Diseases of the Reproductive Organs 249 



The processes concerned in the formation of an egg may 

 be summarized as follows : 



Certain ones of the small oocytes in the ovary (Fig. 55, 

 1) are all the time coming into a state of physiological ac- 

 tivity, while the hen is in a laying cycle. These oocytes 

 grow in size by the deposition of yolk until finally they are 

 of the full size for laying. The time required for this final 

 growth of yolks preparatory to laying is not far from 20 

 days, on the average.^ 



The fully formed yolk, or ovum, leaves the follicle through 

 a rupture of the latter along the stigma (Fig. 55). This 

 process is called ovulation. As it leaves the ovary the ovum 

 is received by the funnel of the oviduct. 



After entering the infundibulum the yolk remains in the 

 so-called albumen portion of the oviduct about three hours 

 and in this time acquires only about 40 to 50 per cent by 

 weight of its total albumen and not all of it as has hitherto 

 been supposed. During its sojourn in the albumen portion 

 of the duct the egg acquires its chalazse and chalaziferous 

 layer, the dense albumen layer, and (if such a layer exists 

 as a distinct entity, about which there is some doubt) the 

 inner fluid layer of albumen. 



Upon entering the isthmus, in passing through which 

 portion of the duct something under an hour's time is 

 occupied instead of three hours as has been usually main- 

 tained, the egg receives its shell membranes by a process 

 of discrete deposition. At the same time, and during the 

 sojourn of the egg in the uterus, it receives its outer layer 

 of fluid or thin albumen which is by weight 50 to 60 per 

 cent of the total albumen. This thin albumen is taken in 

 by osmosis through the shell membranes already formed. 



' Cf. Gerhartz, W., "Uber die zum Aufbau der Eizelle notwendige 

 Energie (Transformationsenergie)." Pfliiger's Arch., Bd. 156, pp. 

 1-224, 1914. 



