326 MOSTLY MAMMALS 



The animal of the highest zoological position occurring 

 among the true cave-fauna is the aforesaid olm, which is 

 the sole representative of the genus Proteus, and is allied 

 to the ordinary salamanders and newts. The olm is a 

 somewhat eel-like creature, measuring about eleven inches 

 in length, and with a uniformly flesh-coloured skin, save 

 that the branching external gills are brilliant scarlet. The 

 limbs are very short and weak, the front pair being provided 

 with three and the hinder with two toes, and the eyes are 

 completely hidden. Now it is a most remarkable fact that 

 the only other salamander referred to the same family 

 (Proteidae) as the olm is a peculiar North American species 

 with well-developed eyes, four toes to each foot, and a dark 

 brown skin, which constitutes the genus Necturus. From 

 this it may be inferred that the ancestral type of the two 

 genera formerly inhabited the northern hemisphere, and 

 that while its transatlantic descendant has preserved the 

 primitive number of toes and adhered to an ordinary mode 

 of life, the European species has become more specialised 

 in regard to its limbs, and has taken to a completely 

 subterranean existence. According to Sir Humphry Davy 

 the olm only makes its appearance in the Adelsberg grotto 

 when the waters rise to an unusual height, remaining at 

 other periods in the streams flowing beneath its floor. 



The only other vertebrate animals belonging to the true 

 cave-fauna are fish of several species. By far the most 

 celebrated among these is the well-known blind-fish 

 (Amblyopsis spelaea), which has been taken in both the 

 Mammoth and the Wyandotte Caves, as well as in the 

 intervening subterranean waters. This fish is the typical 

 representative of a small family allied to the cyprinodonts, 

 which are themselves relatives of the carps. It is quite 

 destitute of external eyes, and its body is completely 



