The Life of the Fly 



the gills, a soft fleece of hairs distributed over 

 the back and belly. 



The piston-stroke affects only the work of 

 breathing; it does not alter the density, makes 

 hardly any change in that which is heavier 

 than water. To lighten the weight, the Cad- 

 dis-worm must first rise to the surface. With 

 this object, it scales the grasses of one support 

 after the other; it clambers up, sticking to its 

 purpose in spite of the drawback of its faggot 

 dragging through the tangle. When it has 

 reached the goal, it lifts the rear-end a little 

 above the water and gives a stroke of the pis- 

 ton. The vacuum thus obtained fills with air. 

 That is enough: skiff and boatman are in a 

 position to float. The now useless support of 

 the grasses is abandoned. The time has come 

 for evolutions on the surface, in the glad sun- 

 light. 



The Caddis-worm possesses no great talent 



as a navigator. To turn round, to tack about, to 



shift its place slightly by a backward movement 



is all that it can do; and even that it does very 



clumsily. The front part of the body, sticking 



out of the case, acts as a rudder. Three or 



four times over, it rises abruptly, bends, comes 



down again and strikes the water. These 



paddle-strokes, repeated at intervals, carry the 



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