the mantle-groove between two of the posterior ctenidia. 



* B. Haller. Beitrage zur Kenntniss der Placophoren, MorpJi. Jahrb. 21. 



FIG. 308. Dorsal view of the kidneys, generative organs, and 

 heart of Chiton discrepans (modified after Sedgwick). a 

 anus ; ct ctenidia ; g.d generative duct ; g.o opening of 

 generative duct into the mantle-groove ; gon generative 

 organ ; h head ; k kidney with its glandular diverticula ; 

 m mouth ; man mantle-fold ; pc wall of pericardium ; p.o 

 opening of kidney into the pericardium; r.o external 

 opening of kidney into the mantle-groove ; v ventricle of 

 heart, the auricles are cut away, but their openings into 

 the ventricle are shown. 



