90 THE PROBLEMS OF EVOLUTION 



the cell and these, as we now know, may bring 

 about profound modification of the chromosomes 

 themselves. But in a normal environment the 

 organization of the cell is apparently a guaranty of 

 constant normal activity, due to the removal of 

 the controlling center in a large degree from the 

 fluctuations of external environment. 



There is every reason to conclude that the soma 

 bears a similar relation to its various parts and to 

 the germ cells within it. The fundamental reason 

 for specialization is the more efficient performance 

 of necessary duties, and in a highly developed 

 organism the total performance of many organs is 

 such as to provide an internal environment in 

 which the fluctuation of conditions is at a mini- 

 mum. ^^ Those parts which establish contact with 

 the outer world — sense organs, alimentary tract, 

 integument — must encounter the uncontrollable 

 fluctuations of nature or evade them, but while 

 the fluctuations are not injurious they stimulate 

 the organism to responses which tend to maintain 

 its normal condition. Parts which are shut away 

 from direct external contacts — kidneys, endocrine 

 glands, — are thus responsive to a more constant 

 environment to whose constancy they contribute 

 in turn, and the germ plasm, which apparently has 

 no part to play in the life of the individual, may 



" Pike, F. H., and Scott, E. L., Am. Nat, Vol. XLIX, pp. 321-359, 1915. 

 present an excellent discussion of this matter. 



