54 THE OYSTER. 



becomes greatly enlarged, and cilia make their appear- 

 ance upon its walls; the mouth becomes connected 

 with the chamber which is thus formed, and which 

 becomes the stomach, and minute particles of food are 

 drawn in by the cilia, and can now be seen inside the 

 stomach, where the vibration of the cilia keep them in 

 constant motion. Up to this time the animal has 

 developed without growing, and is scarcely larger than 

 the unfertilized Q%^<, but it now begins to increase in 

 size. 



Soon after the mouth has become connected with 

 the stomach this becomes united to the body wall at 

 another point a little behind the mouth, and a second 

 opening, the anus, is formed. The tract which connects 

 the anus with the stomach lengthens and forms the 

 intestine, and, soon after, the sides of the stomach 

 become folded off to form the two halves of the liver, 

 and various muscular fibres now make their appear- 

 ance within the body. 



Such is the scientific history of the oyster-embryo. 

 The practical utility of the knowledge, however, to 

 the most of us, is that the American oyster lays a vast 

 number of eggs, but that they are exposed to dangers 

 so constant and innumerable, that under ordinary con- 

 ditions few ever come to life, or at any rate succeed in 

 living long enough to anchor themselves and take on 

 the protection of shells. This is only another exam- 

 ple of a fact well known to naturalists. The number 

 of eggs laid, or even of individuals born,has very little 

 to do with the abundance of a species, which is de- 

 termined, mainly, by the external conditions to which 

 it is exposed. 



