BRANCHIOPODA. 439 



ately bmcath, are shorter than the body, setaceou.'?, and 8 or 9-jointftd; the terminal joints short, and pencilled 

 with Ion;; hairs, form a kind of oar. The mouth is composed of a ridded labiarn ; two lar^e dentate and palpi- 

 geroLis mandibles, the basal joint of the palpi biding famished with a 5-branchcd branchia ; 

 two pairs of maxilla}, the anterior pair also bearing branchial appendages, and the posterior 

 palpigerous. The office of tlie lower lip is performed by a compressed sternum. The legs 

 are 5-jointed ; the two anterior much larger than the others; affixed beneath the antenna;, 

 and directed forwards. The two following legs are directed backwards, and are situated in the 

 middle of the under-side of the body ; but the posterior pair never appear out of the shell, but 

 are bent upwards to give support to the ovaries. The body presents no distinct articulation, 

 and is terminated behind in a tail folded beneath the breast, with two setaceous or conical fila- 

 ments. The eggs are spherical. 

 The laying of the eggs and the casting of the skins of these Crustacea are not less numerous than those of 

 Cyclops and other Entomostraca, and their mode of life is similar. No recent author has been able to detect their 

 sexual organs. Strauss, indeed, discovered the insertion of a great conical vessel, which he considered to be a 

 testicle; but the individuals which he examined were furnished with ovaries, whence it would seem that the 

 Ci/prides are hermaphrodites. He, however, obsen'ed, in disproof of this opinion, that the males may probably 

 exist at a certain period of the year, and that the vessel he describes may belong to the digestive system. 



According to Jurine,the antenna are real fins or paddles, the animals having the power of extending the threads 

 at will, and according to the rapidity with which they are anxious to swim. We also are of opinion that these 

 fdaments may more probably be engaged in respiration, as well as the so-called branchial plates of the jaws. In- 

 deed, the plates of the maxillee appear to me to be a real, but greatly dilated palpus ; and the other two are ap- 

 pendages of the mandibular palpi. Jurine has noticed, that, in swimming, they move these antennae, and two 

 fore-legs, with rapidity, but slowly whilst crawling on water plants. Tliis pair of legs, together with those of the 

 penultimate pair, at such times support the body. He supposes that those legs, which he regards as the second 

 pair, serve to form a current in the water, and to direct it towards the mouth. Tlie two filaments composing the 

 tail unite, and seem to form but one when pushed out of the shell. It is conjectured that they are used in clean- 

 ing the interior of the shell. The female lays her eggs in a mass, fixing them, with a glutinous secretion, to 

 water-plants : this occupation lasts twelve hours. The number of eggs, in the largest species, amounts to twenty- 

 four. Having isolated a packet of eggs, Jurine observed them hatch, and obtained a second generation without 

 the intervention of males. A female wdiich had laid its eggs on the 12th April, had, by the 18th of the following 

 May, changed its skin six times. On the 27th of the same month, it laid a second mass of eggs ; and on the 29th, 

 two days afterwards, a third. He therefore concluded that the number of moultiiigs, in the infancy of these ani- 

 mals, has reference to the gradual developement of the individual, wdrich developement can only be eflected by a 

 general separation of the envelope, now become too small to lodge the animal, which has a determinate limit to 

 its size.* 



[Mr. W. Baird has given a valuable and complete memoir upon this genus in the Mofiaz'tne of Zoolngy and 

 Botani/, vols. i. and ii., describing a considerable number of new British species. He also states that a fossil 

 species occurs in the limestone of Burdiehouse Quarry, near Edinburgh.] 



The third general division of the Branchiopodous Lojjhi/ropa have also only one eye ; and the slicU 

 is bent in two, but \vitliout any dorsal hinge, and is terminated posteriorly in a point. The head is not 

 covered by tlie shell, but is inclosed in a kind of shield like a beak. They have two very large arm- 

 like branched antennae, always exserted, and serving as oars. The legs, ten in number, are terminated 

 by a pectinated or digitated fin, and furnished (except the anterior pair) with a branchial plate. The 

 eggs are situated beneath the back. The body is always terminated by a tail, with two setai at the 

 tip. The front of the body either terminates in a point, or forms an apparently (hitinct head, occupied 

 entirely by a single large eye. 



These are our Cladocera, or the Daphnides of Strauss, and compose Jnrine's second family of 

 Monoculxs. From the form of a pair of their antennae, which resemble branches, and serve as oars, 

 and their power of leaping, the common species has obtained tlie name of the Arborescent Water-flea. 



Latono, Strauss, has the antenna; oar-like, divided into three single-jointed branches. Dnphnia sci/fcra, iMiiller. 



tS/da, Strauss, approaches the other known genera in respect to the antenna?, which are, however, divided only 

 into two branches, one being 2-jointed and the other 3-jointed. Daphnia cristaUina, Rliiller. 



In these and the other genera, there also exists another pair of antennas, very short, especially in the females, 

 situated at the anterior and lower extremity of the head, composed of a single joint, with one or two setee at 

 the tip. 



Poljiphemns, ^U'dler, has the antenna? oar-like, as in Daphnia and Lyncens, divided into two branches, each of 

 which is 5-jointed. Sloreover, the head, very distinct and rounded, and athxed irpon a short neck, is almost 

 entirely occupied by a single eye of large size. The legs are entirely exposed. A single species only is known 

 (iIonociih(S pedicid'is, Linn., De Geer ; PoJfiphemus ocidi/s, Milller; Cephalocidus sfagnonan, Lamarck), [about 

 the size of a flea.] The hgs are uidike those of the Monocidi of this division, being composed of a thigh, tibia, 



* SeuMiillcr; Jurine. Hist, drs Monad fs, 2jid iMvision ; Ramdolir, i fossil species named " C)'Fris ftve," found In t,TC:it aliLimlaiice near 

 Ulnn. iv, Strauss, M6in. (In Mns. d'Uiit. N/it., 7. i, ; Dpsmarcst, Con- the mountain of Oerpfovia, in tlie departemeiit ilu Puy-ilu-ltniiie, below 

 Midiratiuiis and Crust. Fhnsiles, in wliicli liiUcr wofii is iiguicd Ji | Vicliy-des-JJaiiis uiid Uussin;. 



