GERMINAL MEMBRANE. 01 



brane, that is, from such cells as are met with in the area 

 pellucida, so that the embryo is composed, partly of small 

 cells without nuclei, and partly of cells furnished with the cha- 

 racteristic nucleus. It presents, however, besides them, an 

 extraordinary quantity of simple cell-nuclei with nucleoli, around 

 which no cells have as yet formed. 



I have made but few researches with respect to the structure 

 of the vascular layer, and from them, I could not (with the 

 exception of the vessels themselves and the blood) detect any 

 such essential difference between it and the mucous layer, as 

 was exhibited between the latter and the serous laver. As, how- 

 ever, the formation of the vessels themselves, although it ap- 

 pears to depend upon a production of cells, is not a process pe- 

 culiar to the germinal membrane, we shall defer it, to be re- 

 sumed at a subsequent stage of our investigation. 



I have not ascertained the relation which these cells of the 

 layers of the germinal membrane have to the primitive globules 

 of the membrane before incubation, or within eight hours after 

 that process has commenced ; but inasmuch as it is probable 

 that at least one of those kinds of cells owes its origin to the 

 development of the primitive globules, we may be permitted to 

 suppose that those globules are likewise cells. 



For the purpose of giving, in outline, a connected view of the 

 changes which the e^g undergoes, from its first formation up 

 to the period at wdiich the actual development of the embryo 

 commences, — in so far as the foregoing, more or less complete, 

 observations enable us to form a provisional conception of the 

 process of development, — we will proceed on the understanding, 

 that the germ-vesicle is the nucleus of the yelk-cell ; at the same 

 time, however, we expressly refer the reader to the more de- 

 tailed statement above furnished for the certainty both of this 

 and of every other separate point which occurs in the following 

 exposition. It is probable that the germ-vesicle is the first struc- 

 ture, and that the yelk-cell forms around it as its cell-nucleus. 

 Both advance in growth, the latter, however, much more rapidly 

 than the former. A precipitate, the commencement of the ger- 

 minal membrane, next forms around the germ-vesicle. Young 

 cells are simultaneously formed in the remaining space of the 

 yelk-cell, these are the cells of the subsequent yelk-cavity. Then 

 cells of another kind originate beneath the vitelline membrane, 



