EVOLUTION 927 



a primordium, not a vestige. This may be true, for instance, in regard 

 to the electric organ found by Cossar Ewart at the root of the skate's 

 tail. It may be the dwindled relic of a well-developed electric organ 

 such as is possessed by the not distantly related Torpedo of the 

 Mediterranean. But it is much more likely to be a transformation 

 of muscular and nervous tissue that has not yet come to its own. 



PROBLEM OF ORIGIN. — ^When we ask how a structure may 

 become vestigial, the historically oldest answer is that it follows 

 from disuse or from long-continued defective nurture. Thus it is 

 said that a Cetacean has lost its hind-legs as the direct result of not 

 using them, the tail serving as a very efficient propeller. The mole 

 has a much-reduced and very imperfect eye, as the direct result, it 

 is said, of taking to a subterranean life. In the individual lifetime a 

 disused organ sometimes dwindles, as we know in the reduction of 

 the size of the fibres in a muscle which is not exercised. Functional 

 activity is needed if an organ is to keep up its normal size and 

 efficiency. The theory is that reductions directly due to disuse and 

 deficient nurture are hereditarily entailed, and gradually bring 

 about a racial dwindling of the particular organ concerned. This 

 view will be discussed in connection with the general problem of the 

 Transmissibility of Acquired Modifications. 



The second theory is that quantitative germinal variations, plus 

 and minus, are very frequent, and that a reduction in the size of 

 a part may be a positive advantage in certain conditions of life. If 

 the animal has become sedentary a reduction of those muscles that 

 are no longer important will economise space, energy, and forma- 

 tive materials. Thus variants in the direction of the reduction of 

 the useless will be more successful and will lead the race towards 

 simplification. The degree of eye-development is a variable quality 

 in many animals ; if there was a trend of germinal variation towards 

 eye-reduction or eye-weakness, and a dark environment became 

 available, it is quite possible that there would be survival value in 

 dwindling eyes. For not only would the relatively blinder forms be 

 less likely to find their way out again to an illumined environment 

 for which they were ill-suited, but the possession of a relatively 

 simplified and reduced eye would lessen the risks of injury. It may 

 be that germinal variations in the direction of reduction proved 

 themselves profitable in the struggle for existence; and it is quite 

 gratuitous to handicap this theory by refusing to recognise that a 

 well-endowed active organism is in the way of testing its own 

 qualities by unending tentative and experiment. 



But, thirdly, the case of Proteus plainly indicates that for both 

 the theories, which we may call "Lamarckian" and "Darwinian" 

 for short, it is useful to take account of the nurture of the individual. 

 For the experiments with Proteus show that its pale, wan colour is 



