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LIBBIE H. HYMAN. 



about 15 to 30 seconds in the best eggs. In subnormal eggs the 

 time is much longer and the reaction may not be complete, the 

 eggs remaining permanently with membranes partially elevated 

 as shown in Figs. 6 to 8. Such cases serve, I think, to indicate 

 further the progressive character of the fertilization reaction. 



All figures are redrawn from free-hand sketches. In the unfertilized egg the 

 vitelline membrane is not indicated separately from the egg surface as doing so 

 would exaggerate the real appearance. 



FIGS, i TO 5. Five stages in the normal fertilization reaction in Strongylocen- 

 trotus franciscanus. Note progress of the fertilization reaction from the initial 

 place. In 5 the reaction is not yet quite complete as the egg is still slightly excentric 

 within the membrane. 



FIGS. 6 TO 8. Permanent stages of partial fertilization from a subnormal lot 

 of eggs of 5. franciscanus. 



In eggs favorably placed for such observation it has been 

 determined that the point on the egg from which the fertilization 

 changes take their origin is the place to which the successful 

 sperm is attached. This has also been ascertained by so many 

 previous observers, to whom reference will be made shortly, 

 that it seems superfluous to dwell upon the fact. The fertilization 

 reaction begins at the point of contact of sperm and egg and from 

 this point is transmitted in all directions over the surface of the 

 egg- 



The fertilization reaction is essentially the same in all three 

 species studied. The chief difference between the urchin egg and 

 the starfish egg is that in the former the membrane where it 

 first separates from the egg elevates at once in this region to its 



