ACTION OF THE FEMALE. 599 



regarded as indicative of conception. 3. That the presence of the Corpora 

 Cephaloidea of the first order, or of Corpora Mbida, cannot be regarded as in 

 the least degree indicative of Conception ; as they may result from the simple 

 discharge of an Ovum, in the ordinary course of those changes to which the 

 Ovarium is subject. The excess of Corpora Albida above every other appear- 

 ance is due, not merely to their being an ordinary result of the discharge of 

 unimpregnated Ova ; but also to the frequency of their production as degene- 

 rated forms (so to speak) of the Corpora Cephaloidea and Corpora Rubra of 

 the gravid female ; and also to their occasional existence as, from the first, the 

 only Ovarian change following upon Conception. 



745. The object of the changes which have been already described, is to 

 bring the Ovum within reach of the fecundating influence ; and to convey it 

 into the Uterus after it has been fertilized. We have now to consider the 

 changes in the Ovum itself, which take place during the same epoch. At 

 about the same period that the Ovum moves towards the periphery of the 

 Graafian follicle, the Germinal Vesicle moves towards the periphery of the 

 yolk-bag; and it always takes up its position at the precise point of the Zona 

 Pellucida which is nearest the Ovisac, and which is closest, therefore, to the 

 surface of the Ovary. Moreover, the Germinal Spot is always on that part 

 of the Germinal Vesicle, which is in closest contact with the Zona Pellucida. 

 (See , Figs. 9 and 10, Plate I.) Thus, the Germinal Spot is very near the 

 exterior of the Ovary ; but is separated from it by the peritoneal coat of the 

 latter, by a thin layer of its stroma forming the external layer of the Graafian 

 follicle, by the ovisac forming its internal membrane, and by the zona pellu- 

 cida. We have already seen how the obstacle interposed by the three former 

 to the entrance of the Spermatozoon, is overcome ; we shall presently find that 

 the Zona Pellucida undergoes a similar change. Whilst the Ovum is being 

 prepared for fecundation, a series of very important actions take place in the 

 Germinal Vesicle. The exterior or peripheral portion of the Spot, which 

 previously consisted of a collection of very minute granules, begins to develop 

 itself into a ring of new cells of extreme delicacy (Fig. 9, ) ; these gradually 

 enlarge, and a second ring of cells is developed within it, pushing the first- 

 formed cells further away from the centre. Many successive rings of cells are 

 thus formed ; and at last the whole Germinal Vesicle is filled with them, as 

 shown at 6, Fig. 10. Still there remains a pellucid space in the centre of the 

 Germinal Spot (resembling that seen at a, Fig. 12) ; in which no cells are 

 developed. The first-formed cells that have been pushed outwards, are so 

 much compressed by those subsequently formed, as frequently to undergo 

 liquefaction ; and during the time that the Ova are being matured for fertili- 

 zation, there is a continual new production of cells at the centre, and a degene- 

 ration at the circumference. At the same time, the Yolk undergoes changes 

 somewhat analogous ; for it ceases to contain separate oil-globules ; and large 

 elliptical discs or cells are seen in it, especially just beneath the Zona Pel- 

 lucida (Fig. 9, c).* Here, too, the formation of new cells takes place from 

 the periphery towards the centre ; the peripheral ones gradually undergo 

 liquefaction, as is seen in the outer layer of those in Fig. 10, which are 

 becoming indistinct ; and they are replaced by a new layer pushed outwards 

 from the centre. The same process subsequently continues in the Yolk, for 

 some time after fecundation ; and this not only in regard to the yolk as a 

 whole, but in respect to its individual cells, as is shown in Fig. 11, where 

 concentric rings of new cells are seen in each of the parent vesicles. Even 

 in the most advanced of these secondary cells, another generation may be 



* It is to be remembered that the observations of Dr. Barry here quoted, were made on 

 the Rabbit: and are, therefore, probably applicable equally to other Mammalia, but not to 

 Oviparous Animals. 



