554 



First Stage. Origin of the Graafian Follicle. 

 The time of the first appearance of the fol- 

 licle within the ovary is subject to considerable 

 variation in the different orders of Mammalia. 

 In all it occurs at a much later period than 

 the first appearance of the seminiferous tubes 

 in the male. Bischoff, who has devoted much 

 attention to the examination of the follicle in 

 its earliest stages of formation, has never been 

 able to discover the least trace of it in the 

 dog and rabbit before birth. This is also the 

 case in most instances in the human embryo, 

 although examples occur of the ovarian fol- 

 licles being already formed in the new-born 



Fig. 377. 



UTERUS AND ITS APPENDAGES. 



Represents the mode of formation of the Graafian 

 follicle. {After Bischoff.') 



A, portion of ovary of a foetal dog. The Graafian 

 follicles are seen in the first stage of formation, 

 consisting of little groups of primary cells in the 

 midst of a tissue of similar structure. 



B, Portion of ovary of a dog four weeks old ; a de- 

 licate fibrous coat now surrounds the groups of 

 nucleated cells. 



c, Portion of ovary of a pig three weeks old. The 

 follicle is here composed of transparent membrane, 

 the outer surface of which, in the larger ones, is 

 become fibrous. Its inner surface is lined by an 

 epithelium of pale cells (membrana granulosa); 

 within this is the germinal vesicle, surrounded by 

 granules resembling yelk granules. These contents 

 are seen dispersed from a ruptured follicle at </. 



infant, and in advanced embryos. At first 

 nothing is distinguishable in the ovary except 

 a uniform mass of primary cells and cell nuclei. 

 When the follicle or ovisac is about to form, 

 there may be perceived little round or ovoidal 

 aggregations of primary cells, forming groups 

 which are distributed in considerable numbers 

 through the ovary. These, from the circum- 

 stance that the substance of the ovary is like- 

 wise composed of similar cells, are scarcely 

 distinguishable from the stroma in the midst 

 of which they arise {fig. 377. A ). 



Now Barry, who also very carefully exa- 

 mined the early formation of the follicle in 

 the rabbit, maintains that within these little 

 groups of cells the germinal vesicle is already 

 contained. Barry represents the germinal 

 vesicle at its first formation as surrounded by 

 minute oil globules, and a collection of gra- 

 nules, forming together little elliptic masses 

 which are distributed through the ovary. A 

 comparison of the descriptions and illustrations 

 of these two observers leaves no doubt that 

 both refer to precisely the same object. 



Round these little groups of cells is now 

 perceived a delicate transparent membrane, 

 which is at first apparently destitute of or- 

 ganisation. This is the ovisac in its first stage 

 of formation (Jig. 377. B, c). The precise mode 

 of its development has given rise to much 

 speculation, which is interesting chiefly with 

 reference to the question whether the ovisac 

 is to be regarded as the vesicle of evolu- 

 tion of the ovum, or whether the ovum, or 

 parts of it at least, are previously formed, and 

 the ovisac is afterwards superadded. 



Bischoff explains the formation of the fine 

 homogeneous membrane which is first seen 

 surrounding the little groups of cells by sup- 

 posing that those which form the peripheral 

 layer become confluent, and that by their 

 junction they constitute this boundary wall, 

 whilst the original cell contents are dispersed. 



This membrane soon afterwards becomes 

 lined with a stratum of endogenous cells, which 

 form an epithelium upon its inner surface. A 

 close examination shows further that this cell 

 layer is bounded by a homogeneous tunica 

 propria. 



Hence Bischoff concludes that the follicle 

 is, as Henle asserts, a primary secreting fol- 

 licle, which, like all secreting follicles, is not 

 composed of a primary cell membrane, but 

 results from a confluence of cells. He has 

 never seen in it, when still in the condition of 

 a homogeneous transparent membrane, a cell 

 nucleus, as would be the case in a primary 

 cell. The contents of the vesicle, according to 

 Bischoff, consist of a clear fluid containing cell 

 nuclei and granules ; the latter closely re- 

 sembling the subsequently-formed yelk gra- 

 nules. Somewhat later is observed within these 

 follicle vesicles, which in the meantime have 

 become more developed and numerous, a se- 

 cond transparent spherical vesicle, containing 

 a nucleus which closely resembles-, and is con- 

 sidered by Bischoff to be the germinal vesicle. 

 Hence, whilst the observations of Barry, con- 

 firmatory of the views of Baer, and supported 



