260 
CRUSTACEA. 
becomes wider, shorter, and rounder. The two anterior feet, Avliich 
are much larger and are formed like oars, resemble ramous antennae, 
and have been considered as such by some writers * : they exhibit 
four multi-articulated setaceous threads, the two last joints, one of 
them particularly, being much longer than the others, which are si- 
tuated on the internal side or anteriorly. The two at the extremity 
are evidently analogous to the toes of the forceps, the remaining 
two also correspond to as many of the lateral leaflets ; it is easy to 
convince ourselves of this by comparing these parts in young speci- 
mens. After their sixth or seventh change of tegument, the two or 
three following feet of the latter greatly resemble the two anterior 
ones, and even their antennse are longer in proportion than in the 
adult, and are terminated by setae or hairs. The eleventh pair ai’e 
very remarkable f. The first joint, behind the vesicles, presents 
two circular valves, laid one on the other, formed by two leaflets, 
and containing the ova, which resemble granules of a bright red 
colour. Every specimen which has hitherto been examined being 
always found to possess this kind of feet, they have been considered as 
hermaphrodites, and are considered capable of self impregnation. 
These animals inhabit ditches, pools, stagnant waters, &c., and 
usually in myriads. Abducted, when thus assembled, by violent 
winds, they have been seen to descend in rain. They generally 
make their appearance in spring, and in the beginning of summer. 
Their customary food is the Tadpole. They swim well on their back, 
and when they sink into the mud they erect their tail. When first 
produced they have but one eye and four feet, resembling arms or 
oars, furnished with tufts of hairs, the second of which are the 
largest. Their remaining organs are regulaidy developed after each 
change of tegument. M. Valenciennes, an attache of the Mus. 
d’Hist. Nat., has remarked that these Crustacea are frequently de- 
voured by the bird vulgarly called the Lavandiere (a). 
The number of species known being very small, it is unne- 
cessary to imitate Leach in forming a separate genus — Lepi- 
DURUS, Leach — for those which have a lamina between the 
threads of the tail. Such is the Apus prolongatus ; Monoculus 
apus, L. ; Schaeff., Monoc., VI; Limide sirricaude, Herm., Jun.; 
Desmar., Consid., LII, 2. The carina of the shield terminates 
posteriorly in a small spine, which is not seen in the Apus can- 
ciformis ; Binocle d queue en filet, Geoff., Insect., XXI, 4; Li- 
mulus palustris. Mull. ; Schaeff., Monoc. I — V ; Apus vert, Bose.; 
Desmar., Ib., LI, 1; the latter, besides, has no lamina between 
the caudal threads; it is the type of the genus Apus, Leach, or 
* They also seem to represent the two first foot-jaws. 
'h Schaeffer distinguishes them by the name of uterine feet. The preceding nine 
pairs, according to his phraseology, form forceps, those of the first oars, or true 
feet ; finally, those which follow the uterine feet, or the twelfth pair and following 
ones, branchial feet. The vesicular sacs lengthen and lessen just as gradually ; their 
use is unknown. 
tK^{a) The MotaciUa alba, and rinerea, L. — Eng. Ed. 
