206 THE ANIMALS OF LAKES AND RIVERS 
are at all favourable. During the warm season the 
larvae of two flies, a Tipula and a Chironomus, also 
occur in the shore waters, and a water-boatman (Corixa) 
is also found in the lake. Otherwise it is singularly 
barren of animal life. 
Cave Faunas. As caves usually contain a consider- 
able amount of water, something may be said here of 
the more characteristic animals found in them. Cave 
animals live in conditions which in many respects 
resemble those prevailing in the ocean abysses. Thus 
there is often complete darkness, and the temperature, 
though it may be low, is remarkably uniform. Green 
plants, also, are necessarily absent. Some of the charac- 
ters of abyssal forms therefore reappear here ; for 
example, the eyes tend to disappear or become minute. 
But as the light conditions are quite different from 
those which obtain in the ocean depths, where as we 
have seen (p. 172) certain rays penetrate deeply, we 
find that cave animals tend to be white, instead of 
showing the deep-red or black coloration found in 
many animals which live in the ocean near the light 
limit. 
An interesting example of a cave animal is Proteus 
anguinus, found in the caves of Carniola, Dalmatia, 
and Carinthia. This animal is one of the permanently- 
gilled amphibians already described, and reaches a 
length of about a foot. The skin is without pigment, 
and the eyes are below the skin. The animal remains 
permanently within the water, though it rises to the 
surface to breathe if the water is not quite pure. 
Curiously enough, if the white body is exposed to light 
pigment develops in the skin, and perfectly black 
specimens can be produced by gradual exposure. In 
the caves of Texas there is an allied form (7'yphlomolge 
