THE FERTILIZATION-REACTION 



Mere location does not make the ectoplasm and its behavior 

 peculiar, nor the fact that in all cells cytoplasm becomes 

 converted into ectoplasm. If the ectoplasm plays this 

 role in fertilization, for egg-cells this conversion of cyto- 

 plasm into ectoplasm must take place in such wise that 

 new and stimuli-receiving substance comes to the surface 

 of unfertilized eggs as they pass from the unfertilizable to 

 the fertilizable condition. We possess some evidence for 

 the appearance of such a substance in the surface-layer 

 of the egg with the moment that it becomes fertilizable. 



According to the fertilizin-theory of Lillie, eggs (of sea- 

 urchins and of Nereis) in the fertilizable condition contain 

 a substance, fertilizin, located at their surfaces which is 

 necessary for fertilization. Thus, the statement, no fertili- 

 zation without ectoplasm can be amended to read in these 

 cases, no fertilization without ectoplasm-located fertilizin. 

 Whilst the presence of fertilizin has not been demonstrated 

 for all eggs, its occurrence is not limited to those of the forms 

 studied by Lillie. I have detected its presence in eggs of 

 other sea-urchins and of two other worms (Platynereis 

 megalops and P. diimerilii). It has been found in the ^g^ of 

 Ciona, an ascidian. I have elsewhere reviewed the work of 

 fertilizin;' to this review together with Lillie's original 

 papers the reader is referred.^ Here I give only a resume 

 with special reference to the ectoplasm-located fertilizin. 



Fertilizin is held to be a mid-body in the reaction between 

 egg and spermatozoon. Without it, in the eggs named, 

 fertilization does not take place. No cells other than eggs 

 possess it and these only when fertilizable. Neither in 

 immature nor in fertilized eggs can its presence be detected. 

 Eggs treated with means that induce the surface-changes 

 identical to those induced by spermatozoa likewise do not 



1 Just, /pjoc. 



- Lillie, 1913, 1919. 



