SCIENTIFIC PROCEEDINGS. 



Abstracts of Communications. 



One hundredth meeting. 



Laboratory for Experimental Evolution, Cold Spring Harbor, N. Y. 



May 24, 1919. 



President Calkins in the chair. 



69 (1444) 



The results of selection with a Cladocera pure line (clone). 

 By Arthur M. Banta. 



[From the Station for Experimental Evolution, 

 Cold Spring Harbor, N. Y.] 



The writer has studied the effects of long-continued selection 

 upon several parthenogenetic pure lines (clones) of three species 

 of Cladocera, using their reactiveness to light as a basis for selec- 

 tion. In most of the lines the results, though suggestive, are 

 inconclusive; or there is clearly no effect of selection; or (in two 

 lines) the results even suggest slight differences in the reverse of 

 an effect of selection. But with one line of Simocephalus vetulus, 

 line 757, the result of selection is pronounced and convincing. 

 This line was subjected to selection for a period of 54 months 

 covering 181 generations of descent. In the final ten generations 

 the strain selected for greater reactiveness to light had a reaction 

 time less than one third as large as that for the strain of the same 

 line selected for reduced reactiveness to light. 



For the sake of obtaining averages showing less fluctuation 

 than the average reaction times by single broods the data for 

 each strain was averaged by two-month periods of the experi- 

 ment (each period including the data for all the individuals tested 

 in making the selections for six to eight generations). 



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