J. S. Huxley 233 



B C b C 

 No. 7, p. 345. If the cross were y — x j — , we should expect 



1 + .9, black : 2 — s, red : 1, albino. 



The figures were BG, 235; 66', 169; B (b) c, 144; which gives 

 .9 = -7450, with CO. V. = 25-5 %. 



b C b C 

 (d), p. 347. If the cross were ^— x y^ , we should expect 



2 — s (black + black no-white) : 1 + .9 (red + red no-white) 



: 1 (albino -f- colourless). 



The figures were B, C, 162; b, C, 202; B (b), c, 127; which gives 

 .9= -6646, with c.o.v. = 33-54 %. 



The linkage-values for the two latter sets of crosses are in close 

 agreement with my figures; those for the first cross are a sufficient 

 approximation in view of the small numbers. 



The double heterozygotes (No. 4, p. 344) and triple heterozygotes 

 [(e), p. 347] crossed inter se do not show linkage ratios, presumably 

 because the make-up was not always the same, B having sometimes 

 entered with C, at other times with c. 



The work is being continued. But the fact that this is, I believe, 

 the first case of linkage recorded for Crustacea wan-ants its publication 

 at the present stage. 



In conclusion, I would like to thank Mrs Sexton of the M. B. A., 

 Plymouth, for her kindness in providing me with material, and in placing 

 her experience of the species at my disposal, my wife for help in caring 

 for the animals, and Mr J. B. S. Haldane of New College, Oxford, for 

 criticism and advice. The abnormal ratios in Allen and Sexton's paper 

 had, I found, led Mr Haldane independently of myself to suppose that 

 linkage might be present, but he was unable to undertake the experi- 

 mental proof of the hypothesis. 



LITERATURE. 



Allen and Sexton, '17. "The loss of the ej'e-pigraent in Gammarus Chevreu.vi." 



J. Mar. Biol. Ass. Plyiiiouth,\o\. xi. 1917, 273. 

 Haldane, J. B. S., '19. " The probable errors of calculated linkage values, &c." 



Jour a. Genetics, Vol. vilL 1919, 291. 

 Plough, H. H., '17. "The effect of temperature on crossing over." J. E.vp. ZooL 



Vol. XXIV. 1917. 



