20 THE HEN'S EGG. [CHAP. 



protoplasm (Fig. 4, r), imbedded in which is a highly refrac- 

 tive globular or ellipsoidal body (Fig. 4, x), about 310/-1 in 

 diameter, called the germinal vesicle, in the interior of which 

 again is a small body, the germinal spot. 



The rest of the ovum is known as the yolk. This consists 

 of two elements, the white yolk- and the yellow yolk-spheres, 

 which are distributed respectively very much in the same 

 way as in the laid egg, the yellow yolk forming the mass of 

 the ovum, and the white yolk being gathered underneath and 

 around the disc (Fig. 4, iv. y), and also forming a flask- 

 shaped mass in the interior of the ovum. The delicate 

 membrane surrounding the whole is the vitelline membrane. 



Oellaclier's (Untersuckung fiber die Furclmng unci Blatterbildung in Huh- 

 vereie. Studien aus dem Institute fur expcrimentale pathologie in Wien aus 

 dem Jahre 1869, P 1 - l ) account of the ovarian ovum differs considerably 

 from that given above. He finds in the neighbourhood of the blastoderm 

 a finely granular material, within which lies a body appearing circular when 

 viewed from above, but having in section a somewhat quadrilateral shape; 

 its side-walls, however, are curved, with their convexity turned inwards. At 

 the bottom of it lies an oval cavity with doubly contoured walls, and at its 

 upper surface placed somewhat excentrically a semieircular space filled with 

 clear material. 



Oellacher believes that the quadrilateral body which he thus describes is 

 the germinal vesicle which has commenced to undergo a retrogressive meta- 

 morphosis. For the further stages in the metamorphosis, and for further par- 

 ticulars, vide Section 13. The circular hole beneath the vesicle is probably 

 merely filled with fluid and is due to the contractions of the germ. 



12. When the ovarian ovum is ripe and about to be dis- 

 charged from the ovary, its capsule is clasped by the dilated 

 termination of the oviduct. The capsule then bursts, and 

 the ovum escapes into the oviduct, its longer axis corre- 

 sponding with the long axis of the oviduct, the germinal disc 

 therefore being to one side. At the time of the bursting of 

 the capsule the germinal vesicle disappears. 



In describing the changes which take place in the 

 oviduct, it will be convenient, following the order previously 

 adopted, to treat first of all of the formation of the accessory 

 parts of the egg. These are secreted by the glandular walls 

 of the oviduct. This organ therefore requires some descrip- 

 tion. It may be said to consist of four parts ; — 1st. The 

 dilated proximal extremity. 2nd. A long tubular portion, 

 opening by a narrow neck or isthmus into the 3rd portion, 

 which is much dilated, and has been called the uterus; the 

 4th part is somewhat narrow, and leads from the uterus 



