Artificial Parthenogenesis in 



the development of the egg by carrying a substance 

 into the latter which effects an alteration of its surface 

 layer. 



5. We will now discuss the action of the second, 

 corrective factor, in the inducement of development. 

 When we cause membrane formation in a sea-urchin 

 egg by the proper treatment with butyric acid it will 

 commence to develop and segment but will disinte- 

 grate rapidly if kept at room temperature and the 

 more rapidly the higher the temperature. If, however, 

 the eggs are treated afterward for a certain length of 

 time (from thirty-five to sixty minutes at 15 C. for 

 purpuratus and 17^ to 22^ minutes for Arbacia at 

 23 C.) in a solution which is isosmotic with 50 c.c. sea 

 water +8 c.c. 2j^ m NaCl, r they will develop into larvae, 

 many of which may be normal. Any hypertonic solu- 

 tion of this osmotic pressure, sea water, sugar, or a single 

 salt, will suffice provided the solution does not contain 

 substances that are too destructive for living matter. 

 The hypertonic solution produces its corrective effect 

 only if the egg contains free oxygen; and in a slightly 

 alkaline medium more rapidly than in a neutral medium. 

 The time of exposure in the hypertonic solution dimin- 



1 It is necessary to call attention to the fact that sugar solutions of a 

 high concentration (e. g., m solutions) have a much higher osmotic 

 pressure than that which they should have theoretically (Lord Berkeley 

 and Hartley). Delage by ignoring this fact has misinterpreted his 

 experiments with sugar solutions. See Lloyd, D.].,Arch.f. Entwcklngc- 

 mech., 1914, xxxviii., 402. 



