THE PHYSIOLOGY OF FERTILIZATION 141 



ever, the eggs are placed in sea-water for even a few 

 seconds before insemination they cannot be normally 

 fertilized even if the sea-water be filtered off. The 

 effect may be graded by using minimal quantities of 

 sea-water. But the sperm can remain in sea-water for 

 some time, and after filtering off the sea-water they 

 will normally fertilize dry eggs. Washed eggs will not 

 fertilize, but washed sperm will. 



The time factor involved in these experiments is 

 far too short to give any support to the assumption 

 that sea- water "injures" the eggs in other ways; it 

 is also impossible to postulate a membrane effect of 

 the sea-water inhibiting entrance of the spermatozoon, 

 because the effect can be graded readily so as to permit 

 penetration, but in this case cleavage does not occur. 

 The results permit of only one conclusion, viz.: that 

 unfertilized eggs lose in sea- water a substance necessary 

 for fertilization. Just was also able to demonstrate a 

 substance in the sea-water used for washing the eggs 

 that has an agglutinating effect on both Platynereis and 

 Nereis sperm. 



The case of Platynereis is unusual with reference to 

 the very brief duration of the fertilizable condition of 

 the ovum in the medium for development. But there 

 are many other forms in which the fertilizable period 

 is very brief. For instance, Reighard (1893) states 

 that it is not possible to fertilize the eggs of wall-eyed 

 pike that have lain in water, and he gives the follow- 

 ing table (p. 142) in order to substantiate the state- 

 ment. 'Five lots of twenty-five eggs each were prepared 

 for fertilization by placing them in watch glasses in the 

 usual way and to each lot, after it had been a certain 



