STUDIES OF FERTILIZATION 451 
the cortical changes have not been induced. ‘The conception of 
Bataillon (10), moreover, that the egg excretes certain inhibiting 
substances contained in its cortex, as a result of the cortical 
change, is quite readily included in this point of view; indeed, 
the jelly excreted by the egg of Nereis as a result of the external 
stimulus of the spermatozo6n would obviously hinder free inter- 
change between the egg and the medium so long as it exists within 
the egg as a thick cortical layer. 
The second phase in fertilization has been treated by Loeb 
and R. 8. Lillie. Loeb’s interpretation is that the second agent 
in artificial parthenogenesis serves to check the tendency to cytoly- 
sis set up by the first agent; and he extends this point of view to 
the two phases of normal fertilization. In this opinion he is 
followed by Godlewski (11), who has shown that the cytolysis, 
which follows on fertilization of sea-urchin eggs with sperm of 
Chaetopterus, can be checked, and parthenogenetic development 
induced, by a brief treatment of such cross fertilized eggs with 
hypertonic sea-water. R. S. Lillie (11) regards ‘‘the critical 
change in the egg, to which membrane formation and the initia- 
tion of cleavage are due, as a well marked and rapid increase in 
the permeability of the plasma-membrane.” This tends ‘‘to 
destroy the normal osmotic equilibrium and allow abnormal dif- 
fusion of substances into and out of cells’ leading to derangement 
and eventual destruction of the chemical organization of the 
latter. And he regards it as an unavoidable conclusion that one 
essential effect of the after treatment with hypertonic sea-water 
is to restore the normal permeability. 
There is considerable similarity in these points of view; both 
regard the second agent in parthenogenesis essentially as a regula- 
tory factor. Godlewski’s very striking results on the combination 
of cross fertilization and artificial parthenogenesis lead to the 
same kind of conclusion; to quote this author (711): 
Wir haben gesehen, dass weder die Kreuzbefruchtung allein, noch die 
so kurz dauernde Exposition in hypertonischer Lésung allein ausreicht, 
um die Entwicklung auszulésen. Erst durch die Kombination der 
beiden Faktoren ist der ausreichende Anstoss zur Entwicklung gegeben. 
Ich sehe in diesen Tatsachen die Bestitigung der von J. Loeb aufgestell- 
ten Hypothese, dass der Process der Entwicklungserregung sich in zwei 
