MATURATION 155 



one reducing, resulting in the formation of germ cells of two 

 more or less unlike kinds, in equal numbers (Fig. 80). 



Aside from its relation to the phenomena of heredity, the 

 meaning of the maturation process is very problematic. In 

 the Protozoa where definite chromosomes are formed only 

 infrequently, maturation frequently involves a separation 

 between reproductive and vegetative chromatin, as already 

 suggested. Among the Metazoa there is usually a loss of 

 chromatin from the nucleus, but it is very doubtful whether 

 it has a similar meaning. In a great many cells, particularly 

 those which are very active, e.g., gland cells, oocytes, etc., 

 the cytoplasm is constantly receiving substance from the 

 nucleus. This material is frequently chromatic, and the 

 granules of this kind have received a variety of special names, 

 but collectively may be included under the term chromidia. 

 (See Chapter II.) It may be that through some such process 

 as this the nucleus exercises those forms of control and regula- 

 tion of cell life that are its chief function. The loss and 

 degeneration of the chromatin distributed to the polar bodies 

 can have no significance here, for that process is involved in the 

 degeneration of the entire polar bodies, which has an entirely 

 different meaning. But during the growth period of most ova, 

 just after synizesis, a relatively large amount of the chromatin 

 is thrown out into the cytoplasm, and during the later stages 

 of spermatogenesis a somewhat similar loss may be observed. 

 And in the very early history of the germ cells of the organism, 

 when this may consist of only a few cells, the primordial germ 

 cells may often be distinguished by just this process of chro- 

 matin discharge from the nucleus. Such cells are often 

 characterized by unusually large nuclei, and a large fraction of 

 their chromatin content may be liberated into the cytoplasm 

 at each mitosis. It may very well be, therefore, that this is a 

 regular and highly significant process in the formation and 

 maturation of the germ cells, having to do with the unusual 

 activity of the sperm or with the development of various formed 

 substances, both protoplasmic and deutoplasmic, present in 

 the cytoplasm of the ovum. Indeed it may not be too much 



