ARTIFICIAL PARTHENOGENESIS IN ARBACIA. 149 



relatively narrow. It seems that the critical moment does not 

 lie, as in the case of Delage's observations on Asterias, in the time 

 when the eggs are placed in the solution, but rather when they 

 are removed from the solution. 



The stage of development of eggs when placed in solution evi- 

 dently has some bearing on the time required for development. 

 The differences in the states of ovarian eggs would seem to ac- 

 count for the differences in the time required for development, not 

 only for the eggs of different individuals, but as in the experiment 

 given below, for the eggs of the same individual. 



The culture just referred to, the one in which larval develop- 

 ment was obtained after an hour and twenty-two minutes in the 

 concentrated solution, was one of a series of experiments to de- 

 termine the proper length of time and also the time in which eggs 

 of a given female will develop. This experiment also presented 

 the longest period of time within which eggs of the same indi- 

 vidual could be removed from the concentrated solution for sub- 

 sequent development. The eggs were placed in the concentrated 

 sea-water and allowed to remain one hour. Watch-glass cultures 

 of approximately equal number of eggs, the standard being three 

 pipette drops of eggs in each watch glass, were removed every 

 two minutes from the concentrated solution and placed in steril- 

 ized sea-water. The length of time that eggs remained in the 

 concentrated solution is given and opposite are the observations 

 made, beginning seven hours and twenty minutes later. 



Minutes in Con- 

 centrated So- 

 lution. Notes Taken Seven to Ten Hours Afterward. 



62. No segmentation. 



64. A number of fragments from a few eggs that had seg- 

 mented and then broken. 



66. The same. 



68. The same. 



70. Fragments more abundant but nothing in the nature of 

 a cluster of blastomeres. 



72. The same. 



74. The same. 



76. Not so many fragments, a few eggs segmented into two 

 and three blastomeres. 



