Smithsonian miscellaneous collections . earliest known fossil mayflies,found in the Permian, already had gills, the mayfly larva has comedown to us with surprisingly few changes. The larval gills of the mayflies are organs of particular interest be-cause of their apparent likeness to the abdominal styli of modern species the gills are present on the sides of, at most, thefirst seven segments of the abdomen; larvae from the lower Permian,however, had nine pairs of gills, and some Jurassic species had gills are highly variable in form in different species, but they areborn
Smithsonian miscellaneous collections . earliest known fossil mayflies,found in the Permian, already had gills, the mayfly larva has comedown to us with surprisingly few changes. The larval gills of the mayflies are organs of particular interest be-cause of their apparent likeness to the abdominal styli of modern species the gills are present on the sides of, at most, thefirst seven segments of the abdomen; larvae from the lower Permian,however, had nine pairs of gills, and some Jurassic species had gills are highly variable in form in different species, but they areborne singly on lateral lobes of the abdominal segments (fig. 3 B,C)interpolated between the tergal and sternal regions. The gill-bearinglobes fall directly in line with the bases of the thoracic legs (Cx),and thus may be likened to the stylus-bearing plates of each gill is movable by muscles arising in the supportinglobe (C,D). The movements of the mayfly gills has been made the no. 9 INSECT METAMORPHOSIS—SNODGRASS 29. Fig. 3.—Characters of larvae of Ephemeroptera. A, Ephemerella sp. B, Ephoron sp., part of thorax and abdomen, showinggill-bearing lobes in line with coxae of legs. C, diagrammatic cross section ofabdomen. D, a single gill, showing muscles arising in supporting body lobe. E,base of gill, with tracheal trunk and muscles. F, Ephemerella sp., showing ad-hesive disc on venter of abdomen. G, Prosopistoma foliaceus Fourcroy, dorsal(from Vayssiere, 1890). H, same, ventral (from Vayssiere, 1890). ib-4b, bmcls, branchial muscles; Brn, branchia, gill; Cx, coxa of leg; Cx?,gill-bearing lobe of abdomen; en, respiratory entrance; ex, respiratory exit; /,lateral body muscle; S, sternum; T, tergum; Tra, trachea. 30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 122 subject of a special study by Eastham (1938, 1939). Just as thethysanuran styli do not appear until after the first moult, so the gillsof the mayfly larva are absent in the first instar. It is said by I
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