DEVELOPMENT PRIOR TO LAYING 35 



it rapidly withdraws from the surface of the egg to a deeper 

 position near the center of the germinal disc. (Concerning the 



Fig. 12.- — Egg nucleus (female pronucleus) and polar bodies 

 of the pigeon's egg. (After Harper.) 8.30 p.m. x 2000. 

 E. N., Egg nucleus, p. b. 1, First polar body. p. b. 2, 

 Second polar body. p'v. S., Perivitelline space, v. M., Vi- 

 telline membrane. 



general theory of the maturation process see E. B. Wilson, "The 

 Cell in Development and Inheritance/' the Macmillan Company, 

 New York.) 



II. Fertilization 



The spermatozoa traverse the entire length of the oviduct 

 and are found in the uppermost portion in a fertile hen. The 

 period of life of the spermatozoa within the oviduct is considerable, 

 -as proved by the fact that hens may continue to lay fertile eggs 

 for a period of at least three weeks after isolation from the cock. 

 After the end of the third week the vitality of the spermatozoa 

 is apparently reduced, as eggs laid during the fourth and fifth 

 weeks may exhibit, at the most, abnormal cleavage, which soon 

 ceases. Eggs laid forty days after isolation are certainly unfer- 

 tilized, and do not develop (Lau and Barfurth). The so-called 

 parthenogenetic cleavage of such eggs is merely a phenomenon 

 of fragmentation of the protoplasm; there is no true cell-division. 



The ovum is surrounded immediately after ovulation, that is 

 in the infundibulum,by a fluid containing spermatozoa in suspen- 

 sion. In the egg of the pigeon a certain number of spermatozoa 



