RACIAL STUDIES IN FISHES. III. DIALLEL 

 CROSSINGS WITH TROUT {SALMO TRUTTA L.). 



By JOHS. SCHMIDT, D.Sc. 



Director of the Carlsherg Physiological Laboratory, 

 Copenhagen, Denmark. 



In previous papers I have summarized the results of some investiga- 

 tions carried out in the Carlsberg Laboratory in Copenhagen with two 

 viviparous species of fish belonging to the genera Zoarces and Lebistes 

 (Journal of Genetics, Vol. vii, 1918, and Vol. viii, 1919). 



It was shown there that the number of vertebrae, fin-rays, etc. — i.e. 

 so-called "racial" characters — are certainly capable of environmental 

 influences, but still primarily determined by internal, hereditary factors^ 



I shall here give an account of some experiments with a third, 

 oviparous, species of fish, whose conditions of reproduction are very 

 favourable to experimental investigation. With this species it has 

 therefore easily been possible to confirm the results previously arrived 

 at with the two viviparous species, and for the same reason it may, 

 presumably, with advantage be used to elucidate generally the difficult 

 questions of the genetic behaviour of quantitative characters. 



This species with which I have especially worked is the ordinary 

 trout (Salmo trutta L.), with which in this country artificial hatching, 

 applied with a greatly developed technique, is carried on on a large 

 scale. 



With a nutnber of trout I perform what I have called diallel cross- 

 ings. It consists in this that each female is paired with each male. If 

 for instance there are a males-and b females,ax6 offspring-combinations 

 will arise which are all of them different and for which the average 

 values of the character in question are determined by observation. As 



1 Professor R. C. Punnett arrived at a similar result by a statistical examination of 

 the viviparous shark Spinax niger, as is evident from an interesting memoir: " Merism 

 and Sex in Spinax niger " (Biometrika, Vol. iii, No. 4, 1904), which was unknown to me, 

 but of which Prof. Punnett has been kind enough to send me a copy. 



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