100 ^ George Lefevre 



metamorphosis. The oldest larvae, which were still in an active 

 and healthy state, were accidentally killed, but not before the 

 early stages of the transformation into the starfish had already 

 made some progress. Delage, moreover, observed that partheno- 

 genesis in Asterias is independent of the formation of polar bodies 

 and occurs when one, two or no polar bodies have been extruded, a 

 result in harmony with what I have found to be true in Thalas- 

 sema. He states, however, that the treatment must be given at 

 some time during the process of maturation, as it is not effective 

 either before the breaking down of the germinal vesicle or ^fter 

 the formation of the egg pronucleus. It will be seen that this 

 limitation does not hold for the eggs of Thalassema which were in 

 every case subjected to the action of the acid while in the germinal 

 vesicle stage. 



In my experiments I not only found that the inorganic acids, 

 which had been used in a few cases by previous workers, were 

 efficient parthenogenetic agents, but that certain organic acids as 

 well, namely, acetic and oxalic, were equally successful, if not 

 superior. 



A considerable variation was observed in the behavior of the 

 eggs of Thalassema in the solutions employed, and, owing prob- 

 ably to differences in internal conditions, possibly in the degree 

 of ripeness, the same solution and the same duration of immersion 

 did not in all cases produce the same result, either in the character 

 of the development or in the percentage of eggs involved in the 

 process. This variability, moreover, was independent of tempera- 

 ture and could not be controlled. It is true, however, in the case 

 of each acid employed, that an optimum solution and an optimum 

 duration of exposure were found which could be relied upon to 

 yield satisfactory results in the majority of experiments. In 

 favorable experiments, which were the rule and not the exception, 

 from 40 to 60 per cent of the eggs underwent development and 

 gave rise to actively swimming trochophores which closely coin- 

 cided with normal larvae in appearance. 



The following solutions, with the time of immersion, are those 

 that gave the best results; they were, in consequence, most fre- 

 quently used for obtaining embryos and larvae: 



