280 A NATURALIST IN THE GREAT LAKES REGION 



Consider next the dragon-fly nymphs. I quote from Need- 

 ham's " Dragon-Flies of Illinois," Bulletin of the Illinois State 

 Laboratory of Natural History, Volume VI, Article I. This 

 indicates not only that the distribution depends on the size of 

 the stream but also that forms vary according to the rapidity 

 of the current and the character of the bottom. 



In the larger rivers, down to the size of the Mackinaw, in places where 

 the water flows with considerable current over a rocky bottom, Diastatomma 

 may be looked for; where mud or sand bottom and quieter waters prevail, 

 Epicordulia and some species of Gomphns may be found. Other species 

 of Gomphus occur in the bare muddy or sandy bottoms of the sloughs and 

 bottom-land lakes. In tree shaded waters, where driftwood and branches 

 have gathered, or along muddy margins, especially among exposed roots, 

 the lower Aeschnidae may be looked for. In bottom-land lakes where 

 vegetation is abundant, one may find Anax, Agrionidae, Mesothemis, Celethe- 

 mis, Tramea and Pantala amongst the vegetation, the latter two especially 

 on more exposed shores; and Tetragoneuria, Libellula, Epicordulia and 

 Leucorhinia on the bottom underneath. If the situation is inclined to 

 be marshy, Pachydiplax, Perithetnis and Celithemis will be scattered over 

 the bottom; and the shallowest and most temporary waters or wet lands are 

 the especial home of Sympetrum. 



In the smaller and quicker flowing streams, like the upper Mackinaw 

 and Sangamon, quite a different series occurs: Hagenius clinging to stones 

 and driftwood and amongst dead leaves; Boyeria and other dark Aeschnidae 

 on submerged branches, roots and sticks; Cordulegaster and the long-legged 

 Macromia hidden at the bottom in sheltered eddies; Somatochlora; and 

 finally Progomphus, Dromogomphus and certain species of Gomphus bur- 

 rowing in the sandy bottom. In the prairie ponds and slow streams and 

 ditches, Anax, Agrionidae, and Mesothemis and other Libellulidae occur 

 amongst vegetation, and Sympetrium in shallower parts, while Libellula 

 and Plathemis will be found where there is more mud and less vegetation, 

 as in ditches and tile ponds, resting at the lower ends of well defined tracks. 

 In streams of rapid flow but not especially rocky or shaded, the Calop- 

 terygidae are most likely to be found, the imagoes fluttering along the 

 banks. 



Of the above-mentioned the Agrionidae and the Calopterygidae 

 are families of the damsel flies whose nymphs bear three leaflike 

 tracheal gills at the posterior end of the abdomen. The basal 



