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Show 14 CIWSTAC£A. The circumscribed heart( I), of an oval form and with museu~ Iar parietes, gives origin to six trunks ~f vessels, ~hree of which are anterior, tWO inferior, and the SIXth posteriOr. Qf the three anterior arteries, the median-the ophthalmic-is distributed almost exclusively to the eyes; the two othersthe antennaries-spread over the shell, the muscles of the stomach a portion of the viscera and the antennre ; the two inferia: ones-the hepatics-transmit blood to the liver; the last-the sternal-is the most voluminous of the three, and arises from the posterior part of the body, sometimes on the right side and at others on the left; i~s chief co~rse is. t~ the abdomen, and to the organs of locomotiOn. It gtves or1gm to a great number of large vessels, among which we should particularly observe the one called by M. Audouin and Edwards the superior abdominal, because it arises from the posterior part of that artery, at a short distance before the artic~lation of the thorax with the abdomen, vulgarly termed the tad, and because it soon dips into the abdomen-tail,-where it divides into two large branches, running backwards, becoming gradually smaller and terminating at the anus. The blood which has nourished these various organs, and thus become venous, collects from all quarters in two large sinuses(2), one on each (1) These observations are extracted from the excellent Memoir of Messt·s Audouin and Edwards, published in the .B.nn. d' !list. Nat., t. XI, 283-314, and 352-393. See also the Mem. du Mus. d' Hist. Nat., where M. Geoffroi Saint-Ili1- aire has inserted the results ofhis curious researches on the solids, and on the cit·· culation of the Lobster. (2) These learned naturalists compare them to the two lateral hearts of the Ce· phalopoda, and the analogy has been admitt<::d by Baron Cuvier in his general Ue· port on the transactions of the A cad. Roy. des Sc., for 1827; but the idea had been communicated by me toM. Audouin, and was a necessary consequence of my theot·y of the circulation of the blood in the Crustacea, published in a note of my Esquisse d'une Distribution Generale du Regne .B.nimal, p. 5. As the writers alluded to have taken no notice of what I have stated in this particular, both in the pam· phlet quoted, and in my work on the "Families of the Animal Kingdom," I beg leave to produce that note. "I submit the following opinion to the judgment of Zootomists, and of M. Cuvier in particular, viz. that in those of the Vertebrata possessed of a circulation, the organ called heart represents, in its functions, a left ventricle, the arterial and dorsal trunk of Fishes and of the larv~ of the Ba· trachians; that one or two artct·ies, )Vhich in the Cephalopoda hale the form of DECAPOD A. 15 side and above the feet, and formed of venous sacs united in a longitudinal series, or like a chain. It is thrown into an external vessel-efferent-of the branchire, where ~t .is renewed and becomes arterial; thence proceeds into an internal vessel-afferent; and :finally seeks the heart through canalsbranchio- cardiac-laid beneath the arch of the flanks. All the canals of a side unite in one large trunk, and open into the J;tteral and corresponding part of the heart by a ~ingle orifice, the folds of which form a double valve that opens to allow the transit of-the blood from the branchire to this viscus, but prevents a retrograde motion by closing. Examined internally, the heart exhibits numerous fasciculi and muscular fibres, variously int~rcrossed and forming several small chambers before the orifices of the arteries. These cham hers are so many small auricles, which communicate freely with each other when it dilates, but appear to form a similar num her of little cells for each vessel when it contracts, their capacity being proportioned to the quantity of blood in their peculiar vessels. These vessels debouche in the interior of the heart by eight <>penings, the two lateral valvular ones above mentioned included. Such, with the exception of some modifications(!), · is the general system of the circulation in the Decapoda. The superior face of the brain(2) is divided into four lobes, each of the two middle ones furnishing from its anterior margin an optic nerve that plunges directly into the pedicle ·of the eye and there divides into numerous filaments, each of which is destined to a facet in the cornea of that organ. hearts, replace the right ventricle. The focus of the circulation, highly concentrated in the first of the Vertebrata, thus becomes gradually weaker, so that finally there is no circulation whatever. The dorsal vessel of Insects would then be the mere rucljment of the heart of the Mollusca and Crustacea." I will add,. that twenty-five years ago, in my !list. Nat. des Crust. et des Inscctes, I rectified the error ofRresel respecting the nervous cord of the spinal marrow, which had been taken for a vessel. (1) See general observations on the family of the Macroura. (2} These observations are extracted from the Le5;wns d'.B.natomie Comparie of Baron Cuvier. For other details and particular facts see the Memoir of Messrs Audouin and M. Edwards, loc. cit. |
