ORGANS OF DIGESTION. 3G7 



minal cavity embraced by the expanded base of the muscular 

 foot, which thus separates it from the respiratory or thoracic 

 cavity, like a diaphragm. The convoluted part of the canal 

 is generally either covered by the compacted lobes of the 

 liver, or is disposed between that organ and the ovary. The 

 terminal portion of the intestine or the colon, in the solen 

 strigilatusy traverses not only the ventricle of the heart, as in 

 other conchifera, but also a part both of the anterior and 

 posterior aortee which arise from the ventricle. In the mya 

 pictorum the colon passes through the middle of the anterior 

 aorta into the ventricle of the heart, but immediately escapes 

 through the parietes of that cavity and follows along its ex- 

 terior surface ; it again penetrates the posterior portion of 

 this elongated ventricle, and continues for a short distance 

 through the cavity of the posterior aorta. 



There is a firm cylindrical stiliform body, of crystal- 

 line transparency, enclosed in a coecal prolongation or 

 membranous sheath, which opens into the cavity of the 

 stomach in many of the animals of this class. This 

 stiliform gastric dart has a tricuspid free extremity, is of 

 a cartilaginous consistence, and is composed of several con- 

 centric laminae ; it appears to be analogous to the cartilaginous 

 styles common in the proboscis of the gasteropods, and to be 

 connected with mastication; its sheath runs along the duodenal 

 part of the intestine, and opens into the stomach. It was 

 considered as a masticating organ by Meckel, and as an organ 

 destined to close the biliary passages by Poli, who first 

 described it ; it is seen in the cardium, mactra, donax, tellina, 

 Venus, area, solen, and its sheath has sometimes been mis- 

 taken for a second stomach. The rectal part of the intestine 

 terminates near the vent, above the posterior adductor muscle 

 in the dimyaria, and behind the single adductor muscle of the 

 monomyaria, as seen in the oyster (120. A. d.) 9 and in the 

 spondylus (120. B. e.} The long, striated, ciliated, branchi- 

 form labial tentacula vary in their forms in different species, 

 and their fimbriated or ramified varieties lead to the forms 

 of the prolonged arms of the brachiopodous conchifera. In 

 the spondylus gaideropus (120. B. D. F.) the mouth (B. a. 

 F. a.) is bounded by lobed lips (F. b. b.} the lobes of which 

 terminate in elegant red-coloured fimbriated tufts (F. c. c.) 

 and the lips themselves are continued laterally into the usual 

 upper (F. d. d.) and lower (F. e. e.) pair of labial tentacula 



