4 EEV. A. E, EATON ON EECENT EPHEMEEID.E OR MAYFLIES. 



adjacent deposits blotches and fasciae are apt to be produced. The wing-membrane is 

 decvirrent along the sides of the peak of the mesonotum ; in OUgonetiria and some allied 

 forms it is there prolonged into short free subnlate tails, figured by Dr. Hagen in 1855. 

 In most of the Ephemeridse, during the subimaginal stage, the wings are fringed with 

 short cilise along the terminal margin. This fringe (excepting in Ccenis, Frosopistoma, 

 and Trycorytlms) is not retained by the adult fly. 



JVing-neuration in the Ephemeridse is less complicated than it appears to be ; and 

 Avhere difficulty is experienced in ascertaining the homologies of nervures, it is more 

 likely to be occasioned by the suppression of some of them than from there being more 

 in the wing than can be reasonably accounted for. Unstable in minutiee, so closely is 

 the essential plan of the neuration adhered to by nearly related Mayflies, that the 

 general facies of the wings is an important aid to their classification, aff'ording charac- 

 teristics as easily recognizable as the style of branching in the case of trees. Its simplest 

 modifications are displayed in Oligoneurians (PI. III.), its most complex in PI. VI. 



Throughout the whole series of figures illustrative of neuration, the special and serial 

 homologies of the main nervures of the fore wing and hind wing are indicated by 

 numerals (the same number being employed to denote the same nervure in every figure), 

 and these are placed at the distal extremities of the following nervures, excepting the 

 costa and the sutural nervures, whose numbers are not usually appended to tliem : — 

 1, the Costa, coincident with the anterior margin of the wing ; 2, the Subcosta ; 3, the 

 Eadius ; 4, the Sector ; 5, the Cubitus ; 6, the Prtebrachial ; 7, the Pobrachial ; 8, the 

 Anal ; 9\ 9- &c. Axillary nervures ; 10, the Sutural vein coincident with the inner 

 margin. Between these nervures others of an adventitious nature that issue from the 

 wing-margin in certain regions are often interpolated ; in many genera they do not 

 remain free, but annex themselves to the adjacent main nervures, often acquiring the 

 appearance and discharging the functions of branches of these. When necessary or 

 advisable for purposes of elucidation, the numeral of the nervure, dashed, is repeated at 

 the extremity of the hindermost adventitious branch. 



At a meeting of the Entomological Society of London, in February 1879, I remarked 

 upon the tendency of the main nervures of the anterior wing in most of the Ephemeridse 

 to be segregated into three groups, of which the first communicates directly with the 

 thorax, the intermediate is either annexed to the first group, or terminates in the wino"- 

 membrane adjacent to it, close to the base of the wing, while the third is associated with 

 the prominent curved or augulated crease in the membrane which forms the boundary 

 of a depression posterior to the great cross vein and close to the wing-roots. I men- 

 tioned, further, that the anterior nervures of the hinder groups had a proneness to 

 secede from their own set, and transfer themselves to the hindermost nervure of the 

 grotip next in advance of them, so that in other orders of insects they are usually 

 reckoned as branches of the nervures to which they have strayed. An extreme instance 

 of such a transference is shown in the remarkable aberration floured in PI. VII. 11 c 

 where the sector (4), accompanied by most of the neighbouring adventitious nervures, 

 has usurped the trunk of the radius (3), so that this last nervure is not in direct con- 

 tinuation with its own basis, but simulates a branch. 



