196 Harry Lewis Wieman. 



changes which are assumed to be due to the failure of the nuclear 

 membrane to rupture at regular intervals and discharge materials 

 of the nature of oxydases or oxidizing substances into the cyto- 

 plasm, and the result is a reversal in the ususal staining reactions 

 of nucleus and cytoplasm. This change is preceded by the expul- 

 sion from the nucleus into the cytoplasm of a basic staining granule 

 which gradually undergoes solution and disappears. 



In their later history some of the nurse cells pass through a 

 cycle of chemical changes which originate in the center of the 

 nucleus and spread toward the periphery, leaving as a final 

 stage, an acid-staining central area surrounded by three concen- 

 tric shells of alternating basic and acid-staining regions. 



The nutrition of the ovum is derived entirely from the nurse 

 cells by means of an ''egg-string," which is a pseudopodium-like 

 process of the cytoplasm of the egg, that is left behind as the ovum 

 moves down the tube in the early part of the growth period, and 

 the distal end of which comes into relation with the spaces be- 

 tween the nurse cells. This intercellular region from its appear- 

 ance in sections has been likened to a system of ducts into which 

 the nutritive material from the nurse cells is secreted ,and whence 

 it passes via the egg-strings into the eggs. 



The nutritive stream consists of basic staining granules identi- 

 cal with those found in the cytoplasm of the nurse cells. At first 

 these granules are found evenly distributed in all parts of the cyto- 

 plasm of the ovocyte, but later, a definite stream extends from the 

 end of the nurse string to the nucleus. In still later stages the 

 deposition of the yolk in the center of the egg causes a split in 

 the food-stream, compelling the latter to take the form of an oval 

 shell inside of which the yolk masses are embedded. 



Attention is called to a rythm of chemical changes in the de- 

 velopment of the ovum. The cytoplasm of the primordial germ 

 cells shows the presence of an acid-staining reticulum which con- 

 tains basic-staining granules apparently identical with those of 

 the food-stream. As yolk is formed these granules of the food- 

 stream disappear in the central part of the egg, being found only 

 in the superficial cytoplasm. Thus it appears that the basic- 

 staining granules from the nurse cells through interaction with 



