Microns 



Figure 301. — Camera lucida drawing of live unfertilized 

 egg of C. virginica in sea water. Germinal vesicle not 

 visible under yolk granules. 



301). The eggs are devoid of pigment. OU 

 globules of different sizes can be made visible 

 under high magnification by gently pressing the 

 egg under a coverslip; by using fat-staining dyes 

 (Sudan II, III, or Black Sudan B) they become 

 conspicuous (fig. 303). Under the effect of dye 

 (dissolved in weak alcohol) the small granules of 

 lipid yolk, stained dark red or black, gradually 

 fuse into large globules and penetrate the vitelline 

 membrane and a slight pressure will force them 

 through it (fig. 304). The size of the globules 

 increases during the time that the preparation 

 remains under the microscope. These artifacts 

 are due to the fusion of globules under the effect 

 of dye. 



The mitochondria of ( '. virginica can be stained 

 by a 0.5 percent solution of Jaims green in sea 



water. They appear as small rodlike structures 

 uniformly distributed in the subcortical layer of 

 the egg (fig. 305). The origin of fatty or lipid 

 yolk in C. virginica has not been studied. In 

 Myiilus eggs the lipid of the yolk apparently 

 arises in an intimate association with the Golgi 

 apparatus (Worley, 1944). In Lymnaea (Bret- 

 schneider and Raven, 1954) they are formed in 

 certain parts of the protoplasm independently of 

 cell structures visible under the light microscope. 



In the eggs of the Bombay oyster, C. cucuUata, 

 which are similar to those of C. virginica, the fatty 

 yolk, according to Rai (1930), is formed directly 

 from the Golgi vesicles. Mitochondria exist in the 

 eggs of this species in the form of very minute 

 granules forming a circumnuclear ring. Later they 

 grow in size and are more or less uniformly dis- 

 tributed. This conclusion is in agreement with the 

 observations of Gatenby and Woodger (1920), who 

 found that in Helix and Limnaea the Golgi ele- 

 ments gradually spread throughout the ovocyte 

 and probably take part in the formation of yolk 

 bodies. They found no evidence that part of the 

 mitochondrial constituents of cytoplasm meta- 

 morphose into yolk. 



Oyster eggs placed for 5 minutes in a dilute solu- 

 tion (1 to 25,000 or 1 to 30,000) of toluidin blue 

 and washed in sea water are colored metachro- 

 matically. Pasteels and Mulnard (1957) found 



Microns 



20 



FiGDRE 302. — Camera lucida drawing of live egg of 

 C. virginica a few minutes after fertilization. 



332 



FISH AND WILDLIFE SERVICE 



