ORGANS OF THE BODY. 



545 



"When a Graafian vesicle arrives at this epoch of its existence it under- 

 goes a further increase in size, owing to continuous proliferation of the 

 cells of the internal membrane of the follicle and accumulation of fluid 

 within it. t It now gives rise to a prominence on the surface of the ovary, 

 from the fact of its being tense and swollen, and no longer situated in the 

 stroma of the organ, but merely covered by a thin layer of connective- 

 tissue. 



Finally, there comes a moment at which the wall of the follicle becomes 

 so stretched and distended that it must succumb to the forces acting on 

 it, and it ruptures. The rent always takes place at the point of least resist- 

 ance, and consequently in the external surface of the ovary, which is 

 only covered by a thin fibrous envelope. For the reception of the ovum 

 at this time the ostium abdominale of the Fallopian tube is closely 

 applied to the surface of the ovary. 



The ovum now commences its journey down the tube towards the 

 uterus, in which it arrives after some days. After it has escaped from 

 the Graafian follicle, the inherent energies of the encapsuled cell are 

 aroused by the penetration of spermatozoa into its yolk, and the process 

 of segmentation commences (fig. 537, 1), which has been already described. 

 This process continuing for 

 some time (2), a mulberry- 

 like aggregation of cells is 

 formed (3), which constitutes 

 the material for the con- 

 struction of the new indivi- 

 dual. This process was for- 

 merly very generally sup- 

 posed to be preceded by the 

 disappearance of the nucleus 

 of the ovum or so-called ger- 

 minal vesicle ; but from re- 

 cent observation it would 

 appear that this does not take 

 place, but that by its divi- 

 sion it is bound up with seg- 

 mentation of the cell in the 

 usual manner of endogenous 

 growth. 



But when impregnation 

 does not take place, the ovum 

 is destroyed within the gene- 

 rative organs by a process of liquifaction or solution. This is what occurs 

 in by far the greater number of cases with the egg of the human female. 

 And if we take into consideration the number of menstruations which 

 occur during the whole time that a woman is capable of bearing, we shall 

 gain some idea of the number of follicles requisite to supply the ova. 

 This is, nevertheless, exceeded by far by the enormous production of 

 the latter. 



We have now to consider the destiny of the ruptured and emptied 

 Graafian vesicle (fig. 538). The latter, soon after the fulfilment of. its 

 functions, is to be found filled up with cicatricial connective-tissue, con- 

 stituting what is known under the name of the corpus luteum, after which 

 it gradually disappears entirely in the stroma of the organ. 



Fig. 537. Division of the mammal ovum (half diagram- 

 matic). 1. The yolk divided into two globules (cells) 

 with nuclei. 2. Quadrupled. 3. A large number of 

 nucleated cells. 4. a, 6, isolated cells. 



