RACIAL STUDIES IN FISUKS 



II. EXPERIMENTAL INVESTIGATIONS WITH LPJlilSTES 

 RETICULATUS (PETERS) REGAN 



By JOHS. SCHMIDT; D.Sr. 



Director of the Carlsberg Physiological Laboratory, 

 Copenhagen, Denmark. 



(With OnoGi-aph.) 



I. Introduction, 



The purpose of the experiments about to be discussed was to 

 contribute information on the rather obscure question whether, or to 

 what extent, quantitative racial characters are hereditary. 



The tropical -Americiin Cyprinodont Lehistes reticulatus (Peters) 

 Regan' wjis employed in the experiments. I have previously used this 

 little aquarium-fish in experimental investigations, namely for the 

 purpose of demonstrating the importance of environment on the 

 numbers of organs (dorsi\l rays). 



Lebistes reticulatus is, like so many of its relatives, viviparous, and 

 under favourable conditions the female brings into the world, at intervals 

 of about 4 weeks, a considerable number of young. The young jx)ssess 

 at birth the full number of vertebrae, dorsal rays, etc, which is therefore 

 recognisable immediately after birth. 



The ex}:)eriments fall into two groups, of which the first helps to 

 elucidate the importance of eodernal factors (temperature) upon the 

 number of dor&il rays. The second is concerned with the <juestion 

 whether hereditary differences, i.e. differences dependent upon internal 

 factors, may be proved to exist in different individuals. Before I proceed 

 to discuss the experiments, I may draw attention tu the fact that the 



* C.Tate Began, "A revision of the Cyprinodont Fishes of the Subfamily Poeciliinae," 

 Proc. Zool. Soc. London 1913, Vol. ii. pp. 977—1018, 1913. 



