14 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
of the egg the oxidations in the unfertilized egg are accelerated 
from four to six times their natural rate. 
This idea is further supported by the fact observed by 
Wasteneys and the writer that if we cause complete cytolysis 
of the unfertilized eggs of the sea-urchin by saponin or by 
‘distilled water, the rate of oxidation is thereby raised to the 
Same amount as if the eggs were fertilized by sperm, although 
these eggs are dead. This suggests the idea that the cytolysis 
of the cortical layer removes an obstacle by which the oxidations 
become possible. It may be that the cortical layer of the 
unfertilized egg contains an oxidase which cannot act, or an 
oxidizable substance which cannot readily undergo oxidation, 
unless the cortical layer is liquefied (cytolyzed). R. Lillie 
assumes that the cortical layer of the unfertilized egg prevents 
the diffusion of CO, from the egg and that this CO, prevents 
oxidation. This view meets with the difficulty that CO, is a 
good agency for calling forth the membrane formation in un- 
fertilized eggs, and we shali see that only such substances can 
do this as diffuse into the egg. 
9. The earlier biologists had realized that the unfertilized egg 
dies quickly and that the act of fertilization prevents its death. 
The question arises: How can the spermatozoon accomplish 
this act? The causation of development requires two factors, 
the one is the membrane-forming factor, the other the corrective 
factor which in the methods of artificial parthenogenesis is 
supplied by the hypertonic solution. We may raise the question: 
Is only one of these factors responsible for the prolongation 
of the life of the egg, or are both responsible? At first sight it 
would seem as if the second factor alone were responsible fer 
this effect, since the membrane formation alone raises the rate 
of oxidations and also hastens the disintegration of the egg. 
If, however, the eggs are treated with the hypertonic solution 
they live and develop. This would make it appear as if the 
membrane formation alone only hastened the natural death 
