66 REPRODUCTIVE SYSTEM OF THE ADULT FROG 



Stage 5 germinal vesicle of Rami catesbiana. Shows chromosome pairs with 

 but few lateral loops and peripheral nucleoli outside of the chromosome frame. 

 (Courtesy, W. R. Duryee, 1950, Ann. N. Y. Acad. Sci., 50, Art. 8.) 



Stained with crystal violet in a calcium-free medium. Amphibian 

 cells are among the largest in the animal kingdom and the frog's 

 egg nucleus is large enough to see with the naked eye. It can be re- 

 moved with considerable ease and examined beneath the binocular 

 microscope. 



Before the time of hibernation the eggs that are to be ovulated for 

 the next spring are in the fully grown primary oocyte stage, having 

 their full complement of yolk, cytoplasm, and pigment. Externally 

 more than one-half of the egg appears densely black, due to surface 

 pigment granules, while the rest is creamy white. The nucleus is pre- 

 pared for the maturation divisions. Such an egg measures about 1.75 

 mm. in diameter. The surface layer of the amphibian egg is formed 

 before fertilization and it is definitely not hyaline, as it is in some 

 Invertebrate eggs. It contains many small yolk grains and irregular 



