M 



M, P 



z.t 



Microns 



40 



Figure 329. — Several stages of development of the egg of C. gigas. Redrawn from Fujita, 1929. a — Two-cell stage, 

 Ant. — anterior, Pst. — posterior ends; b — Four-cell stage, formation of blastomeres A, B, C, and D; c — 12-cell stage and 

 the formation of the first somatoblast (cell X), viewed from the animal pole; d — embryo viewed from vegetative 

 pole after the formation of the mesomere M; e — cleavage of mesomere M and the first somatoblast X, posterior 

 view optical section; f — advanced stage of development showing the arrangement of the mesomeres M, M, and the 

 somatoblasts, X, X, X,, X,, posterior view optical section. Cleavage nomenclature as given by Fujita. 



Microns 



20 



Figure 330. — Larva of C virginica ready to hatch. 

 Drawn from photomicrograph of live larva. 



fine ciliation, and two polar bodies still remain 

 attached to the animal pole. The beating of the 

 cilia is not coordinated at this stage, and the 

 movements of the larva are irregular and spas- 

 modic. A few minutes later a girdle of powerful 

 cilia is formed, the polar bodies are lost, and the 

 larva begins to swim upward (fig. 331). In a 

 finger bowl containing cleaving eggs, the newly 

 hatched larvae appear as white columns rising from 

 the layer of fertilized eggs on the bottom of the 

 container (fig. 332). The larvae can be pipetted 

 off easily, transferred into larger containers and 

 provided with suitable food. 



The time requu-ed to complete the development 

 of an oyster egg varies, depending on condition 

 of eggs, temperature, salinity, oxygenation of 

 water, and other environmental factors. Records 

 of three sets of observations made in the Woods 



EGG, SPERM, FERTILIZ.\TIOX, AND CLEAVAGE 

 733-851 O— 64 23 



349 



