384 FRANK R. LILLIE 
begun as the first factor of the developmental stimulus. This 
conclusion was formed as a result of two kinds of experiments: 
In the first Loeb found that the best results in artificial parthen- 
ogenesis are obtained, in the egg of a Californian sea-urchin, by 
a double treatment: first using a cytolytic agent and then follow- 
ing it by treatment with hypertonic sea-water, or by inhibiting 
oxidation for a while. In the second class of experiments Loeb 
and Elder found that mere membrane formation might be induced 
in sea-urchin eggs by external contact of starfish spermatozoa, 
but farther development did not take place except in the relatively 
few cases in which the spermatozoon entered the egg (Loeb 
’09b, p. 249), or unless the eggs were treated after membrane 
formation with hypertonic sea-water. Although this experiment 
is complicated by the hybridizing, yet it demonstrates the same 
distinction between external and internal functions of the sperma- 
tozoon in fertilization that I have shown for Nereis by a different 
method. 
Artificial parthenogenesis may be induced in the sea-urchin 
egg without membrane formation and this fact appears te me to 
indicate that the internal function of the spermatozoon is prob- 
ably at least as fundamental as the external function (membrane 
formation), though, as Loeb points out, development without 
membrane formation takes place in a less normal fashion than 
after membrane formation. But inasmuch as we may have 
membrane-formation without development, and development 
without membrane formation, it would seem premature at least 
to consider membrane formation as the chief function of the sper- 
matozoon in fertilization. 
The experiments described in this paper show that in Nereis 
fertilization by the spermatozoon is incomplete after the forma- 
tion of the membrane. The question then arises, when is the 
function of the spermatozoon in fertilization completed? Zieg- 
ler’s and Wilson’s experiments show that it is incomplete even 
some time after entrance of the spermatozoon. Ziegler’s experi- 
ments (’98) consisted “‘in so constricting the egg of the sea-urchin 
alter penetration of the spermatozoon that the one part contains 
the sperm nucleus, the other part the female sex-nucleus. The 
