6O LIBBIE H. HYMAN. 



ous as the investigators concerned. These explanations have in 

 general proved inadequate and unsatisfactory and fail to account 

 for the facts. The most obvious explanation, proposed at first 

 by Stockard, that the defects are the consequence of a specific 

 action of the chemicals employed upon the embryo, was later 

 abandoned by him and must be regarded as untenable. The fact 

 that a large number of substances and conditions call forth the 

 same defects at once shows that their action must be a very gen- 

 eral one and not at all specific. The osmotic pressure of the solu- 

 tions cannot be the effective factor, since solutions of varying 

 osmotic pressure yield similar results. McClendon's proposal 

 that the solutions alter osmotic conditions in the egg by changing 

 the permeability of the surface cannot be accepted in view of the 

 fact that the same defects are produced by injuring the sperm 

 only and keeping the eggs in normal sea-water. Stockard's final 

 conclusion that the defects are due to a general depression of the 

 eggs by the agents to which it is exposed contains part of the 

 truth but fails to account for the fact that only certain parts 

 of the embryo are affected. Werber believes that the defects are 

 due to a blastolytic destruction or dispersal of the embryo ; but 

 outside of the fact that such blastolysis cannot be demonstrated 

 the theory fails like the others to account for the differential ac- 

 tion of the effective agents on the embryo. Kellicott sought the 

 explanation in a disturbance of the normal organization of the 

 egg with abnormal arrangements and distributions of the egg 

 materials. This theory likewise does not account for the dif- 

 ferential effect on the embryo. 



It is perfectly obvious that the outstanding fact which must be 

 taken into consideration is that all of the reagents and condi- 

 tions affect some parts of the embryo more than they do other 

 parts. These affected parts have already been enumerated. It 

 is quite impossible to account for this except on the assumption 

 that certain parts of the embryo are more susceptible to altera- 

 tions of conditions than other parts. The necessity for this as- 

 sumption has been recognized clearly by Stockard, McClendon, 

 and Werber, but it does not seem to have occurred to them that 

 when this assumption is granted no further explanation is neces- 



