INSECTS OF REVERSED BEHAVIOR. 393 



when hunting, react negatively to the cooler situations of the 

 habitat, the warmer the place the better, until 100-105 is 

 reached when some species begin to become inactive. 



The second obvious adjustment necessary is in the time of 

 emergence. All lowland species of /Eshna, as far as known, 

 emerge at night, those the writer has reared, nmbrosa and con- 

 stricla, emerging at or near midnight. This appears to be an 

 adjustment of value in that the imagoes have hardened suffi- 

 ciently by daylight for flight and so escape the blackbirds and 

 other marsh fowl that enjoy soft freshly emerged insects. But 

 .it .in ele\ .ition of 7,000-9,000 feet with snow fields spread about, 

 the nightly temperatures are never far above freezing and fre- 

 quently below, making night emergence precarious as the young 

 dragonfly \M,uld be too chilled to crawl out of its nymphal skin. 

 Here .1 -e. .,nd adjustment to this elevated habitat appears. 

 Tin- emer^in^ nymph of ncvadensis instead of -being negathelv 

 in the dark is negatively geotropic in the light, so that 

 i he \\ in^ed adult emerges in the broad daylight when the tem- 

 perature i- hiij) enough to insure a successful withdrawal from 

 t IK- n\ inphal skin. The writer found numerous individuals 

 i IIH i <in^ in the bright sunshine in the early afternoon hour-. 



Tim- \\e see that sEshna ncvadensis has left the general \\arm 

 loul.md en\ ironment of the genus and has entered an entirely 

 dillerent re^inii through having two of the tropisms normal to 

 .1 -hn.i i. \ ri sed. 



While in the mountains of eastern Tennessee last spring, the 



\\riter di-i<. \ritd a mayfly, Ephemera guttulata Pictet, which ap- 



pears to < " t ii| >\ a hal)itat entirely different from that < if an\ i it her 



>p ' l.plu-mera. It too appears to have certain of it b 



lion- the n \t i>c of those of the other species of tin- -enus 



Epht mi ra : :tt!nl<ita is a most interesting maytl\- in >e\ eral \\ a\ s, 

 It is one of our large mayflies. Its wings are so heavily clouded 

 that at a little distance they appear almost black, especially as 

 contrasted against the abdomen, which is immaculate >no\v- white. 

 This bi/arre insect lives in the smaller of the perennial, spring-fed 

 mountain torrents that flow down the higher of the Eastern 

 Tennessee Mountains. On Chilhowee Mountain these streams 

 pour down deep Y-shaped ravines over beds of small stones and 

 coarse grit, in a succession of miniature water! alls, for they 



