304 ANIMAL SKETCHES. CHAP. 



beneath a sort of hood under the hinge. It lies in the 

 vestibule, a cavity which extends for some distance above 

 the body. The mouth leads into a coiled alimentary canal 

 which terminates just above the hinder end of the sickle- 

 shaped gills in another large chamber. 



I am beginning to despair of the oyster's remaining so 

 long uneaten. But if it be still unswal lowed, the self- 

 denying observer will have no difficulty in recognizing the 

 curved gills with their delicate radiating striations, will 

 readily find the vestibule and mouth at their upper ends, 

 and may pass his toothpick into the large posterior chamber 

 which runs along the whole length of their inner edges, 

 communicating with the tubes of their somewhat spongy 

 substance, and opening widely beneath and behind the 

 body. (See figure.) 



We have seen that on the sides of the gills and around 

 the microscopic slits by which they are pierced, there are 

 myriads of delicate, translucent hairs continually lashing 

 the water. Upon the activity of these hairs the oyster 

 depends for food, for oxygen, for very life. At first sight 

 the oyster would seem to be in bad case. It is fixed and 

 sedentary all its adult life. Its ancestors had indeed, like 

 most bivalve mollusks that now exist, a fleshy foot project- 

 ing between the inner gill-plates, by means of which 

 they could perform some sort of sluggish motion. But 

 through lazy and sedentary habits the oyster tribe has lost, 

 or well-nigh lost, this foot ; the oyster has literally one 

 foot, and that its only one, in the grave. This, however, 

 is no very great disadvantage, for though the cockle is able 

 to hop with some effect, the monopedal progression of 

 mollusks would give them but a lame chance of a liveli- 

 hood had they no other means of capturing their prey. 

 The food of the oyster consists of such microscopic organ- 

 isms and organic particles as float freely in the water. By 



