OVUM. 



[89] 



avoid injuring the ova, and that the examina- 

 tion must be made at first in the dry state. 



Origin and Formation of the Mammiferous 

 Ovum. This subject has already been ad- 

 verted to in the previous section in connection 

 with the history of the formation of the bird's 

 egg. Dr. Martin Barry was led, by his numer- 

 ous observations, to form the conclusion, that 

 the germinal vesicle is the first part which 

 makes its appearance in the ovarian stroma at 

 the commencement of the formation of the 

 ova. All observers seem now to be agreed, 

 that of the parts belonging strictly to the 

 ovum itself, the germinal vesicle is the first 

 formed ; but the observations of Valentin, 

 Bischoff and others appear rather to support 

 the view, which is opposed to that of Barry, 

 that the Graafian follicles may be detected in 

 the ovarian stroma before any part of the 

 ovule is distinguishable. 



The ovules are formed at a comparatively 

 early period in the ovary. Carus was the 

 first to point out * that in the ovary of 

 the human female child the follicles con- 

 taining distinct ovules are perceptible at 

 birth. Vallisnieri had long previously, it 

 appears, made a similar observation. Bis- 

 choff has, with more precision, pointed out, 

 that there is considerable variation in dif- 

 ferent children of the same aize as to the 

 degree of advancement of the germs of ova 

 within the ovarium ; in some nothing more 

 than a perfectly uniform ovarian stroma is 

 perceptible at birth, while in others the follicles 

 are distinctly formed, even at an earlier period. 

 By the age of ten or eleven years a number of 

 the vesicles are found to be approaching ma- 

 turity, and almost all have left their earliest 

 condition. Both Barry and Bischoff, how- 

 ever, are of opinion that new sets of Graafian 

 follicles and ova may continue to arise within 

 the ovaries during the whole child-bearing 

 period of the human female; and there can be 

 little doubt that this takes place in most of the 

 lower animals. 



Bischoff describes the Graafian follicles as 

 taking their origin from minute heaps of 

 granules in the ovarian stroma; but he has 

 not been able to confirm the statement of 

 Valentin that the earliest follicles proceed 

 from primitive gland tubes stretching from 

 the attached border towards the surface of 

 the ovary, f In various animals the follicles 

 and ova begin to be formed at an earlier 

 period than in the human female : according 

 to. Bischoff, they arise very early both in the 

 cow and pig. 



When the primary follicle can be perceived, 

 it consists of a small vesicle scarcely more than 



S i j oo // in diameter. To this primary vesicle 

 artin Barry has given the appropriate name 

 of Ovisac. Soon afterwards, when the vesicle 

 has expanded somewhat, it is found to con- 

 tain the rudiment of the ovum ; first in the 

 shape of the very small germinal vesicle, gene- 



* Muller's Archiv. for 1832, p. 379. 

 t Handbuch der Entwickelungsgeschichte, 1835, 

 p. 389. ; and Muller's Archiv for 1838, p. 529. 



Fig. 62 *. 



Development of the Ovarian ovum of Mammalia. 

 (From Bischoff.} 



A represents a very small portion of the ovary of 

 a foetal dog. The commencing Graafian follicles 

 are visible in the granular or cellular stroma of 

 the ovary, constituting dark heaps of more opaque 

 granules or small cells. 



B, fragment of the ovary of a dog three weeks 

 after birth. The Graafian follicles are now seen in 

 the fibro-granular ovarian stroma, each surrounded 

 by a homogeneous and fibrous covering, and filled 

 with granules. 



c, fragment of the ovary of a pig three weeks 

 old. The Graafian follicles are now seen to be 

 formed of a fine transparent vesicular membrane, 

 and round the larger ones fibres are beginning to 

 be deposited. The wall of the follicles are lined 

 internally with delicate epithelial cells. The ger- 

 minal vesicles now visible within consist of a fine 

 clear cell with a nucleus or dot, and a few vitelline 

 granules have begun to be deposited round the 

 germinal vesicles. 



g, one of these Graafian follicles burst with a 

 needle, showing the contents of the follicle; there 

 being as yet no zona or vitelline membrane. 



rally surrounded by a small quantity of granu- 

 lar fluid. Soon afterwards the outer follicle 

 is lined with a few extremely delicate or hya- 

 line hemispherical cells, which have somewhat 

 the appearance of those of epithelium, and 

 which thus give rise to a clear space between 



