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REPORTS ON THE STATE OF SCIENCE, ETC. 



generation. The second is the 50 per cent, point, i.e. the strength of poison at 

 which half the nauplii which have survived natural death, die by poison. 

 The value of this parameter varies from brood to brood, its variation being 

 the measure of heterogeneity among broods. The third parameter is the 

 natural death-rate, which varies only slightly from brood to brood. As 

 was said above, its evaluation does little to eliminate the heterogeneity 

 between broods of the same line-generation. 



The introduction of this laborious method of statistical treatment has 

 resulted in a considerable time lag between the actual experiments and the 

 interpretation of results. This makes it impossible, at the present time, to 

 give a fuller discussion of the extensive data accumulated during the year. 



Efforts are being continued to discover the causes of heterogeneity, 

 and to devise other improvements in experimental technique which will 

 increase precision. 



The data obtained during 1937-38 are given in Tables IV-X. In Table III 

 are given the strengths of sodium arsenite corresponding to the letters used 

 in the other Tables. 



The Committee asks to be reappointed with a grant of £20. 



Table I. 



Table II. 

 Illustrating variation of susceptibility between broods of the same parents. 



