92 POULTRY PRODUCTION 



position. While the nucleus is still at the centre a deposit 

 of extremely fine granules of yolk is formed around it and 

 gradually extends toward the cell wall. This deposit is what 

 is later recognized as the latebra of the flask-shaped mass 

 of white yolk. 



When the ovum has reached a size approximating 0.66 

 mm. the nucleus migrates lo a position at the end of the flask- 

 shaped formation and just under the vitelline membrane. 



Successive layers of yellow yolk are deposited around the 

 central mass of white yolk by the activity of the peripheral 

 layer of protoplasm. These layers are somewhat correlated 

 with the periodic daily physiologic rhythm of the vitality 

 of the hen. 



When the yolk comes to full size, it escapes from the ovary 

 by the rupture of the follicle along the stigma, into the funnel 

 of the oviduct, which, as Lillie^ states, "swallows it, so to 

 speak, and it passes on by peristaltic contraction of the ovi- 

 duct. The escape of the ovum from the follicle is known as 

 the process of ovulation." 



"The stimuli which initiate the peristaltic action of the 

 oviduct and attract the funnel to the mature follicle are 

 among the unsolved problems of physiology. The yolk is 

 already oriented in the follicle before the funnel encloses it."^ 

 "Internal pressure due to continued yolk formation is prob- 

 ably the most important factor in the normal rupture of the 

 follicle, since closing the funnel or removing the duct appar- 

 ently does not greatly delay ovulation."' 



Fertilization takes place almost immediately after ovula- 

 tion, the spermatozoa having made their way through the 

 entire length of the oviduct. Lillie* states that " The ovum 

 is surrounded immediately after ovulation ... by a 

 fluid containing spermatozoa in suspension. The entrance 

 of several spermatozoa (into the ovum) seems to be char- 

 acteristic of vertebrates with large ova." 



Only one of these (spermatozoa) serves as a functional 

 sperm nucleus: the remainder or supernumerary sperm 



' Oppoa. cit. 



= Curtis, Maine Bulletin No. 228. 



" Pearl and Curtis, Journal Experimental Zoology, vol. vii, No. 3. 



'Oppos. oit. 



