OF VITAL PHENOMENA 161 



Hertwig and Morgan observed that the unfertilized sea urchin's 

 egg may be caused to segment by treatment with certain solu- 

 tions. Loeb continued these experiments with the object of ob- 

 taining complete development, calling it artificial parthenogenesis. 

 Delage succeeded in raising several such sea urchin's beyond the 

 larval stage. Bataillon reared several parthenogenetic frogs, and 

 Loeb confirmed his experiment. 



Loeb observed that cytolytic agents cause membrane formation 

 on sea urchins' eggs, considering this due to a superficial cytoly- 

 sis, also considering the development of the egg to be due to 

 two factors, first, membrane formation, and second, a corrective 

 factor which was not clearly defined. 



R. Li Hie supposed the development of the eggs to be due to 

 increase in permeability. It was found that the electric con- 

 ductivity of the sea urchin's egg increased when it was made 

 parthenogenetic to the same degree that it did when it was fer- 

 tilized (McQendon 1910 c, e). The eggs were made partheno- 

 genetic by treatment for a few seconds with a dilute solution 

 of acetic acid in sea water, then being thoroughly washed 

 in sea water. This increase in conductivity must be interpreted 

 as an increase in permeability of the eggs to ions. 



The permeability of the frog's egg increases when it is made 

 parthenogenetic (McQendon, 1914 a). It had been observed 

 that the frog's egg will commence segmentation if a no volt 

 alternating current is passed through the water containing the 

 eggs from electrodes about two inches apart, for about one second 

 (McQendon, 191 1 b). This stimulation increases the permea- 

 bility of the eggs to the same extent that fertilization does. 



Since both fertilization and artificial stimulation act in the 

 same way in increasing the permeability of the eggs, we have 

 cumulative evidence to indicate that the increase in permeability 

 is essential to segmentation. 



The kinds of stimuli capable of inducing artificial partheno- 

 genesis are very numerous. Heilbrunn (1913) claims that they 

 all decrease the surface tension of the egg. It seems more prob- 

 able, however, that the surface tension is increased, since the 

 egg becomes spherical. It was found possible to cause the eggs 

 of Arbacia punctulata to segment by treatment with any one of 

 the following: hypotonic solutions, isotonic solutions of acids 



