INTRODUCTION. 
could possibly detect the slightest relationship of appearance or 
structure between the caddis-worm and the adult caddis-fly. 
Though caddis pupz are not active, like the corresponding stages 
in some insects, they are not entirely quiescent. There is always 
a rhythmic undulation of the abdomen, sending a constant stream 
of water through their cases, and during the latter part of their 
lives they are capable of walking. 
Trichoptera are the only insects, possibly excepting a very few 
Diptera (of the genera Simulium and Chironomus), with aquatic 
pupz. In several other orders one finds a few species with sub- 
merged pupe, but they all tap the stems of aquatic plants, entrap 
air in dome-like covers, or in some other way breathe free air. 
The pupz or Trichoptera are as much aquatic as are their larve. 
The eggs of caddis-flies are round or slightly oval in form. 
The eggs of all, except, perhaps, a few of the Rhyacophilide, are 
laid in masses of gelatin. ‘The masses, when extruded from the 
bodies of the females, are comparatively small, but rapidly absorb 
water until they are many times their original size. In form the 
gelatin mass, and the arrangement of eggs within the mass, is often 
quite characteristic of the species. In laying the eggs, the females 
of some species descend beneath the surface of the water and glue 
the mass fast to some support. Other species dip their abdomens 
into the water while in flight, apparently washing the extruded 
mass from the ovipositor, and still other species fasten the eggs to 
stick or stones above the water, the young falling to the water 
after hatching. 
Very little is known of the eggs and egg-laying habits of most 
American species. 
Trichoptera occur in all parts of the earth where any insects 
life can exist, but their greatest abundance is reached in the north- 
ern temperate zone, and their numbers of species seem to decrease 
as one nears the equator. 
They inhabit all kinds of fresh-water situations, from the most 
rapid torrents to stagnant swamps and pools. Some species seem 
to show a decided preference for temporary pools that are filled 
with water when the autumn rains come, and dry completely with 
the drought of summer. How these species of Trichoptera, to- 
gether with some members of several other orders of insects, pass 
over the period of drought is not altogether certain, but evidence 
seems to show that they burrow beneath the ground. All known 
5 
