STUDIES ON GERM CELLS 411 



be distinguished for a considerable period during early embryonic 

 development. It seems necessary to conclude therefore that 

 in Chrysomelid eggs both germ cells and somatic cells possess 

 the full amount of chromatin, or else the elimination of this 

 substance takes place in some other way. This point will be 

 more fully considered later (p. 465). 



The differentiation of the nuclei of the blastoderm cells, pri- 

 mordial germ cells, and vitellophags. The conclusion that no 

 chromatin-diminution process occurs during the early cleavage 

 divisions in the eggs of Chrysomelid beetles necessitates the 

 search for some other method of differentiation among the 

 cleavage nuclei. The insect egg is particularly advantageous 

 for testing Roux's hypothesis of qualitative nuclear divisions, 

 since we have here the production of an enormous number of 

 nuclei before any cell walls are formed, and an egg that is re- 

 markably definitely organized, as indicated by my experiments 

 (Hegner, '09b, '11a), before the blastoderm is formed. 



I have been unable to find any differences in the nuclei before 

 the energids fuse with the keimhautblastem, but as soon as this 

 does occur, a gradual change takes place, and at the time when 

 the blastoderm is completed three sorts of nuclei are distin- 

 guishable: (1) The nuclei of the primordial germ cells (fig. 53) 

 are larger than the others and contain comparatively few spheri- 

 cal chromatin granules evenly distributed. The cytoplasm of 

 these cells is distinguishable from that of all other cells because 

 of the presence of granules from the pole-disc; (2) The nuclei 

 of the blastoderm cells (fig. 54) are small and completely filled 

 with large spherical chromatin granules; (3) The nuclei of the 

 vitellophags (fig. 55) resemble the early cleavage nuclei; they 

 are midway between the other two kinds in size, and their chro- 

 matin is more diffuse. 



Whether these three kinds of nuclei were all potentially alike 

 before their differentiation is an important question. Visibly 

 they are all similar until they become localized in definite regions 

 of the egg, and associated with particular cytoplasmic elements. 

 One can but conclude that they were all potentially alike and 

 that their differentiation was brought about through the influence 



