28 



THE DEVELOPMENT OF THE CHICK 



line membrane (Fig. 7). It becomes elliptical, and later the outer 

 surface is flattened against the vitelline membrane, the inner 

 surface remaining convex (Fig. 8). The point on the surface to 

 which the germinal vesicle migrates is situated away from the 

 surface of the ovary, and thus in the position of the pedicle of 



/:S.- 



, V Jtr^r '.J*- -*^, V ft Ou/' 



Fig. 7. — Section of an ovarian ovum of the pigeon; drawn from a prepara- 

 tion of Mr. J. T. Patterson. The actual dimensions of the ovum are 1.44 

 X 1.25 mm. 



f. s., Stalk of follicle. G. V., Germinal vesicle. Gr., Granulosa. L., 

 Latebra. p. P., Peripheral protoplasm, pr. f., Primordial folhcles. Th. ex., 

 Theca externa. Th. int., Theca interna. Y. Y., Yellow yolk. Z. r., Zona 

 radiata. 



the follicle, when the latter projects from the surface of the ovary 

 (Fig. 7). This determines the position of the future germ disc. 

 The nucleus increases in size with the growth of the ovum; in the 

 youngest ovocytes its diameter is about 9 /x; in the ripe ovum it is 

 flattened and may measure 455 ju in diameter by 72 ^ in thickness. 



