SECT. 5] IN ONTOGENESIS 795 



found that this absorption of water was stopped by hypertonic electro- 

 lyte solutions, but not by hypertonic solutions of non-electrolytes. 

 The ordinary laws of diffusion and osmosis, therefore, will not ex- 

 plain the formation of the perivitelline liquid. This conclusion is in 

 accordance with the views of Svetlov. Hayes found in the case of the 

 Atlantic salmon, Salmo salar, that the egg membranes are impermeable 

 to electrolytes or colloidal substances. 



Gray has also worked on the trout tgg. He began by enquiring 

 what the forces were which maintain the teleostean egg's high con- 

 centration of electrolytes against the low osmotic pressure of the 

 fresh- water medium, and where they were located. The membranes 

 could not, he thought, be impermeable to electrolytes, for the embryo 

 could not then take in any inorganic substances from outside. Moore; 

 Osborne; and Donnan had all urged that the presence of colloidal 

 substances inside a cell would cause a differential distribution of 

 inorganic ions within and without, but Gray was not convinced that 

 this would explain the state of affairs in the trout egg. 



Gray found experimentally that death of the eggs was accompanied 

 by a marked increase of electrolytes in the surrounding water. Thus 

 the resistance of the water in which eggs were standing was as follows : 



Ohms 

 Before shaking ... ... 3550 



I hour after shaking ... 305 



This was confirmed afterwards by Kronfeld & Scheminzki, who got 

 less striking figures : 



Ohms 

 Before addition of alcohol 3200 



3 hrs after addition of alcohol 2700 



But during normal development no appreciable amount of electro- 

 lytes was lost from the eggs ; thus, in an experiment where the original 

 resistance of the water was 6520 ohms, after 3 hours in contact with 

 fertilised eggs it was 5000 ohms, a difference amply accounted for 

 by carbon dioxide production. Direct measurement on egg-Breis 

 before and after fertilisation showed that the amount of diffusible 

 electrolyte within the egg is hardly affected at all by this event. 



Ohms 

 Unfertilised ... 1040 



Fertilised ... 1070 



