THE BIOLOGY OF THE CELL SURFACE 



process to all Intents and purposes is instantaneous, and 

 therefore ectoplasmic. And this reaction that brings about 

 a fundamental change in the egg which renders it incapable 

 of reacting to other spermatozoa present and initiates the 

 egg's development is the fertilization-reaction. 



The rapidity with which the complete fertilization-reac- 

 tion terminates, obviously depends upon the speed at which 

 the reaction runs. If the egg's ectoplasm is highly reactive 

 the reaction will proceed at a rapid rate. In another egg the 

 rate normally may be slower and yet sufficiently rapid 

 to inhibit polyspermy under natural conditions where eggs 

 and spermatozoa are fully normal. In these, experimental 

 polyspermy may be induced with greater facility. The 

 reaction will be slowest in normally polyspermic eggs. If 

 the block to polyspermy also in normally polyspermic eggs 

 is taken as the indication that the fertilization-reaction is 

 complete, this end would come in such eggs when finally 

 they can receive no more spermatozoa. 



Normally monospermic eggs can be rendered polyspermic 

 by experimental treatment as staling (long residence in 

 sea-water), treatment with alkali, acids or poisons, subjec- 

 tion to low temperature, in short, by methods for inducing 

 injury or weakness. The eggs also tend to be polyspermic 

 when below optimum condition as, for example, those 

 obtained toward the end of the breeding season or from 

 moribund animals. Polyspermy in them thus is a sign 

 of weakness and hence pathological. In all conditions fav- 

 orable to poly-sperm-entry the ectoplasmic response differs 

 from that in normal fertilization. If, for example, eggs of 

 a sea-urchin after having been kept at low temperature, 

 around 5°C., are inseminated, they show polyspermy and 

 the vitelline membrane separates only very slightly, which ■ 

 Indicates abnormal ectoplasmic activity. If treated witlr 

 an organic acid, e.g., 2 cc. Ko normal butyric acid plus 

 50 cc. of sea-water, for one minute or more, eggs of sea- 



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