' STUDIES ON GERM CELLS 397 



this end in view, the problem is still unsolved. It is evident 

 from the preparations that the oocyte is nourished by and grows 

 at the expense of the nurse cells (figs. 28-32) . It is also absolutely 

 certain that these nurse cells are not derived from the oogonia, as 

 is true in so many insects, but, are modified mesoderm cells 

 (figs. 38, 39, 27). At first, the growth of the oocyte takes place 

 so slowly as to make almost no perceptible difference in the char- 

 acter of the cytoplasm contained within it. The oogonia are 

 remarkably easy to distinguish during the embryonic develop- 

 ment because (1) of their comparatively enormous nuclei, filled 

 with large chromatin granules; and (2) the deeply staining 

 quality of their cytoplasm, consisting of the corresponding 

 deeply staining substance of the 'polares Plasma' of the ma- 

 ture egg (figs. 31-32). As the oocyte grows its cytoplasm be- 

 comes less deeply colored and presents a uniform appearance 

 not distinguishably different from the cytoplasm of the other 

 cells (fig. 40). Sometime before the oocyte is ready for matura- 

 tion, however, deeply staining cytoplasm appears in the neigh- 

 borhood of the nurse chamber and a substance begins to accumu- 

 late at the posterior pole which has a strong affinity for various 

 dyes (fig. 28). The former is evidently elaborated under the 

 influence of the nurse cells; the latter, which represents the 

 'polares Plasma,' may be derived from the nurse cells, but if it 

 is, the process is so slow and its mass compared with the mass of 

 the remaining egg contents so small that its passage from the 

 nurse chamber to the posterior end of the oocyte is indistinguish- 

 able. We must conclude, therefore, that the 'polares Plasma' 

 may originate from or under the influence of the nurse cells, but 

 that this has not been demonstrated and probably never can be 

 established. 



A second hypothesis which may account for the presence of 

 the 'polares Plasma' in succeeding generations is that of continu- 

 ity and growth. Each oogonium is supplied with a portion 

 (typically one sixty-fourth) of the 'polares Plasma' of the mature 

 egg. Hence a certain amount of this substance, as well as a like 

 amount of nuclear material, is passed on from one generation to 

 the next. What is more probable than that this part, although 



