82 Artificial Parthenogenesis and Fertilization 



and die in an earlier larval stage the longer they have been 

 exposed to lack of oxj'gen (or to KCN). Eggs which remained 

 in the cyanide sea-water only two or three hours after mem- 

 brane formation produced plutei in relatively greater numbers 

 than those that remained longer in this solution (see chap. iii). 



The optimum length of exposure of the eggs to the potassium 

 cyanide solution depends also upon the concentration of KCN 

 in it. In a mixture of 50 c.c. of sea-water-|-2 c.c. 1/20 of 1 per 

 cent KCN, three hours seem to represent the optimum length 

 of exposure. If the eggs remain only two hours in the cyanide 

 solution, larvae are usually, but not always, obtained. Thus, 

 in one experiment the eggs were placed two hours after arti- 

 ficial membrane formation in 50 c.c. of sea-water -)-2 c.c. of 1/20 

 of 1 per cent KCN. Of the eggs which were removed from this-. 

 solution after two hours, washed twice in sea-water, and then 

 transferred to normal sea-water, 50 per cent developed into 

 good larvae; 90 per cent of those removed after three hours 

 grew into larvae; but the length of life of the former was greater 

 than that of the latter. 



The method of treating the eggs after membrane formation 

 with lack of oxj'gen or with KCN has, however, the disad- 

 vantage that it is technically very difficult and, secondly, 

 that the time that must elapse between artificial membrane 

 formation and transference to the potassium cyanide solution 

 is obviously not always the same. I have always found that 

 if the eggs are transferred to the cyanide solution immediately 

 after membrane formation, none, or only a few, of the eggs 

 develop; but I am unable to say how long after membrane 

 formation one ought to wait before placing the eggs in the 

 cyanide solution. 



These experiments prove at least that it is possible to sub- 

 stitute for the corrective influence of a short treatment with a 

 hypertonic solution a suppression of the development of the egg 

 for a longer period of time. After such a treatment the egg 



