Ill AQUATIC HYMENOPTERA 223 



Uragon-fly. The larva before long casts its envelope 

 and appears as a segmented worm-like animal with 

 peculiar provisional organs and especially with a pair 

 of stout hooks at the head end. Rudiments of the 

 permanent appendages then begin to appear. When 

 all the contents of the Dragon-fly's egg have been 

 devoured, which happens in a few days from the time 

 of penetration, the Polynema pupates. The larval 

 appendages dwindle or are cast off by moulting. The 

 last segment enlarges greatly and is converted into 

 the abdomen of the imago. The fly emerges after a 

 pupal stage of ten or twelve days. 



We have scanty information respecting a number 

 of aquatic Insects, which, like the terrestrial Ichneu- 

 mons, lay their eggs in the bodies of living Insects. 

 The larvae hatch out and devour the bodies of their 

 hosts little by little, delaying fatal injury until the 

 parasite is full grown. One such form, Agriotypus 

 preys upon Caddis-worms. The female was long 

 ago observed to enter the water, and later on Siebold 

 reared it from cases of Caddis-worms. The history 

 of the parasite has recently been more fully explored 

 by Klapalek,^ so well known by his researches into 

 the life-history of the Trichoptera. Klapalek finds 

 that in Bohemia Agriotypus commonly attacks the 

 cases of a Caddis-worm known by the name of Silo 

 pallipes. On warm days in April the Agriotypi may 

 be seen swarming like Ants about the banks of the 

 brooks, and also flying above the water. The 

 females descend stems and grasses into the water, 

 and creep under stones on the bed of the stream 

 ' /t;i/. M(mth. Mag. 1889, p. 339. 



