580 STRUCTURE OF THE BIRD'S EGG. 



own substance is scarcely distinguishable. Not only thousands 

 but tens of thousands of eggs are often produced by a single 

 individual, their aggregate forming what is known as the 

 "hard roe;" whilst the "soft roe" or "milt" is the corre- 

 sponding mass of sperm-cells produced by the male. 



755. After the ovum of the Bird has quitted the ovarium, 

 and is passing through the oviduct towards its outlet, it 

 receives layer after layer of albumen poured out in a viscid 

 condition from the lining membrane of the oviduct, forming 

 the "white" of the egg (fig. 315, g) ; and this is inclosed in 



Fig. 315. SECTION OF FOWL'S EGG : 



o, cicatricula; b, yolk-bag; c, membrane lining shell; d, attachment of chalazag; 

 e, chalazse ; /, air-space ; g, albumen. 



a double membrane composed of a network of fibres, which 

 is formed by the consolidation of a, plastic exudation ( 391), 

 poured out after the albuminous exudation has been com- 

 pleted. The outer layer of this membrane is consolidated by 

 the deposit of calcareous particles in the interspaces of its 

 fibrous matting, so as to form the " shell " of the egg ; an 

 arrangement that gives the necessary protection, without cut- 

 ting-off the contents of the shell from that communication 

 with the atmosphere which is requisite for the development 

 of the embryo. The inner layer, which forms a lining to the 

 shell, separates into two laminae at the large end of the egg ; 

 and, inclosed between these, there is a bubble of air (/), which 

 serves to give the young bird, just before it is hatched, the 



