78 MODERN IDEAS OF EVOLUTION 



of touch. No one doubts that they are merely 

 varieties of species living outside the caves, and that, 

 if gradually accustomed to sunlight, they might 

 regain the powers they have lost. They are there 

 fore in no respect truly distinct species, and some of 

 them even pass by imperceptible gradations into the 

 ordinary types from which they arose ; yet for con 

 venience of reference distinct specific and even 

 generic names have been given them, and in this way 

 a long list of names of cave fishes, crustaceans, 

 insects, &c, can be made out. These curious 

 creatures cannot therefore be taken as evidence of 

 the origin of new species. (Jhey are no more distinct 

 species of cray-fish, insects, &c. than a blind man is 

 a distinct species of the genus Homo. They are 

 clearly merely varietal forms. They cannot be con 

 sidered to be products of natural selection, but of 

 disuse of certain organs and special demands on 

 others. They have, in short, varied, as Packard 

 explains to us, on the Lamarckian, not on the Dar 

 winian principle^ They show the effects of change 

 of conditions of life, and they show great powers of 

 adaptation to new circumstances, acting along with 

 isolation, and the tendency to transmit acquired 

 characters to offspring. Packard even shows reason 

 to believe that they are reproductive with individuals 

 of the ordinary forms of those species which may 

 stray or be carried by floods into these caverns. At 

 the same time many of their peculiarities, as, for 



