14 C. M. CHILD. 



upon this point. All the facts point to the conclusion that 

 sexual reproduction is a process characteristic of the physio- 

 logically old organism. If the germ plasm is continuously present 

 and independent of the soma why should sexual reproduction 

 always be associated with a certain stage of development? Why 

 should it not occur earlier in one individual and later in another? 

 To maintain that the germ plasm cannot obtain sufficient nutri- 

 tion for its needs until the activity of the soma is on the decline 

 is certainly not in accord with the facts, for even during the 

 growth period the organism may store up reserves, i. e., an excess 

 of nutritive material may be present, but this does not induce 

 sexual reproduccion. The assumption of some sort of activation 

 of the sexual organs is merely an assumption of the existence of 

 physiological correlation between the parts concerned and is 

 incompatible with the assumption of independence. On the 

 other hand, we are well aware thac, at least in many cases, the 

 gonads when present, influence the metabolism of the soma. 



The facts then point almost irresistibly to the conclusion that 

 the formation of gametes is a function of the organism, of the 

 soma, like the formation of leucocytes or any other organ. When 

 the gonads arise early they develop as integral functional parts 

 of the individual and not as parasites. When they arise late 

 or periodically, they arise from parts which have previously 

 been functional parts of the organism and which undergo dediffer- 

 entiation and redifferentiation to form gametes in consequence 

 of altered correlative conditions which in turn are associated 

 with advancing senescence. 



2. The Differentiation and Physiological Condition of the Gametes. 



It is customary to think of the gametes as consisting of or 

 containing " undifferentiated germ plasm" all ready to develop 

 into a new organism after fertilization. What are the actual 

 facts concerning this point? The primitive germ cell, as a 

 matter of fact is more or less similar in appearance to what we 

 commonly call undifferentiated or embryonic cells, but with 

 the beginning of the growth period the germ cell enters upon 

 a period of differentiation. In the case of the egg this period 

 involves an enormous increase in size and often a very great 

 degree of cytoplasmic differentiation. In most cases also the 



