THE BIOLOGY OF THE CELL SURFACE 



they go to pieces, cytolyze. Hence, for the unfertilized egg 

 sea-water is normally cytolytic. The length of time which 

 eggs can remain in sea-water before they begin to cytolyze 

 depends largely upon the temperature of the sea-water and 

 the ratio of the volume of eggs to the volume of sea-water; 

 also it varies with eggs of different species.^ Now the fer- 

 tilization-capacity of eggs in sea-water diminishes with time; 

 here also the factors, temperature and volume of eggs come 

 into play. The rate at which the fertilization-capacity 

 drops also varies with eggs of different species. But it holds 

 generally that the fertilization-capacity disappears before 

 cytolysis begins — obviously, It must have disappeared at 

 the latest at the moment when cytolysis begins, for a dead 

 egg can not be fertilized. As a matter of fact, the capacity 

 of an egg in sea-water to respond to an experimental means 

 falls off more rapidly than its fertilization-capacity. This is 

 strikingly brought out by the above mentioned effect of 

 warm sea-water on the egg of Nereis. Its response to 

 treatment with warm sea-water is not so good if it has 

 been in normal sea-water before treatment, whilst its 

 fertilizability is thereby not lessened. So we consider the 

 cytolytic action of the sea-water as the antipode of the 

 initiation of development by spermatozoon or by experi- 

 mental means. 



By the addition of any one of a number of substances to 

 sea-water the rate at which eggs cytolyze can be increased. 

 Among these is butyric acid. But the action of butyric 

 acid in accelerating cytolysis is by no means invariable. 

 On the contrary, the effects which this acid produces depend 

 upon its concentration in sea-water and, in the case of 

 each concentration which is effective for calling forth mem- 

 brane-separation, upon the duration of time that the eggs 



^ In making comparisons of the rate of cytolysis of eggs of different 

 species one must be careful thai the experimental conditions are 

 uniform in the compared cases. 



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