THE OYSTER. 53 



The body of the oyster, like that of all animals, 

 except the very simplest, is made up of organs, such 

 as the heart, digestive organs, gills and reproductive 

 organs, and these organs are at some period in the 

 life of the oyster made up of microscopic cells. Each 

 of these consists of a layer of protoplasm around a 

 central nucleus, which, in the egg, is a large, cir- 

 cular, transparent body, known as the germinative 

 vesicle. Each cell of the body is able to absorb food, 

 to grow, and to multiply by division, and thus to con- 

 tribute to the growth of the organ of which it forms a 

 part. The ovarian eggs are simply the cells of an 

 organ of the body, the ovary, and, so far as the micro- 

 scope shows, they differ from the ordinary cells only 

 in being much larger and more distinct from each 

 other ; and they have the power, when detached from 

 the body, of growing and dividing up into cells, which 

 shall shape themselves into a new organism like that 

 from whose body the egg came. Most of the steps 

 in this wonderful process may be watched under the 

 microscope, and, owing to the ease with which the 

 eggs of the oyster may be obtained, this is a very good 

 egg to study. 



About fifteen minutes after the eggs are fertilized, 

 Plate IV, Fig. i, they will be found to be covered with 

 male cells. In about an hour the egg will be found to 

 have changed its shape and appearance. It is now nearly 

 spherical, and the germinative vesicle is no longer 

 visible. The male cells may or may not still be visible 

 upon the outer surface. In a short time a little trans- 



