I XII 



PHYLUM MOLLUSCA 



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 caecum and usually a 

 double row of lateral caeca, itn the Placophora the buccal cavity 



Ibrn 



cten. 



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 Aplacopnora 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, 



m ^3p!li\ dia.} separates the 



n^p/r~~^~~~^^LL i posterior part of the 



body, containing the 



FIG. 613. Diagrammatic longitudinal section of Chiton, -rkorinarrlinrn (<n0<r<i\ 



specially intended to show the relations of the parts of P ( L \P en )> 



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



with a thick line. an. anus ; ent. enteric cavity ; ft. foot ; ..-., 



gon. gonad ; hd. head-lobes ; M. heart ; liv. liver ; mo. PlaCOphora 



mouth; neph. kidney; peri, pericardial cavity. (From *frjc ^ ClOT~" 

 Simroth, after Haller.) 



peri 



VOL. T 



an exten- 

 Y Y 



