OVUM. 



view which he had previously taken, that the 

 zona becomes the chorion, or at least that a 

 new deposit is not in all Mammalia necessary 

 for the formation of that membrane. 



Fig. 57*. 



[85] 



Fig. 58*. 



Ova of the Rabbit from the Fallopian tube three days 

 after impregnation. 



A, shows on a dark ground one of these ova, of 

 which B is an explanatory outline, y, s, are the 

 yolk segments of which there were eight; z, the 

 zona ; a, the thick layer of albumen which in this 

 animal is always deposited on the exterior of the 

 zona after the granular cells have been removed 

 from it. 



c and D. Other ova from the same animal ; in D, 

 are shown three projections of the albuminous 

 covering which have been taken for villi of the 

 chorion ; but which according to Bischoff are not 

 so. This ovum was farthest down in the Fallopian 

 tube. 



In a series of observations made by myself 

 on the ovum of the dog and rabbit dining 

 their descent from the ovary to the uterus, 

 in the summer of 1840, I was induced to 

 adopt the opinion that a new deposit does 

 really occur on the surface of the ovum in 

 both of these animals. I repeatedly ob- 

 served the large gelatinous or firm thick 

 albuminous covering on the rabbit's ovum 

 when it had just entered the cavity of the 

 uterus; and in several instances 1 thought 

 I could perceive the first formation of the 

 villi of the chorion by sprouting or budding 

 from the surface of the newly deposited sub- 

 stance, which, as in Wharton Jones' and 

 Barry's observations, it was quite easy to dis- 

 tinguish from the membrane of the zona. In 

 the ovum of the dog I admit, with Bischoff, 

 the appearance is very different ; but yet my 

 observations appeared to me to demonstrate 

 that in that animal also a substance is super- 

 added to the surface of the zona, for that mem- 

 brane, which presents at an earlier period a 



Ovum of the Dog from the Fallopian tube ten days 

 after impregnation. 



A. The yolk has undergone division into eight 

 segments, and there is a thin irregular deposit of 

 albumen on the outer surface of the zona. (This is 

 represent> d too light in the figure.) 



B. Explanatory outline of the same; y,s, yolk 

 segments ; z, zona pellucida ; a, layer of albumen, 

 from which in connection with the zona the chorion 

 takes its origin. 



perfectly distinct and smooth outline on its ex- 

 ternal surface, becomes in the course of the 

 descent through the Fallopian tubes and by the 

 time of its first arrival in the uterus, not only 

 irregularly flocculent on its surface, but also 

 thickened ; in fact, presents all the appearance 

 of a gramilo-mucous substance having been 

 deposited upon it. 



It may be proper to explain here, that it has 

 now been fully sho\\n by Bischoff's excellent 

 observations, that in both the animals men- 

 tioned, and also in the guinea-pig, the cells 

 of the tunica granulosa, which adhere to the 

 surface of the zona when it leaves the Graafian 

 follicle.are completely separated from it within 

 the first two or three days of the residence of 

 the ovum within the tube, so as to leave the 

 external surface of the zona perfectly smooth. 

 Bischoff has shown, indeed, as I have also 

 repeatedly observed, that a change has oc- 

 curred in the cells of the proligerous disc, 

 adherent to the ovum while it is still within 

 the ovary, which indicates its approaching 

 maturity. This change consists, as already 

 stated, 'in these cells becoming somewhat 

 spindle-shaped or pyriform, their narrow or 

 pointed ends being attached to and radiating 

 from the surface of the zona. (See as before 

 fg. 55. L>.) It is quite easy, therefore, after 

 this separation takes place, to distinguish 

 any change bv addition of new matter or 

 otherwise which the suiface of the zona 

 may undergo. No one can fail to perceive the 

 [G 3] 



