198 



Aquatic Organisms 



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Fig. 104. Caddis-worms: larvae of Halesus guttifer. 



creature, half soft and pale 

 where constant ly protected by 

 the walls of the case in which 

 it lives, and half dark colored 

 and strongly chitinized where 

 exposed at the ends. There 

 are stout claws at the rear 

 for clutching the wall of the 

 case; there are soft pale fila- 

 mentous gills arranged along 

 the side of the abdomen, and 

 there are three spacing tuber- 

 cles upon the first segment 

 of the abdomen for insuring 

 that a fresh supply of water 

 shall be admitted to the case 

 to flow over the gills. The 

 legs are directed forward, for 



Fig. 105. The larval case of 

 Limnophilus, attached end- 

 wise to a submerged flag leaf, 

 in position of transformation. 



