36 



BRANCH MOLLUSCA. 



by the left valve, and thus remains anchored for life. 

 An opening in the mantle allows water to enter and 



Fm. 50. 



Os tree' a vir gin i fi'na. Partly diagrammatic view of the soft parts of an Oyster as they lie in 

 their original situation, upon the left valve. 0, Situation of mouth, on each side of which 

 are the Palps, P. G, Gills. Jf, Mantle. A. Adductor muscle. H. Heart C, Cut edge of 

 mantle of upper, right, side. L, Region of hinge of left valve. The arrows indicate the 

 course taken by the water as it enters the mantle cavity. 



bathe the gills, passing around the so-called "stomach," 

 which is a mass of liver and eggs, in which the intestine 



is coiled.* The Scallops (skoi'lups) 

 are closely allied, though, instead of 

 being sedentary, they are capable of 

 progressing by rapidly opening and 

 closing their valves. The edges of 

 the mantle are in these animals beau- 

 tifully fringed, and are ornamented 

 with rows of eye-spots. The strong 

 muscle, which closes the shell, is the 

 only portion used as food. 



Pec' ten ir r<T eft arts. 

 Scallop-shell. 



* The hard part, always cut in opening the shell, is the adductor muscle whose 

 office is to shut the valves. These open naturally about one half of an inch. 

 The mantles on the two sides of the shell meet at the aperture. Their edges are 

 fringed with cilia the English call them the oyster's "beard which can be pro- 

 truded from the shell and conduct the current which brings inside animalcules 

 and the spores of algae for food. The lime for building the shell is secreted by 

 the mantle. The heart, shaped like an old-fashioned purse, has an auricle and 

 ventricle, and circulates a limpid colorless blood. If the shell be opened with 



