THE BIOLOGY OF THE CELL SURFACE 



contain It. Repeated changing of the sea-water in which 

 eggs lie can wash them free from it so that fertilization is 

 no longer possible. Also, by bathing the eggs in sea-water 

 containing the animals' body fluid, the fertilizin present in 

 them can be bound: fertilization is inhibited. 



That washing the eggs removes the fertilizin is evidence 

 of its ectoplasmic location. Further, I found that after 

 eggs In sea-water containing body-fluid have been mixed 

 with spermatozoa, the spermatozoa attach themselves to 

 the ectoplasm and even penetrate it but do not fertilize the 

 eggs.^ If however these eggs are soon thereafter thor- 

 oughly washed, they develop. From these facts it can be 

 concluded that the inhibition to fertilization, by the block- 

 ing of fertilizin by body-fluid, takes place in the ectoplasm. 

 Moreover, the rapid loss of fertilizing capacity following the 

 ectoplasmic changes which underlie the separation of the 

 vitelline membrane whether induced by spermatozoon or 

 by other means, Indicates that the fertlHzIn is located in 

 the ectoplasm. 



The presence of fertilizin can be detected only if some of 

 It escapes from the egg into the surrounding sea-water. 

 The means of detection is simple. Sea-water in which 

 fertllizable eggs have been lying has marked effects on sper- 

 matozoa of the same species. If a drop of this sea-water 

 be added to a dense suspension of spermatozoa, they are 

 first stimulated to intense activity and rushing together 

 adhere in masses by means of their heads. This agglutina- 

 tion endures for some seconds — or minutes. If the sea-water 

 is highly charged with the agglutinating substance, fer- 

 tilizin — and then passes off". This agglutination-reaction 

 Is a striking and Interesting phenomenon capable of nicely 

 quantitative study. Its value is that of an indicator of 

 the presence of the fertilizin that escaped from the eggs; 

 it may itself have no significance for fertilization although 



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