f;;KABs.l 



MUSEUM OF ANIMATED NATURE. 



299 



the blow of the tail which is made towards the 

 thorax, the lobster makes a backward progression, 

 and such is the vigour displayed, that by a single 

 sweep of the tail the lobster will dart back instan- 

 taneously to a distance of eighteen or twenty feet. 



In the Crustacea generally the digestive organs 

 are simple. In the lobster the gullet leads directly 

 to the stomach, which is of considerable size : its 

 pyloric portion is supported by strong calcareous 

 pieces, and is further furnished with three hard 

 grinding teeth, moved by powerful muscles, the 

 whole constituting an efficient apparatus for bruis- 

 ing. This apparatus is popularly known as "the 

 lady in the lobster." The alimentary canal is very 

 simple. The liver consists of two large masses 

 enclosing the pylorus, and is composed of agglome- 

 rated clusters of minute sacculi. 



We may here notice the organs of respiration. 

 Connectea with the base of the jaw-feet and of the 

 true feet, is a series of pyramidal tufts, consisting 

 each of a stem covered with vascular filaments. 

 These tufts or gills are shrouded beneath the cara- 

 pace on each side, and fill a sort of shallow chamber 

 lined with a fine membrane. Each chamber freely 

 admits the water by a wide fissure, while an orifice 

 near the mouth permits its egress ; this latter orifice 

 IS closed by a semi-membranous flap (flabellura) 

 continued from the second of the jaw-feet, and so 

 arranged that every motion of the jaw-feet tends to 

 create a circulation of the water imbibed. The 

 movements of the true limbs also add to this circu- 

 lation, and maintain a due current over the branchial 

 surfaces. The stems of the branchial plumes en- 

 close each an artery and a vein. 



With respect to the circulation, we find a heart of 

 an oval shape below the plate of the thorax near its 

 margin ; it consists of a single cavity with strong 

 muscular walls, and gives off several main arteries, 

 which ramify over different parts. Of these main 

 trunks one goes to the stomach, antennae, eyes, and 

 mouth, another is ramified over the lobes of the 

 liver ; a posterior vessel supplies the great muscles 

 of the tail, while a thoracic vessel, directed down- 

 wards, sends a branch anteriorly, supplying the 

 limbs, jaw-feet, and the branchiae, and another 

 branch posteriorly supplying the false limbs. The 

 blood returns from every part by a system of veins, 

 Which merge into a series of extensive but very 

 shallow reservoirs along the doreal region. The 

 largest occupies the thoracic part, and communi- 

 cates with the heart by several short trunks, guarded 

 at their entrance by valves. The blood poured into 

 the heart is of two kinds, viz., purely venous, and 

 renovated or arterial blood from the branchiae ; 

 hence the blood sent through the arteries of the 

 system generally is of a mixed character. 



It must be observed, however, that Milne Edwards 

 and .\udouin regard the heart as purely systemic, 

 and the reservoirs as the sole recipients of the venous 

 blood, which, without passing through the heart, is 

 transmitted at once to the branchiae, and thence 

 returned purified to the heart by a scries of vessels. 

 It is, however, fully established that though the 

 venous reservoirs send a portion of their blood to 

 the branchiie for renovation, they also send a portion 

 through four valvular orifices to the heart, the valves 

 being so constructed as to prevent its reflux during 

 the action of the latter. The nervous system in the 

 lobster, as in the other Crustacea, is ganglionic. 

 We have already alluded to the different degrees of 

 ganglionic centralization exhibited by the crusta- 

 ceous groups in accordance with their development 

 of external organization. In the crab, for example, 

 the abdominal and thoracic ganglia become com- 

 pacted into one great central mass, from which 

 nerves radiate to the limbs and various organs. 

 This increase of centralization is not only exhibited 

 by the progressive series of forms as they ascend 

 the scale of development, but by the individuals of 

 the highest grade as they advance from an imma- 

 ture to a perfect condition. For example, in the 

 river crayfish (Astacus fluviatilis), there are at first 

 eleven distinct pairs of ganglia : in a short time the 

 first six pairs unite, forming six single masses; 

 afterwards the four anterior ganglia consolidate 

 into one mass, and the fifth and sixth unite to form 

 another mass, while the other pairs continue dis- 

 tinct. It has been suspected that in insects the 

 nerves are of two kinds, viz., nerves of motion and 

 nerves of sensation ; and this condition of the ner- 

 vous system has been found by Mr. Newport to 

 obtain in the Crustacea. Yet we need not thence 

 infer any high degree of susceptibility, for there is 

 •till no brain, unless, indeed, we give this term to the 

 oesophageal ganglia, which, no doubt, they merit to 

 a certain extent. Yet we may spare half our pity 

 for crabs, lobsters, and shrimps while boiling, and 

 bestow that half upon the over-worked horse, the 

 ill-used dog, or the suffering of our own species. 



There are certain circumstances connected with 



the growth of the Crustacea which we must not here 



omit to notice. Imprisoned within their armour, 



the necessity of frequent changes of it, in order that 



Vol. II. 



the body may develope in size, is imperative ; for 

 the plates of mail, when once formed, remain unal- 

 tered, and cannot be increased by subsequent addi- 

 tions. Strange to say, however, it is not only the 

 shelly plates of these animals which are changed, 

 but also the covering of the eyes, the lining mem- 

 brane of the stomach, the teeth connected with it, 

 and also the calcareo-tendinous expansions to which 

 the muscles of the claws are attached. Released 

 from its hard encasement, the soft body suddenly 

 pushes forth its growth, and shortly acquires a new 

 coat of armour, to be again cast off at the due 

 period. 



Reaumur, who watched the process of exuviation 

 in the river crayfish (Astacus fluviatilis), describes 

 it as attended with many efforts and much struggling. 

 " A few days previous to the commencement of the 

 operation (early in autumn) the creature abstains 

 from all solid nourishment ; the carapace and ab- 

 dominal segments will be then found to offer less 

 than the usual resistance to the pressure of the 

 finger. Shortly afterwards the crayfish appears rest- 

 less, and rubs its legs against each other; it then 

 throws itself on its back, agitates and distends its 

 whole body, by which the membrane joining the 

 carapace to the abdomen is burst, and that great 

 dorsal plate is raised. Some degree of rest follows 

 these first struggles, but after a short time the ani- 

 mal again puts all its organs in motion ; the cara- 

 pace is seen to rise gradually from the legs beneath, 

 and in less than half an hour the animal has ex- 

 tricated itself from this portion of its slough. By 

 retracting its head, the antennae, eyes, and legs are 

 withdrawn as Irom a case, and the extrication of 

 the last being the most difficult and complicated 

 operation, is attended with so much pain, that the 

 effort sometimes occasions the loss of one or more 

 of these organs. The hinder parts are withdrawn 

 with less difficulty ; the head is conducted below 

 the carapace, and the abdominal plates are thrown 

 off by a forward motion, attended by a brisk and 

 distensive action. The creature is now seen di- 

 vested of all its incumbrances, and the case is left 

 unbroken, as if no struggle had ever taken place 

 within it." 



To this account we may add. as was found by 

 Professor Jones, that the segments of the chelae, but 

 not of the ordinary legs, are split in the neighbour- 

 hood of the joints, and the articulating ligaments 

 ruptured ; the internal broad tendinous plates re- 

 main attached to the moveable joint of each pincer, 

 and the stomach-lining with its teeth is contained 

 within the rejected carapace. 



In the prawn, shrimp, &c., the process of exuvia- 

 tion has not been watched ; in the lobster, the cir- 

 cumstances as detailed by Mr. Couch (' Mag. Botany 

 and Zool.' vol. i., p. 171), differ from those attend- 

 ing the exuviation of the River Crayfish. The 

 lobster to the last is ravenous, and vigorous, and in- 

 stances have been known in which, enticed by the 

 bait, lobsters about to cast their slough have entered 

 into the fishermen's creels or traps, and on the men 

 commencing to handle their prize, the animal has 

 slipped away, leaving its empty husk in the grasp 

 of the astonished fisherman. " It was by a circum- 

 stance somewhat similar," says Mr. Couch, "that 

 the opportunity is afforded me of giving a minute 

 description of a very perfect case, left by the crea- 

 ture when it made its escape, for escape it did, to 

 the no small annoyance of the fisherman, who had 

 calculated on the possession of a prize of somewhat 

 above the ordinary magnitude. I cannot find that 

 any extraordinary actions or contortions have been 

 observed in the lobster when engaged in delivering 

 itself from its trammels, or that the time is pro- 

 longed, as in the case of the crayfish; and it is cer- 

 tain that when freed it possesses great activity in 

 effecting its escape. In the specimen referred to, 

 the cases of the antennae and palpi were perfect to 

 their minutest extremities ; the stalk also, and the 

 transparent covering of the eyes, were uninjured ; 

 the segments and joints of the posterior part of the 

 body with the caudal plates were all joined together, 

 but without any intervening membrane ; and the 

 inferior parts from beneath the snout, including the 

 jaws, thejaw-feet, the chelae and legs, with the sternal 

 (breast) plate, oesophagus, and internal coat of the 

 stomach, formed one connected portion, with no fur- 

 ther separation than arose from the absence of every 

 portion of membrane." The manner in which the 

 animal escaped was not to be mistaken. " Through 

 the middle of the carapace ran a line as straight as 

 if it had been cut with a knife, and evidently formed 

 by a natural process of separation, for it even pro- 

 ceeded through the centre of the snout, to the ter- 

 minal pointed process at the root which turned 

 off to the right side, so that the least effort by the 

 animal was sufficient to afford it a passage." 



In the common crab, according to the same ob- 

 server, the exuviation takes place by a separation 

 of the dorsal from the under part of the carapace, 

 the animal lying on its back during the process. 

 Previously to this event, in the crab, and, as it would 



appear, also in the lobster, the fleshy contents of 

 the limb-cases, and especially of the great chelae, 

 shrink very considerably, wasting away to mere ru- 

 diments ; were it not so, the flesh of the chela; could 

 not be extricated, for it does not appear that the 

 claw-cases of the crab and lobster are fractured. 

 "The newly extricated crab, not unlike a lump of 

 dough enclosed in a membrane, has at first strength 

 enough only to enable it to crawl to a place of 

 safety, some hole or fissure. There it absorbs as 

 much fluid as will distend its organs, and their com- 

 mon covering, now as flexible as velvet, to the full 

 extent of their capacity, by which means the depo- 

 sition of the calcareous crust is made according to 

 the newly acquired bulk of the animal, which is 

 proportionately the most increased in the youngest 

 individuals. 



In the earlier stages of life the exuviation and 

 sudden pushing forward of growth occur several 

 times in the course of the year, but at more and 

 more distant intervals as the animal verges towards 

 maturity. When the full size is attained, the shell 

 is most probably never cast off and renewed. We 

 have ourselves examined a large Norway lobster, in 

 a living state, the carapace of which formed a bed 

 upon which a multitude of full-grown mussels were 

 firmly attached in close array, presenting a curious 

 picture. Mr. Couch has found oysters two inches 

 and a half in diameter adherent to the carapace of 

 living crabs ; and many specimens of crabs with 

 oysters firmly agglutinated to their carapace are to 

 be seen in the British Museum. 



There is another curious fact in the history of the 

 Crustacea, which we must not omit to notice, namely 

 the power they possess of reproducing their limbs 

 when lost by accident. The loss of a leg seems to 

 be of little importance ; nay, when suddenly alarmed 

 a lobster will frequently throw off its claws with a 

 violent jerk, and indeed, when a limb is injured, the 

 animal generally breaks it off, at the joint second 

 to its junction with the trunk, where the growth of 

 a new limb the most speedily takes place. No pain 

 appears to attend this strange operation ; the wound 

 1 becomes covered with a delicate pellicle, and a new 

 claw is in due time produced. It remains, however, 

 unprotected by a hard shell until the next general 

 moult, and seldom or never acquires the size of the 

 corresponding claw, although it is perfect in all its 

 parts. 



It has been asserted by many physiologists, and 

 among them by Cavolini, that the Decapod Crus- 

 tacea undergo several metamorphoses, after exclu- 

 sion from the egg before obtaining their permanent 

 figure. Mr. Thompson in the 'Philosophical Trans- 

 actions ' describes the changes in the common crab, 

 of which, according to him, the newly hatched 

 young differs so much from the adult as to have 

 been placed in a very distinct group of crustaceans, 

 and described under the name of Zoea pelagica.. 

 The question, however, is by no means set at rest ; 

 Rathke, who has most elaborately traced the deve 

 lopment of the crayfish, asserts that the Decapods, as 

 far as he has examined their habits and economy, do 

 not undergo the changes described by Mr. Thompson 

 in the case of the crab, adding that " at the end of 

 their existence in the egg, they have exactly the 

 same aspect, and are as fully developed (except as 

 to size) as the full grown individuals " (' Ann. Nat. 

 Hist.' 1837.) Mr. Westwood has dissected the eggs 

 of the land-crab of the West Indies, and also denies 

 the fact of any metamorphosis in that species. (See 

 ' Phil. Trans." 1835.) 



We may now turn to our pictorial specimens illus- 

 trative of the general structure of the Crustacea. 

 Fig. 3094 represents the Carcinus maenas, a species 

 of crab common on our coasts, with the upper por- 

 tion of the carapace removed to show the arrange- 

 ment of the internal organs, a, a, a, a, the sto- 

 mach ; b, b, parts for a special purpose ; c, the 

 heart; d, d, the branchiae ; e,_f,f, the liver. 



Fig. 3095 represents the river crayfish, Astacus 

 fluviatilis, similarly laid open, a, h, and c, denote 

 the same parts as in Fig. 3094 ; d, d, d, d, the liver ; 

 e, the branchiae ; /,/, muscles of the mandibles. 



Fig. 3096 is the upper surface of the carapace of 

 Carcinus maenas ; «, b, andc, are regions correspond- 

 ing to the parts marked by the same letters in Fig. 

 3094 ; d, the posterior hepatic region ; e, e, the 

 branchial regions ; f, f, the anterior hepatic re- 

 gions. 



Fig. 3097, the carapace of Astacus fluviatilis. 

 The regions into which it is artificially divided are 

 marked by the same letters as in Fig. 3096. 



Fig. 3098, the under surface of the female crab, 

 with the tail extended ; a, b, c, d, e, sternal pieces ; 

 f, g, h, i, latero-sternal pieces ; k, k, orifices ; I, I, I, 

 abdominal appendages, or false feet. 



The detached figure (a) represents one of the false 

 feet removed. 



Fig. 3099, a view of the under surface of the male. 

 The detached figure (a) shows one of the false 

 feet. 



Fig. 3100 represents the jaw-feet of Thelphusa 



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