140 



LEAVES FROM MY NOTE-BOOK, 



proper upper surface is so buoyant that the raft has great power 

 of self-righting ; while the instant that it comes to the top, the 

 excess of water drains off, leaving the eggs perfectly dry on their 

 upper surface. 



The larvae of the minute gauzy-winged fly, Simulium, show a 

 wonderful adaptation to their environment. These tiny worm-like 

 creatures, not more than five-eighths of an inch in length, are 

 perfectly at home in rushing streams and "especially in the rapids 

 above waterfalls." Their food is altogether microscopic ; their 

 stomachs are found filled with the flinty valves of Desmids 

 and Diatoms, with here and there bits of a small crustacean. 

 Their mouth parts are provided with fan-Hke appendages, each 



Fig. 5. — Head of larva of Simulium^ dorsal view, showing eye-spots, 

 antennae, and fringed appendages. 



bearing about fifty long filaments (Fig. 5), which are feathered 

 along one side, and sweep the food into the gullet. Great pains 

 are taken to keep these delicate appendages — so necessary to the 

 Hfe of the larvae — from getting clogged, and, by the help of a 

 lens, the larvae can often be seen combing them out with their 

 mandibles. 



The life of a submerged insect in a rapid current has, of course, 

 its own special difficulties, met with, as usual, by special adapta- 

 tions. The Simulium larva has to creep from leaf to leaf to change 

 its position as the stream rises and falls, and to avoid enemies. 

 Of these enemies, Caddis worms are the commonest and most 



