9 



eacli i'lirruw there are minute openings, the water pores, which 

 open into the water tubes, thus forming a communication be- 

 twt i.'U the two divisions of the mantle chamber. 



Each rod, or filament, contains a minute blood vessel which 

 runs its entire length, and in these vessels tlie blood is purified 

 by the water which liils the gills and the chamber in which 

 they hang. 



If a filament of one of the gills is examined with a micro- 

 siope, it will be found to be covered with minute hairs, or cilia, 

 arranged in rows (Place III, Fig. 3, c). Each of these cilia is 

 constantly swinging back and forth with a motion mueli like that 

 of an oar in rowing; but as the cilia are fastened to the gill, 

 which is immovable, they do not move forward through the 

 water, but produce a current in the opposite direction. The 

 united action of the cilia on the gills produces quite a vigorous 

 stream of water, which is drawn in through the open ends of 

 the shell, then forced through the water pores into the water 

 tubes, and from these passed to the cloaeal chamber and so 

 out of the shell again. 



The food of the oyster consists almost entirely of micro- 

 scopic plants, which are more or less motile. These are drawn 

 into the gill chamber with the water; but as the water is forced 

 through th«' pores into the water tubes, the food organisms are 

 caught on the surface of the gills by an adh?sive slime that 

 covers the entire surface of the gills. The cilia striking against 

 the entangled food organisms push and roll them along toward 

 the mouth until they reach the end of the gills where they fall 

 between the palps. The palps are also -ciliated and carry tha 

 food forward until it falls into the mouth, which is always 

 open, and is ciliated so that the food is forced through thv3 

 oesophagus into the stomach. This process is going on when- 

 ever the shells are open, and the oyster is breathing, so that the 

 supply of food is practically continuous so long as the oyster 

 i' undisturbed. 



Tn order to trnco the eourso of the di<_'osliv«' cnvify. ih.^ 

 body of an oyster jnay be si)lit wilh a sharp Unif'r (.r razor. 

 Tf the cut is in the middle of the body, eaeli linlf will sliow 

 sections of the short oesophacrus. runnino- ;ip fi-opi the mouth. 

 and the irr<"'iil;ir stomach v.-fth thick Avails, surrounded bv the 



