260 CRUSTACEA. 



becomes wider, shorter, and rounder. The two anterior feet, which 

 are much larger and arc 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 antennae are longer in proportion than in the 

 adult, and are terminated by setae or hairs. The eleventh pair are 

 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 regularly 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; Limule 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- 

 ci for mis ; Binocle a queue en filet, Geoff., Insect., XXI, 4 ; Li- 

 mulus palustris , Mull.; Schaeff., Monoc. I V; Apus vert, Bosc.; 

 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. 



f- 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. 



The Motacilla alba, and cinerea, L. ENG. ED. 



