54 MAXDIBULATA. NEUROFTERA. 



more particularly detailed in the notice of the only family in which 

 they are embraced : it may, however, be here remarked that they 

 may be known by their minute antennae, porrected anterior legs, the 

 filamentous appendages to the abdomen, and by the great dissimilarity 

 in the size of the two pair of wings, the second, or posterior, being 

 sometimes entirely absent ; again, the insects are nearly, or totally in 

 some instances, destitute of a mouth, and the eyes are usually very 

 large. 



Family III.— EPHEMERID.^, Leach. 



AntenncE inserted on the inner margin of the eyes, triarticulate, the two basal 

 joints very short and thickened, the third long, and resembling a slender 

 tapering bristle ; mouth wanting ? body elongate, soft ; head as wide as the 

 thorax, transverse; eyes large, suboval, united on the forehead in the 

 males ; ocelli three, placed triangularly ; thorax suhcylindric ; wings two or 

 four; abdomen elongate-conic, with two or three very long setas, or 

 filaments, at the apex, composed of numerous joints, and two or three 

 shorter setaceous ones (also jointed) beneath; legs slender, anterior remote 

 from the others, inserted, to appearance, beneath the head, much longer 

 than the others, their femora thickened, the intermediate and anterior pairs 

 with the femora less robust; all the tibiae simple, and forming at first 

 sight, as it were, the basal joint of the tarsi, being gradually attenuated 

 from the base, the tor^z consisting of a few cylindric articulations, of which 

 the first is shortest, and the terminal one is furnished with two unequal mem- 

 branous compressed claws, the smallest having a horny tooth at the apex, 

 and the other being broader and obtuse. The metamorphosis is quadruple, 

 • inasmuch as the insect is furnished wdth wings, enveloped in an outer case, 

 which is ultimately slipped off before the true imago is declared. 



The insects of this family, as previously alluded to, are remarkable 

 for undergoing a quadruple metamorphosis, as, in addition to the 

 ordinary states of egg, larva, pupa, and imago, there is an interme- 

 diate one to the last two, inasmuch as a sort of representative of the 

 imago is produced after the pupa, but which has to undergo a further 

 ecdysis, or shedding of its skin, before the true insect appears : in 

 this state the insect is capable of flying, the true wings being encased 

 in a delicate membrane, which is cast very expeditiously, when suffi- 

 ciently mature : in this operation a slit is made on the back, through 

 which the insect forces itself, and gradually withdraws its body, 

 limbs, and wings, leaving its exuvium, exactly corresponding with its 

 previous form, excepting that portion which enveloped the wings. 



