Dr Martin Barry's Researches in Embryology. 49 



in the Bird's " egg ;" which latter I found to be originally a 

 perfect " zona pellucida," — its consistence almost fluid.*) 



If the analogies now pointed out be admitted, they will of 

 course be found applicable, more or less, to the ova of other 

 animals, as well as to the ovum of the Bird. 



They will also serve to explain the occasional presence in 

 the Bird's " egg" of more than one yelk (ovum) ; obviously 

 referable to the same cause as that (to be presently men- 

 tioned) sometimes producing in Mammalia several ova in one 

 Graafian follicle. For, it must be remembered, the founda- 

 tion of the Graafian follicl$ in Mammalia is the ovisac ; and 

 the ovisac I have just stated my belief to become the shell- 

 membrane of the Bird's " egg."t 



(The existence of my retinacula is actually among the 

 facts that Bischoff has denied. I must confess that this ap- 

 pears to me to imply investigation so superficial, that I do 

 not wonder at denial in the same quarter of facts requiring 

 far more profound research. For instance, the penetration 

 of the Spermatozoon into the ovum, my observation of which, 

 — though the fact was stated to have been demonstrated to 

 an Owen and other men of eminence, — Bischoff ridiculed as 

 " born of the imagination. 1 ' Those who, from such denial, 

 have been led to doubt the existence of the retinacula, may 

 be convinced of it without the trouble even of opening a 

 Graafian follicle, by simply examining the latter in the Bab- 

 bit, or still better in the Ferret (Mustela Furo), from the ex- 

 terior of the ovary with a good pocket lens.) 



I cannot refrain from again referring to the egg-like form, 

 tapered at one end (this end often found to be the position 

 of the ovum), among my figures of the ovarian ovisac, which 

 I believe to become the shell-membrane of the Bird. For 

 such an early appearance of that tapered form suggests the 



* Phil. Trans., 1838, Plate 5, fig. 25. 



t In the Dog, I have frequently seen three, and not rarely four ova in one 

 Graafian follicle ; and in the Ferret, such instances of plurality are still more 

 frequent. 



VOL. LVL NO. CXI. — JANUARY 1854. D 



