•1.0 }JL 



Figure 310. — Reconstruction of the sperm head of C. 

 virginica made from a large number of longitudinal 

 sections, a. — aorosome; ax. b. — axial body; ax. f. — 

 axial filament of the tail; b.p. — basal plate of the tail; 

 c. — centriole; c. ax. b. — core of the axial body; d.f. — 

 double filament on the periphery of the tail; m.b. — 

 mitochondrial body; n. — nucleus; t. — proximal part of 

 the tail. 



compartments filled with material of lesser electron 

 density. The central radial strands are similar 

 to the "spokes" described by Afzelius (1955) for 

 the sperm of the sea urchin Psammechinu.s miliaris. 

 They are not present in the proximal portion of 

 the tail where there are no axial filaments, but 

 otherwise the ultrastructure of the sperm tail is 

 similar to that of cilia and flagella of various 

 animals and plants. 



FERTILIZATION 



The spawned eggs of C. trirginica and C. gigas 

 are heavier than water and quickly sink to the 

 bottom. The time tliey remain in suspension may 

 be prolonged by horizontal currents and upward 

 movements of the water, and consequently the 



338 



chances of fertilization are increased. Because 

 spawning is usually initiated by the males, the 

 water into which the eggs are discharged already 

 contains active spermatozoa and fertilization takes 

 place within a few minutes following ovulation. 

 It is obvious that the success of reproduction of 

 an oyster population in which spawning is mutually 

 stimulated by the discharge of sex cells is depend- 

 ent on close proximity of the sexes and their 

 simultaneous response to spawning stimuli. 



Eggs and sperm secrete substances called 

 gamones which play an important role in fertili- 

 zation. Secretion from an unfertilized egg has a 

 significant effect on spermatozoa. This effect can 

 be observed if a suspension of eggs is permitted to 

 stand for 15 to 20 minutes and the supernatant 

 fluid is decanted or filtered and added to the sus- 

 pension of sperm. The resulting so-called "egg 

 water" (Lillie, 1919) causes the agglutination of 

 sperm. To observe the agglutination reaction 

 with the naked eye, a drop of egg water must be 

 added to a sperm suspension, which shortly forms 

 ii-regular lumps (fig. 313). Under a high-power 

 light microscope one sees that the heads of agglu- 

 tinated spermatozoa stick together to form large 

 aggregates (fig. 314). 







Micron 



I 



Figure 311. — Drawing based on electron micrographs 

 of the cross section of the lower part of the middle 

 piece of the spermatozoon of C. virginica. Centriole, 

 at the center, is surrounded by four mitochondrial 

 bodies. 



FISH AND WILDLIFE SERVICE 



