234 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
three or four cells instead of into two. The writer has measured 
the rate of segmentation in these eggs and found that the inter- 
val between addition of sperm and cleavage is identical with 
that of eggs fertilized by only one sperm. This proves that 
the sperm induces development, either by removing an obstacle 
e.g., a substance which inhibits development, or by activating 
a substance contained in the cortical layer which was inactive 
before and which is needed for development. The obstacle 
which inhibits development is obviously the state and constitu- 
tion of the cortical layer of the unfertilized egg. The cytolysis 
or destruction of this layer (which results in membrane for- 
mation) allows the egg to develop. 
Another set of experiments confirms this view. It is con- 
ceivable that the fatty acids or alkalies by which we call forth 
the membrane formation might act as catalyzers. If that 
were the case, the superposition of the fertilization of the egg 
by sperm and by a treatment with a fatty acid should accelerate 
the rate of development in such an egg. If eggs are first ferti- 
lized by sperm and then treated with butyric acid for that 
length of time which is required for artificial membrane forma- 
tion, no acceleration of the rate of cell division is observed. If 
we call forth artificial membrane formation first by butyric 
acid, no spermatozoon can enter the egg since the fertilization 
membrane is impermeable to a spermatozoon. But we can 
destroy the membrane by shaking it. If we then add sperm 
to such eggs, the spermatozoa enter, cause a second membrane 
formation (in which the membrane fits tightly around the egg), 
and the eggs develop at room temperature without requiring 
any further treatment with the hypertonic solution; which 
indicates that the spermatozoa have entered the egg. In 
such eggs the rate of cell division is exactly the same as in 
normally fertilized eggs.} 
1 The idea that the spermatozoon does not induce development by carrying 
a catalyzer into the egg was set forth in The Dynamics of Living Matter, 1906. 
