PHYLUM MOLLUSCA 



697 



Very characteristic of the group as compared with other Molluscs 

 is the presence of a straight intestine devoid of coils, and 

 having connected with it a single dorsal csecum and usually a 

 double row of lateral caeca. In the Placophora the buccal cavity 



mo 



FIG. 612. Chaetoderma nitidulum , longitudinal section, an. anus ; brn. brain ; ccec. gland- 

 ular cseca of mesenteron ; cten. ctenidium ; dia. diaphragm separating off the posterior 

 portion of the body ; gon, gonad; mo. mouth ; peri, pericardium and heart ; rod. radula ; 

 reel, rectum. (After Simroth.) 



always contains a well-developed odontophore and radula. The 

 intestine is elongated and coiled. There are salivary glands and 

 a large paired liver (Fig. 613, liv.). 



Body-cavity. In the Aplacophora the interstices between the 



organs and the body- 

 wall are filled with a 

 form of connective- 

 . tissue with muscular 

 fibres ; a vertical 

 diaphragm (Fig. 612, 

 dia.) separates the 

 posterior part of the 

 body, containing the 



FIG. 013. Diagrammatic longitudinal section of Chiton, ^ p rf ] : rn (ma r i\ 



specially intended to show the relations of the parts of . ^ 



the calome, which, except the genital parts, are bordered from the rest. In the 



with a thick line. an. amis ; cut. enteric cavity ; ft. foot ; _. n 4.l* a ~1 



gon gonad; M. head-lobes ; Jit. heart; liv. liver; mo. rlaCOphora tnecceiome 



mouth; neph. kidney; peri, periranlial cavity. (From on,- fi -i o\ : an PX fp n _ 

 Simroth, after Hal!.'.-.) 



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