104 George Lefevre 



In each of the two cases cited above, the eggs were taken from 

 the same females and placed in the solutions at the same time, the 

 only difference being that the second solution was stronger than 

 the first by i cc. of the dilute acid. 



2 Artificial Membrane Formation and Parthenogenetic 

 Development 



The unfertilized eggs of Thalassema after transference from 

 the acid solution to normal sea-water, throw off a membrane iden- 

 tical with that which is formed upon entrance of the spermatozoon. 

 The artificial production of a membrane has been observed by 

 former experimenters. O. and R. Hertwig ('87) first discovered 

 that, by the addition of chloroform to the sea-water, the unfertilized 

 eggs of the sea-urchin may be caused to form a fertilization mem- 

 brane which is entirely normal in appearance. 



Herbst ('93) later confirmed the result obtained by the Hertwigs, 

 and found that not only chloroform but several other substances, 

 namely, clove oil, creosote, xylol, toluol and benzol, act in a 

 similar manner, the best results being given by benzol. More 

 recently Herbst ('04) has obtained a normal membrane formation 

 by the use of silver salts. Loeb ('o5d, '056) tested the action of 

 hydrocarbons in this respect and found that the ripe eggs of 

 Strongylocentrotus and Asterina, when put into 50 cc. of sea-water 

 which has been shaken with i cc. of benzol or amylene, immediately 

 form membranes which are identical in appearance with the 

 normal fertilization membrane. By subjecting unfertilized eggs 

 of Strongylocentrotus purpuratus to a 2J to i^ n NaCl solution or 

 to a 2^ n cane sugar solution, he also succeeded in causing a mem- 

 brane formation, but in these experiments the osmotic pressure 

 was so high that the eggs were greatly injured and underwent 

 cytolysis without subsequent development. Solutions of lower 

 osmotic pressure caused development, but not membrane forma- 

 tion ('05a, p. 79). 



It should be mentioned that Wilson ('01, p. 533) states for 

 Toxopneustes that "some of the magnesium eggs showed a 

 faint ragged membrane, but others were absolutely devoid of a 

 membrane," although he gives no details of his observations on 



