ADAPTATIONS TO HIGH ALTITUDES 55 



Spring Tails. They have a curious spring bent for- 

 wards beneath the body from near the tail end, and 

 when this is released at a critical moment they jump 

 into the air. On a stretch of the mer de glace at 

 Chamonix a naturalist saw not long ago an army of 

 "glacier fleas" (Desoria nivalis) over twenty yards 

 broad by over a mile long. He estimated the number 

 at about forty millions. On another occasion in 

 Carinthia the surface of the snow was black for half 

 a mile with a marching army of Spring Tails. It is 

 not very clear what these mass movements of tiny 

 insects mean. There are places specially suitable for 

 laying the eggs, and when the young insects are 

 hatched they disperse in great bands in search of food. 

 There are also places where they lie low through the 

 winter, and from which they migrate in spring. In 

 other cases, perhaps, the march of the tiny insects may 

 be simply a trekking in search of food and more com- 

 fortable quarters. We wonder that they subsist at all, 

 for Spring Tails (Collembola) and some of their rela- 

 tives the Bristle-Tails (Thysanura) are found high up 

 the mountains in most inclement situations. Life is 

 truly insurgent and indomitable. Over thirty different 

 kinds of Spring Tails are known from the snow-level 

 of the Central Alps. They feed on decaying plant 

 remains, on Lichens encrusting the rocks, and on the 

 showers of pollen that the wind sometimes blows up 

 from the pine forests. What they most avoid is 

 drought. For a coldblooded animal among the snow, 

 black is physiologically the best colour, and most of 

 these little insects are very dark. Perhaps the hairs 

 on their body are also of some protection against the 

 cold. But there is another defence, which few of us 



