EGG OF COMMON FOWL 



515 



As the egg increases in size it bulges out beyond the surface of 

 the ovary, becoming eventually dependent from the ovary by a thin 

 stalk at the end of which it is enclosed within the distended follicle. 

 The wall of this is richly vascular except on the side away from the 

 stalk where an elongated patch — the " stigma " — marks the position 

 in which the follicle-wall will rupture to set the egg free. 



When this process (ovulation) is about to take place the thin 

 membranous lips of the oviducal funnel become active, apply them- 

 selves to the follicle containing the ripe egg and grip it tightly. The 

 follicle then ruptures and the egg is as it were swallowed by the 

 oviducal funnel. Within the funnel fertilization takes place pro- 

 vided that spermatozoa are present. 1 



The egg proceeds now to travel slowly down the oviduct, propelled 

 onwards by the peristaltic contraction of the oviducal wall, the entire 

 passage occupying about 22 

 hours. As it does so the 

 albumen is deposited on its 

 surface by the secretory activity 

 of the oviducal epithelium. The 

 first to be deposited is rather 

 denser than that formed sub- 

 sequently. It forms a sheath 

 immediately outside the vitel- 

 line membrane and extending 

 in tapering spindle-like fashion 

 for some distance up and down 

 the oviducal cavity : the two 

 prolongations are the chalazae 

 (Fig. 223, ch). 



The envelope of dense albu- 

 men enclosing the egg is not merely propelled onwards; it also 

 undergoes a clockwise rotation about the axis along which it is 

 travelling, caused probably by the cilia present on the oviducal 

 epithelium. Owing to the prolongations of the albumen in front 

 and in rear of the egg not undergoing this rotation the chalazae 

 become twisted upon themselves in opposite directions. 



Layer after layer of albumen (Fig. 223, alb) is deposited round 

 the egg and chalazae until the full size is reached. The character of 

 the secretion then changes and the shell membrane (Fig. 223, s.m) 

 is formed. Finally in the dilated hinder part of the oviduct ("uterus") 

 the secretion is in the form of a thick white fluid which, deposited on 

 the surface of the shell membrane, gradually takes the 'form of the 

 hard and rigid shell perpetuating the characteristically "oval" 

 form impressed upon the egg envelopes during the passage down the 

 oviduct. In composition the egg-shell consists of calcium salts 

 infiltrating a slight organic basis of keratin-like material. Structur- 



1 The spermatozoa remain alive and active within the oviduct for a period of about 

 three weeks. 



Fig. 223. — Unincubated egg of the Fowl. 



a.s, air-space ; alb, albumen ; ch, chalaza ; s.m, 

 shell membrane. In the centre — at the apical pole — 

 is seen the germinal disc with 'the white " Nucleus of 

 Pander " showing through it. 



