HEREDITY 



matin contribution of the egg to the production 

 of a new individual. It is possible that other 

 cell constituents undergo a similar reduction 

 by half during maturation, but of this we have 

 no present knowledge. 



The known fact of chromosome reduction, 

 of course, favors the current interpretation 

 that the chromosomes are bearers of heredity, 

 though it by no means proves the correctness 

 of that interpretation. In the egg of Nereis, 

 as well as in that of the mouse, two matura- 

 tion divisions precede the fertilization of the 

 egg. See Fig. 2. In B the first maturation 

 division is in progress; in C the second is in 

 progress; and in D both polar cells are fully 

 formed, while egg and sperm nuclei are unit- 

 ing. Similar processes occur in eggs gener- 

 ally, prior to their fertilization. 



Like changes occur also in the development 

 of the sperm-cells. In Fig. 5 the original or 

 unreduced condition of the chromosomes in a 

 cell of the male sexual gland is shown (at A) as 

 one of four chromosomes to a cell. After a series 

 of changes involving as in the maturation of the 

 egg two cell-divisions, we find (at H) that the 



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