Artificial Parthenogenesis in Tludassona Mellita 107 



over-exposure for Strongylocentrotus, according to the figures 

 given by Loeb. 



The most striking difference, however, between the behavior 

 of Strongylocentrotus and that of Thalassema is seen in the subse- 

 quent events, after the membrane has been produced by the acid 

 treatment. Whereas, in the former the unfertilized eggs undergo 

 no further development unless exposed to hypertonic sea-water, 

 in Thalassema the action of the acid, or perhaps the changes 

 which the egg undergoes as a result of the membrane formation, 

 is suficient to lead the egg on to cleavage and the ultimate forma- 

 tion of a swimming larva. Treatment with hypertonic sea-water 

 is, therefore, unnecessary for the further development of the 

 unfertilized eggs of Thalassema. 



During a brief stay at Beaufort, N. C, in June, 1906, I had ; n 

 opportunity of repeating Loeb's experiments w^hile testing the 

 effect of his combination of methods upon the eggs of Thalassem?.. 

 Although the membrane was formed, as it always is in Thalassema 

 after treatment with an acid, the subsequent use of hypertonic 

 sea-water not only did not give rise to larvae, but actually inter- 

 fered with the development which would otherwise have taken 

 place with the acid alone when used in the proper concentration. 

 When the unfertilized eggs, after an exposure to an acid, were 

 placed in a solution of NaCl, either no developmental changes 

 occurred and the eggs early disintegrated, or at best only a few 

 early cleavages, usually irregular in character, were produced. 

 I at first tried the same solutions and exposures as Loeb had used 

 with Strongylocentrotus, and, after finding them to be futile, I 

 varied the different factors between wide limits. The acids were, 

 of course, used in solutions strong enough to call forth the mem- 

 brane formation, but too weak to cause the eggs to develop, in 

 order to test the ability of NaCl solutions to bring about develop- 

 ment after the membrane had been previously produced by acids. 

 In no case, however, did I succeed in discovering a combination 

 that could cause a normal development and the formation of swim- 

 ming embryos. The following solutions gave the best results 



obtained: 10 cc. — HCl + go cc. sea-water for five minutes, and 

 10 ^ 



