148 Racial Studies in Fishes 



number of dorsal fin rays in Lebistes reticulatus varies from 5 to 8. By 

 far the most usual number is 7. 



A more detailed account appears in Vol. XIV, Nos. 1 and 5, of the 

 Comptes-Rendus des Travaux du Lahoratoire de Carlsberg, Copenhagen. 



II. Importance of External Factors. 



The principle was to vary the temperature for the same pair of 

 parents from one period of pregnancy to the other, and then determine 

 the number of dorsal rays in the various broods of offspring. In the 

 beginning I had no means of maintaining a constant temperature in 

 the aquaria, and was therefore compelled to limit myself to stating that 

 the animals in the experiments were kept at a " low," " medium " and 

 " high " temperature, in wHich " medium " temperature was ca. 6° above 

 " low " and ca. 3° below " high." " Low " temperature was generally 

 equivalent to ca. 19° Centigrade, varying between. ca. 17° and ca. 23°. 



In the experiments 5 different pairs of Lebistes reticulatus were 

 used. The results of these investigations can be seen from Tables I — V, 

 each of which shows the number of rays in several broods from the 



TABLES I — V. Number of dorsal rays in offspring of the same pairs 

 of parents at different temperatures. 



