ARTIFICIAL PARTHENOGENESIS 641 
contained practically all the constituents of normal sea-water. 
Yet if unfertilized eggs of Arbacia are left in such a solution 
for from one and one-half to two hours, as many as 50 per cent. 
of the eggs may reach the blastula stage when put back into 
normal sea-water. Many of these eggs die in the blastula 
stage and only a small number reach the gastrula or pluteus 
stage. The blastule are like those which I described in one 
of my former papers.’ In the majority of cases more than 
one blastula develops from one egg. I have seen as many 
as six moving blastule arise from one egg. The tendency 
to give rise to more than one embryo is greater in the egg 
of Arbacia than in the egg of Strongylocentrotus. This 
difference is probably due to the fact that even the unferti- 
lized egg of Strongylocentrotus often forms a fine membrane 
which is much thinner than the one produced through the 
entrance of a spermatozoon, but which is sufficient to keep 
the blastomeres together. The addition of NaCl or KCl to 
sea-water favors the formation of this membrane. 
4. In all the experiments mentioned thus far the increase 
in the osmotic pressure had been brought about by the 
addition of electrolytes. This might be considered as an 
indication that the electrically charged ions in the sea-water 
played an important rdle in the production of partheno- 
genesis. I myself was originally inclined to such an assump- 
* tion. I have convinced myself, however, that an increase in 
the osmotic pressure of the sea-water through the addition 
of cane-sugar or urea can produce parthenogenesis. My 
stock solution of cane-sugar (rock candy) was 2n and con- 
tained 684.3 g. in a liter, while the stock solution of urea 
was 24n and contained 150.31 g. in a liter. I found that 
the unfertilized eggs of Arbacia were able to develop after 
they had been for from one and one-half to two hours in one 
of the following solutions: 
1 Part II, p. 576. 
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