152 NATURAL HISTORY OF ARTHROPODS. 



veined, and the hinder pair are much smaller than the fore ; and in certain forms, as 

 the species of Cloeon and Ccenis, the hinder pair are entirely wanting. Returning to 

 the structure of the head : while the eyes are very large in the males, meeting, as in 

 the dragon-flies, on top of the head, the antennae are also minute, slender, and awl- 

 shaped. The singular condition of development of the mouth-parts indicates that 

 these insects take no food during their ephemeral existence out of the water. The 

 mouth-parts are in an unusually rudimentary condition. We have been unable, in 

 a common Ephemera, to find any traces of mandibles, while the maxillae are very rudi- 

 mentary, the palpi being entirely wanting. 



The Ephemera, weak as it is individually, maintains itself in the world by means 

 of its prolificacy. Brooks and ponds are richly populated with their young, and through 

 the summer, when they come to maturity and take their flight, these delicate beings 

 appear in immense numbers. They rise from the waters of our great inland lakes, 

 fall a rapid prey to the waves, and are washed ashore, in enormous quantities, their 

 dead bodies forming windrows, comparable in extent with the sea-wrack of oceanic 

 shores. They settle down in dusky dun-colored clouds in the streets of the lake cities, 

 obscuring the street-lamps, and astonishing the passer-by. We may feel some aston- 

 ishment at the hosts of these winged Ephemeras when we bear in mind their useful- 

 ness in the larva state as food for other insects, Crustacea, and fish. Westwood states 

 that the swarms of one species, with white wings, has been compared to a fall of snow, 

 " whilst in some parts of Europe, where they abound, it is the custom to collect their 

 dead bodies into heaps, and use them for manure. The fishes, at such time, eagerly 

 wait for them ; and so great are the numbei'S which fall into the water, that the fisher- 

 men call them manna." They are well known to the angler as excellent bait for trout, 

 and they are a favorite food of the smaller dragon-flies. 



The may-flies pair while flying over the surface of the water, and the female drops 

 in the water her minute eggs, which are deposited in two long, cylindrical, yellow 

 masses. The species of Baetis creep down into the water and deposit their eggs in 

 rounded patches on the underside of stones. ' The larvae may be known by their long, 

 flat, slender bodies, provided with gills, arranged in pairs along the 

 sides, or upon the back, of the body. These so-called gills are some- 

 times leaf-like, either simple or with the edges often fringed with fila- 

 ments, or they are long, narrow pads or lobes, also fringed. In some 

 remarkable cases, as in the singular genus Jtcetisca, the gills are 

 covered by broad plate-like expansions of the thorax. In its larval 

 and pupal condition the entire thorax above forms one piece, like 

 the carapace of a shrimp, instead of being divided into three seg- 

 ments. This shield-like plate extends over one half of the abdomen, 

 in the form of a large shield, giving the insect, as Walsh says, "a 

 very crustacean appearance." While in most Ephemera larvae the 

 FlG> 2 Jo><Isra Upa f am ple gills are used in swimming, as well as for breathing, in JBcetisca 

 they are covered over by the shield, and are of no use in locomotion. 

 A similar larva is that of Prosopistoma, which has long been known, but whose life- 

 history has only recently been discovered. Here, as in Jlcetisca, the entire thorax and 

 the basal half of the abdomen is covered with a large shield, which conceals the broad 

 gill-sheets. 



The Ephemeras, both in their larval and pupal states, are sometimes cai'nivorous, 

 preying upon other insects, and their jaws are well developed, sometimes remarkably 



