EFFECTS OF AGING UPON GERM CELLS. 377 



in volume with age. Physiologically good eggs show an initial 

 rapid increment, region A of the curve; then a progressively 

 slower increment, region B; thirdly a progressive diminution, 

 region C, towards D or even below the norm of the species to E. 

 Eggs in moderately poor physiologic condition at liberation 

 have already undergone physiologic deterioration, corresponding 

 with part A within the body of the mother. Upon liberation 

 they show only parts B, C, D, etc., of the curve. Eggs in very 

 poor condition upon liberation have undergone changes repre- 

 sented by parts A and B, within the body of the mother, and 

 upon liberation show only parts C and D, etc. 



The significance of this increment with age lies in the changed 

 permeability of the cortical layer which is denoted by increase 

 in volume. This progressive increase in permeability permits 

 increasing volumes of sea water to penetrate the egg and thus 

 enlarge it. This process continues until partial cytolysis (frag- 

 mentation) reduces the size once again towards the norm, or 

 until complete cytolysis destroyed the eggs altogether. 



The change in size with age really measures the change in per- 

 meability of the cortical layer. 



Similar observations were made upon Arbacia eggs, and the 

 changes are so much in agreement with those of Hipponoe 

 that it seems unnecessary to describe them here. There is the 

 same initial increment followed by the secondary diminution 

 with age. * And the rate of change depended upon the physiologic 

 condition of the eggs at the time of liberation and upon tem- 

 perature. The two species differ in the markedly slower rate of 

 change of Arbacia, due in largest part to the lower temperature 

 of the sea water. 



EFFECT OF AGE UPON THE JELLY LAYER. 

 Hipponoe and Arbacia. 



The jelly layer of the same sea-urchin eggs were made clearly 

 visible by adding Chinese black to the sea water, as suggested by 

 F. R. Lillie. Samples of 150 to 200 consecutive freshly removed 

 (and unfertilized) eggs of each female were examined, avoiding 

 mechanical or chemical removal of the jelly, and the presence or 

 absence of the jelly layer recorded. At successive intervals 



