INTRODUCTION 1: 
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of the egg, while the second factor, the treatment of the egg 
with the hypertonic solution, was the life-saving factor. Yet 
this conclusion is unwarranted. It makes no difference whether 
the treatment of the unfertilized egg with a hypertonic solution 
follows or precedes the artificial membrane formation (except 
that the length of time of exposure of the eggs to the hyper- 
tonic solution differs in both cases). The writer found recently 
that if once the unfertilized eggs have been treated with a hyper- 
tonic solution they possess the second factor or substance 
necessary for development, as long as they are alive. If at 
any time 24 or 48 hours later they are submitted to the process 
of artificial membrane formation they will not disintegrate, 
but develop normally at room temperature. Now if the treat- 
ment with the hypertonic solution—our second factor—were 
really the life-saving agency in fertilization or artificial partheno- 
genesis, unfertilized eggs which had been treated with a hyper- 
tonic solution alone (without membrane formation) should live 
indefinitely. This is, however, not the case. If we treat un- 
fertilized eggs with a hypertonic solution only, such eggs will 
die just as fast as unfertilized eggs not treated in this way. 
If, however, such eggs are subsequently submitted to the 
process of artificial membrane formation they will develop 
and live indefinitely. To such eggs the artificial membrane 
formation becomes a life-saving agency. From these facts 
we must conclude that both factors of artificial partheno- 
genesis are required to preserve the life of the egg and prevent 
its death. 
This conclusion is supported by the fact that for a small 
percentage of starfish eggs or annelid eggs the mere act of mem- 
brane formation suffices for development and the prevention of 
the death of these eggs. We are forced to conclude that such 
eggs contain or form a substance which prevents the disintegra- 
tion hastened as a rule by the process of membrane forma- 
tion; and which in the sea-urchin egg must be produced by the 
