Animal Kingdom V.3

Page 56

78 CRUSTACEA. .. for natation, or arc fin-feet. Their shell is divided into two portions, the anterior of which supports the eyes and in­termediate antcnnre, or composes the head, without giving origin to the foot-jaws. These organs, as well as the four anterior feet, are frequently approximated to the mouth on two lines that converge inferiorly, and hence the denomina­tion of Stomapoda affixed to this order. Judging hy the . Squill::c, the most remarkable gc~ms of this order, and the only one hitherto studied, the heart is elongated, and similar tu a large vessel. It extends along the whole length of the back rests upon the liver and intestinal canal, and terminates postc~ riorly and near the anus, in a point. Its parietes are thin, transparent, and almost membranous. From its anterior ex­tremity, placed immediately behind the stomach, arise three principal arteries, the mediate of which-the ophthalmic­giving off several branches on each side, is more particularly directed to the eyes and intermediate antennre, and the two lateral ones-the antennarics-pass over the sides of the sto­mach .and are lost in the muscles of the mouth and of the ex­ternal antennre. No artery arises from the superior surface of the heart, but a great many issue from its two sides, each pair of which, as it appears to us, corresponds to a particular segment of the body, commencing with the foot-jaws, whether these segments be external, or concealed by the shell, and even very small as is the case with those that are anterior. On a level with the first five abdominal annuli, or those to which the natatory appendages and the branchim are attached . . ' this superior surface of the heart receives, near the median line, five pairs of vessels-a pair to each segment-proceeding from these latter organs, and which, according to Messrs Audouin and Milne Edwards, are analogous to the brancldo­cardiacs of the Dccapoda. A central canal (1) situated under (1) See our general observations on the Macroura. Neither this vessel nor the venous sinuses have been observed in the subsequent orders; but the heart pre· serves the same elongated form, and presents similar antel'ior arteries. From its sides also arise other arteries corresponding to the articulations of the body. In addition to the pre-cited Memoir, see the Le~ons d' Anatomic Comparee of the Baron Cuvier. STOMAPODA. 79 the liver an(l intestine receives the venous blood which is poured into it from all parts of the body. On the level of each segment to which the foot-jaws and branchim are attach-ed it gives off a branch on each side, running to that part of th; branchire which is situated at the base of the correspond-ing foot-jaw. The parietes of the~e vessels appear to the above mentioned gentlemen to be smooth and continuous, but formed by a layer of lamellated cellular tissue glued to the neighbouring muscles, rather than by a membrane proper; these vessels also appeared to them to communicate with each other near the lateral margin of the annuli, but they could not positively affirm it. The afferent or internal vessels of the branchire, which in these Squillre form tufted bunches, are continuous with the branchio-cardiac canals, are no longer lodged in cells, pass between muscles, turn obliquely over the lateral part of the abdomen, reach the anterior margin of the preceding ring, and terminate on the superior s,urface of the heart near the median line, one partly mounting on the other. The medullary cord, exclusive of the brain; presents but ten ganglions, of which the anterior furnishes nerves to the mouth, the three following, those of the six natatory feet, and the last six, those of the tail. Thus, although the four last foot-jaws represent the four anterior feet of the Decapeda, they never­theless form a part of the organs of manducation. The sto­mach of these Crustacea-Squillro-is small and has but a few very smail teeth(l) near the pylorus. It. is followed by a straight and slender intestine ~hich e~tends along the whole abdomen, accompanied on the right and ·left by glandular lobes which appear to supply the want of a liver. A ramous ap­pendage adhering to the inner base of the last pair of feet . appears to characterize the male. The teguments of the Stomapoda are thin, and in several, nearly membranous or diaphanous. The shell is sometimes formed of two shields, of which the anterior corresponds to the head and the posterior to the thorax, and sometimes of ( 1) They form two ranges of transverse and parallel stria:.