OCR Text |
Show 122 CRUSTACEA. hardly equal to one-third of the others; the body, properly so called, inflated and almost ovoid; tail narrow and formed of six segments. The colou1· varies gt·eatly; some are reddish, others whitish or greenish. The whole length of the animal is two lines. This species is very common( 1 ). The second general division of the Lophyropa Branchiopoda, or that in which the shell is formed of two valves united by a hingeOsTRACODA, Lat.; Ostrapoda, Stt·aus-is composed of two subgenera, the fir·st of which, Cythere, since the interesting and valuable observations of the latter upon the second or Cypris, appeat·s to solicit a more profound examination than that of Muller, our only authority with respect to its characters, in order that they may be clearly defined. According to Mtiller we find in the CYTHERE, MiilJ.-Cytherina, Lam. Eight simple feet(2), terminating in a point, and two equally simple, setaceous antennre, composed of five or six joints, furnished with scattered hairs. They are found in the salt and brackish waters of the sea-coast among the Fuci and Confervre(3). CYPRIS, Miill. But six feet( 4); the two antennre terminated by a bundle of setre resembling a pencil. The shell forms an oval, laterally compressed body, with an arcuated and convex back, or towards the hinge; the opposite side is almost straight, and slightly emarginated or reniform. Before the hinge and on the median line is the eye, forming a large, blackish, round point. The intermediate antennre, inserted above, are shorter (1) Desmar., Consid., p. 364. For the other species, see the same work,p. 361-364, LlV; Mull., Entom., CYcLors; Jurine, Uist. des Monoc., p. 1-84, prem. faro. des Monoc. a coquille univalve; Rand., Monoc., I, II, III. (2) It is probable there are but six. See Cypris, note 4. (3) If these Entomostraca inhabit salt-water exclusively, it is easy to see that Jurine and other observers whose geographical position limited their researches to the fresh-water genera, could not have spoken of the former. See Mull., En· tom., CYTUERE, and Desmar., Consid., p. 387, 388, LV, 8. ( 4) Four according to Randohr, and eight according to Jurine; the first consi· dering the two last as appendages of the males, and the second looking upon the palpi of the mandibles and the branchiallaminre of each upper jaw-the two first feet of his second division of the body, those which he says are composed of but one joint and terminated in a dentated spoon-as so many feet. The latter does not include in this numhe1· those which the former considers as sexual organB; he states them-p. 161, 166-to be five jointed tln·ends issuing laterally from the pouch of the matrix, of the usc of which he is ignorant. BRANCHIOPODA. 123 h body setaceous, composed of from seven to eight joints, than t e ' f f Which are shortest and terminated by a bundle o twelve the last o . , . . fir Setre serving as fins. I he mouth conststs of a carmated or teen ' . . . two large dentated mandibles, each furmshed wlth a tn-labrum, . . 1 ted palpus to the first segment of whtch adheres a small arucu a ' • • . . • branchial Jeafwith five dtgttatwns(l), and of two patrs of Jaws. The two superior are much. t~e largest, a~d have four mova~le and silky appendages on thetr mternal margm, and a large, pectmated, b nchial lamina on their anterior edge; the second are composed of t:: joints, with a short, nearly conical, inarticulated palpus(2) 'lky at the end, as is the extremity of the jaws themselves. A sort :~compressed sternum fulfils the functions of a lower lip(3). The feet are divided into five joints, the third representing the femur, and the last the tarsus. The two anterior feet, inserted under the antennre, are much shorter than the others, incline forwards, and are furnished with rig·id setre, or long hooks united in a bundle at the extremity of the last joints. They are deficient in the four fol· lowing feet. The second, situated in the middle of the under part of the body and at first dil·ected backwards, are arcuated and terminated by a long and strong hook inclining forwards. The two last are never visible externally, but are turned up, applied to the posterior sides of the body in order to support the ovaries, and terminate in two very small hooks( 4). The body presents no distinct articu· Jation, and terminates posteriorly in a kind of soft tail which is doubled underneath, with two conical or setaceous threads furnished with three setro or hooks at the end, directed backwards and issuing from the shell. The ovaries constitute two large, simple and conical vessels forming a cul-de-sac at their ot·igin, and situated on the posterior sides of the body, undet·neath the shell, and opening, side by side, in the anterior portion of the abdorpen whet·e the canal formed by the tail establishes a communication he tween them. The ova are spherical. These Crustacea spawn, and change their skin, as frequently as the Cyclopes and other Entomostraca, and their mode of life is the same. Ledermuller states, that he observed them in coitu. Modern naturalists, who have most closely studied them, however, have never been able to discover their sexual organs with certainty, not· been fortunate enough to see them in actu. M. Straus (1) Interior lip, Randohr. (2) Forked in the Cypris strigata, Id. (3) Exterior lip, Id. (4) In the figure given by Randohr these feet consist of but three joints, and the last is somewhat dilated and ema1·ginated at the end, with a hook in the middle of the emargination. |