192 INSECTA. 



four compound eyes, two of which are elevated and much larger than 

 the others, called from their form turbaii'd or columnar eyes. The 

 junction having been effected, the couples place themselves on trees 

 or 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 ani- 

 mals have to fulfil, for they take no nourishment, and frequently die 

 on the day of their metamorphosis, or even within a feAV hours after 

 that event. Those which fall into the Avater become food for Fishes, 

 and are styled Manna by fishermen. 



If however we trace them back to that period in which they existed 

 as larvre, we find their career to be much longer, extending from two 

 to three years. In this state, as Avell 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 alwaj's excavated in clay, bathed by water, which occupies its ca- 

 vities ; it is even supposed that the larvae feed on this earth. 



Although allied to the perfect Insect, when it has undergone its 

 ultimate metamorphosis, in some respects they differ. The antennae 

 are longer; the ocelli are wanting ; and the mouth presents two projec- 

 tions resembling horns, which are considered as mandibles. On each 

 side of the abdomen is a range of laminae or leaflets, usually united 

 at base by pairs, which are a sort of pseudo-branchiae over Avhich the 

 tracheae extend and ramify, and which not only enable them to re- 

 spire but also to swim and move with greater facility; the tarsi have 

 but one hook on their extremity. The posterior extremity of the 

 body is terminated by the same number of setee 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 develop- 

 ment has arrived, it leaves the water, and having changed its skin, 

 appears under a new form — but, by a very singvilar exception, it has 

 still to experience a second change of tegument, before it is prepared 

 to propagate its species. The idtimate 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 Phryganese, De Geer formed an 

 order founded on the absence or extreme exiguity of the mandibles. 

 In the " Tableau Elementaire de I'Histoire Naturelle des Animaux" 

 of the Baron Cuvier, they also constitute a separate family, that of 

 the Agnathes, but still forming part of the order of the Neuroptera. 



The number of wings and that of the filaments of the tail furnish 

 the means of dividing the genus of the Ephemerae. 



E. Sxoamvier (liana, Lat. ; E. Icngicauda, Oliv., Swamm., 

 Bib., Nat., II, xiii. 6, 8. The lajgest species known; four 

 wings ; two filaments to the tail twice or thrice the length of 

 the l;ody, which is of a russet-yellow ; eyes black. Holland and 

 Gejmany, along the great rivers. 



