78 



THE INFLUENCE OF INANIMATE SURROUNDINGS. 





to the law of degeneration, in consequence of their disuse. This 

 explanation, it is obvious, presupposes that such blind animals 

 are descended from a parent form that could 

 see ; and it cannot be denied that many of the 

 facts hitherto ascertained seem to justify this 

 view. Some of the so-called blind animals are 

 not, accurately speaking, sightless ; thus the 

 blind Proteus (fig. 20, «), an Amphibian of 

 the caves of Carniola, has an eye deeply 

 seated in the head and entirely covered by the 

 '»t« skin. The structui'e of this organ is very re- 



markable ; it possesses all the characteristic 

 parts of the eye, but they have been arrested at 

 an almost embryonic stage, with the exception 

 of the cr3'stanine lens, of which every trace is 

 absent (fig. 20, b) ; the pigment-layer of the 

 retina is scarcely coherent, and consists of only 



h 



V , 



-5^. 



Fiu. 20.— a, Protens of the .Adelsberg grotto, reduced ; b, vertical 

 section of tlie rudimentary eye ; vpi, the optic nerve ; cc, corpus 

 ciliare retiiiEB, the inner portions of which meet in front becuuse 

 the lens is absent ; cv, the internal cavity of the eye -without 

 any vitreous hnmour. The ciOJ-Jayers of the retina {ret) are 

 unusually thick ; the pigment-layer, p^ very slightly developed. 



a few scattered pigment-cells. We may tlierefore be very doubt- 

 ful as to wbetber this Proteus can receive a clear im.age of the 

 objects that surround it even in a place where there is light ; 



