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ROBERT W. HEGNER 



2. THE KEIMBAHN IN THE NEMATODA 



The classical example of the Keimbahn in animals is that of 

 Ascaris megalocephala as described by Boveri ('87, '92). The 

 first cleavage division of the egg of Ascaris results in two daughter 

 cells, each containing two long chromosomes (fig. 19, ^). In 

 the second division the chromosomes of one cell divide normally 



Fig. 19 Ascaris (redrawn from Boveri, '92). A-D, stages showing chro- 

 matin-diminution in all cells except the stem-cell (s). • 



and each daughter cell receives one half of each (fig. 19, .B,*'s). 

 The chromosomes of the other cell behave differently; the thin 

 middle portion of each breaks up into granules (fig. 19, A). which 

 split, half going to each daughter cell, but the swollen ends (fig. 

 19, B, C) are cast off into the cytoplasm. In the four-cell stage 

 there are consequently two cells with the full amount of chromatin 

 and two with a reduced amount. This inequality in the amount 



