l] the frog. 155 



rarely seen, as it only occasionally lies in the 

 plane of section. 



ii. ]^2xamine under a high power. 



a. The smaller ovisacs. 



a. The 07'7/m ; the central large cell ; its proto- 

 plasm^ uniformly finely granular and deep- 

 staining. 



/?. Germijial vesicle; often irregular in outline; 

 germinal spots diffused or arranged peri- 

 pherally in a single row. 



7. Ovaria7i follicle ; a single-layered epithelial 

 investment for the ovum. 



b. Compare the hu'ger ovisacs. 



a. Protoplasm of ovian. Peripherally, black and 

 pigmented, otherwise converted, for the most 

 part, into an imm.ense aggregate of small ellip- 

 soidal or irregular refractive yolk granules. 



p. Germinal vesicle. Look for specimens in 

 v/hich tliis is visible ; the germinal spots arc 

 mostly, if not wholly, aggregated in the middle 

 of the same. 



y. Ovarian follicle ; still recognizable, but gene- 

 rally flattened. 



Z. Vitelline membrane ; obvious as a thin faint 

 line, interposed between the ovum and the 

 follicle. Look for it in ova whose investing 

 structures may have been ruptured. 



c. The germinal epithelium ; a cellular mass imme- 

 diately beneath the investing membrane of the 

 ovary. Look for young ovisacs still in connection 

 with it. 



