SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 125, NO. 1, PL. 1£ 



*. *.-v ^ "^F^-^i 



I. Mature stream. Note how the region adjacent to the stream lias been brought to 

 tlie slope of the stream bed ; also, the formation of sand bars. Such streams serve as the 

 principal breeding places of zoophilic species of black flies, although some of the 

 anthropophilic species will also breed therein. 



2. Old stream, flowing thrdugh terrain with a gentle, rolling topography and with 

 a minimum slope. Such streams have wide beaches, practical!}' no emergent vegetation, 

 and the tree and shrub line is removed from the water's edge. They support the breed- 

 ing of zoophilic species only. 



