12 



THE HEN S EGG. 



[chap. 



Examined with care tlie ovum, which is tolerably uni- 

 form in appearance, will be found to be marked at one 

 spot (generally facing the stalk of the capsule and form- 

 ing the pole of the shorter axis of the ovum) by a small 

 disc differing in appearance from the rest of the ovum. 

 This disc which is known as the germinal disc or discus 



Fig. 4. 



Section through the Germinal Disc of the ripe Ovarian 

 Ovum of a Fowl while yet enclosed in its Capsule. 



a. Connective-tissu e caps ule of the ovum. b. follicular epithe- 

 lium, at the surface of which nearest the ovum lies the 

 vitelline membrane, c. granular material of the germinal 

 disc, which becomes converted into the blastoderm. (This 

 is not very well represented in the woodcut. In sections 

 which have been hardened in chromic acid it consists of fine 

 granules.) w. y, white yolk, which passes insensibly into 

 the fine granular material of the disc, x, germinal vesicle 

 enclosed in a distinct membrane, but shrivelled up by the 

 action of the chromic acid, y, space originally completely 

 filled up by the germinal vesicle, before the latter was 

 shrivelled up by the action of the chromic acid. 



proligerus, consists of a lenticular mass of protoplasm 

 (Fig. 4, c), imbedded in which is a globular or ellipsoidal 

 body (Fig. 4, x), about 310/i in diameter, called the 

 germinal vesicle. This has a delicate wall, and its con- 

 tents are clear and fluid in the fresh state, but become 

 granular upon the addition of reagents. 



