CHAPTER IV 

 MATURATION 



Ix this chapter we shall describe certain events which are in 

 reality essential steps in the processes of oogenesis and sper- 

 matogenesis, namely, the maturing of the nuclei of the definitive 

 germ cells. In animals these maturation processes are the 

 final steps in the complete specialization of the germ cells, and 

 must be accomplished before the two gametes can fuse com- 

 pletely and thus begin the life of the "new" organism as an 

 individual. As a matter of fact, the processes of maturation 

 may be inaugurated before the growth and differentiation of 

 the germ cells are entirely completed, and these processes may 

 then all go on together. They are considered here separately, 

 and without complete regard for then* normal time relations, 

 partly as a matter of convenience, looking toward simplicity 

 of description, and partly to emphasize their great importance 

 as a period in the development of the organism. Such a sepa- 

 ration is easy because the maturation processes are not visibly 

 connected with the genesis of the germ cells as such, for, mor- 

 phologically at any rate, they concern only or chiefly the 

 nuclei alone; the accompanying cytoplasmic modifications of 

 structure have already been described. 



That morphological characteristic chiefly distinguishing the 

 fully matured germ cells is the possession of but one-half the 

 number of chromosomes, and of but a smaller fraction of the 

 amount of chromatic material, possessed by the somatic cells 

 (Van Beneden) . We should include under the term maturation, 

 the whole series of events leading to this reduction in number 

 of chromosomes and amount of chromatin. It should be noted, 

 however, that the terms " oogenesis" and " spermatogenesis " 

 have sometimes been used in a restricted sense to mean what 

 we here term " maturation," but we have understood the former 



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