MOLLUSC A. ly 



In order to carry on these observations properly, the 

 leaves of the mantle must be cut open, so as to expose the 

 flaps of one side. 



To do this without lacerating the soft body of the oyster, 

 pass a probe, a burnt match, a straightened hair-pin, a 

 knitting-needle, or piece of blunted wire round the flaps, 

 and hold the mantle out until you see where to slit it open. 

 Then you can readily, with a pair of scissors, remove this 

 entirely from one side, and afterwards the outer flap or 

 palp, the same side as in Fig. 15,/'. 



When this is done, without tearing the parts, you can 

 be sure of finding the wrinkled cavity of the mouth by 

 bending the end of your probe into a small hook, and pull- 

 ing gently aside one of the large muscles in Fig. 15, oin, 

 which run forward on either side, from the bases of the 

 inner palpi or flaps, and form the two sides of that aperture. 



It will have been already noticed by the observant, 

 that a certain portion of the blueing, dropped on the 

 gills, disappeared in the interior. This evidently passed 

 through their sieve-like surface, because they also saw 

 it coming out again under the borders of the mantle 

 on the concave side in two streams, — one immediately 

 before and one behind the large muscle. Both of 

 these currents serve to carry off the excretions of the 

 body and the feculent matter from the anus, and are 

 really branches of a stream issuing out of the interior 

 of the gills. 



The circulation of water, then, in the oyster, when 

 living, takes place by the entrance of a continuous 

 stream in at the outer convex edges, and its passage 

 through the gills and out on the other side in the man- 

 ner just described. 



In order to understand this, lift with the probe, and 



