STUDIES ON GERM CELLS 443 



of chromatin results in different sized nuclei (fig. 19, C); those 

 with entire chromosomes (.s) are larger than those that have lost 

 the swollen ends (c). In the third division one of the two cells 

 with the two entire chromosomes loses the swollen ends of each; 

 the other (fig.. 19, D, S) retains its chromosomes intact. A simi- 

 lar reduction in the amount of chromatin takes place in the fourth 

 and fifth divisions and then ceases. The single cell in the 32-cell 

 stage which contains the full amount of chromatin has a larger 

 nucleus than the other thirty-one cells and gives rise to all of the 

 germ cells, whereas the other cells are for the production of somat- 

 ic cells only. The cell lineage of Ascaris is shown in the accom- 

 panying diagram (fig. 21). 



Meyer ('95) extended the study of chromatin diminution to 

 other species of Ascaris. In A. lumbricoides no diminution 

 takes place until the four-cell stage; then three of the nuclei 

 become deprived of part of their chromatin. A diminution of 

 this sort had been described by Boveri as a variation in the proc- 

 ess observed in A. megalocephala. In A. rubicunda the differ- 

 entiation of the cleavage cells seems to resemble A. megalocephala 

 more than it does A. lumbricoides. Only late cleavage stages of 

 A. labiata were obtained by iVIeyer, but there is no doubt that 

 a similar process occurs here. The general conclusion is reached 

 that the cleavage cells of all Ascaridae undergo a chromatin 

 diminution. 



Bonnevie ('01), 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 nigro- 

 venosa. 



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 reside in the chromatin of the nucleus. The 

 more recent experimental investigations of Boveri ('10a, '10b), 

 indicate, however, that it is not the chromatin alone that deter- 

 mines the initiation of the diminution process, but that the cyto- 

 plasm plays a very important role. Dispermic eggs were found to 

 segment so as to produce three types as follows (fig. 20, A, B): 



