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 2^n NaCl 

 solution the eggs can be forced to develop and reach the 

 blastula stage, if put back afterward into normal sea-water. 

 I 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 1 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 blastulse 

 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. 



' Part II, p. 576. 



