SOME AQUATIC INSECTS 97 



very transparent; they consist of a colourless 

 or slightly bluish gauzy membrane. The fly 

 immediately after emergence, and for some days 

 subsequently, has a greenish tint; then it 

 gradually turns dark. The six legs are long, 

 but the fly does not stand high above the 

 surface on which it rests. The antennae are 

 very long, longer than the body, gradually 

 tapering, and of many joints. The legs are com- 

 pound, like those of other Flies and Butterflies." 

 The graceful, pretty May- flies have gained 

 their scientific name of Ephemerce from the 

 extreme shortness of the life of the perfect 

 insect, for the majority perish a few hours after 

 reaching their full development. They are 

 delicate, soft-bodied insects, with long, slender 

 abdomens with two or three very long, jointed 

 filaments ; while the graceful wings, of which 

 the front pair are the largest, the back pair being 

 smaller or altogether absent, are often very 

 beautifully reticulated. In the perfect winged 

 stage, the mouth of the May-fly is quite rudi- 

 mentary in structure, so that the insect cannot 

 take in any food, and the short hours of this 

 climax of its existence is devoted to sexual inter- 

 course for the perpetuation of the species, and 

 to light, airy dances over the surface of the pool 

 in which the early stages of its life had been 

 spent. Enormous swarms of these insects 

 suddenly appear for two or three evenings in 

 succession, and then are ; seen no more until the 

 following year at the same season ; a phenomenon 

 due to the fact that these insects are always 

 produced in great numbers, and that the whole 



