8 EEV. A. E. EATON ON EECENT EPIIEMEEID^ OE MAYFLIES. 



the tarsus, or of the tibia, or of both of them ; but in the other legs it is generally brought 

 about by extension of the tibia and femur. The fore tarsus is often as long as the tibia ; 

 indeed in the male it frequently is much longer than it : the hinder tarsi are usually 

 shorter, and only in a very few forms are they longer than it (e. cj. in Batisca, where the 

 proximal joint of the tarsus by itself is as long as the tibia). The maximum number of 

 tarsal joints is 5 ; the apical projection of the tibia which, in some genera, forms a basis 

 for the insertion of the fore tarsus of the male, resembles at first sight a sixth joint, but 

 it conforms in colour to the tibia and not to the tarsus. All of the tarsi may alike have 

 five joints, or the fore tarsus may be five-jointed, while the others have only four distinct 

 joints, and a very ill-defined trace of the fifth ; or all of them may have only four joints : 

 in atrophied legs, however, the tarsi of the hinder legs may be two-jointed, or even 

 jointless. The ungues of the fore tarsus are sometimes both alike in form and size ; bu.t 

 this is often not the case : the same may be said of the ungues of the hinder tarsi, which 

 further may resemble or differ from the ungues of the fore tarsus in form. 



The forceps of the male (specialized legs of the ninth abdominal segment) are seldom 

 jointless (Ccenis, Campsurus, &c.), but are usually two-, three-, or four-jointed, with the 

 basal joint or the next the longest. In some genera they afford good distinctive cha- 

 racters of species. 



Much diversity is exhibited in the number and relative proportions of the caudal setse. 

 They are often all of one length ; but the median seta is occasionally a little longer or a 

 little shorter than the others, sometimes considerably shorter, frequently atrophied to a 

 mere rudiment, and in many instances altogether cast off. The outer setae are always 

 persistent (in the absence of accident), and either many times exceed, or else equal or 

 fall short of, the body in length, according to sex or genus. The setse are commonly 

 glabrous, or almost so, seldom pilose or plumose : their component joints, transverse in 

 the basal portion, assume a more elongated form in the distal portion of the seta, where 

 in some cases they attain rather attenuated dimensions. 



Habits of the Plies. 



The popular supposition, that Mayflies are strictly ephemeral, is fallacious in most 

 instances. It is true that the adult insect cannot eat, owing to atrophy of its mouth-organs 

 and to the condition of its alimentary canal ; but, provided that the air be not too dry, 

 the imagines of many genera can live without food several days. Tradition states that 

 Curtis kept a female Cloeon alive three weeks ; this is an exceptionally long period, for in 

 general an individual in confinement becomes perceptibly shrunken within three days, 

 and is dead by the fourth day, if not before. Apparently there is some correspondence 

 between the length of time spent in the subimago stage and the duration of the life of 

 the imago : when the former amounts to twelve or twenty-four hours and upwards, the 

 latter lasts more than a day ; but when the change into imago takes place within a few 

 minutes of the insect's quitting the nymph skin, its life is fugitive, passing away in the 

 course of the evening or early morning. In some genera of sliort-lived Ephemerida3 the 

 subimago skin is partially or altogether persistent in one or other of the sexes ; and such 



