XIII 

 DEVELOPMENT OF THE CHICK 



Oogenesis. — The egg during its genesis passes 

 through three stages — division, gro^vth, and 

 maturation. The first stage takes place before 

 the female chick is hatched, and comes to an 

 end about the time of hatching. It consists 

 of the rapid increase of small ova by repeated 

 division ; with the result that the ovary 

 of the newly-hatched chick contains a large 

 number of large cells from which the eggs, 

 as we know them when laid, are to be produced. 

 About the time of hatching the ova enter 

 into the second stage, during which there is 

 a considerable increase in size accompanied 

 by the formation of yolk. The ova are now 

 contained in definite follicles within the ovary. 

 Each ovum is surrounded by a layer of cubical 

 epithelial cells (Figs. 40 and 41), and the follicle 

 is provided with a theca formed by a con- 



110 



