MANIPULATION OF EGGS 



113 



contains also some egg albumen or serum albumen. Since proteins 

 evidently cannot pass through the zona pellucida (p. 90) the influence 

 must reside in their osmotic effect at the surface of this membrane. 

 Active transport of potassium ions seems to be demonstrable in 

 eggs. Rat 2-cell eggs maintained for 18 hr in isosmotic solutions 

 of differing Na:K ratio displayed distinct differences in volume — 

 those in the higher concentrations of the potassium ion expanding 

 to the limits of the zona pellucida (Fig. 76). 



Fig. 76 



Rat 2-cell eggs after being held for 18 hr in media consisting of different proportions of 

 isosmotic sodium-chloride and potassium-chloride solutions, (a) NaCl alone; (b) 9.5 ml NaCl, 

 0-5 ml KC1; (r) 8 ml NaCl, 2 ml KC1; (d) 5 ml NaCl, 5 ml KC1. X 330. 



Fertilized i-cell rabbit eggs placed in homologous serum at 20 C 

 containing 2-5, 3-75, 5 and 7-5 per cent glycerol were observed to 

 contract and re-expand during the hour they were left at each stage. 



