NaturaL DEATH AND FERTILIZATION 743 
formed in the parthenogenetic animals which favors the 
processes of development. We know that an exceedingly 
small amount of hydrogen ions suffices to bring about devel- 
opment in unfertilized starfish eggs; that an exceedingly 
small amount of calcium causes the unfertilized eges of 
Amphitrite to develop; and that a trace of potassium ions 
brings about the development of unfertilized Chetopterus 
eggs.’ It is entirely possible that the specific ions or other 
substances necessary to start the development of the eggs of 
the bee are formed within the egg itself through the chemi- 
cal changes taking place during or after maturation, and 
that without the formation of these substances develop- 
ment is impossible. In the case of sea-urchins and starfish 
eggs one might also believe that the processes of maturation 
and the processes of development pass over into each other. 
For it has often been observed that the unfertilized eggs of 
these forms after having resided in ‘‘normal” sea-water for 
about twenty-four hours begin to cleave shortly before death. 
This cleavage, however, never goes beyond the two- or four- 
celled stage. This might be explained by the fact that the 
eggs begin to die at this time. After I had found this year 
that the eggs of sea-urchins can still be fertilized after a 
residence of five days in sterilized sea-water (at summer tem- 
perature), I decided to study this question of spontaneous 
cleavage somewhat more closely. If it were true that indi- 
vidual sea-urchin eggs begin to cleave in ordinary sea-water 
after about twenty hours, and cease to develop any further 
only because they soon die, it would be expected that many or 
all should cleave when kept alive four or five days, and that 
a number of them should reach a fairly advanced stage of 
development. A lot of sea-urchin eggs were distributed 
into a series of flasks containing sterile sea-water. One of 
the flasks was opened every morning and a careful search 
was made for developed eggs. 
1 LoeB, FISCHER, AND NEILSON, loc. cit, 
Digitized by Microsoft® 
