l^iitritioii of the Ovum of Scolia Diibia. 137 



follicle cell, lie against each other in a compact mass. At the prox- 

 imal base of the follicle is found a core of follicle epithelial cells. 

 Into this eelhilar core the ovnm sends a cytoplasmic process. The 

 nurse cells have in the meantime undergone an intermediate period 

 of rest and growth (Fig. G). 



With the approach of the second phase of functional or secreting 

 activity the migrated follicle nuclei (described at p. 132) appear 

 within the cytoplasm of the ovum (Fig. 0). The chromatin of the 

 nuclei of the nurse cells becomes evenly distributed. This chromatin 

 feature remains little changed in those cells that have functioned 

 through yolk ducts. In the others the charge of chromatin distribu- 

 tion travels as a wave from the i)roximal region distally throughout 

 the follicle. The distal nuclei, therefore, are the last to show this 

 chromatin feature. 



The nurse cells continue to grow. Their nuclei become more or 

 less irregular in contour. Vacuoles appear in their cytoplasm. 

 Within the ovum the migrated nuclei become abundant and lie at 

 the pole next to the nurse follicle. A large irregidar vacuole ap- 

 pears within the egg cytoplasm as the evident recipient of the secre- 

 tion of the nurse cells (Fig. 10). With these appearances the second 

 phase of nutrition may be considered well under way. 



The secretion continues at the expense of the nurse cells. The 

 cytoplasm of some of the proximal cells breaks down. The remain- 

 ing cells become loosely disposed within the follicle. As the process 

 continues, a wave of cytoplasmic disintegration passes more or less 

 regularly distally through the nurse follicle which is closely followed 

 by the disintegration of the nuclei. In the meantime the nurse 

 follicle collapses (Fig. 10). 



The follicle epithelium cells between ovum and nurse cells become 

 loosely arranged so that the secretions of the nurse cells pass freely 

 into the greatly enlarged ovum. These secretions continue to form 

 a vacuole in the multinuclear cytoplasm at the distal pole of the egg 

 cell. By the interaction of the contained nuclei and cytoplasm the 

 material thus taken up is transformed into yolk spherules which are 

 deposited in the proximal half at the periphery of the ovum (Fig. 

 10? !/• U-)- The deposition of yolk continues until all the cytoplasm 



