30 MARVELS OF FISH LIFE 



through. One chamber was painted white, the other 

 was covered up and quite dark. The pike was first 

 placed with his head in the dark chamber, and with his 

 body and tail in the light chamber. Here he remained 

 for two hours, water running through the tank all the 

 time. At the end of the two hours a photograph was 

 taken, and you will see that in consequence of the eye 

 of the pike being in the dark chamber the pigment cells 

 remained relaxed, and the body of the fish was, there- 

 fore, dark. 



The pike was then turned round so that the head 

 was now in the light. In three minutes a second photo- 

 graph was taken. The entire fish at once became pale, 

 as shown in the illustration, in consequence of the con- 

 traction of the dark pigment cells caused by the stimulus 

 of light acting through the eye. 



Fear and emotion cause a similar contraction of the 

 dark pigment cells, thus a fish becomes pale when 

 alarmed. This point has already been illustrated in the 

 first chapter when considering the emotions of fishes. 



Next let us consider the tench. The colouring on 

 this fish may be taken as an example of that found in 

 fishes inhabiting dark open waters, such as the sea and 

 deep ponds. The sides are a golden olive-green, the back 

 is very dark, and the under-surface white. When seen 

 as in nature, the tench, like the dace, becomes of a 

 uniform shade, the under-parts darkening and the back 

 becoming lighter, so that the whole is brought to the 

 same shade as the sides of the fish. 



