REPRODUCTION— CONCERNING EGGS 211 



of uniform structure throughout, but that there is a portion of 

 it having the shape of a flask with a funnel-shaped neck, and 

 containing a quantity of more or less fluid matter. The ex- 

 panded neck of this flask-shaped space is situated immediately 

 under the small white spot or disc, while its bulbous portion 

 extends to the middle of the egg. The fluid contents of this 

 flask are known as the "white yolk," and similar white yolk 

 will be found throughout the rest of the yellow yolk, disposed 

 in the form of concentric layers enclosing yellow yolk between 

 them, the final layer lying immediately under the vitelline 

 membrane, and becoming continuous with the expanded neck 

 of the flask just described. The " white yolk '' differs, as might 

 be expected, from the yellow yoke in its microscopic characters, 

 but into these differences we need not enter. 



The clear jelly-like outer investment of the yellow yolk con- 

 stitutes the " albumen " of the egg, and from its appearance 

 when boiled is known as the "white" of the egg. If carefully 

 examined in the unboiled egg there will be found at each pole, 

 embedded within this albumen and extending from the vitel- 

 line membrane, a little spirally twisted "cord" of denser struc- 

 ture, that at the narrow end of the egg being more or less 

 firmly fixed to the shell, or rather to the membrane lining this. 

 These bodies serve to keep the yolk in position, as well as the 

 purpose of pads to reduce the effect of shock. From the fact 

 that the interior of these cords presents the appearance of a 

 succession of white knots, these cords are known as " chalazae " 

 (hailstones). 



If an opening be cut through the side of the shell of a fresh 

 egg, the germinal portion will always be found at the top. This 

 is due to the lighter specific gravity of the yolk in the neigh- 

 bourhood of the disc, and not to the control of the chalazae. 



In birds the left ovary alone is functional. Each egg is en- 

 closed in a capsule, and on the completion of its store of yolk, 

 that is to say when ripe, bursts its capsule and escapes into the 

 oviduct, and here the completion of its growth commences. 

 This consists in the addition of the albumen and the shell 

 membranes and the shell, which are formed by the glands of 

 the walls of the oviduct. 



The true egg then consists only of the germinal protoplasm 

 and the yolk, since these only are produced by the ovary. The 



