CHAP, iv.] 



OF ANIMAL GENERATION. 



325 



an imperfect cell composed of an enveloping membrane and of 

 a mass of granulations. 



At the same time the vitellus is drawn back toward the centre 

 of the cell, and a transparent zone then separates the cellular 

 membrane from the granulous content (Fig 48 A). Another phe- 

 nomenon, the utility of which is not yet well known, is afterwards 

 produced. It can take place also independently of fecundation. 

 It is the emergence of the polar globules. According to M. Ck 

 Robin, these globules are formed by a sort of vitelline germination. 

 We see successively appear on the surface of the vitellus two 



FIG. 48. 

 A, ovum of she dog immediately before the B, ovum of she dog some hours later. The epi 



commencement of segmentation. Tlie 

 contraction has given to the vitellus a 

 polyhedrical form. a, epithelial colls ; 

 c, space between the contracted vitellus 

 (d) and the vitelline membrane or pellucid 



thelial cells are further diminished ; the 

 vitellus separated into two segments or 

 spheres of fractionment. Between these 

 two halves are seen the bright vesicles (c) 

 called vesicles of direction. The letters as 

 before. 



or three projections, which take the hemispherical form, and 

 separate by division from the mass which has engendered them, 

 remaining interposed between the cellular membrane and the 

 vitellus. These are the polar globules (Fig. 49, A e). 



All the evolutive phenomena which we have just signalised 

 can be accomplished before fecundation ; they can also be posterior 

 thereto. But in certain species the spontaneous ovular evolution 

 goes much further, since, in the cases of parthenogenesis the 

 whole development of the embryon is effected without the succour 

 of fecundation. This ovular generation, without males, this 

 parthenogenesis, which the doctors of Catholic theology are sure 



