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Show 62 INSECTA. t'rel membranous or very soft The other Subulicornes have an en 1 y • . • Th . t . ts that are rather mdtstmct. elr arsL mouth, composed of pa: . r • 'ngs at·e much smaller than the . f fi · · t . thetr m1er10r Wl const~t o ve ]OlD s, . d their abdomen is terminated by two superiOr, or even wantmg, an or three setre. They form the genus EPHEMERA, Lin. So called from their short term o f r~ · tl eir perfect state. Their 1 c, m 1 • • 1 b • 1 ft lonrr tapering, and termmatecl postenor y y body IS extreme Y SO ' o' ll two or three long and articulated setre. The antennce are very sm~ and com osed of three joints, the last of which is very l.ong, and m the Ir Ot'm po f a com. ca1 thre.a d . The anterior part of thetr dh ead pro.- . ects in the manner of a clypeus, frequently carinated an ema:gt· ~ated covers the mouth, the organs of which are so soft and e:x.Igu-us t~at they cannot be distinguished. The wings of those !~sects ~re always placed perpendicularly, or slightly inclined posterl~rl.y, like those of an Agrion. The legs are very sle?der, .and the tlblre l Ort and almost confounded with the tarsi, whtch frequently very s 1 , · d h present but four joints, the first having nearly dtsappeare ; t e two hooks of the last one are strongly compressed into the form of a J'ttle palette· the two anterior legs, much shorter than the others, a 1 re inserted 'almost under the head and directed forwards. . The Ephemerre usually appear at sunset, in fine weather, m sum· mer and autumn, along the banks of rivers, lakes, &c., and some· times in such innumerable hosts that after thei~· de~th the ~urfa.ce of the ground is thickly covered with their bodtes; m certam dts· tricts cart-loads of them are collected for manure. The descent of a particular species-the albipennis-remarkable for the shortness of its wings, recals to our minds a heavy fall of snow in winter. These Insects collect in flocks in the air, flitting about and balanc· ing themselves in the manner of the Tipulre, with t~e terminal fila· ments of their tail divergent. There the sexes umte. The males are distinguished from the females by two articulated hooks at the extremity of their abdomen, with which they seize them. It also appears that their anterior legs and caudal filaments are long~r than those of the females, and that their eyes are larger: some of them even have four compound eyes, two of which are elevated and much sexu:ll differences are carefully indic:..ted, works that have gt·ently facilitated the disentangling of their synonomy. NEUlWl'TEHA. 63 larger than the others, called from theit· form turban'd or coZ.umnar eyes. The junction having been effected, the couples place themselves on trees ot' plants to complete their coitus, which lasts but for a moment. The female soon after deposits all her eggs in the water, collected in a bundle. · The propagation of their species is the only function these animals have to fulfil, for they take no nourishment, and frequently die on the day of their metamorphosis, or even within a few hours after that event. Those which fall into the water become food for Fishes, and are styled !Vlanna by fishermen. If however we trace them back to that period in 'which they existed as larvce, we find their career to be much longer, extending from two to three years. In this state, as well as that of semi-nymphs, they live in water, frequently concealed, at least during the day, in the mud or under stones, sometimes in horizontal holes divided interiorly into two united canals, each with its proper opening. These habitations are always excavated in clay, bathed by water, which occupies its cavities; it is even supposed that the larvce feed on this earth. Although allied to the perfect Insect, when it has undergone its ultimate metamorphosis, in some respects they differ. The antennre are longer; the ocelli are wanting; and the mouth presents two projections resembling horns, which are considered as mandibles. On each side of the abdomen is a range of laminre or leaflets, usually united at base by pairs, which are a sort of pseudo-branchire over which the trachece extend and ramify, and which not only enable them to respire but also to swim and move with gt·eater facility; the tarsi have but one hook at their extremity. The posterior extremity of the body is terminated by the same number of setre as that of the perfect Insect. The seminymph only differs from the larva in the'presence of the cases which enclose the wings. . When the moment of their development has arrived, it leaves the water, and having changed its skin, appeat·s under a new form-but, by a very singular exception, it has still to experience a second change of tegument, before it is prepared to propagate its species. The ultimate exuvium of these Insects is frequently found on trees and walls; they sometimes even leave them on the clothes of persons who may be walking in their vicinity. With this genus and that of the Phryganere, De Geer formed an order founded on the absence or extreme exiguity of the mandibles. In the" Tableau Elemantail·c de l'Ilistoire Nat.urelle des Animaux" of the Baron Cuvier, they also constitute a separate family, that of the .IJ.gnathea, but still forming part of the order of the Neuroptera. |
