28 



THE DEVELOPMENT OF THE CHICK 



Although the nuculeus (germinal vesicle of authors) may 

 be excentric in position in the youngest ovocytes, it always 

 occupies an approximately central position in those slightly 

 older. The nucleus increases in size with the growth of the 

 cell-body; in the youngest ovocytes its diameter is about 9 /x. and 



f.s.- 



P.P. 



-Th.int. 



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 follicles. Th. ex., 



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



radiata. 



in the ripe ovum it is flattened and measures about 117 x 

 315 ja. It retains its central position until the ovum is about 

 0.66 mm. in diameter, and then moves to the surface where 

 it lies almost in contact with the vitelline membrane (Fig. 

 7). It becomes elliptical, and later the outer surface is flat- 



