Microns 



Figure 300. — Photomicrograph of eggs in the follicles of the ovarv of C. virginica at the beginning of the spawning season. 

 Ovocytes and small indifferent cells line the wall; mature eggs are either free or connected to the wall with long 

 peduncles. Kahle, hematoxylin-eosin. 



Cleland states that in the uncentrifuged mature 

 egg they are unrecognizable. From hontogenates 

 the M granules can be separated by centrifuging 

 for 10 minutes at 10,000 times gravity. Cyto- 

 phism also contains submicroscopic or S granules 

 (according to Cleland's terminology), which are 

 separable by appljang a centrifugal force of 

 20,000 times gravity for 30 minute?. These S 

 granules are probabh' homologous to mammalian 

 microsomes, i.e., the submicroscopic ribonucleo- 

 protein particles whicli are considered to be the 

 major sites of protein synthesis (a discussion of 

 this problem is found in Shaver, 1957, and 

 Novikoff, 1961b). 



With the exception of pure lipid granules, the 

 cytoplasmic components of the egg of C. com- 

 mcrcialis show an increasing content of nucleic 

 acid with decreasing size of granules, the ground 

 cytoplasm containing the highest concentration 



of nucleic acid. Cleland's observations need to 

 be corroborated, using the eggs of different species 

 of oysters. 



The formation and composition of yolk in the 

 eggs of animals other than bivalves liave been 

 studied by many investigators, frequently wdth 

 different and sometimes contradictory results. 

 As Brachet (1944) stated nearly 20 years ago, the 

 problem cannot be resolved at present. This 

 uncertainty about yolk and other granules still 

 persists and probably will continue until the 

 ultrastructure of the marine egg is thoroughly 

 explored by electron microscopy. 



Examination with the light microscope of ripe, 

 unfertilized, and unstained eggs of C. virginica 

 discloses a multitude of tightly packed minute 

 granules in the cytoplasm which obscure the inner 

 portion of the egg. The granules appear to be 

 uniforndy distributed around the nucleus (fig. 



EGG, SPERM, FERTILIZATION, AND CLEAVAGE 



331 



