which is distributed in the Holarctic region; the larvae of this family retain 

 certain primitive characters (simple shape of the head and its primary 

 chaetotaxy). The most recent, highly progressive branch of the ancestors of 

 169 Arctopsychidae is the now flourishing family Hydropsychidae; this family 

 is distributed throughout the world; it is the largest family of Annulipalpia 

 (according to data to 1944 it contains 646 species) and the second largest 

 family of the Trichoptera;* the larvae are highly specialized and have a 

 rich secondary chaetotaxy, including minute covering setae extending to the 

 head (which is rare in Trichoptera). The larvae of Hydropsychidae live 

 only in flowing water;** however, the ecological range of the family is 

 unusually wide, including shallow, slowly flowing brooks, mountain streams 

 of various types, and large rivers in the plains, the bottom of which is 

 densely inhabited along thousands of kilometers with larvae of Hydro- 

 psychidae; the adults of these species of higher Neochaetoidea often "flood" 

 the area. 



The evolutional trend in the original stem II represents the development 

 of some groups, the larvae of which ceased to live in immovably attached 

 tunnel-shaped tubes and changed to a free and mobile life, building portable 

 cases or living without cases. The further evolution in this direction 

 (as in stem I) was determined by the method of feeding of the larvae and the 

 character of their building activity. The primary divergence of stem II 

 found expression in the development of the larvae of the ancient Trichoptera 

 along two different lines: line 3, which resulted in the recent fauna in 

 builders of shieldlike cases resembling the pupal cases of some inhabitants 

 of tunnel-shaped tubes, and line 4, which resulted in the builders of a 

 different type of portable cases. 



According to the method of feeding, the later evolution along line 3 took 

 two different trends: branch 3' developed into predators and branch 3" into 

 algophages. In the recent fauna, branch 3' developed into the Rhyacophilidae, 

 which is the only family of the whole complex which developed in the 

 direction of stem II; this family is closely related to the inhabitants of 

 immovable tubular shelters in the absence of a portable case, in their 

 general appearance and in their biological cycle; the larva ends its feeding 

 and growth period in the 5th stage; it begins to build its shelter from 

 mineral particles only then; the larva pupates in this shelter; the same is 

 done by the inhabitants of immovable structures; some of these, e. g., the 

 Stenopsychidae and some species of Hydropsychidae build pupal shelters 

 as skilfully and strongly as the Rhyacophilidae. The rudiment of the tunnel - 

 shaped tube of the other Paleochaetoidea is possibly represented in 

 Rhyacophila by a filament which is produced from the 1st stage onward, 

 and dragged behind the larva when it moves (this filament is attached to 

 different points on the body of the larva). A closed pupal cocoon built of 

 thick tissue is a characteristic phenomenon inside the case in the recent 

 fauna only in the Rhyacophilidae and the closely related Glossosomatidae, 

 i. e., the two families of the genetic line 3. 



For the first time in the history of the larvae, in the family Glossosoma- 

 tidae (branch 3"), building a case (resembling the pupal case but portable 

 and with a ventral wall) begins in the first larval stage and continues 



* After the Limnophilidae with 676 species (Schmid, 1955). 

 ** If isolated species are excluded which occur also in the open surf at the shore of large lakes. 



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