PROBLEM OF CAVE BLINDNESS 247 



some frailty of constitution or by having fallen 

 behind the times. Some are relices of a Glacial 

 fauna. Their closest analogues are to be found 

 among the shy " cryptozoic " creatures who hide 

 under stones and bark and seldom venture forth. 

 The true cave-dwellers are more or less adapted to 

 the permanent conditions darkness, constant tem- 

 perature, humid atmosphere, and absence of green 

 plants. They include (apart from bats and mice) 

 the weird Amphibian Proteus of the great caves of 

 Carniola and Dalmatia, three or four North Amer- 

 ican salamanders, quite a lot of small fishes, a few 

 snails, numerous beetles and a sprinkling of other 

 kinds of insects, many spiders (who insinuate them- 

 selves everywhere), and a few Crustaceans, besides 

 some still smaller deer. After making sundry reser- 

 vations, we recognize that those cavernicolous ani- 

 mals that have open-air relatives with which they 

 may be compared tend to be dwarfish, to be mo- 

 notonous or deficiem> in coloration, to have ex- 

 quisitely developed tactility, and to have more or 

 less rudimentary eyes. It is on this tendency to- 

 wards blindness that we wish to focus attention. 



There are considerable differences in the degree of 

 degeneration which the eyes of cave animals exhibit, 

 but there are few that have remained unaffected. In 

 the pale Proteus, which has no pigment in its skin, 

 the eye is without a lens and does not reach the 

 surface of the head. This reminds us of the buried 

 eye of the deep-water hagfish and of the way in 

 ;yvhich the very lids of the eyes of the Cape Golden 



