ARTIFICIAL PARTHENOGENESIS 645 
unfertilized eggs of this starfish for about two hours into 
a mixture of 88 c.c. of sea-water and 12 c.c. of a 24n NaCl 
solution the eggs can be forced to develop and reach the 
blastula stage, if put back afterward into normal sea-water. 
T have not yet found the optimal condition for the partheno- 
genetic development of Asterias, but the facts thus far ob- 
tained suffice to state that a certain increase in the osmotic 
pressure of the surrounding solution (and a loss of a certain 
amount of water on the part of the egg) causes the egg of 
this form to develop parthenogenetically. 
I have mentioned in another place’ the precautions and 
control experiments used to guard against the presence of 
spermatozoa. I do not consider it necessary to repeat these 
statements in this paper, but will mention one additional 
precaution, for which I am indebted to the collector of the 
Marine Biological Laboratory, Mr. Gray. Mr. Gray selects 
the females of Arbacia for my experiments,so that in all 
these later experiments I have not had one male in the labo- 
ratory. Not one egg developed in the control material. All 
the sea-water used in these experiments was heated to the 
temperature of 70° C. 
CONCLUSIONS 
The results of my experiments are as follows: 
1. Through a certain increase in the osmotic pressure of 
the surrounding solution the unfertilized eggs of some 
(probably all) Echinoderms (Arbacia, Strongylocentrotus, 
Asterias) can be caused to develop into normal blastule 
or even plutei. 
2. This increase in osmotic pressure can be produced by 
electrolytes as well as by non-conductors. It is therefore 
probable that the parthenogenetic development is caused by 
the egg losing a certain amount of water. 
1 Part II, p. 576. 
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