OCR Text |
Show 68 CRUSTACEA. rounded: The two fila~ent~ of the mediate antennre are ~uch longer than the1r peduncle. 1 he stdes of the shell are entire or not incised. In some, all inhabiting salt water, the last segment of the tail or that which occupies the middle of the terminal fin, presents no tr~nsverse suture. Those whose lateral antennre have a large scale on their peduncle whose eyes are very large and reniform, and the forceps of whos; two anterior cla~vs nre narrow, elongated, prismatic, and equal, form the genus NEPHROPS of Leach, the type of which is the Cancer norwegicus, L.; de Geer, Insect., VII, XXI; Herbst., XXVI, 3; Leach Malac. Brit., XXVI. The two anterior claws are furnished with ?entated spines and ridges, and the superior surface of the tail 1s sculptured. It is found in the seas of the north of Europe and· the Mediterranean. 10 !hose in which the peduncle of the lateral antenn:;e presents no. thm~ but t~o short projections in the form of teeth or spines, whose eyes are nelther large nor reniform, and whose forceps are more or less oval, compose, with the fresh water species, the genus .B.stacus, properly so called, of the same a~ho1· . .B.stacus mari~us, Fab.;. Cancer gammarus, L.; Herbst., X~V; Penn.,Br1t. Zoo~., V,x, 21; (the Common Lobster). The pomt or rostru~ of the anterior extremity of the shell has tJvee teeth on each stde, and another double one at its base. The an· terior claws are very large and unequal; the largest finger of the forceps is oval, with great molar teeth, the other is elongated, and has numerous small ones. Old individuals are sometimes mo:e than h~lf a metre in length. Its flesh is highly esteemed. It IS found m the European Ocean, in the Mediterranea\, and even on the eastern coasts of North America. Its internal structure has been carefully studied by Messrs Victor Andouin and Milne Edwards. ' . I~ the f:esh water species, which otherwise resemble the preced· mg m t~e1r antennre: eyes, and form of the claws, the last segment of the tatl, or the rmddle one of its terminal fin, is transversely di· vided by a suture. The .B.stacus communis; Cancer astacus L. • Rresel Insect III liv .. T ' ' ' ., ' ' vu.. he Craw-Fish has its anterior forceps granulated, and the mner edges finely dentated. There is a tooth on each s~e .of the snout, and two at its base; the lateral edges of the seg· ments of the tail form an acute angle. Its colour, which is u.sually a greenish brown, is sometimes altered by accidental c11·cumstances. This specJes, -which inhabits the fresh waters of Europe has been more particularly studied, both as respects its ana;omy DECAPODA. 69 d habits and the faculty enjoyed by the Crustacea of regene-arna ting thei' r anten<e and feet when they are either mut1'1 ate d. or destroyed. When about to cast its shell, two stony concretions are found in the stomach, formerly much used in medical practice as an absorbent, but now replaced by the carbonate of .m~gnesia. It conceals itself in holes, or under stones, never qutttmg its retreat except to search fo1· food, which consists of small Mollusca and Fishes, and the larvre of Insects. It also feeds on putrid flesh, the carcases of quadrupeds, for insta~ce, which are placed as a bait for them in nets, or in the centre o~ fagots of wood. They are also taken in their holes by the hght of torches. It chano-es its shell towards the end of spring. Two months after coidon, which takes place ventribus junctis, the female produces her ova, which are at first collected in masses, and glued to the false feet by means of a viscid h4mour. They are of a reddish brown colour, and enlarge before they are hatched. The young Astaci, at first extremely soft and precisely like their parent, shelter themselves under her tail and remain there several days, until their bodies acquire a certain degree of solidity. . The term of existence assigned to the Astac1 seems to be twenty years and upwards, their size augmenting in proportion to their age. Those are preferred for th: .table. which inh~bit running streams of fresh water. A pat'asttlc ammal belongmg to the Annelides, is found on their branchire, long ago observed by Rresel, but imperfectly known until the researches of M. Odier(l). . The fresh-waters of North America produce another spec1es, the A. Bartonii, figured by Bosc.-Hist. Nat. des Crust., II, ~' 1. A third inhabits the rice-fields of the same country, to wluch, according to Major Le Conte, one of the best naturalists of the United States, it i!i very injurious. . In the fourth section, that of the CARIDES, the intermedial anten-nre are superior or are inserted above the laterals: the peduncle of these latter is completely covered by a large scale. . Their body is arcuated, almost gibbous, and of a less s.ohd con sistence than that of the preceding Crustacea. The front 1s always drawn out into a point, and most frequently so as to resemble a rostrum or pointed lamina compressed and dentatecl along the edges. ( 1) See his .Memoire sur le Branchiodelle, inserted in the Mem. de la Soc. d'Hist. Nat. tome I, p. 69, et seq. |