CH. IV 



AQUATIC CATERPILLARS 



227 



bitten through, and the two pieces, quite similar in 

 shape and size, fastened together with silk, formed a 

 movable sheath which protected the body of the larva, 

 as it crept about in search of food. 



The larva itself is about an inch long when full 

 grown. The body is thickish towards the middle, 

 but narrowed at the two ends. It appears smooth to 

 the eye. Its colour is nearly white, but with a tinge 

 of yellow ; the upper surface of the thorax is darker. 

 The head, which is small and half-retractile, is dark 

 brown or nearly black. Like most land caterpillars, 



FIG. 80. Larva of Hydrocampa nymphseata, side-view. 



it is provided with sixteen legs, the last pair being 

 very short. The spiracles or breathing pores have 

 the usual number and arrangement. Although the 

 larva is constantly submerged, it breathes air like 

 other caterpillars ; Reaumur found that when it was 

 oiled, so as to cut off the supply of air through 

 the spiracles, it died in less than a quarter of an 

 hour. If the larval case is opened under water, it is 

 found to be full of air, and the larva perfectly dry 

 within it. The larva is indeed incapable of being 

 wetted. A multitude of very fine and close-set 

 prominences cover its whole body, and between 



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