80 OYSTERS, AND ALL ABOUT THEM. 



the same direction, the tongue acts like a rasp, the pro- 

 jecting teeth abrading the surface of the plants, just as the 

 horny papillae of the lion's tongue act on the flesh of the 

 stag, or any other of his victims. The periwinkle, too, 

 has a similar structure. And yet of the oysters race, firmly 

 attached to their rocky homes it may be said : 



" - -In their pearly shells at ease, attend 

 Moist nourishment." 



The mode by which this is obtained may well recall 

 the words of the poet : 



" In human works, though laboured on with pain, 

 A thousand movements scarce one purpose gain ; 

 In God's, one single can its end produce, 

 Yet serves to second, too, some other use." 



The two vascular laminae already described, forming 

 the gill-plate, are really sieves to separate suspended atoms 

 from the surrounding water, on its passage from the 

 inhalant to the exhalant orifice, a structure perfectly 

 adapted not only to a breathing, but a feeding apparatus. 

 The action that takes place is as remarkable as the structure. 

 For the tubes that pass between these living sieves lead 

 directly to the exhalant syphon. Thus, when from this 

 the water flows out, there is a tendency to form a vacuum 

 in the chamber and in all the tubes within the gill laminae ; 

 and by this means, combined with the action of the cilia 

 lining the meshes, the water introduced into the branchial 

 chamber by the inhalant tube is drawn to the meshes, and 

 all the suspended particles of matter are retained on the 

 surface of the gill. 



The water being filtered, as it were, allows the particles 

 to accumulate, and then by the aid of other cilia they are 

 formed into defined streams. This is certainly one of the 

 most beautifully adapted organic mechanisms that can be 



