The Microscope. 81 



live in great numbers in the stomach and in the intestine of the 

 common oyster. 



Nature seems to hnve placed the mouth of this "luscious 

 bivalve " at the wrong end of the body ; it appears to be at the 

 posterior extremity, because it is located near the hinge of the 

 shell, and not, as one would be likely to suppose, at the end 

 toward the free margins of the shell. But as the arrangement 

 seems to be satisfactory to the oyster, the human animal has 

 nothing to complain of, except, perhaps, of tlie difficulty in 

 finding it when he desires to remove the stomach contents for 

 microscopical examination. 



The large, pearly, somewhat cartilaginous mass often called 

 the " heart," is the severed muscle that holds the valves of the 

 shell together. Place the oyster so that this muscle shall be 

 towards you and on your right hand side. In the left hand 

 maro-in is included several membranes. Pick up with the for- 

 ceps the first and lay its whole length back on the body of the 

 oyster. This is the mantle. To lay aside the whole length it 

 will be necessary to tear the anterior border for perhaps a 

 quarter of an inch. The gills (the "beard ") are now exposed, 

 but they need not be disturbed. In front of them, however, and 

 entirely free from them, is an almost semi-circular appendage, 

 separable into four parts. These are the oyster's lips. They 

 differ in appearance from the gills, being slightly different in 

 color and less conspicuously striated. Lift one and lay it on 

 the upturned surface of the mantle. If the latter has been 

 sufficiently torn at the anterior margin, the oyster's mouth will 

 now be plainly visible at the extreme end of the body as an oval, 

 widely open aperture. 



Into this ever open mouth gently thrust the point of a glass 

 tube having a rubber bulb at one end. When the point of the 

 tube has penetrated for half an inch or less it will be in the 

 oyster's stomach. Allow the bulb to expand and the stomach 

 contents will rush in and be at the microscopist's disposal. The 

 liquid is turbid, slightly brownish and usually three or four 

 drops in amount. It will probably contain many infusorial 

 parasites which we are seeking, and which are always present in 

 the alimentar}^ canal and usually more or less abundant in the 

 stomach. 



You may use any objective from a half-inch upwards, and it 



