FERTILIZATION OF THE OVUM. 451 



is thrown into wrinkles, which are directed towards the interior, so as 

 to occasion the contraction of the cavity ; and thus it comes to be 

 entirely filled with the new growth, the centre of which is marked by 

 a sort of stelliform cicatrix. This substance speedily becomes of a 

 paler hue than at first, and is known from its colour as the corpus 

 luteum. The escape of the ovule from the ovarium involves pro- 

 cesses which are essentially the same, whether it be impregnated or 

 not ; but the subsequent changes differ in the two cases, so that the 

 corpus luteum which accompanies the pregnant state is usually a 

 much larger and more highly-organized body, than that which is 

 found in the ovary of the unimpregnated female. This difference 

 may be due in part to the absence, in the latter case, of that special 

 determination of blood to the genital organs, which takes place in the 

 former. It is obvious, then, that the presence of a small and imper- 

 fect corpus luteum in the ovary, merely indicates that an ovum has 

 been matured and discharged, and affords no evidence of impregna- 

 tion or sexual intercourse. The presence of a large and character- 

 istic corpus luteum, on the other hand, may be regarded as affording 

 undoubted evidence that impregnation has taken place. When fully 

 formed, the corpus luteum may be rather more than half an inch in 

 one of its diameters, and rather less in the other ; it usually forms a 

 projection on the surface of the ovary, and occupies from one-fourth, 

 to one-half of the whole area of its section. It is frequently, how- 

 ever, much smaller than this ; and on the whole it may be said that 

 the presence of a corpus luteum as large as a full-sized pea, is toler- 

 ably certain evidence of impregnation. After delivery, the size of the 

 corpus luteum rapidly diminishes, and in a few months it ceases to be 

 recognisable as such ; the cicatrix by which the ovum has escaped, 

 however, remains visible for some time longer. 



801. The increase of size which is observable in the ovule that is 

 being prepared for fecundation, is chiefly due to an augmentation in the 

 substance of the Yolk ; and this also becomes more firm and granular 

 than before. But the most curious change is that which takes place in 

 the Germinal Vesicle ; for this, although previously in the centre of the 

 yolk, now moves up towards the side of it which is nearest the surface 

 of the ovary, and becomes flattened against the yolk-bag. At the same 

 time, it ceases to present its ordinary pellucidity and becomes obscure ; 

 and this alteration appears to be due to the development of a brood of 

 young cells in its interior. From the recent observations of Mr. New- 

 port and others, it would seem that it then bursts and sets these free, 

 so that they become diffused through the yolk ; and as this change may 

 happen before fecundation, it must be regarded as being preparatory to 

 it, or at any rate as being independent of it. 



802. The ova thus matured and prepared for fecundation, are dis- 

 charged from the surface of the ovary by the process already described, 

 whether sexual intercourse take place or not ; and being received into 

 the Fallopian tubes, they are by them conducted towards the uterus. 

 Their transmission may be effected by a kind of peristaltic movement 

 which is observed to take place in these tubes during the periods of 

 heat ; or, it may be, by the action of the cilia which line them ; the di- 



