EFFECTS OF AGING UPON GERM CELLS. 407 



Change in Jelly Layer. 



Practically all freshly liberated eggs in good physiologic con- 

 dition possess a jelly layer. Those in poor condition have a 

 correspondingly less per cent. 



With age the jelly layer was lost in an increasing number of the 

 eggs. 



The rate of loss depended upon the condition of the eggs at the 

 time of liberation (all other conditions remaining constant). 



For fresh eggs in good physiologic condition, the rate of loss per 

 hour was 0.81 and for equally fresh eggs in poor condition 2.65 or 

 over 3 times as rapid. 



Essentially similar results were obtained in all three species. 



The loss of jelly layer was a second symptom and index of the 

 extent and the rate of ageing or senescence of the eggs. 



Change in Membrane. 



Freshly liberated eggs in good physiologic condition formed 

 fertilization membranes within two minutes. The rate depended 

 partly upon the sperm but primarily upon the physiologic condi- 

 tion of the eggs. 



With increasing age the time required to form the fertilization 

 membranes was at first accelerated and later retarded. In very 

 aged eggs no membranes were formed. 



Freshly liberated eggs in poor physiologic condition showed 

 direct retardation in the rate of membrane formation. 



Aging eggs which no longer formed membranes when fer- 

 tilized by old sperm could be made to form membranes with 

 fresh sperm. 



The rate of membrane formation is practically independent of 

 the sperm. It is essentially determined by the condition of the 



egg- 



As the eggs aged the membrane appeared closer and closer to 

 the surface of the egg; it became thinner and ultimately none was 

 formed. 



These observations are essentially the same for all three species. 



The rate and character of membrane formation affords a third 

 means of measuring senescence in eggs. 



