THE INFLUENCE OF LIGHT ON LIFE. 243 



they will be colourless. Whether that is really the fact or not, I 

 can't quite say, as I have been unable to find any other experiment 

 confirming it. In a somewhat old edition of the Encyclopcedta 

 Britafinica an experiment by a Dr. Edwards is quoted. Dr. 

 Edwards said that if the spawn of frogs be kept in total darkness, 

 the eggs will not hatch, and further that if tadpoles be kept in the 

 dark they will not develop into the mature frog. They will 

 increase in weight, but their tadpole state will be preserved. This 

 experiment seems almost too simple to allow of any mistake being 

 made, but that we cannot pin our faith to it implicitly is manifest 

 when we find Prof Semper quoting an almost similar experiment, 

 in which the larvae of frogs were reared in completely dark cellars 

 without discovering any difference in their development beyond a 

 retardation due to the diminished warmth. If it were only the 

 proper season of the year, we could easily prove which of these 

 two scientific gentlemen is correct ; but, in the meantime, we 

 must just set the two experiments like an equal negative and posi- 

 tive quantity against each other. In support of the non-develop- 

 ment of frog-spawn in the dark, it is only fair to say that Dr. 

 Carpenter states that the eggs of silkworms are not hatched nearly 

 so well in the dark as in the light. 



If, however, these experiments are somewhat inconclusive, we 

 can get more certain information by examining the creatures which 

 are found inhabiting mines or caves. In some of these caves — 

 as, for instance, the famous caves of Kentucky — the darkness is 

 complete, a single ray of light never entering their silent depths. 

 Travellers who have visited such places tell us strange stories of 

 the sights which are there to be seen. At present we do not 

 concern ourselves with the caves themselves. But let us suppose 

 that we have quitted the daylight and dived into the dark passage 

 which leads to the innermost recesses of some great cave. After 

 passing, in our journey, many mysterious passages which strike 

 away into unknown darkness, and crossing great chasms yawning 

 into unfathomable depths, we are at last led by our guide into a 

 central hall, and there, by the aid of our torches, is seen a silent 

 lake occupying the centre. In the dark waters of that lake the 

 traveller may see a number of strange-looking fish gliding swiftly 

 about. We are told that the skin of these fish is of a whitish 



