lo8 George Lefevre 



15 cc. 2^ m NaCl+ 85 cc. sea-water for from 40 to 50 minutes. 

 The percentage of eggs that divided, after treatment with this 

 combination, was low (about 10 per cent), the cleavage was 

 abnormal, and in no case was a ciliated embryo produced. It 

 should be stated that such developmental changes as did occur 

 in experiments like this must be ascribed to the effect of the hyper- 

 tonic sea-water, since control eggs showed that the same acid 

 solution, when used alone, was too weak to cause any develop- 

 ment. 



It was clear from a great many experiments which I made that 

 the use of hypertonic sea-water combined with the acid treatment 

 is not only not an improved method of artificial parthenogenesis 

 for Thalassema, but, on the contrary, yields immeasurably poorer 

 results than the method employed in my original experiments. 

 I might also add that the combination of methods gave absolutely 

 negative results with the eggs of the sand-dollar Mellita pentapora, 

 which I subjected to a similar treatment. 



Loeb ('o5e) also found that the eggs of a starfish, a species of 

 Asterina occurring in the Bay of Monterey, form a membrane 

 after exposure to solutions of a fatty acid, although a higher con- 

 centration is necessary for this form than is required for Stron- 

 gylocentrotus. The eggs, however, do not have to be subsequently 

 treated with hypertonic sea-water, as the process of artificial 

 membrane formation is sufficient to cause development in Aste- 

 rina, and in this respect the case is similar to that of Thalassema. 



In harmony with the observations of Delage ('02c) on Asterias, 

 Loeb also found that the eggs of Asterina, which maturate nor- 

 mally upon being placed in sea-water, could not be made to 

 develop by exposure to an acid solution until after the breaking 

 down of the germinal vesicle. Thalassema eggs, on the other 

 hand, differ markedly in this respect from those of the starfish, 

 for, unless they are fertilized by sperm or acted upon by a par- 

 thenogenetic agent, the germinal vesicle remains intact, however 

 long they may lie in sea-water. 



