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 S. 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 Giinther 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. 
radium bromide or for twelve hours to 10 mg. radium bromide.' 
1‘*Die Radiumkrankheit tierischer Keimzellen,” Arch. f. mikr. Anat., 
LXXVII, 1911, Abteilung f. Zeugungslehre; ‘‘Die Radiumstrahiung in ihrer 
Wirkung auf die Entwicklung tierischer Eier,’’ Sitzgsber. Akad. Berlin, 1910; 
““Mesothoriumversuche an tierischen Keimzellen, ein experimenteller Beweis 
fiir die Idioplasmanatur der Kernsubstanzen,”’ Sitzgsber. Akad. Berlin, 1911; 
“Radiumbestrahlung unbefruchteter Froscheier und ihre Entwicklung nach 
Befruchtung mit normalem Samen,”’ Arch. f. mikr. Anat., LX XVII, 1911; “Ver- 
ainderung der idioplasmatischen Beschaffenheit der Samenfaden durch physikal- 
ische und durch chemische Eingriffe,’’ Sitzgsber. Akad. Berlin, 1912. 
