184 



INVERTEBRATE ANIMALS. 



gullet, stomach, intestine, and anus (fig. 129), with the exception 

 of a few forms in which the intestine ends blindly. In some the 



be 



_, 129.— Diagram of the structure of a typical Mollusc (the Common Whelk). / The 

 muscular " foot " ; op Tlie operculum ; t One nf the tentacles, or feelers, with an 

 eye at its base; ji The proboscis, retracted, with the mouth at its extremity; oe 

 Gullet ; g Stomach ; i Intestine, terminating in the anus ; n n Salivary glands ; 

 I The liver and the ovary; h The heart; he The gill, contained in a hood of the 

 mantle ; s Breathing-tube or siphon ; c and c The main nerve ganglia, the one 

 above the gullet being the cerebral ganglia, and the one below the gullet being 

 the combined pedal and parieto-splanchuic ganglia. 



mouth is surrounded by ciliated tentacles {Polyzoa^ fig. 132); in 

 others it is furnished with two long ciliated arms {Brachiopodaj fig. 



Fig. l^O.—Terebraiula vitrea. 1. Showing the ciliated "arms " ; 2. Showing the 

 shell with its loop for the support of the arms. (After Woodward.) 



130) ; in the Bivalves {LameUihranchiata\ it is mostly furnished 

 with four membranous processes or " palpi " (fig. 139, p) ; in others 



