ZOOLOGY: F. R. LILLIE 
159 
tion of the ovum by the spermatozoon is due to the inception of the 
fertilization reaction, and not the reverse, as was previously assumed. 
We cannot therefore accept this theory. 
The second theory is that the spermatozoa lose their activating sub- 
stance, sperm receptors in my terminology, which agrees very well with 
the demonstrated ineffectiveness in spite of the observed persistent mo- 
tility. That the rate of loss should increase with dilution is to be ex- 
pected if we regard the loss of the sperm receptors as a diffusion phe- 
nomenon; and, if we regard it as an active process of secretion, we should 
expect such a result owing to general increase of functional activity under 
conditions which appioach more nearly the normal. 
The second mode of explanation, which I have actually adopted, fits 
in with the necessary postulate that the spermatozoon bears such a sub- 
stance, and with the fact that the spermatozoon carries out the initial 
fertiHzation reaction while it is still intact and external to the ovum. 
The postulated activating substance of the spermatozoon must be Hb- 
erated before penetration, and these experiments give us some idea as 
to the manner of its Hberation. 
Glaser {Biol. Bull. 26, 84-91; 1914) has recently maintained that 
more than one spermatozoon is necessary for fertilization of the same 
form which I have studied. His observations may also find their expla- 
nation imder the same point of view, inasmuch as he was not aware of the 
significance of the time factor in inseminations with highly dilute sperm. 
We thus obtain the following additional point of view with reference 
to fertiHzation: the spermatozoon arriving at the egg while still intact 
Hberates an activating substance which initiates the fertiHzation reac- 
tion; as one consequence among others of this reaction the spermatozoon 
is taken up by the egg, and completes the process of fertiHzation in its 
interior. This point of view is consistent, as far as it goes, with my own 
theory of the fertiHzation reaction; and it is also perfectly consistent 
with Loeb's quite different point of view. 
My previous experiments had shown that eggs lose a certain substance 
in sea- water (fertiHzin) which is necessary for their fertiHzation; fertiHzed 
eggs no longer produce this substance and are incapable of fertiHzation. 
Both eggs and spermatozoa, therefore, contain substances, more or less 
liable to loss, which are necessary for fertiHzation. The mechanism of 
fertiHzation cannot possibly, therefore, be regarded in the simple manner 
postulated by Loeb's theory. The existence of parthenogenesis demon- 
strates the efficacy under given conditions of the egg-substance alone; 
we must therefore regard the spermatic substance essentially as an acti- 
vator of the fertiHzin of the egg. 
