AUTO-PARTHENOGENESIS IN ARBACIA AND ASTERIAS. 391 



IMPROVED METHOD OF AUTO-PARTHENOGENESIS. 

 Loeb's improved method of artificial parthenogenesis consists 

 in following the treatment with parthenogenetic agents, by an 

 after-treatment with hypertonic sea-water, 8 c.c. of 2.5 M NaCl 

 + 50 c.c. sea-water. It seemed likely therefore that a better 

 yield of larvae could be secured if eggs, after having been sub- 

 jected to the action of the secretion for two hours, were afterwards 

 treated with the hypertonic solution for forty minutes. This 

 surmise proved correct. The following is an outline of a typical 

 experiment : 



Time. 



A 



Time. 



10.20 A.M. i c.c. eggs + i c.c. secre- 10.12 A.M. 



tion. 

 12.12 P.M. j Began hypertonic treat- 1.12 P.M. 



rnent. 

 Ended hypertonic treat- j 1.52 



12.52 

 2.30 

 5-45 



ment. 



Considerable number of 2, | 2.45 

 3, and 4-cell stages. 



Numerous 2, 3, and 4-cell 



stages. 



Very few 32-64-cell stages. 

 9.30 A.M. ' i active larva, many dead. 



6.00 



7-30 



9.45 A.M. 



4.00 P.M. 



i c.c. eggs + i c.c. secre- 

 tion. 



Began hypertonic treat- 

 ment. 



Ended hypertonic treat- 

 ment. 



Many cleavages; 2-8 cells. 



Many normal. 



Many 2, 4, 32, 64 and 128- 

 cell stages. 



Cleavages in every field. 



Some blastulae but not 

 free. 



12 fine active larvae. 



50 per cent, of cleavages 

 arrested. 



Hundreds of slowly moving 

 blastulae. 



In experiment B the time of exposure to the secretion was three 

 hours instead of two as in earlier experiments with the hypertonic 

 after-treatment. From this one might infer that better results 

 could have been obtained in the experiments in which the secre- 

 tion alone was used, but the results do not warrant this assump- 

 tion. Controls also show that with the hypertonic after-treat- 

 ment, three hours of exposure to the secretion is better than two. 

 We must believe therefore that the success of experiment B 

 and all the others carried out in the same way, depended on 

 the hypertonic after-treatment. 



The differences in the length of exposure to the secretion are 

 for the present purely empirical. 



In all the experiments both with as well as without the hyper- 

 tonic after-treatment, development was much delayed in many 



