IIKIiKDITY AM) SEX 



are broughl into relation with a spindle-shaped system 

 of lines, and move apart along these lines to opposite 

 sides of the cell. The protoplasm of the cell next con- 

 stricts to produce two daughter cells, each containing 

 a group of daughter chromosomes. 



4 







-5' 



mmw 



. 



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•*:. 





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Fio. 1!(. — Fertilization and polar-body formation of Nereis. The 

 four smaller figures show cut ranee of sperm. The extrusion of the first 

 polar body i- shown in lower left-hand figure and of the second polar body 

 in the two large right-hand figures. The last three also show the formation 

 of thr sperm asters, which is the beginning of the first cleavage spindle in 

 v- i I R. Lillie.) 



The egg is also a cell, and in its earlier stages contains 

 the -Mine number of chromosomes as do the other cells of 

 the body; but after two peculiar divisions that take 

 place at maturation the number of the chromosomes is 

 reduced to half. 



