390 



MOLLUSCA. 



S> on 



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- 

 niic, 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 

 aorta, and of two 

 symmetrical auricles, 

 each of Avhich has 

 two openings into 

 the ventricle (in 

 Chiton magnificus 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. Beitiiige zur Kenntniss der Placophoren, Morpli. Jahrb. 21. 



pc 



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

 heart of Chiton discrepans (modified after Sedgwick). n 

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

 generative duct into the mantle-groove ; gon generative 

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

 HI mouth ; man mantle-fold ; JH: wall of pericardium ; p.o 

 opening of kidney into the pericardium ; r.n 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. 



