Note 1 — INTRODUCTION.

The Ephemeræ in the larva and pupa state reside in the water concealed during the day under stones or in horizontal burrows which they form in the banks. Although resembling the perfect insect in several respects, they differ materially in having longer antennæ, in wanting ocelli, and in possessing horn-like mandibles; the abdomen has, moreover, on each side a row of plates, mostly in pairs, which are a kind of false branchiæ, and which are employed not only in respiration, but also as paddles.—Cuvier’s Animal Kingdom, p. 576. London, 1840.