156 r. 11. KRECKER Vol. XXII, No. 6 



of the water and usually at night. The grown nymph swims 

 up and floats. A rent appears in the skin of its back. The 

 subimago suddenly emerges from this rent, its wings expanding 

 almost full size instantly. It stands a moment on the surface 

 and then rises and flies away to the shore." Heptagenia was 

 seen emerging under laboratory conditions by Clemens. He 

 says, "they were observed to crawl up sticks placed in the 

 breeding jar for the purpose and transform just above the 

 water-level. " 



Some species are apparently able to adapt themselves to 

 varying conditions, as is shown by their ability either to crawl 

 up some solid support or else arise directly from the surface 

 of the water. This is the case in Chirotenetes albomanicatus as 

 described by Miss Morgan. She writes: "They crawl up 

 on the shore, leaving their cast skins clinging to the stones or 

 less often they flew up directly from the mid-current. " Need- 

 ham's ('05) statement regarding the same species: "Trans- 

 formation takes place at the surface of the water as in other 

 species," was made some years before Miss Morgan published 

 her observations. It is merely an example of the fact that our 

 knowledge of habits is subject to modification and it leaves 

 open the possibility that the case I have described may concern 

 some species for which other descriptions have been given, 

 perhaps a Hexagenia or a Heptagenia. 



Of the various accounts concerning emergence given in the 

 literature, a description by Miss Morgan for Iron fragilis 

 (Heptageninas) appears to resemble the instance reported to me 

 most closely, so far as the ability to fly immediately upon 

 emerging from the water is concerned. I do not mean to imply 

 any identity of species. Miss Morgan says, "The nymphs 

 popped from the surface of the water and flew unsteadily 

 upward. * * * " She was probably not in a situation 

 which enabled her to describe what occurred before this, but 

 presumably some preliminary processes took place beneath 

 the surface. Another account which bears some resemblance 

 to the one I have given is by W. E. Howard and concerns 

 Polymitarcys albus. "I have seen the subimagos emerge and 

 arise from the surface of the water in great numbers, but always 

 just far enough from shore so that the nymph skins were 

 immediately swept into the current. * * * " Somewhat 



