CHAPTER VI 
THE SEGREGATION OF THE GERM CELLS IN NEM- 
ATODES, SAGITTA, AND CERTAIN OTHER MET- 
AZOA 
1. Toe KempBauHN IN THE NEMATODA 
THE classical example of the keimbahn in animals 
is that of Ascaris megalocephala as described by 
Boveri (1887, 1892). The first cleavage division of 
the egg of Ascaris results in two daughter cells, each 
containing two long chromosomes (Fig. 51, A). In 
the second division the chromosomes of one cell 
divide normally and each daughter cell receives one 
half of each (Fig. 51, B, S). The chromosomes of 
the other cell behave differently; the thin middle 
portion of each breaks up into granules (Fig. 51, A) 
which split, half going to each daughter cell, but the 
swollen ends (Fig. 51, B, C) are cast off into the cyto- 
plasm. 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 of chromatin results in different-sized nuclei 
(Fig. 51, 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. 51, D, S) retains its chromo- 
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