INTRODUCTION 13 
compressed in the ovary, they can be caused to form membranes 
and to cytolyze. Moreover, starfish eggs that are caused to 
develop by shaking form membranes first of all; this is the 
immediate effect of the mechanical agitation. 
8. We may now raise the question as to how the artificial 
membrane formation induces the development of the egg. The 
writer reached the conclusion that for the sea-urchin egg this 
was due to an acceleration of oxidations. This suggestion was 
confirmed by Warburg, and since by Wasteneys and the writer. 
The entrance of the spermatozoon raises the rate of oxidations in 
the egg of the sea-urchin to from four to six times its usual 
amount; and the artificial membrane formation has the same 
effect. There are two possibilities by which this result can be 
produced: either a catalyzer (an oxidase) is carried into the 
egg by the spermatozoon; or the change in the surface layer 
itself causes the increased rate of oxidation. Everything 
speaks in favor of the second assumption. We know that with 
the concentration of the catalyzer the rate of chemical reactions 
increases either in proportion to the concentration of the cata- 
lyzer or in the ratio of the square root of the concentration; 
and the investigations of the temperature coefficient of develop- 
ment of the egg show that the rate of development is deter- 
mined by chemical reactions. If therefore the spermatozoon 
increased the rate of oxidation by carrying an oxidase into the 
egg the rate of segmentation in an egg fertilized by more than 
one spermatozoon should be increased in the ratio of 1:2 or 
1:1/2. Observations show that the velocity of segmentation 
in eggs fertilized by two spermatozoa is identical with that 
found in eggs fertilized by one spermatozoon. This fact proves 
that the spermatozoon causes development, not by carrying an 
oxidase or some other catalyzer into the egg, but by removing 
an obstacle to development. The same must hold for the 
explanation of the influence of membrane formation upon 
development. Through the cytolysis of the cortical layer 
