ARTIFICIAL PARTHENOGENESIS 569 



sea-urchin eggs, which normally die if not fertilized. Morgan, in 1899, 

 produced segmentation in unfertilized sea-urchin (Ai-ba^cia) eggs, by 

 immersing them in sea water to which a dry salt had been added, such 

 a solution being called hypertonic sea water, and having a greater 

 osmotic pressure than ordinary sea water. Loeb, immediately after- 

 wards, produced swimming larvse in sea water made hypertonic by the 

 addition of magnesium chloride. Since then many investigators have 

 studied the subject. Eggs of various animals have been made par- 

 thenogenetie by putting them in solutions containing salts, acids or 

 alkalis, sugar, fat solvents, blood sera, alkaloids, or by means of asph3^ia- 

 tion, or by mechanical, thermal or electric changes. The concentration 

 of the solution in which the eggs are treated may be the same as that 

 of the fluid in which they normally live, or it may be of a greater or 

 less concentration. 



It has been fairly well demonstrated that the artificial agents — used 

 in producing parthenogenesis — act primarily on the surface of the egg, 

 and E. Lillie supposes they tend to increase its permeability. Loeb 

 recognizes a " superficial cytolysis," the exact nature of which is, how- 

 ever, unknown. "Wlien cells containing soluble coloring matters un- 

 dergo cytolysis, the colored substances come out of the cells. Cytolysis 

 has, therefore, been considered to consist of, or be accompanied by, an 

 increase in permeability of the protoplasm. 



The electric conductivity method of Kohlrausch suggested itself to 

 the writer as the best way of settling this question of the permeability 

 of the egg. The principle of the method lies in the fact that an electric 

 current is carried through wet substances by the movement of elec- 

 trically charged atoms or "ions." If the permeability increases, the 

 ions move faster and the current is greater. The use of this method 

 showed that the permeability increased immediately after fertilization, 

 on the application of agents producing parthenogenesis.^ These results 

 were confirmed by Gray,^ who observed further that tlie permeability 

 decreased again about fifteen minutes after fertilization. Lyon and 

 ShackelP observed that the permeability of the egg to certain dyes in- 

 creased on fertilization, and also that more of the red substances came 

 out of the fertilized than out of the unfertilized eggs. E. N. Harvey 

 observed independently that the permeability of the eggs to certain dyes 

 and caustic soda increased on fertilization. Finally, Glaser has recently 

 concluded from his experiments that fertilization increases the egg's 

 permeability. 



There is another proof that the egg of one species (the frog) be- 

 comes more permeable to salt on beginning development. The writer 



1 McClendon, Am. Jour. Flnjsiol., 1910, 27, 240. 



2 J. Gray, Jour. Marine Bio. Assn. United Kingdom, 1913, X., 50. 



3 Science, 1910, 33, 249. 



VOL. LXXXVI. — 39. 



