THE EARLY DEVELOPMENT OF THE CHICK 241 



but it is known that this occurs immediately after ovulation, 

 while the ovum is in the infundibulum. Polyspermy is normal, 

 five to twenty-four spermatozoa having been counted within 

 a single ovum (Patterson). Entrance of the spermatozoa 

 affords the stimulus to the completion of maturation, which 

 offers ho unusual features. After the second maturation division 

 the egg nucleus unites with one of the sperm nuclei and the first 

 cleavage spindle is typically established. 



C. FROM THE BEGINNING OF CLEAVAGE TO THE TIME 

 OF LAYING 



Before continuing our account of the development of the 

 ovum we must outline the series of events occurring during 

 the passage of the egg down the oviduct; we shall follow the 

 accounts given by Patterson, and Pearl and Curtis. 



The first cleavage furrow appears about three hours after 

 ovulation. During this interval the egg has traversed the 

 entire glandular portion of the oviduct, the walls of which have 

 secreted the denser layers of albumen and the chalaza3 (40 to 

 50 per cent, of the entire weight of albumen) . The egg is carried 

 along chiefly by peristaltic contraction of the oviducal wall, 

 and as it passes it is rotated about the long axis of the oviduct, 

 so that the germ disc describes a spiral path; this accounts for 

 the spiral arrangement of the albumen around the yolk. Dur- 

 ing the next hour or so (Pearl) the egg traverses the isthmus, 

 the walls of which secrete the shell membrane over the surface 

 of the dense albumen as the egg enters this region. The fluid 

 layer of albumen is added while the egg is traversing the isth- 

 mus and the upper part of the uterus. The formation of this 

 fluid . albumen, which passes through the shell membrane 

 already laid down, is completed five to seven hours after the 

 egg enters the uterus (nine to eleven hours after entering the 

 oviduct). Before this the calcareous shell substance has begun 

 to be laid down on the shell membrane. The egg usually 

 occupies twelve to sixteen hours longer in completing its 

 passage through the uterus and vagina. At the end of this 





