THE PERMANENT OVA. 



347 



ova fuse together to form a bi-nuclear or poly-nuclear mass, in 

 which all the nuclei but one may disappear, the fused mass 

 with the remaining nucleus becoming a permanent ovum ; while 

 in other cases it is stated that after a follicle has been formed 

 round the fused mass, the entire mass, with the follicle, may 

 divide into two or more permanent ova. 



The development of the permanent ova proceeds from the 

 surface of the ovary towards its deeper parts. In young 



Fig. 133.— Section through part of the ovary of an adult Rabbit. The section 

 is taken vertical to the surface of the ovary, and shows one fully formed 

 Graafian follicle, and others in various stages of development, x 50. 



GrA, follicle cells surrounding an ovum. GrB, outer layer of Graafian follicle, or 

 • tunica granulosa.' GC, inner layer of Graafian follicle, or ' discus proligerus.' GK, 

 cavity of Graa fian follicle. OE, outer layer of columnar epithelial cells, investing the 

 ovary. OW. ovum. OY, primitive ovum. OZ, nests of epithelial cells derived from 

 the deeper layers of the genital epithelium. 



rabbits, about a week after birth, the surface epithelium of the 

 ovary contains numerous primitive ova in process of formation ; 

 deeper down, beneath the tunica albuginea, are nests of epi- 

 thelial cells in which are permanent ova in the early stages of 

 their formation, surrounded by imperfectly formed follicles ; 

 while still lower, in the deepest parts of the germinal epithelium, 

 the nests are in many places broken up into isolated follicles, 

 each containing a large and well-formed permanent ovum. 



