THE POLE DISC OF CHRYSOMELID EGGS. 



185 



Does the fact that the granules of the pole disc are derived 

 from the food stream in any way modify our conception of their 

 significance ? Were they derived from the chromatin of the 

 nucleus, the fact might be regarded as supporting their hypo- 

 thetical role of germ cell determinants, inasmuch as it would be 

 in accord with the view that the chromatin plays a primary part 

 in directing and perhaps determining the activity of the cell. On 



Fig. 6. Longitudinal section of the posterior end of the early embryo. X 600. 

 p.c, pole cells ; p.d., pole disc ; y., yolk. 



the other hand, if they represent so much food material, their 

 significance as germ cell determinants appears in a different light. 



The granules of the food stream are derived from the cyto- 

 plasmic granules of the nurse cells, which are germ cells that 

 have lost the function of reproduction and that have taken up 

 secondarily the function of secreting material for the growth and 

 development of the ova. In early stages the nurse cells do not 

 differ in any regard from their sister cells destined to become 

 ovocytes. In my paper referred to above I have described what 

 appear to be some of the factors in the differentiation of the 

 primordial germ cells into nurse cells and sex cells, and shall 

 not enter into the matter here. 



At the time of this differentiation the nurse cells pass through 

 a period of amitotic divisions, at which time the usual staining 

 reactions of nucleus and cytoplasm become reversed, i. e., the 

 nucleus stains with the acid dye, while the cytoplasm, including 

 the granules which later form the nutritive stream, stains with 

 the basic dye. 



