74 C. J. CONNOLLY. 



longed stimulus of different colored backgrounds indicate that 

 the species tested do simulate the background. 



The subjective significance of the phenomenon of color simula- 

 tion, is not considered here. It is important first to know, as 

 Uhlenhuth (1911) pointed out, whether lights of different wave- 

 length bring about different responses. This has been found to 

 be true of Fundulus heteroclitus. 



This research was suggested to me by Prof. G. H. Parker and 

 carried out under his supervision. To Prof. Parker I am in- 

 debted for many helpful suggestions, for the privileges of the 

 Harvard Laboratory and for many other courtesies extended 

 while making this investigation. 



VI. SUMMARY 



1. Adaptive changes in shade occur in Fundulus heteroclitus 

 when placed on white, gray, and black backgrounds. This adap- 

 tation is brought about by the contraction or expansion of the 

 melanophores. 



2. On colored backgrounds for short periods, adaptation in 

 only shade occurs. 



3. Prolonged stimulation by colored backgrounds brings about 

 adaptation in color. This occurred in yellow, red, green, and 

 blue environments. 



4. The experiments with spectral lights of different wave- 

 lengths but of the same radiant energy or intensity, show that the 

 melanophores respond similarly at all wave-lengths, the contrac- 

 tion being due to light intensity. 



5. The response to the longer wave-lengths, red and especially 

 yellow, in causing an expansion of the xanthophores, though in- 

 tensity was the same as in the blue or short wave-length end of 

 the spectrum, shows that the quality of light or wave-length has 

 a specific influence on the coloration of Fundulus. 



6. The stimuli causing changes in shade and color are received 

 through the eyes. 



7. The changes in color are brought about by the degree of 

 expansion or contraction of the melanophores and xanthophores 

 combined with the optical properties of the guanophores or irido- 



