302 VERA DANCHAKOFF 



sees in the cytoplasm division itself a differentiation factor, 

 which accompUshes the segregation of different substances in the 

 cytoplasm. Lately interesting observations were made in the 

 laboratory of Prof. C. McClung by Dr. Wenrich and Miss Car- 

 others, on formation of heteromorphic chromosomes in the 

 spermatogenesis of grasshoppers. The admission of similar 

 unequal chromosome-division in somatic cells may explain the 

 gradual development of different mitosis figures characteristic 

 of different tissues. The small sizes of the somatic cells do not 

 allow to gain direct data on the inequality of the daughter cells. 

 However, the examples cited above sufficiently explain the 

 possibility of simultaneous persistence of young stem cells and 

 their further differentiation. 



In connection with the problem of cell differentiation, the 

 existence of a large number of amitotic cell divisions, may be 

 mentioned. Lately Patterson has described in the Keimblattern 

 of the pigeon, the presence of numerous amitoses. In regions of 

 intense proliferation the cells seemed to undergo a full amitotical 

 division, and give rise to apparently normal daughter cells, 

 which could themselves multiply mitotically. Maximow (25) 

 ('08) found similar conditions in certain regions of embryos in 

 mammals. In early stages of spleen development in chicks, 

 when the nuclei proliferate intensely in the mesenchymal spleen 

 anlage, numerous pictures of amitotical nucleas division may be 

 encountered. Figure 14 illustrates four cells in a stage of amito- 

 tic nuclei division. As a result of the division of the nucleus two 

 daughter nuclei arise, which can have both the same dimensions, 

 or differ considerably in size. Both daughter nuclei receive 

 always a part of the nucleolar substance. In most cases the nuclei 

 divisions are not followed by cell divisions, for the very fact that 

 their localization in the syncytium mass of the mesenchyme does 

 not allow a division of the cytoplasm. However, sometimes free 

 'cells may be observed undergoing amitotic nuclei division (fig. 

 13, 14 d). The further destiny of such nuclei cannot be followed 

 directly. The frequence of occurrence of amitotic nuclei di- 

 vision must, however, lead in the spleen mesenchyme to a 

 production of a larger number of nuclei, derived through 

 amitosis. These nuclei contribute in a great part to the growth 



