DEVELOPMENT OF THE FROGS EGG. 273 



the present ones. In NaCl 0.5 per cent, development was nearly- 

 normal ; in 1.0 percent, only the 16- and 32-cell stages were 

 reached; in 1.5 per cent, only the 16-cell stage, and in 2.0 per 

 cent, only the 8-cell stage, and in the 2.5 per cent, only the 4- or 

 8-cell stage was reached, while in the 3.0 per cent, the eggs died 

 without developing further. Similar results were obtained in 

 another series of the same kind. In a third series of smaller 

 range it was found that in a 0.5 per cent, solution the later cleav- 

 age stages were reached ; in a 0.7 per cent, solution also only 

 the late cleavage stages appeared ; in a 0.9 per cent, solution the 

 cleavage had not gone so far, while in a 1.0 per cent, solution 

 only the 32- or 64-cell stages had been formed. 



The upper limit for NaCl lies, therefore, somewhere between 

 0.5 and 1.0 per cent, and not above 2.0 per cent, as previously 

 stated. This difference in the results may possibly have been 

 due to some impurities in the NaCl, not present in the salt used 

 the previous year. The osmotic pressure for 0.5 per cent, is 

 3.55 atmospheres and for 1.0 it is 6.96. The latter is above that 

 of LiCl 0.65 per cent., which is 6.16. 



Action of Solutions Containing both Salts and Sugars. 



Previous work on the frog's egg had indicated that when to a 

 salt solution, too weak in itself to prevent development, a certain 

 amount of sugar is added the development may be prevented ; 

 and a comparison of the osmotic pressures showed that in such 

 a solution the pressure is higher than that when the salt alone 

 produces the same results, but lower than that necessary for the 

 sugar alone to produce the effect. Similar results have been ob- 

 tained for the salt-water fish, Fundulus, where the outcome is 

 even more striking owing to the fact that the eggs of this fish 

 will not develop in a fresh water solution of salt and sugar that 

 has an osmotic pressure lower than that of sea water in which 

 they normally develop. 1 We have gone over these results with 

 the frog in order to make sure that the effects were not due to 

 the inversion of the cane sugar previously employed (that would 

 1 increase its osmotic pressure) or that the effects were not due to 

 an adulteration of the cane sugar with other sugars. 



1 Stockard, C. R., "The Influence of External Factors, Chemical and Physical, 

 on the Development of Fundulus heteroclitus," Jour. Exp. Zobl., IV., 2, 1907, 



