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 



