THE BIOLOGY OF THE CELL SURFACE 



content with mere assumption; evidence at hand amounts 

 to proof that the chief event in fertilization is a reaction 

 between the egg's ectoplasm and the spermatozoon. This 

 evidence will now be set forth. 



The proposition that the main event in fertilization is a 

 reaction between egg-ectoplasm and spermatozoon is 

 supported by the following: (i) The ectoplasm is necessary 

 for fertilization. (2) The onset and loss of fertilizability is 

 correlated with the appearance and disappearance of an 

 ectoplasmic substance. (3) Specificity in fertilization 

 depends upon the integrity of the ectoplasmic layer. 

 (4) Polyspermy obtains when the ectoplasm is slow in 

 reacting, 



I first cite an observation of my own.^ 



If uninseminated eggs of the fiat sea-urchin, Echinarach- 

 nins, stand in shallow dishes of sea-water, they undergo 

 a change due to the increasing salinity of the sea-water 

 caused by evaporation, a change which manifests itself by 

 an alteration of the eggs' surface. This same change is 

 induced by placing the eggs in sea-water made hypertonic 

 by the addition of sodium chloride (6 parts of 232 M NaCl 

 plus 50 parts sea-water). In either case the surface-layer 

 of the eggs on return to normal sea-water is seen to be of a 

 thickened and translucent jelly-like nature. Many of these 

 eggs, having thus been exposed to hypertonic sea-water, 

 under pressure, as by forceful ejection from a pipette, form 

 each a protrusion. These vary in size. By other methods 

 eggs may be induced to form protrusions; often they show 

 them after having lain in normal sea-water for some time. 

 Eggs of other sea-urchins, Arbacia, Strongylocentrotus, 

 Echi7iiis, Echinocardium, treated with hypertonic sea-water 

 likewise form these protrusions when they are brought into 

 normal sea-water. The explanation of the formations is 



1 Just, 1923a. 



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