THE WONDER OF LIFE 593 



organism has a characteristic power of registering experi- 

 ences, and the next step in our argument is that these 

 experiences may have lasting effects. Let us take one 

 illustration from the results of imprisonment in darkness. 

 Light, as every one knows, has many effects on the Uving 

 creature : — ^it is used by the green leaf in building up organic 

 substances ; it makes our pulse beat more quickly ; it 

 serves as a Hberating stimulus for the development of pig- 

 ment. These are only three of the many relations between 

 light and life. We inquire therefore with interest iato the 

 negative side — the influence of darkness, and we shall 

 refer to Ognefi's very interesting experiments on gold-fishes. 

 He kept them in a roomy tank and with plenty to eat— 

 earthworms and ' blood- worms ' (larvse of Chironomus, 

 the harlequin fly) — ^but in absolute darkness. He kept 

 this up for over three years, and observed the modifications 

 that occurred in the fish. 



The colour first became black, but in the second year 

 it became golden again, and the reason for this is interest- 

 ing. To begin with, the dark pigment-ceUs (melanophores) 

 spread out and covered up the subjacent layer of waste- 

 crystals (iridocytes) which give the gold fish its golden 

 sheen. But subsequently the wandering amoeboid cells 

 or phagocytes devoured the dark pigment-ceUs and thus 

 re-exposed the golden layer. 



The changes in the eye were even more interesting, 

 A complete alteration occurred in the structure of the 

 pigment-epithehum of the eye, and there was a complete 

 disappearance of the rods and cones, and of some other 

 characteristic features of the eye. Profound atrophy 

 of the eye occurred in the absence of any functioning, and 

 the fish became totally blind. This experiment is of great 



Q Q 



