GERM CELLS IN NEMATODES, SAGITTA 177 



no doubt that a similar process occurs here. The 

 general conclusion is reached that the cleavage cells 

 of all AscARiD^ undergo a chromatin diminution. 



Bonnevie (1901), however, while able to confirm 

 Meyer's results so far as A. lumbricoides is concerned, 

 could discover no process of diminution in Strongylus 

 paradoxus and Rhabdonema nigrovenosa. 



The elimination of chromatin from all of the 

 somatic cells of Ascaris and not from the germ cells 

 led to the conclusion that the germ-plasm must re- 

 side in the chromatin of the nucleus. The more 

 recent experimental investigations of Boveri (1910a, 

 19106), however, indicate that it is not the chromatin 

 alone that determines the initiation of the diminu- 

 tion process, but that the cytoplasm plays a very im- 

 portant role. Dispermic eggs were found to segment 

 so as to produce three types as follows : 



Type I, with one stem cell (P) and three primordial 

 somatic cells (AB) ; 



Type II, with two stem cells and two primordial 

 somatic cells ; and 



Type III with three stem cells and one primordial 

 somatic cell. 



Fig. 53, B shows a cleavage stage of Type II. 

 Here are represented two stem cells (P) with the com- 

 plete amount of chromatin, both of which are pre- 

 paring to divide to form the stem cells (P2) of the next 

 generation. From the study of these dispermic 

 eggs Boveri (1910) concludes ^ that it is "die unrich- 



^ " Durch die simultane Vierteilung eines dispermen Ascaris-Eies 

 entstehen (vielleicht mit ganz seltenen Ansnahmen) Zellen, welche die 



N 



