Il6 George Lefevre 



normal in character and their stroke apparently as vigorous as in 

 embryos and larvae produced from fertilized eggs, yet I have never 

 observed a single instance where the trochophores rose to the sur- 

 face of the w^ater. They invariably swim close to the bottom, if 

 not in actual contact with the dish. This peculiarity in behavior 

 has been observed with remarkable constancy by most experi- 

 menters on artificial parthenogenesis, although Delage in the 

 starfish, after treatment with CO2, and Loeb in the sea-urchin, 

 by the use of his combination of methods, has succeeded in obtaining 

 larvae that rise in the usual manner to the surface. In Thalas- 

 sema, however, none of the methods which I have employed has 

 produced trochophores that are free from the abnormality in 

 question. 



Unless the parthenogenetic larvae were isolated, they would 

 rarely live over 36 hours, for the eggs which had failed to develop 

 were soon attacked by bacteria, much sooner in fact than the con- 

 trol eggs which had not been exposed to the solutions, and con- 

 taminated the dishes to such a degree that the larvae speedily 

 succumbed. It was, moreover, extremely difficult to separate 

 the larvae, as they did not rise to the surface, and had to be picked 

 out individually from among the non-developing eggs with a very 

 fine pipette. The trochophores, however, that were isolated were 

 kept in separate dishes and the water frequently changed, yet in 

 no case did I succeed in rearing them longer than a little over 

 three days. The oldest trochophore raised lived about 80 hours. 

 There was no appreciable advance in development, however, 

 beyond the second day, as the larvae seemed to enter upon a station- 

 ary period at that time. As they grew older, their movements 

 became more and more feeble and irregular, and they gradually 

 disintegrated, the body finally rupturing and the protoplasm 

 flowing out. 



5 Abnormalities of Cleavage and Behavior 



Although in experiments where the optimum conditions were 

 present the great majority of the dividing eggs segmented in a 

 normal manner, an endless variety of irregular cleavages were 

 encountered, especially in cases where the strength of the solution 



