180 



EVOLUTION AND ANIMAL LIFE 



with growth atrophy sets in affecting different species differ- 

 ently, in some cases the muscles, in others the lenses, but in all 

 cases reducing the size of the organ to a functionless structure 

 more or less covered by the skin. In all cases, the ancestry of 

 these blind species can be traced to forms with well-developed 

 eyes inhabiting the same region. Among the species examined 

 are the blind fish of Mammoth Cave {Ainhlyopsis spelmis), the 

 cave bhnd fish of Kentucky and Indiana (Typlichthys siibterra- 



neus) , descended from 

 the Dismal Swamp fish 

 {Chologaster cornutus) , 

 the Missouri blind fish 

 (Troglichthys rosce), the 

 blind fishes of the caves 

 of Cuba (Lucifuga suh- 

 terranea, and Stygicola 

 dentata) and the blind 

 goby of Point Loma 

 ( Typhlogohius calif orni- 

 eiisis) . 



In Dr. Eigenmann's 

 opinion, the retention 

 of eyes in these species 

 is due to the influence 

 of heredity, the vesti- 

 gial structures being 

 each and all necessary 

 to life in the light. Their degeneration he ascribes to the 

 inheritance of the individual effects of disease, a matter we 

 discuss in another chapter. 



Hundreds of cases of vestigial organs in plants have been 

 recorded, among which we may mention the barren stamen in 

 Pentstemon which completes the number of five usual in the 

 group of Scrophulariacese to which Pentstemon belongs. Other 

 illustrations are the rudimentary leaves, with rudimentary 

 stomata, found on the joints of species of cactus (Opuntia), etc.; 

 the cilia found on the spermatozoa of cycads, which would en- 

 able these structures to move freely in the water, although they 

 are not deposited in the water, and these cilia are never actually 

 used. 



By the theory of special creation it was supposed that these 



Fig. 114. — Fishes showing stages in loss of eyes 

 and color: A, Dismal Swamp fish, Chologaster 

 cornutus, ancestor of the blind fish; B, Agassiz's 

 cave fish, Chologaster agassizi; C, cave blind fish, 

 Typhlichthys subterraneus. 



