26 MODERN CLASSIFICATION OF INSECTS. 
a thickened rib half way down the centre, and slit through the frontal 
half. As the life of these insects ordinarily extends but for a few 
hours, the parts of the mouth are almost obsolete, being minute, fleshy, 
and filled with fluid, so that their structure is not easily discernible. 
Latreille describes them doubtingly, as consisting of four short multi- 
articulate palpi, more slender at the tip. Mr. Curtis having examined 
living specimens, says that the parts of the mouth seem to consist of 
two large triarticulate ? palpi, with two compressed elongated sublinear 
lobes between them (maxilla, jig.61. 2.), and a dilated labrum with 
two large divaricating fin-like lobes (palpi? jig. 61. 3.). Reaumur’s 
figure of the under side of the head (tom. vi. pl. 43. f. 11.), represents 
aspace “ou devroit étre la bouche et d’ot on ne fait sortir qu’une 
vessie, au dessous on voit quatre languettes charnues, dirigées vers la 
and Savigny has represented the parts of the 
? 
partie postérieure ; i 
mouth of a Baetis, in the great work on Egypt ; but it is impossible 
satisfactorily to make out their analogies. The thorax is oval and 
convex ; the prothorax small, narrowed in front, the mesothorax 
large ; the abdomen is elongate, narrow, of nine segments in both 
sexes, the terminal segments being longest, and gradually narrowed ; 
it is furnished at the apex, in both sexes, with two or three 
long, slender, multiarticulated filaments * ( jig. 61. 4. ¢.), and in 
the males with four, two short setaceous articulated appendages, and 
two shorter straight ones, which are sometimes not exserted +; the 
wings are of unequal size, the anterior being much larger than the 
posterior, and elongate-trigonate, considerably reticulated; at rest they 
are generally carried erect; the posterior pair are wanting in some 
species (Cloeon, Ephemera diptera Zinn.). The legs are slender and 
simple; the anterior pair, in the males being porrected, and greatly 
elongated, with the tibize and tarsi appearing soldered together ; the 
basal tarsal joint being very minute ; the tarsi are 5-jointed, simple, and 
terminated in the fore legs of the males by two oval pulvilli; in the 
four posterior legs the tarsi are short, 5-jointed; the basal joint (in 
the males of E. vulgata), being shortest, and soldered to the tibia (so 
* Latreille (Hist. Nat. Ins. vol. xiii. p. 80.) states that the males differ from the 
females in having the middle anal filament very short, whereas it is as long as the 
others in the females. This is the case in a species observed by Reaumur ; but in the 
true Ephemerz, the middle seta is nearly, but not quite, as long as the lateral ones 
+ In Eph. vulgata 3, they have been overlooked by Curtis, but the extremities 
are distinctly exserted in my specimens. I have seen no species with three of these 
short appendages as described by Latreille, Gen. Cr. vol. ui. p. 184. 
