EFFECTS OF AGING UPON GERM CELLS. 25 



These seven groups of tests or symptoms of senescence also 

 indicate the fundamental nature of the chemical and physical 

 changes involved in the aging process, namely a change in the 

 cortical layer of the egg, and a change in oxidation. The change 

 in the cortical layer, i. e., the change in permeability, affects the 

 membrane, the cleavage, and all the other consequences of aging 

 above enumerated. 



It is very probable that the changed cortical layer with its , 

 train of consequences, as well as the change in respiration, are 

 fundamentally reducible to the one phenomenon, namely, 

 changed metabolism. 



These results afford a common explanation of apparently diverse 

 phenomena, such as change of sex with age (Riddle, Hertwig, etc.) , 

 senescence (Minot) , reduced productivity (Pearl, King, etc.) , physi- 

 ologic differences in cross fertilizations (Tennant.etc.), etc. (For 

 details see discussion.) 



