298 REPORTS ON THE STATE OF SCIENCE, ETC. 



ARTEMIA SALINA. 



Report of the Committee appointed to investigate the progressive adaptation 

 to nezv conditions in Artemia salina (Diploid and Octoploid, Partheno- 

 genetic v. Bisexual) (Prof. R. A. Fisher, F.R.S., Chairman ; Dr. K. 

 Mather, Secretary ; Dr. J. Gray, F.R.S., Dr. F. Gross, Dr. E. S. 

 Russell, O.B.E., Prof. D. M. S. Watson, F.R.S.). 



Owing to the appointment of Dr. F. Gross elsewhere the work has been 

 carried on at the Galton Laboratory by Miss S. B. North under the super- 

 vision of Dr. K. Mather. 



The work of last year showed, among other things, that different parallel 

 families within strains had different powers of resistance to sodium arsenite 

 poisoning. Consequently it was considered advisable to concentrate atten- 

 tion on families within one strain. The strain chosen was the diploid 

 bisexual form from the Western U.S.A., most of the material coming, in 

 fact, from California. Various substrains were explored and some interesting 

 differences were found, as will be shown below. 



The technique of testing the resistance of the young nauplii has been 

 improved. Previously it was the practice to test the whole of each brood 

 in one concentration of arsenite solution. It was, however, found that 

 different broods of the same parents often had different powers of resistance. 

 The revised testing technique was designed to overcome this difficulty. 

 Fifteen solutions of arsenite were made in such a way that their strengths 

 went up in geometrical progression, with the eighth just twice as strong as 

 the first, and the fifteenth twice as strong as the eighth. These were 

 lettered A to O, A being the weakest at a strength of N/40 and O the 

 strongest at N/10. 



Each brood is subdivided into six or eight groups, the groups being 

 subjected to the range of testing solutions considered appropriate for 

 them. All the broods of each set of parents are dealt with in this way 

 and the average of their behaviour over the range of solutions employed 

 is taken as a measure of their resistance. This method clearly reduces 

 the inter-brood differences. 



In other respects the method of testing the nauplii was the same as 

 before. 



The technical difficulties of failure of breeding, or the production of 

 eggs in the place of nauplii, by some of the pairs, were again encountered 

 to a rather severe extent, in spite of precautions. Hence the testing has 

 not taken place as regularly or extensively as was hoped. 



Of the lines tested C2 has shown itself to have a much higher resistance 

 than any other. In test solution N it showed practically complete survival 

 and in test solution O, the strongest, the death rate was only 50 per cent. 

 Stronger concentrations of arsenite are readily available in strengths fitting 

 the chosen series by a slight modification of the testing technique, and so 

 it will be easy to test this line in higher concentrations. The line Ci 

 had an extremely low 50 per cent, survival level (D-E) but the remaining 

 three lines all showed this point in the region covered by test solutions F-H. 



The lines C4 and C5 have been selected for one and two generations 

 respectively, and, as the Table shows, in C4 the resistance has not increased 

 to a noticeable extent. There is, however, a suggestion of increased 

 resistance following selection in C5, but the data are at present scanty, 

 particularly for the second selected generation. The apparent effects of 

 selection are smaller than last year's. 



