225 



CRUSTACEA. 



CRUSTACEA. 



226 



each of the six openings is closed by a valvular apparatus, which 

 prevents the regurgitatiou of the blood. 



" The first of the three anterior vessels is situated in the median 

 line, and is distributed to the eyes, in cousequence of which we have 

 entitled it the ophthalmic artery. Lodged within the substance of 

 the general teguinentary membrane, it continues its course without 

 undergoing any subdivision along the median line through the whole 

 length of the thorax, until, arrived opposite the eyes, it subdivides 

 and terminates in two branches, which penetrate the ocular peduncles. 

 On the two sides are the two antennary arteries. They run obliquely 

 towards the antennae, sending off numerous branches to the teguinen- 

 tary membrane, in which they are at first lodged ; they then plunge 

 more deeply, sending branches to the stomach and its muscles, and to 

 the organs of generation, between which they insinuate themselves 

 by following the folds of the same membrane which parts them. 

 Lastly, each of these vessels subdivides into two branches, one of 

 which proceeds to the internal and the other to the external antenna. 



" Two hepatic arteries arise from the fore part of the inferior sur- 

 face of the heart, and penetrate the liver, there to be ramified ; but 

 they are only found double and distinct from one another so long as 

 the liver ia met with divided into two lobes, aa it is in the crawfish 

 and lobster. 



" From the posterior part of the same surface of the heart there 

 proceeds a large trunk, which, from its importance, might be com- 

 pared with the aorta. This is unquestionably the vessel which many 

 authors have spoken of as a great vena cava ; we have entitled it the 

 sternal artery. It bends forward, giving origin to two abdominal 

 arteries, dips into the sternal canal, distributing branches to the 

 different thoracic rings, as also to the first five cephalic rings, which 

 it passes over in its course. Meeting with the oesophagus, it bifur- 

 cates, but still sends branches to the mandibles and the whole of the 

 anterior and inferior parts of the head. 



" The bulb presented by the sternal artery at its origin, in the 

 Moeroura, is the part which Willis characterised as auricle of the 

 heart. AB concerns the two abdominal arteries, which may be distin- 

 guished into superior and inferior, and which arise from the kind of 

 cross which it forms almost immediately after its exit, they are in 

 precise relationship in point of size with the magnitude and import- 

 ance of the abdomen itself. In the Brachynra they^re mere slender 

 twigs ; in the Macroura, on the contrary, they are capacious stems, 

 and the inferior of the two sends branches to the two posterior pairs 

 of thoracic extremities. 



" The disposition of the first three vessels is the same in the Stoma- 

 poda aa in the preceding species ; but the great vessel which represents 

 the heart being extended through the whole length of the body, sup- 

 plies immediately other arterial branches in pairs, and in number 

 equal to those of the rings. 



" The blood returns from the different parts of the body by canals, 

 or rather vacuities, among the tissues (for they have no very evident 

 appropriate parietes), which terminate in the venous sinuses situated 

 close to the branchiae. 



" In the short-tailed Decapoda we find no more than a double series 

 of these sinuses included within the cells of the planes above the 

 articulation of the extremities. They communicate with one another, 

 and they appear to have no parieties other than laminae of cellular 

 membrane, of extreme tenuity, which cover the neighbouring parts. 

 Each of them, nevertheless, receives several venous conduits, and 

 gives origin at its superior and external part to a vessel, which, tra- 

 '>g the walls of the planes at the base of the branchiae, conducts 

 the blood to the latter organs. This is the external or afferent vessel 

 of the branchiae. 



" \Ve find the same lateral venous sinuses in the Macroura ; but 

 instead of communicating with one another athwart the thoracic 

 septa, as is the case in the l]r>-li */" -'. they all empty themselves into 

 a great median vessel, which is itself a venous sinus, and occupies the 

 sternal canal. In the Stfuilta this sinus is almost the only vessel which 

 serves as a reservoir to the venous Mood. 



" The blood, after being arterialised in its passage Uirough the 

 capillaries of the branchiae, is poured into the efferent vessel which 

 runs along the internal surface of each branchia. It enters the thora- 

 cic cells in the same manner as the afferent vessel passed out from 

 them, bends upwardly under the vault of the flanks, and thus takes 

 iU course towards the heart. It is to this portion of the canal that 

 we have given the name of brauchiocardiac vessel." 



The anatomical accuracy of the above description is generally 

 admitted; but the physiological deductions of M. Lund ilitl'ur from 

 those of Messrs. Audouin and Milne-Edwards. He regards the heart 

 tined to propel, not only the pure blood from 'the gills, but also 

 mixture of venous blood which enters the cavity of the heart by 

 four orifices, seated on its dorso-lateral aspects, and distinct from 

 those in which the branchial veins terminate. The French anatomists 

 have objected that these orifices described by Lund are" closed by a 

 nii-uiljrane ; but we find them plainly shown, and provided with the 

 v ilvular apparatus fur preventing a reflux of the blood, in a prepara- 

 N'o. 898 a.) added by Mr. Owen to the Hunterian Series illus- 

 trating the same subject in the Museum of the College of Surgeons. 

 .I'lhn Hunt. T Imd long ago arrived at the same conclusions as to the 

 mixed condition of the blood which is scut from the heart, and iu a 



XAT. HIST. DIV. VOL. II. 



series of elaborate researches on the circulation in the Crustacea 

 and Insects, first discovered the diffused state of the venous blood in 

 extensive and irregular venous sinuses ; the general disposition of 

 which, in the lobster, is well displayed in the four beautiful plates 

 (15, 16, 17, and 18) illustrative of John Hunter's account of the circu- 

 lating system of the lobster, in the ' Catalogue of the Physiological 

 Collection,' vol. ii. 



With regard to the circulation in the Amphipoda, Mr. Spence Bate 

 has pointed out to us that there appear to be no vessels, and that the 

 fluid circulates between the muscular structure. 



The vascular system just described is regarded by most authors as 

 a true sanguiferous system, but Professor Agassiz has stated his rea- 

 sons for believing that the fluid which circulates is not blood but 

 chyle, and that this system must be regarded as chyliferous. (' Ann. 

 Nat. Hist.,' 1851.) 



The respiration of the Crustacea is carried on generally by means 

 of branchiae. We say generally, because there are some forms where 

 no special organs have been detected, and where it is presumed that, 

 oxygen is obtained from the water through the medium of the exter- 

 nal tegument. But where, as in the great mass of these animals, 

 branchial respiration is present, the variety in form and disposition of 

 the apparatus, and in some cases the complexity of it, are very great. 

 Thus, in the Bnmchiopoda the lamellar form of all the thoracic extre- 

 mities and the two external appendages corresponding to the palp 

 and flabellum present membranous vesicles, flat in shape, highly vas- 

 cular and soft, whose office is to facilitate the action of the air upon 

 the blood. In the Amphipoda and Lcemodipoda we begin to perceive 

 a gradual departure from this type. In the Lcemodipoda the vesicu- 

 lar bodies produced by the flabelliform appendage of a certain number 

 of pairs of the thoracic extremities, only perform the functions of 

 branchiae ; and in the Isopoda the locomotive extremities cease to act 

 as respiratory organs, the first five pairs of abdominal extremities 

 being exclusively devoted to those duties. The Staniapuda, which in 

 some cases are without determinate respiratory organs, in others pre- 

 sent an organisation analogous to that of the Decapodous embryo, and 

 again in the Squillie and Thysanupoda exhibit a highly-complicated 

 structure of branchiae, which, though superior even to the highest 

 type in complexity, still fall short of the perfection manifested in 

 that type, inasmuch aa the branchiae float in the water unprotected 

 by any envelope. 



M. Milne-Edwards thus reviews the respiratory apparatus in its 

 state of greatest complexity, commencing with it in the embryo, and 

 following it in its progressive development. It should however be 

 recollected that the larvie of Antaeus Jiumatilis undergo no metanioB- 

 phoeis, and can hardly be regarded as typical of the Cnutacea : 



" In the earliest periods of embryotic life of the common Astacus 

 fluriatilii we discover no trace of brauchiie ; but at a somewhat more 

 advanced stage of the incubation, though still before the formation of 

 the heart, these organs begin to appear. They are at first small lamel- 

 lar appendices of extreme simplicity, attached above the three pairs 

 of maxillary extremities, and representing the flabelliform portions of 

 these limbs. Soon these lamellar appendages elongate and divide into 

 two halves, one internal, lamellar, and triangular, the other external, 

 small, and cylindrical ; lastly, upon the surface of this, striae are 

 observed to appear, which are the rudiments of the branchial fila- 

 ments. During this interval the thoracic extremities have become 

 developed, and above their bases other branchiae have made their 

 appearance, presenting in the beginning the form of tubercles, and 

 subsequently that of stilets, smooth and rounded on their surface, 

 but by-and-by becoming covered with a multitude of small tubercula- 

 tions, which, by their elongation, are gradually converted into branchial 

 filaments similar to the preceding. During this period of the de- 

 velopment of the branchiae, these organs are applied, like the extremi- 

 ties, to the inferior surface of the embryo ; but they subsequently 

 rise against the lateral parts of the thorax, become lodge i within a 

 cavity situated under the carapace, and thus are no longer visible 

 externally. 



" The cavity destined to protect in this manner the branchial appa- 

 ratus is neither more nor less than an internal fold of the common 

 tegumentary membrane. It shows itself first under the guise of a 

 narrow groove or furrow, which runs along the lateral parts of the 

 thorax, below the edge of the lateral piece of the carapace. This lon- 

 gitudinal furrow is not long of expanding, and becomes consolidated 

 by its superior edge with the internal surface of the carapace, which, 

 by being prolonged inferiorly, constitutes the external wall of a cavity, 

 the opening of which, situated above the base of the extremities, 

 becomes more and more contracted, and ends by being almost entirely 

 closed. The space in this way circumscribed incloses the branchiae, 

 and constitutes what is called the respiratory cavity of the Decapod 

 Crustaceans. 



" From what has just been said, it would appear that the embryo 

 of Atfacus Jluviatilia presents four principal periods with reference 

 to the state of the respiratory apparatus : 1, that which precedes the 

 appearance of this apparatus ; 2, that during which the branchiae are 

 not distinguishable from the flabelliform appendages of the extremi- 

 ties, or in which it consists of simple lamellar or stiliform processes, 

 which appear as mere processes of other organs especially dedicated to 

 locomotion or mastication ; 3, that charaoUrisud by the transformation 



