EFFECTS OF AGING UPON GERM CELLS. J 



cent, of the total. When 5 hours old, the number had increased 

 to 46 per cent, of the total. In Arbacia, experiment 16, the 

 average per cent, of irregularity of the 7 females when their eggs 

 were 1^2 hours old was 12 per cent, of the total. When i8j^ 

 hours old, 12 per cent, of the non-cytolized and non-fragmented 

 eggs cleaved irregularly. When 24 hours old, the number of 

 irregular eggs had increased to 40 per cent, of the non-cytolized 



e^gs. 



These deteriorated and irregularly cleaving eggs were short 

 lived. With increasing age they died in increasing numbers, 

 and at earlier and earlier stages in their development. The more 

 deteriorated the eggs, the less completely did they develop. This 

 differential mortality served as another index of the vitality or 

 physiologic age of the eggs of any female. 



These results give substantial support to Pearl's hypothesis of a 

 varying degree of virility of the different eggs of an individual. 



Irregular cleavage, with the consequences above enumerated, 

 was due to several causes. In the first place the loss of jelly and 

 the absence of the membrane made it increasingly possible for 

 polyspermy to occur, particularly when fresh sperm in high 

 concentration was used. Polyspermy in old eggs had been 

 observed before by the Hertwigs, '86. These polyspermic eggs 

 gave rise to irregular mitosis and irregular cleavage. In the 

 second place the changed permeability, with its consequent 

 excessive inflow of sea water, gave rise to mechanical or physical 

 interference, dissolved certain of the protoplasmic granules, 

 caused an excessive metabolism and an accumulation of metabolic 

 products, gave rise to a very viscous condition of the protoplasm, 

 etc., all of which were contributory agents in producing the 

 various and increasing irregularities in cleavage. 



SEPARATION OF BLASTOMERES. 



Another quite characteristic manifestation of extreme age or 

 physiologic deterioration was the more and more complete 

 separation of the blastomeres. As the eggs increased in age, 

 there was, as I have pointed out, an increasing viscosity of the 

 cytoplasm and membrane, ultimately a complete loss of the 

 fertilization membrane, or membrane-forming substance, with a 



