INHABITANTS OF THE DESERT. 71 



is derived from the circumstance that the young are hatched 

 in the mother's belly, and are born alive like the young of a 

 mammal. This statement, too, holds good with respect to the 

 viper, which also endures the cold of elevated regions. 



INFERIOR ANIMALS. 



Our information is still very incomplete so far as relates to 

 the molluscs, the arachnida, and the insects which inhabit the 

 frigid zone. The Alpine snail (Helix Atyicola), so remarkable 

 for its transparency, appears to be the sole mollusc which, in 

 certain localities, attains to an elevation of 7000 feet. It is, 

 however, surpassed by the earthworm, which is not only 

 distributed over the surface of every country, but ascends to 

 the snowy summits of the loftiest mountains. Few animals 

 have their geographical distribution so extended both hori- 

 zontally and vertically j and only some species of spiders and 

 millepeds keep company with the earthworm. 



Among the other inhabitants of the snows have also been 

 observed a dozen species of butterflies, nearly all diurnal, for 

 the phalsense (?), or nocturnal Lepidoptera, appear to be much 

 more sensible to the cold. M. Agassiz saw the " Little Vulcan " 

 ( Vanessa urticce) fluttering in the snowy desert which borders 

 on the glacier of Aar, as if it were completely in its element. 

 The wings of the majority of these butterflies are sombre- 

 coloured ; their caterpillars live upon the auriculas, and seem 

 to accomplish' their metamorphoses in regions uninhabitable 

 to us. The leaf-wasp (Tenthredo spinacula) appears to de- 

 posit its larvae, at a height of nearly 10,000 feet, in the galls 



