GERMINAL MEMBRANE. G3 



as a portion of the germinal membrane separating from the 

 whole by a constriction. Both layers contribute to its forma- 

 tion, and it therefore consists of small transparent cells, some 

 of which (probably those pertaining to the mucous layer) con- 

 tain no nucleus, whilst others (those derived from the serous 

 layer) exhibit the characteristic cell-nucleus with its nucleoli. 

 In addition to these cells it contains a great many nuclei, 

 around which no cells have as yet formed. Between the 

 two layers of the germinal membrane other cells arise, which 

 may be regarded as representing a third layer, the vascular, 

 although they do not really form a connected independent 

 layer; of these we shall treat hereafter. These three layers 

 then, and pre-eminently the first two, form the mediate basis 

 of all the subsequent tissues. 



The yelk is not a lifeless aliment for the embrvo, — as it is 

 when taken as food by the adult, to whose organism it is dead 

 and must be chemically dissolved, — but the cells of the yelk 

 take part in the vitality called forth by incubation. They 

 effect an alteration in their contents, wherebv the albumen 

 which they contain loses its property of coagulating, and the 

 granules become dissolved, in the same manner in which the 

 granules of starch dissolve in the cells of the vegetable embrvo. 

 In short, the yelk bears the same relation to the embryo as 

 regards its nutritive property, that the albumen bears to the 

 vegetable embryo. 



In accordance with the analogy between the cells we are 

 treating of and those of vegetables, all the changes in the egg f 

 the growth of the germinal membrane, and even the first forma- 

 tion of the embryo, proceed entirely without vessels. 



