THE EARLY DEVELOPMENT OF THE FROG 



75 



G 



II 



FIG. 26. Oogenesis in the frog (R. temporaria). A-E, After Lams. F-I, 

 After Lebrun. A. Primary oocyte in synizesis. B. Primary oocyte with vitel- 

 line substance of mitochondrial (chromidial) origin in the cytoplasm. C. 

 Primary oocyte showing feathery chromosomes and chromatin nucleoli. D. 

 Primary oocyte with ring-like vitelline mass. E. Primary oocyte showing cyto- 

 plasm in two zones. F. Nuclear region of primary oocyte after dissolution of 

 the nuclear membrane, showing the small chromosomes and large chromatin 

 nucleoli. Egg still in ovary. G. First polar spindle in primary position. From 

 egg in body cavity. H. First polar spindle in metaphase. From egg in uterus. 

 /. First polar body formed and second polar spindle forming. From egg in 

 uterus, a, Attraction sphere; c, chromosomes; /, follicle cells; g, contents of 

 germinal vesicle; n, chromatin nucleoli; v, vitelline substance of mitochondrial 

 (chromidial) origin; y, yolk plates; /, first polar spindle (polar body, in /); 

 //, second polar spindle. 



