OCR Text |
Show 134 CRUST .ACEA. the same time as the females, which is during the month of June, and are unknown'. Limnadia Hermani, Ad. Brongn., Mem. du Mus. d'Hist. Nat., VI, xiii; .Daphnia-gigas, Herm., Mem. Apterol., V. Found in great numhers in the little pools of the forest of Fontainebleau. • 'f.here, each eye is situated at the extremity of a pedicle, formed by a lateral prolongation, in the shape of a horn, of each side of the head, The body is naked, without a shell, and annulated throughout. The ova of the females are contained in an elongated capsule, situated near the base of the tail in those which are thus terminated, or in the poster·ior extremity of the body and thorax in those which have no tail. Some are provided with a tail. ARTEMIA, Leach. Eyes placed on very short pedicles; the head confounded with an oval thorax, furnished with ten pairs of feet, and terminated by a long and pointed tail. The antennc:e short and subulate. .fl. salina; Cancer salinua, L.; Montag., Trans. Lin. Soc. XI, xiv, 8-10; Gammarus salinus, Fab.; Desmar., Consid., p. 393. A small species found in the salt marshes of Lymington, in England, when nearly dry, of which as yet we have but a very imperfect account. BRANOHIPus, Lat.-0/Lirocephalus, B. Prevost, and Jurine. Eyes placed on projecting pedicles; the body narrow, elongated and compressed; the head distinct from the trunk, furnished with appenda.ges varying according to the sex, and with two appendage& resembling horns between the eyes; eleven pair of feet; the tail termi· nated by two leaflets more or less elongated and edged with cilia. A~though Sch::effer and Benedict Prevost( 1) have published very ?etalled mo~ographs of two species of this genus, they are still Imperfect wrth respect to the profound and comparative study of the organs of the mouth and of some other parts of the head. Con· siderin~ the two sexes together, we find the following general con· formatton; the body is almost filiform, composed of a head separated f1·om the trunk by .a .kind of neck; of a trunk 01• t borax longitudinally hollow beneath, d1v1ded, at least above, exclusive of the neck, into eleven segments, each bearing a pair of branchial, strongly com· pressed feet, usually composed of three foliaceous joints, with a (1) M~m. s~r le Chirocephale printed at the end of the Hist. des Monoc. ofthe late Lew1s Jurme, and previously published in the Journal de Physique. BRANCHIOPODA. 135 r inge of hairs or bearded thr·eads along the edges; and of an elon· rated tail tapering to a point, consisting of nine segments terminated ~y two more or less elongated leaflets fringed with cilia. Under its second segment we find the male organs of generation, a d in the female an elongated sac containing the ova she is ready to produce. In the head we observe, 1. Two r·eticulated eyes situated at the extremity of two flexible peduncles formed by lateral prolongations of the head; 2. Two antennre at least, frontal, scarcely longer than the bead, slender, filiform and composed of very small joints; 3. Two projections under them, sometimes resembling a uniarticulated horn, and at others digitiform-the premier doigt des mains, Bened. Pre'' ost-and biarticulated; 4. A mouth underneath composed of two kinds of dentated mandibles without palpi, and of some other parts. We suspect that these horn-like projections are merely an appendage, larger and differently formed in the males, of the frontal antenore; the two other antennre may be wanting or .he obliterated in the female, and form in the other sex of one of these species-Ohirocephala diaphana, Prevost-those singular appendicated and dentated tentacula, in the form of a soft proboscis which is susceptible of being spirally convoluted, designated by Benedict Prevost unrler the name of doigts des mains, or fingers. It is probable that, as in Apus, the mouth is furnished with two pairs of jaws, a ligula and a labrum, but their respective form and situation have not yet been well ascertained. I am convinced that the part resembling a rostrum mentioned by Schreffer·, and which Pt·evost calls a valve (soupape) is the labrum; that the four bodies or tubercles placed on the sides, mentioned by the former, are the mandibles and the two upper jaws; and that the parts considered by the second as cirri (barbillons) are also maxillar·y. The two first feet, which, according to Schreffer, are composed of but two joints, the last terminating in a point, would represe~t the two first foot-jaws of the Crustacea Decapoda, and the two large antenniform feet of an A pus( 1 ). The chief of the male organs of generation, at least those which are considered as such, consist in two conoid biarticulated bodies, which only project by pressure (Schreffer), situated under the second ring, in which vessels terminate that arise fr·om the first. •M. Prevost presumes that the two vulvre of the female are placed at the extremity of the tail, but that they afford no issue to the ova. This issue (two apertures according to Schreffcr ), is in the second ring, and communicates internally with the sac containing the eggs, which acts as an external ( 1) See Mem. surles Anim. sans Verteb., Savjgn. partl. |