CHAP. XXI 



INSECT A : NEUROPTERA 



321 



second and third abdominal segments lie close under the top 

 of the case, the dorsal median tubercle being much shorter, and 

 at this point muscular contractions occur at intervals, which 

 cause an undulatory movement to pass down the body, driving 

 the water out of the open hind end of the case, and thus causing 

 more to enter in front. These movements can be made 



Fig. 242. — The Cases of different genera of Caddis- worms. 



P, Pht^gaTiea ; ^it, Ajuibolia ; S, Stenophylax ; M, Molamrn ; L and L', LivmopMlus ; 



L./. LvmnophUusJlavUiomis', L.r, LvmnopMlus rhcimbicus ; r, TriaenodesA 



apparent by repeating the experiment devised by Professor 

 Miall, in which a caddis -worm was induced to make a 

 transparent case of small, regularly cut pieces of mica, an 

 experiment very easy to repeat if the right kind of caddis- 

 worm can be made to use the mica, namely, such a one as 

 Phryganea grandis (Fig. 242, P), that makes a regular and 

 smooth case. 



Caddis-worm cases vary greatly according to the 



Caddis- species which makes them (see Fig. 242), but all are 



alike in being open at both ends, though the open- 



VOL. I Y 



