SUPPLEMENT. 1203 



surrounded by a layer of a granular, slightly opaque yolk." 

 Perfectly ripe eggs will be seen to be clean, sharply 

 defined, and separate from each other. If the specimen 

 be male, a glance through the microscope shows some- 

 thing quite different from the fluid of a female. " There 

 are no large bodies like the eggs, but the fluid is filled with 

 innumerable numbers of minute granules, which are so 

 small that they are barely visible when magnified 100 dia- 

 meters. They are not uniformly distributed, but are much 

 more numerous at some points than at others, and for this 

 reason the fluid has a cloudy or curdled appearance. By 

 selecting a place where the granules are few and pretty 

 well scattered, very careful watching will show that each 

 of them has a lively dancing motion, and examination with 

 a power of 500 diameters will show that each of them is 

 tadpole-shaped, and consists of a small, oval, sharply- 

 defined ' head,' and a long, delicate ' tail,' by the lashing 

 of which the dancing is produced." These are the sperma- 

 tozoa, or male cells, whose union with the eggs or ova of 

 the female is necessary to the fertilization of the latter, 

 and the consequent hatching of living oysters. 



The number of male cells which a single male will 

 yield is great beyond all power of expression, but the 

 number of eggs which an average female will furnish may 

 be estimated with sufficient exactness. A single ripe egg 

 measures about one five-hundredth of an inch in diameter, 

 or five hundred laid in a row, touching each other, would 

 make one inch ; and a square inch would contain five 

 hundred such rows, or 500 by 500=250,000. 



. . . . Oystermen believe that the male may be 

 distinguished from the female by certain characteristics, 

 such as the presence of black pigment in the mantle ; but 

 microscopic examination shows that these marks have no 



