ARTIFICIAL PARTHENOGENESIS 585 



writer has shown that the mere membrane formation leads to 

 the death of the sea urchin egg unless the latter is put into the 

 hypertonic solution for a sufficiently long time. If the eggs 

 do not remain in the hypertonic solution a sufficient period 

 of time after the artificial membrane formation they will per- 

 ish. Such was the case in this experiment. In order to make 

 this clear another set of experiments must be discussed. 



7. Variation of the time of exposure to the hypertonic solution 



In the experiments thus far mentioned the eggs of Arbacia 

 were always exposed to the neutral hypertonic solution for 

 fifteen minutes at a temperature of about 22°C. When the 

 eggs had previously been treated for about twenty-five min- 

 utes with a mixture of 50 cc. m/2 (NaCl + KCl + CaClo) + 

 0.3 cc. TTT NH4OH the exposure of fifteen minutes to a neutral 

 hypertonic solution as a rule sufficed to cause all or many of 

 the eggs to develop. If the eggs remain in the hypertonic 

 solution for a longer period, they develop in a less regular way 

 and perish, as a rule, at the time of the blastula formation, 

 probably on account of irregular (multipolar?) mitosis. A 

 shorter exposure than fifteen minutes at this temperature is, 

 as a rule, inadequate to protect the eggs from disintegrating 

 during the first segmentation. As was to be expected from 

 the author's former experiments, the optimal time of exposure 

 of the eggs to the hypertonic solution varies, if the time of ex- 

 posure to the alkaline solution varies. 



Unfertilized eggs of Arbacia were put into a mixture of 50 

 cc. m/2 (NaCl + KCl + CaCy + 0.3 cc. ^ NH4OH. One 

 part of the eggs was transferred to the neutral hypertonic solu- 

 tion after ten minutes, and the rest after thirty minutes. After 

 different intervals some of the eggs were transferred to normal 

 sea water. The result is indicated in the following table. Tem- 

 perature 23 °C. 



(a) Eggs hi 0.3 cc. to NHiOH for ten minutes and subsequently in the neutral 

 hypertonic solution for 



16 minutes: The eggs begin to segment, but disintegrate. No larvae 

 formed 



