142 



ANIMALS OF THE SEASHOBE 



June and along the southern Atlantic or Gulf Coast, 

 it may occur as early as March. 



The embryo produced by the spawning is a 

 minute (0.25 mm.) spherical body. It is able to 

 move over the surface of the water by means of its 

 small hair line cilia or swimming organs. This free 

 swimming stage may last two or three weeks. 

 However it soon wearies of a free swimming exist- 

 ence and falls down through the water and "sets'' 

 or attaches itself to the substratum. If the young 

 oyster happens to fall on something hard, it 

 will immediately attach itself, and lose forever its 

 cilia. On the other hand, if it falls on something- 

 soft, such as mud, it will be unable to set, and will 

 consequently soon die. It is therefore to the great 



Fig. 23 

 Oyster shells, Bivalve, N. J. 



interest of the oystermen, that the young oyster 

 find something hard when it begins to set. It is 



