178 



SEVENTEENTH LECTURE. 



of the primitive kidney, an epithelial thickening appears, into 

 which the connective tissue of this organ sprouts in a hill-like 

 form. The latter becomes the frame-work substance ; from 

 the former originate the germinative epithelium, the epithelial 

 cells of the Graafian follicle, and, as the favored daughters of 

 the latter, the ova. 



This section of the development is represented by our Fig. 

 159, a copy from Waldeyer's excellent monograph. The first 

 embryonic ovula, the "primitive ova," are, therefore, of epi- 

 thelial origin. 



Pfliiger had, even before Waldeyer, acquired interesting 



conclusions concerning the ovaries of the creature after birth. 



From time to time, soon after birth, and then towards the 



period of parturition, in the adult mammalial animal, the 



old embryonic affinity reasserts 

 itself. The germinal epithelium 

 again proliferates downwards 

 in a conical form, and is at last 

 separated from the point of 

 origin. Thus arise irregular, 

 occasionally cord-like, and cy- 

 lindrical masses. These are 

 Pfliiger's follicular chains. I 

 have called them the egg strands 

 (Fig. 160). In their axis we 

 meet with certain of the epithe- 

 lial cells which have grown to 

 be ova. By constriction (2, a), 

 new Graafian vesicles are 

 formed. 



What becomes of the follicles 

 of the ovary ? 



Before sexual maturity they 

 appear to be frequently de- 

 stroyed by fatty degeneration 

 and also by colloid metamor- 

 phosis (Slayjansky, Frey). During the period of propagation, 



Fig. 160. — Follicular chains from the ovary 

 of the calf; i, with ova forming ; 2 at a, 

 showing constriction into Graafian vesicles. 



