KEIMBAHN-DETERMINANTS 217 



The writer can only conclude (1) that the metanu- 

 cleoli differ in nature from ordinary plasmosomes, 

 chromatin-nucleoli, and double-nucleoli ; (2) that 

 these bodies are definitely segregated in a certain part 

 of the egg or in a certain blastomere, probably by 

 protoplasmic movements; (3) and that their disin- 

 tegration and the distribution of the resulting frag- 

 ments or granules are controlled by reactions between 

 them and the substances in which they are embedded. 

 Chromatin. In two genera of animals the differ- 

 entiation of the primordial germ cells is accompanied 

 by a diminution of the chromatin in the nuclei of 

 the somatic cells, so that eventually the nucleus of 

 every germ cell is provided with the full complement 

 of chromatin, whereas the nucleus of every somatic 

 cell lacks a considerable portion of this substance, 

 which remains behind in the cytoplasm when the 

 daughter nuclei are reconstituted. These two genera 

 are Ascaris and Miastor. This diminution process 

 was described by Boveri (1892) in the former and 

 confirmed by O. Meyer (1895) and Bonnevie (1902), 

 and by Kahle (1908) in Miastor and confirmed by 

 Hegner (1912, 1914a). For details of these processes 

 reference should be made to Figs. 15-16, 51-52, and 

 pp. 57 and 174. It may be pointed out here that 

 although the final results are similar the process differs 

 in the two genera. In Ascaris both ends of each 

 chromosome are split off, whereas in Miastor approxi- 

 mately one-half of each daughter chromosome is left 

 behind to form the " Chromosomenmittelplatte " 

 (Fig. 16) and later the *'Chromatinreste" (Fig. 18). 



