12 HISTORY OF THE OYSTER. 



CHAPTER III. 



NATUEAL HISTOEY AND ANATOIHY OF 

 THE OYSTEE. 



The Oyster belongs to that division of MoUusca called 

 Concliifera, or bivalve shells, having .two separate 

 shells joined together by a ligament, and forming a 

 hinge. When the shells are shut, they enclose the 

 animal. The shells are made to shut by means of a 

 very strong adductor muscle (PL I. a), attached to 

 both upper and lower valve by the elasticity of the 

 hinge-ligament (PI. V. fig. 2). Thus, if the adductor 

 be divided by a thin knife introduced between the 

 valves, they immediately open. Oysters are acepha- 

 lous, or without any distinct head, although they 

 have a mouth (PI. II. b) ; but are completely deprived 

 of eyes. In their adult state they are devoid of all 

 locomotion, being found, wdien undisturbed from their 

 nativity, always attached to other shells, rocks, or 

 other hard substances. It is not, like the Cockle and 

 many other Conchifera, furnished w^ith a foot (PI. III. 

 fig. 2, a), wdiich enables the latter to travel slowly 

 on a soft bottom ; neither has it those curious ap- 



