OUDER 1. Div. IT. 



BRANCHIOPODA. 



439 



Fiif. 18. — Cypris 

 vidua, magHiHeU. 



ately beneath, are shorter than the body, setaceous, and 8 or 9-jointed ; the terminal joints short, and pencilled 

 with long' hairs, form a kind of oar. The mouth is composed of a ridged labium ; two large dentate and palpi- 

 g-erous mandibles, the basal joint of the palpi being furnished with a 5-branched branchia ; 

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

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

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

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

 Ci/prides are hermaphrodites. He, however, observed, 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 antennae 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. AVe also are of opinion that these 

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

 deed, the plates of the maxillae 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. This 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. The 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- 

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

 the intervention of males. A female which 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 moultings, in the infancy of these ani- 

 mals, has reference to the gradual developement of the individual, which developement can only be eftected 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 Magazine of Zoology and 

 Botang, 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 Braucliiopodous Lophyrojja have also only one eye ; and the shell 

 is bent in two, but without any dorsal liinge, and is terminated posteriorly in a point. The head is not 

 covered by the shell, but is inclosed in a kind of shield like a beak. They have tvi'o 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 setae at the 

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

 entirely by a single large eye. 



Tliese are our Cladocera, or the Daphnides of Strauss, and compose Jurine's second family of 

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

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



Latona, Strauss, has the antennae oar-like, divided into three single-jointed branches. Daphnia setifera, Miiller. 



Sida, Strauss, approaches the other known genera in respect to the antennae, which are, however, divided only 

 into two branches, one being 2-jointed and the other 3-jointed. Daphnia cristallina, Miiller. 



In these and the other genera, there also exists another pair of antenna;, 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 setae at 

 tbe tip. 



Polyphemus, Miiller, has the antennae oar-like, as in Daphnia and Lynceus, divided into two branches, each of 

 which is 5-jointed. Moreover, the head, very distinct and rounded, and affixed upon 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 

 (Monoculus pecticulus, himi., DeGeer; Polyphemus oculus, MuUer; Cephaloculus stagnorum, Lamarck), [about 

 the size of a flea.] The legs are unlike those of the Monoculi of this division, being composed of a thigh, tibia, 



• See Miiller; Jurine, Hist, des Monocles, 2nd (iivision ; Raindohr, 

 Mon. iv. Strauss, Mt-in. da Mus. d'Hist. Nat., 7. i. ; Desmarest, Cuu- 

 iidirationt and Crust. Fossiles, ia which latter work is figured a 



fossil species named "Cypris f^vc,'' found in ^reat abundance near 

 the mountain of Gergovia, in the departemeut du Puy-dC'Dome, below 

 Vichy'dcs-Baias and Cugsac. 



