328 THE RIVER-SIDE NATURALIST. 



placed at the extremity of its last segment ; alimentary 

 canal capacious and filled with gas. The fore-wings are 

 usually trilateral, ample, and rounded off at the extremities ; 

 the margins unequal in extent, erect or spreading in repose, 

 plaited lengthways, but not folded up. The hind-wings 

 when developed are sometimes very minute never large, 

 generally oblong-ovate in form. The inner margin of the 

 fore-wing and anterior margin of the hind-wing hitch 

 together automatically to a larger or smaller extent when 

 the wings are spread open. The legs are slender, femora 

 strong, the fore coxae somewhat distant from the others. 

 The legs present great differences in their relative lengths 

 of the several pairs, either sexual or generical. The fore- 

 legs are always longest in the male, and generally longer 

 than the hinder pairs usually three pairs, with five tarsal 

 joints. 



The forceps of the male is two, three, or four-jointed, 

 and in some genera (according to Mr. Eaton) afford good 

 distinctive characters of species. 



As regards the caudal setae, Mr. Eaton says there is 

 much diversity in the number and relative proportions. 

 Often all of one length, but the middle one is often either 

 shorter or longer than the others ; often atrophied to a 

 mere rudiment, or altogether absent. The outer setae per- 

 sistent, and, according to sex or genus, exceed many times, 

 or fall short of, the length of the body. 



Mr. Eaton says : " The popular supposition that May- 

 flies are strictly ephemeral is fallacious in most instances. 

 Provided the air be not too dry, the imagines of many genera 

 can live without food several days. The diurnal Epheme- 

 ridce } of which our May-fly is one, in very hot weather rest 

 during the midday heat, generally flying in the cooler hours 

 of sunshine, or just after sunset. Many species fly by 

 night only, and most of them couple by night, male below, 

 gradually sinking nearer the ground ; then, when accom- 

 plished, the male rises again in the air to resume its search 

 for other females." 



The eggs in some of the short-lived species, when laid 

 by the female, are discharged from the ovaries in egg- 



