7O C. J. CONNOLLY. 



D. Red Adapted. Vase-dilation. 



The melanophores on the superficial distal portions of the scales 

 were likewise contracted in fishes exposed to a red environment 

 for the same period as in the preceding test, but those in the proxi- 

 mal portions and in deeper parts were not fully contracted. The 

 xanthophores, however, were not fully expanded as in the yellow 

 adapted fish. There was a denser spherical concentration of the 

 pigment giving an orange tint. There are no red pigment cells 

 in Fnndulus. But the color of the specimens adapted to a red 

 background, was quite distinct from that in the yellow. Instead 

 of the bright yellow of the latter they showed a pink color. It 

 was at first thought that this might be caused by the partially con- 

 tracted xanthophores giving a deeper yellow or orange to the cells, 

 in combination with the melanophores. On further examination 

 it was seen that the dorsal region of the head, usually pale, was 

 quite red due to the dilated condition of the blood capillaries. The 

 opercular region showed a striking network of vessels. The capil- 

 laries of the trunk were likewise dilated giving a pink color to the 

 fish. Before the melanophores are more fully contracted by the 

 prolonged stimulus, the color is brownish. 



The pink color is without doubt, due to the blood in the capil- 

 laries. As in the cases of experiment with fishes on other colored 

 backgrounds which ran concurrently through the winter months, 

 the results here were always the same. The only exceptions were 

 those fishes taken late in the spring which did not seem normal and 

 were affected by the sudden change in temperature on being taken 

 from the sea. Many of these died and those that lived were ex- 

 ceedingly slow in assuming the light shade when placed in a white 

 vessel before being exposed to the red environment. And 

 strangely enough, though not revealing any blood vessels over 

 trunk and head, the caudal find of one of these specimens was 

 very red, due to vaso-dilation. The general coloration of these 

 late-spring specimens on a red background approached the yellow, 

 but was more sombre. The fact that in these specimens lacking 

 the pink coloration, the blood capillaries were not visible, as in 

 other specimens on a red background, confirms this explanation. 



While the distinctive color is then due to the blood in the capil- 

 laries, there still remained the possibility that the cutaneous vessels 



