318 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



After a final stirring, the beaker should be allowed to 

 stand for about five minutes, to allovy the eggs to settle to 

 the bottom, and the fluid above them should then be drawn 

 off through a siphon, reaching nearly but not quite down 

 to the eggs. A fresh supply of sea-water should then be 

 added, and the eggs being stirred and allowed to settle, 

 the water should be drawn off as before, and this should 

 be repeated until the water, after the eggs have settled to 

 the bottom, remains clear. 



The beaker may now be set aside where it will ifot be 

 exposed to sudden changes of temperature, and the eggs 

 will require no further attention until the embryos beiriu 

 to swim. The little embryos must of course be supplied 

 with fresh sea-water from time to time during their devel- 

 opment, and as they are so small that the water cannot be 

 drawn off after they begin to swim, they must be supplied 

 with fresh water by transferring them from time to time 

 to larger and larger beakers. In two hours or so after the 

 eggs are fertilized the embryos of the oyster begin to 

 swim, .and crowd to the surface of the Avater in great num- 

 bers, and form a thin stratum close to the surface. This 

 layer of embryos may be carefully siphoned off into a 

 very small beaker, and a little fresh sea-water added. In 

 an hour or so there will be a new layer of embryos at the 

 surface of beaker No. 1, and these should also be siphoned 

 into No. 2, and this should be repeated as long as the 

 embryos continue to rise to the surface of the first beaker. 

 Every five or six hours a little fresh sea-water should be 

 poured from a height of a foot or more into beaker \o. 2, 

 until it is filled. The contents should then be poured into 

 a larger beaker, and sea-water should be added four or 

 five times a day as before. In this way the embryos may 

 be kept alive for a week, although they have by this time 



