244 THE INFLUENCE OF LIGHT ON LIFE. 



fleshy colour and transparent enough to allow of the heart and 

 liver being seen within. They have four legs and a long eel-like 

 body, and they breathe both by gills and lungs. On closer exami- 

 nation two black spots may be seen upon the head. These black 

 spots are situated at some distance beneath the skin, and prove on 

 investigation to be all that remains of the creature's eyes. For 

 generations these animals have lived in perpetual darkness, and as 

 they have therefore never had opportunity to exercise the power 

 of their eyes the faculty of vision has been lost, and by the law of 

 degeneration the very organ itself has been changed, bidding fair 

 to be, in the course of time, entirely absorbed or extinguished as 

 unnecessary. We thus see at once that certain hfe is possible 

 under the entire absence of light, but we also see that vital 

 changes have been made. 



Other animals, besides those just referred to, are also to be 

 found in dark caves, and all of them either half-blind or altogether 

 bUnd. A spider discovered in these regions has developed very 

 long antennae, thus making up for its loss of sight by unusually 

 prominent powers of touch. A blind rat, also, which inhabits 

 those caves has grown very long and sensitive whiskers. These 

 are undoubtedly very strong evidences of the result caused by the 

 absence of light, and they are strengthened by the finding of 

 blind fish at very great depths in the sea where no light ever finds 

 its way. Like most observations of this kind, there are several 

 exceptions, but they do not affect us at present, as we are dealing 

 more particularly with the general question, which is clear enough. 



In the caves just referred to, it is noted further that the pre- 

 vailing colour of the animals and insects is white — a condition 

 which, it seems fair to conclude, has been brought about by their 

 continual dwelling in such a dark abode. We know, however, 

 that the colours of animals are not dependent entirely upon light 

 for their production, as, in the case of a brightly painted butterfly, 

 it is complete in its beauty as soon as it leaves the chrysalis stage, 

 although the pupa may have been buried in the earth, and, there- 

 fore, been developed quite in the dark. But if this butterfly spent 

 all its days in the dark, and succeeding generations did the same, 

 we should no doubt find that its colours would disappear in the 

 course of time, till, if it could exist at all, nothing but a whitish 



