THE GAMETES IN PLANTS AM) AMMALS 355 



It is evident that whatever the cytological or hereditary signifi- 

 cance of the chromosome behavior in maturation, this behavior 

 must have a physiological basis, it must be associated with certain 

 physiological conditions. The discovery of similar behavior in 

 other cells and the experimental production of it serve at least to 

 pave the way for the determination of its physiological significance. 

 The fact that the "heterotypic" behavior can be experimentally 

 induced by means of narcotics seems to show that its occurrence 

 is connected with a low rate of metabolism. In maturation, both 

 in plants and in animals, it occurs at the end of a developmental 

 period. In most plants with alternation of generations the matura- 

 tion divisions occur in the formation of the spores, and a more or 

 less extended period of dedifferentiation, cell division, and pro- 

 gressive development, i.e., the gametophyte generation, occurs 

 between maturation and fertilization. In animals, on the other 

 hand, no cell division occurs between maturation and fertilization. 

 But the important point is that in all cases the maturation divisions 

 occur in cells which are in an advanced stage of developmental 

 history and physiologically old and which therefore possess a low 

 metabolic rate. The occurrence of heterotypic behavior in cancer 

 cells is probably likewise due to a low metabolic rate, though not 

 in consequence of differentiation and advanced age, but because 

 of partial asphyxiation or intoxication of certain cells in the rapidly 

 growing cell mass. 



According to this conception, then, the peculiar characteristics 

 of the maturation divisions find their physiological basis in a low 

 metabolic rate which may result from differentiation and senescence 

 or be induced experimentally or otherwise. Other features of 

 maturation which indicate a low metabolic rate are the absence 

 of the usual nuclear growth between the first and second divisions 

 and, in animal eggs, the slow progress of maturation and its frequent 

 cessation until a further stimulation from without occurs, and the 

 very slight influence of the nuclear division upon the cytoplasm, the 

 cytoplasmic divisions resulting in the formation of the minute iK)lar 

 bodies and leaving practically the whole volume of the egg intact. 



In the animal egg, where maturation occurs after the enormous 

 growth of the egg cell is completed, the process appears to be 



