THE OYSTER. 



31 



minute animalcules, most interesting when examined 

 under the microscope. 



The oyster possesses an organ of respiration similar 

 to that of a fish — ^branchiae or gills, in fact {hr), which 

 are fringed by a mantle or beard di-vided into two 

 lobes {m), filled up by small membranous fibres which 

 terminate in the mouth (i), in the form of rays, serving 

 the ianimal also with power to catch and eat.^ Unlike 

 other shelled mussels the oyster has no feet ; thus it 

 is unable to make any other voluntary movement, save 

 that of opening and closing its shell, as already named, 

 in order to receive its food, which consists principally 

 of small microscopical spores and young shoots of 

 marine plants, made soft and thin by the action of the 

 waves ; whence arise the green beards or mantles. AYith 

 some difficulty I have been enabled to separate a small 

 portion of this vegetation from the mantle of an oyster, 

 and having placed it under a strong microscope, dis- 

 covered sea weed, of precisely the same species as that 

 in which oysters are packed.' They also feed on an 

 infusion of sea worms called oyster animalcules. These 

 are veiy accurately described in the '^ Journal des 

 Savans," by M. Auzout. Some are irridescent, but 

 others are not, and good specimens of all may be secured 

 immediately the oyster has been taken from the sea. 



By means of the beard or mantle described {m), the 

 oyster secures his food, bringing it gradually, by means 

 of Kttle hooks bent inwards, to its mouth {b), wherein 

 it is crushed and slowly consumed. 



The stomach {i) is situated near the mouth, and all 

 the organs are very simple. The mantle {m and w') 



