THE NATURAL HISTORY OF THE OYSTER. 13 



cowry or Cypraea, if an adult shell, you will find that, while the entire 

 shell is covered with a shining enamel, there is along the whole length 

 of the back of the shell "a line of pale color." The animal extends 

 both folds of the mantle outside of itself and over the shell, and that 

 line is where the lips of the folds meet. This mantle has much to do 

 with obtaining food. The oyster opens its shells about a quarter of 

 an inch apart. These membranes, that make the mantles from both 

 sides of the animal, meet just at the opening of the shell. They are 

 fringed at their edges with rows of tiny cilia, or soft fleshy hairs of 

 extreme delicacy. This pallial fringe in an eminent degree serves the 

 oyster as organs of touch. Probably this sense, though distributed 

 somewhat over the entire surface of the body, is along this fringe ex- 

 quisitely acute. The English call this fringe the oyster's beard. It 

 is protruded just a little out of the shell ; and these cilia, almost num- 

 berless, keeping up their rapid movements in the water, make as it 

 were two parallel vibrating curves, which beget a sort of aquatic 

 vacuum inside the shell, into which the water flows, as in a diminutive 

 whirlpool. The stream thus affected brings with it the algae spores 

 and animalcules which constitute the oyster's food. But where is the 

 oyster's mouth ? Speaking popularly, it is away back near the hinge 

 of the shell, as shown in the cut. To this point the current flows. 

 Now, it must not be supposed that all is fish that comes to the oyster's 

 net. Far from it. Hence this mollusk has eclectic functions. Doubt- 

 less a sharp spicule of a sponge may occasionally get into the mouth, 

 even as a bone splinter can get by accident into a human throat. The 

 word " tentacles," in the cut, refers to certain organs, that might be 

 called labial or lip fingers. These, it will be noticed, have immediate 

 relation to the mouth. They are the organs for discriminating food 

 functionally they are manipulating lips. The stomach is not shown 

 in the cut, being overlaid by the other organs. The intestine, at least 

 a part of it, is exposed, and its extremity is really the anus or vent. 

 So much, then, is apparent, that the oyster possesses an alimentary 

 system of some complexity. 



A series of plates or plaited frills, lies on the mantle, if indeed it 

 is not a specialized portion of that organ. These plaits are the bran- 

 chiae or gills. In the respiratory system of an oyster these branchiae 

 or gills are precisely the same to it as are the gills to a fish, or our 

 lungs to us. Through these gills the water is passed. After impart- 

 ing to the blood the oxygen taken from the air which the water con- 

 tained, that water, now laden with carbonic-acid gas, is expelled at the 

 respiratory aperture, or ex-current orifice, the dark spot in the figure 

 immediately under the end of the intestine, which we have already 

 said is the anus or vent, whence this refuse water, like a cleansing 

 stream, passes directly out of the shell. This contrivance is certainly 

 very beautiful. It is in fact a miniature sewer carrying off promptly 

 and quickly the excrements as fast as they are made. 



