FEMALE REPRODUCTIVE CELLS 



453 



GROWTH AND MATURATION OF THE FEMALE REPRODUCTIVE 



CELLS 



The female reproductive cells are usually indistinguishable from the 

 male, so far as any visible cytological differentiation is concerned, until 

 near the time of yolk accumulation and maturation. They can usually 

 be determined a long time before this by their position, or by the devel- 

 opment of accessory sexual tissues in the organism that are not in direct 

 contact with them. 



FIG. 416. A half-grown ovum of Molgula manhattensis. f.c., outer row of follicle cells; 

 n.c., nurse.cells moving from follicle into cytoplasm of ovum. X 1200. 



The first noticeable feature in the development of the young female 

 reproductive cell is its relation to the cells which are going to aid it in 

 securing and storing in its body the great amount of food material that 

 will be needed later. It appears probable that, owing to its necessary 

 occupation with its own internal preparations, or perhaps owing to the 

 enormous quantity of food required, or possibly to the lack of food-pre- 

 paring structures in its own make-up, that the ovum is always asso- 

 ciated with such accessory nurse cells. 



A primitive method of food acquisition is for the young egg cell to 

 wander among the surrounding tissue cells and ingest them. This 



