430 P, M, BALFOUR. 



follicle cells were derived from the stroma ; but even at this stage 

 the position of the cells which will form the follicular epithelium, 

 their passage by a series of gradations into obvious cells of the 

 germinal epithelium and the peculiarities of theirnuclei,so different 

 from those of the stroma cells, supply a sufficient series of cha- 

 racters to remove all doubt as to the derivation of the follicle 

 cells. Apart from these more obvious points, an examination of 

 the follicle cells from the surface, and not in section, demon- 

 strates that general resemblance in shape of folHcle cells to the 

 stroma cells is quite delusory. They are in fact flat, circular, or 

 oval, plates not really spindle-shaped, but only apparently so in 

 section. While I thus fundamentally differ from Foulis as to 

 the nature of the follicle cells, I am on this point in complete ac- 

 cordance with Waldeyer, and my own results witli reference to the 

 follicle cannot be better stated than in his own words (pp. 4;3, 4-i). 



At six weeks after birth the ovary of the rabbit corresponds 

 very much more with the stages in the development of the ovary, 

 which' Foulis has more especially studied, for the formation of 

 the follicular epithelium, than during the earlier stages. His 

 figure (' Quart. Journ. Mic. Sci.,' PI. XVII, fig. 6) of the 

 ovary of a seven and a half months^ human foetus is about the 

 corresponding age. Different animals vary greatly in respect to 

 the relative development of the ovary. For example, the ovary 

 of a lamb at birth about corresponds with that of a rabbit six weeks 

 after birth. The points which may be noticed about the ovary at 

 this age are first that the surface of the ovary begins to be some- 

 what folded. The appearances of these folds in section have given 

 rise, as has already been pointed out by Foulis, to the erroneous 

 view that the germinal epithelium (pseudo-epithelium) became in- 

 voluted in the form of tubular open pits. The folds appear to me 

 to have no connection with the formation of ova, but to be of 

 the same nature as the somewhat similar folds in Elasmo- 

 branchs. A follicular epithelium is present around the majority 

 of the ova of the middle layer, and around all those of the inner 

 layer of the germinal epithelium. The nests are, morever, much 

 more cut up by connective tissue ingrowths than in the previous 

 stages. 



The follicle cells of the middle layers are very flat, and spindle- 

 shaped in section, and though they stain more deeply than the 

 stroma cells, and have other not easily characterised pecularities, 

 they nevertheless do undoubtedly closely resemble the stroma 

 cells when viewed (as is ordinarily the case) in optical section. 



In the innermost layer many of the follicles with the enclosed 

 ova have advanced considerably in development and are formed of 

 columnar cells. The somewhat heterodox view of these cells pro- 

 pounded by Foulis I cannot quite agree to. lie says (' Quart. 



