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Show 124 C~USTACEA. observed, under the origin of the mandibies, the insertion of a stout conical vessel filled with a gelatinous substance, which appeared to communicate with the re8ophagus by a straight canal, that he sus. pects may be a testis or salivary gland. The individuals which were the subjects of these observations having ovaries, the Cy. prides according to the first supposition must be het·maphrodites. This is so much the more doubtful, howevc1·, as he himself remarks that it is possible the males may only exist at a particular season of the year, and that the vessel alluded to seems to be more nearly comrected with the function Of digestion than with that of gene. ration( 1 ). Accot·ding to Jurine, the antennre are true fins, the threads of which are spt·ead out or united at the will of the animal, and in pro· portion to the degree of velocity it wishes to communicate to its motions; sometimes but a single one is visible, at others they are all displayed. We also think that these threads, and those of the two anterior feet, may be considered as aiding in respiration, quite as much as the laminre of the mandibles, and of the two superior jaws, which M. Straus distinguishes by the name of branchial. The last . ' or those of the Jaws, appear to me to be true but greatly dilated palpi, and the two others are appendages of the mandibular palpi. See Jurine, Hist. des Mon. VI, 3. According to the naturalist of Geneva before mentioned, these animals, while they are switnmiug, move their anteriot· feet as ra· pidly as their antennre, but very slowly when walking over the sur· face of aquatic plants. These feet, conjointly with the two termi· nated by a long hook, or the penultimates, then support the body. He supposes that those which, according to him, form the second pair, are destined to ct·eate an aqueous current and to direct it to· ward the mouth, thet·eby assimilating their functions to those of the second inferior antennre, which he calls antennulre. The two threads composing the tail unite on leaving the shell, and seem to form but one; they serve, as he supposes, to brush out its interior. The female deposits her ova in mass, fixing them on plants or the mud by means of gluten. During this operation, which lasts about twelv~ hours~ and in the largefit species produces twenty-four eggs, she chngs With her second feet, and in such a manner as not to fear the sho~k of the water. He collected some of these packets of newly latd eggs, and after separating them, observed the hatching of the young ones, and obtained a second generation without the in· (1) See the alimentary canal of the Daphnia pulez, igured by Jurine, X, 7,and Randohr, Monoc., Tab. V, ii, cl, d, and x. BRANCHIOPODA. 125 · f the males. A female which had deposited her ova on tervenuon o . . . • d 1 f April changed her skm ~1x t1mes between that per10 the J2t 1 o ' I 18th of the following May. On the 27th of the same and t te f h h h Spawned a second time, and two days a terwards, on t e mont s e tl . d From this, he concludes that the number of these 29th, a ur · changes •0 the young animal is in proportion to the gradual devet l t Of the individual; that this development can only take opmen lace by the general separation of an envelope be.come too sma~l to p · the animal· and that the size of the latter has a determmed contatn ' limit to which it must attain( I). The Polyropha of our third divlsion-CLADOOERA1 Lat.; Daph- 'dea Straus-from the second family of the Monoculi of Jurine. mTh e f' orm of two of their antennre, which resemble rnm1'f i e d arms and serve as oars, and the faculty of leaping which they possess, have acquired for one of the most common species, the name of the aquatic arborescent flea. The first of these naturalists, who has given us an excellent mono-graphy of the Daphnire, a subgenus of this divis~on, establishes t'~o new ones· one by the name of LATONA, characterized by antenn~, m the form 'or oars, divided into three branches, of but one joint(2); and the other by that of SrnA, which approaches ot·her known subgenera of the same division, in havin~ similar antennre, d~v~ded into two branches only, but of which one IS composed of two JOmts, and the other ofthree(3). The Daphnice, according to him, are distinguished ft·om the preceding and from the Lyncei, inasmuch as one of the two branches of these oars is composed of three joints and the other of four. Jurine, however-Hist. des Mon. P· 92-states, that each branch is composed of three joints; but it seems that he did not include the first of the posterior branch, a very short one, it is true( 4). The last, in all these Lophyropha, is terminated by three threads, and each of the preceding ones gives out another; these threads are either simple or barbed. There are also two other but very short antenn~-particularly in the females-situated at (1) See Mull., Entom. genus Cypris; Uist. des Monoc., second divis., Mon. a coquilles bivalves, p. 159-179, XVII-XIX; Rand., Mon., IV; Straus, Mem. clu Alus. d'Uist. Nat., VB, 1; Desmar., Consid., p. 380-386, LV, 1-7. DesmarestCrust. Foss., XI, 8-has figured a fossil species which he calls Cyprisfeve, found in great abundance near the Gergovian mountain in the Puy-de Dome, and between Vichy-Les-Dains and Cussac. (2) Daphnia setifera, Mull., En tom. (3) Daphnia cristallina, Ejusd. Ibid. (4) Randohr has given it in the fig., II, vii, tab. V, of these antennce. |