VASODILATATION IN FUNDULUS DUE TO A 

 COLOR STIMULUS. 



C. J. CONNOLLY, 

 CATHOLIC UNIVERSITY, WASHINGTON, D. C. 



In a previous issue of the BIOLOGICAL BULLETIN, 1 the writer 

 gave an account of the results of experiments with differently 

 colored environments on Fundulus. These experiments were 

 carried out in the Harvard Zoological Laboratory during the 

 winter of 1922-1923. It was stated in that article, that the 

 distinctive coloration obtained when Fundulus was placed in a 

 red environment was due to a vasodilatation. It was further 

 stated in a postscript that similar experiments were carried out 

 elsewhere by the writer during the summer of 1924 with the 

 same adaptive color changes occurring, but that no vasodilatation 

 was observed when Fundulus was placed in a red background. 

 It was suggested that the different results might be due to 

 seasonal or local differences in the fishes. 



During the past summer further tests were made at the U. S. 

 Bureau of Fisheries Laboratory, Woods Hole, to determine the 

 factors causing this difference. Positive results were obtained 

 which will be briefly reported here. 



In these experiments the fishes were first made to assume the 

 light shade by being placed on a white background and from this 

 stock they were selected for the various tests. Five specimens 

 were placed in each of four battery jars containing fresh water 

 and the jars placed in the differently colored boxes. Adaptation 

 to yellow, blue, green, and red backgrounds were obtained with 

 a vasodilatation occurring in specimens from the red background. 



The experiments were repeated under the same conditions 

 except that salt water was used. Adaptation to the various 

 colored backgrounds occurred, but vasodilatation was not ob- 

 served in the specimens placed in the red environment at the 

 same period of exposure to the stimulus. 



1 Adaptive Changes in Shades and Color of Fundulus, BIOL. BULL., Vol. XLVIII., 

 January, 1925. 



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