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THE POPULAR SCIENCE MONTHLY 



A 



F 



Fig. 35. Oogenesis of a Nematode Woem (Ancyracanthus) . A, egg mother cell 

 containing 12 chromosomes before their union into pairs; B, early stage of first ma- 

 turation division ; all the chromosomes have united into 6 pairs, each of which 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 G 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 below and contains 5 chromo- 

 somes in one case and 6 in the other ; the former becomes a male with 11 chromo- 

 somes, the latter a female with 12 chromosomes. 



(c). The Maturation Period 

 Finally at the close of the growth period both oocyte and spermato- 

 cyte undergo two peculiar divisions one following immediately after the 



