The Cellular Basis 

 A B 



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FIG. 52. OOGENESIS OF A NEMATODB WORM (Ancyracanthiis) . A, Egg 

 mother cell containing 12 chromosomes before their union into pairs. B, 

 Early stage of first maturation division ; all the chromosomes have united 

 into 6 pairs, and all but one of these has split in two so that the pairs are 

 really four-parted (tetrads). C, The six tetrads in the first maturation 

 division. D, Egg containing 6 chromosomes, after both first and second 

 maturation divisions; the eliminated chromosomes are shown as the polar 

 bodies at the margin of the egg. E and F, Eggs after fertilization; the 

 egg nucleus is above and contains 6 chromosomes, the sperm nucleus is 

 below and contains 5 chromosomes in one case and 6 in the other; in the 

 former case the egg becomes a male with n chromosomes, in the latter 

 a female with 12 chromosomes. (After Mulsow.) 



