STUDIES ON GERM CELLS 465 



gration and the distribution of the resulting fragments or granules 

 are controlled by reactions between them and the substances in 

 which they are imbedded. 



Chromatin. In two genera of animals the differentiation 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 comple- 

 ment 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 recon- 

 stituted. These two genera are Ascaris and Miastor. This 

 diminution process was described by Boveri ('92) in the former 

 and confirmed by O. Meyer ('95) and Bonnevie ('01), and by 

 Kahle ('08) in Miastor and confirmed by Hegner ('12). For 

 details of these processes reference should be made to figures 

 3, 4, and 32 and pp. 390 and 442. 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 approximately one-half of each 

 daughter chromosome is left behind to form the 'Chromosomen- 

 mittelplatte' (fig. 32, cMp) and later the 'Chromatinreste' (fig. 

 34, cR). 



The elimination of chromatin during the maturation and early 

 cleavage divisions of the egg, as well as during the mitotic divi- 

 sions of other kinds of cells, has often been recorded. For 

 example, Wilson ('95, p. 458) estimates that only about one- 

 tenth of the chromatin in the germinal vesicle of the starfish is 

 retained to form the chromosomes during the first maturation 

 division, and Conklin ('02) finds that "in Crepidula the outflow 

 of nuclear material occurs at each and every mitosis" (p. 51). 

 Furthermore, Rhode ('11) argues that chromatin diminution is a 

 normal histological process, and describes such phenomena in 

 blood cells, nerve cells, and cleavage cells of several Amphibia, 

 comparing conditions with the chromatin-diminution in Ascaris 

 and Dytiscus. His conclusion is as follows: 



In der Histogenese der allerverschiedensten Gewebe tritt uns also 

 die Erscheinung entgegen, dass die sich entwicklenden Zellen, bzw. 



