768 STUDIES IN GENERAL PHYSIOLOGY 
factory parthenogenetic plutei by using sea-water the con- 
centration of which had been increased 30 per cent. to 40 
per cent. by evaporation. ‘When the eggs were introduced 
for one to two hours into this concentrated sea-water they 
developed beautifully when returned to normal sea-water. 
A second important circumstance which perhaps plays a 
role in these experiments is the temperature. The experi- 
ments at Woods Hole (as well as Wilson’s experiments in 
Beaufort) were all made at summer temperature when the 
temperature of the water was 20° C. or higher. In Califor- 
nia the temperature varied considerably in my experiments. 
It was often pretty low and I was occasionally unsuccessful 
in bringing about artificial parthenogenesis. I attributed this 
at that time to the immaturity of the eggs. Possibly this was 
right, and possibly this explains the negative results of most 
of the European investigators who worked in winter. Since 
then, however, I have thought that perhaps the temperature 
affects the results of the experiments in such a way that 
below a certain temperature artificial parthenogenesis does 
not occur, or at least only with difficulty. This idea is 
strengthened by a letter from Mr. Doncaster who has 
worked in Naples, and who informs me that he at first 
obtained only negative results, that he then suspected, how- 
ever, that the temperature of the water in Naples was too 
low, and so made experiments in water of the temperature 
of about 20° C. In the latter case he obtained positive 
results. 
2. What has been said thus far refers only to experiments 
on sea-urchin eggs, especially Arbacia. Especial care is 
necessary when working with starfish eggs. A. Mathews 
has observed that the unfertilized eggs of starfish (Asterias) 
after maturation in sea-water can be made to develop by 
shaking, and that a time exists at which the agitation con- 
nected with transferring the eggs from one dish to another 
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