Artificial Parthenogenesis in Starfish Eggs 379 



general the optimum for enzyme action — gave extremely promising 

 indications. The remainder of the investigation was then devoted 

 to determining the influence of such temperatures acting for vari- 

 ous brief periods. 



In the following experiments the eggs were exposed for brief 

 periods (varying from a few seconds to several minutes) to the action 

 of sea-water previously warmed to a definite temperature. The 

 procedure employed is as follows: the eggs are transferred at 

 a known period after removal from the animal to a small beaker 

 in which a thermometer is placed; sea-water at a temperature 

 slightly above that selected for the particular experiment (e.g., 35°) 

 is then added rapidly to the small beaker in quantity sufficient to 

 bring the temperature to the desired point; this temperature is 

 maintained constant during the definite time-period of the experi- 

 ment by partly immersing the small beaker, whenever necessary, 

 in a larger vessel of water at somewhat higher than the experi- 

 mental temperature. After the lapse of the selected time-period 

 (e. g., 70 seconds) the contents of the small beaker are suddenly 

 transferred to a large volume of sea-water at normal temperature 

 contained in a finger-bowl. The temperature of the eggs is thus 

 suddenly reduced again to the normal. It may safely be 

 assumed, when one considers the small volume of each egg and 

 the correspondingly large surface for thermal interchange with the 

 medium, that during at least the greater part of the period of 

 immersion in the warm sea-water the eggs have themselves been 

 at the same temperature as the medium. The agitation involved 

 in the two transfers is unavoidable with this procedure; but at the 

 stages with which I have worked — mostly early maturation — 

 mechanical shock is in itself ineff'ective in causing development. 

 Mere transfer from one dish to another produces no visible result. 

 The efi^ects observed are therefore to be ascribed wholly, or at 

 least in chief part, to the change in the thermal conditions prevaiUng 

 in the egg-system. 



Experiments zuith Arhacia Eggs 



The results with sea-urchin eggs have been almost entirely 

 negative so far as concerns production of development by momen- 



