Action of the Spermatozoon upon the Egg 229 



urchin. I believe the reason to be this, that as soon as the 

 spermatozoon of S. purpuratus touches the protoplasm (the 

 fertilization cone) of the egg of the same species it is taken so 

 quickly into the interior of the egg that it is already safely 

 inside by the time the membrane-forming substance can act. 

 If we fertilize the eggs of »Si. purpuratus with their own sperm, 

 in about two minutes or less all the eggs have formed a ferti- 

 lization membrane. If we fertilize them with starfish sperm, 

 it takes from ten to sixty minutes to bring about the same 

 result. I am inclined to see in this difference of time the 

 reason why it is possible to separate the two agencies in the 

 living sperm of the starfish, but not in that of the sea-urchin. 



4. Very striking experiments have recently been carried 

 out by Oskar Hertwig with Gunther and Paula Hertwig, on 

 the effects of radium on sperm. When the spermatozoa of 

 the frog were exposed a short time to radium before they were 

 added to the eggs, the eggs were sickly and died in the early 

 stages of development. When, however, the spermatozoa were 

 exposed a longer time to the radium, the eggs could develop 

 much better and the larvae were able to live as long as two 

 weeks. This paradox finds its explanation in the fact that when 

 the spermatozoa had been exposed a longer time to the radium 

 they were able to enter the egg, but the sperm nucleus was no 

 longer able to fuse with the egg nucleus. The spermatozoon 

 thus imparted only the developmental influences to the eggs, but 

 not the' hereditary effects. In order to produce this result it was 

 necessary to expose the spermatozoa for four hours to 60 mg. 

 raditun bromide or for twelve hours to 10 mg. radium bromide.' 



i"Die Radiumkrankheit tierischer Keimzellen," Arch. f. mikr. Anat., 

 LXXVII, 1911, Abteilung 1. Zeugungslehre; "Die Radiumstrahlung in ihrer 

 Wirkung auf die Entwicklung tierischer Eier," Sitzgaber. Akad. Berlin, 1910; 

 " Mesotlioriumversuclie an tlerischen Keimzellen, ein experimenteUer Beweis 

 flir die Idioplasmanatur der Kemsubstanzen," Sitzgsber, Akad. Berlin, 1911; 

 " Radiumbestrahluug uubefruchteter Frosclieier und Uire Entwicldung nach 

 Belruchtung mit normalem Samen," Arch. f. mikr. Anat., LXXVII, 1911; "Ver- 

 anderung der idioplasmatischen Bescliaflenheit der Samenfaden durch physikal- 

 ische \md durch chemische Eingrifle," Sitzgsber. Akad. Berlin. 1912. 



