88 Dr Barry's Researches in Embryology, 



the unfecundated ovarian ovum. So far from thinking that such 

 is the case, the author beUeves the whole substance of the ci- 

 catricula in the laid agg to have its origin within the germinal 

 vesicle, in the same manner as in the ovum of mammalia. 



There is no fixed relation between the degree of development 

 of ova, and their size, locality, or age. The variation with re- 

 gard to size is referable chiefly to a difference in the quantity 

 of fluid imbibed in different instances by the incipient chorion. 

 Vesicles filled with transparent fluid are frequently met with 

 in the Fallopian tube, very much resembling the thick tran- 

 sparent membrane of the ovarian ovum. These vesicles are 

 probably unimpregnated ova, in the course of being absorbed. 

 The so-called " yelk " in the more or less mature ovarian ovum, 

 consists of nuclei in the transition state, and exhibiting the 

 compound structure above described. The mass of these be- 

 comes circumscribed by a proper membrane. They and their 

 membrane subsequently disappear by liquefaction, and are 

 succeeded by a new set, arising in the interior, and likewise 

 becoming circumscribed by a proper membrane, and so on. 

 This explains why some observers have never seen a membrane 

 in this situation. After the fecundation of the ovum, the cells 

 of the tunica granulosa, that is, part of the so-called " disc," 

 are found to have become club-shaped, greatly elongated, filled 

 in some instances with cells, and connected with the thick 

 transparent membrane by their pointed extremities alone. 



That the thin membrane described by the author in his se- 

 cond series as rising from the thick transparent membrane in 

 the Fallopian tube, and imbibing fluid, is really the incipient 

 chorion, was then shewn by tracing it from stage to stage, up 

 to the period when villi form upon it. There remained, how- 

 ever, two questions undecided ; viz., whether the chorion is 

 formed of cells, and if so, whether the cells are those of the so- 

 called " disc,'* brought by the ovum from the ovary. The 

 author now states that the chorion is formed of cells, which 

 gradually collect around the thick transparent membrane, and 

 coalesce ; and that the cells in question are not those of the 

 " disc," brought with the ovum from the ovary. The cells 

 which give origin to the chorion are intended to be more par- 

 ticularly described in a future paper. 



