2O8 C. J. CONNOLLY. 



To make a more precise comparison of the effects of a red 

 environment, two tests were made at the same time under 

 identical conditions except that in one set fresh water was used, 

 in the other, salt water. When both sets were compared on a 

 white surface on the third day, there was a decided difference in 

 the appearance of the fishes, those in the salt water lacking the 

 striking pink coloration. There was, of course, a general simi- 

 larity in coloration, due to definite states of contraction of the 

 chromatophores whether in salt or fresh water, but the pink 

 condition due to vasodilatation was absent in the former case. 

 There was however a slight vasodilatation even in the specimens 

 placed in salt water, especially under a prolonged stimulus, yet 

 not sufficient to give the distinctive pink coloration of specimens 

 placed in fresh water. The salt water must therefore inhibit, 

 though not completely, the vasodilatation. 



The rapidity with which this vasodilatation occurs varies with 

 the age and vigor of the fishes. In young vigorous specimens 

 from 6 to 9 cm. in length, placed in fresh water it never fails to 

 occur, generally on the second or third day of exposure to the 

 red background, though it is frequently intensified by the fifth 

 day. An adaptive change due to the movements of the chro- 

 matophores occurs much earlier being already noticeable in a 

 few hours. 



If the specimens from the red environment are immediately 

 placed on a white surface in good light, the condition of vasodi- 

 latation can readily be observed. It is most noticeable about 

 the head, especially in the two large vessels of the dorsal region; 

 also at the end of the spinal column and the base of the fins. 

 The peripheral vessels along the dorsal median axis of the trunk 

 are also strikingly dilated. It is interesting to observe here, 

 the rapid disappearance of the dilation. If one fixes the atten- 

 tion on definite peripheral vessels, the change will be noticeable 

 within one minute, and in about two minutes the phenomenon 

 of vasodilatation largely disappears. 



A close approximation to the condition produced by the red 

 environment in Fundnlus was obtained with the use of adrenalin. 

 The fishes were first made to assume the very dark shade by 

 being placed on a black background until their melanophores 



