3<H CKUSTACEA. 



(1005.) The structure of the articulations which unite the different 

 segments of the skeletons of the Articulata, and the general arrange- 

 ment of their muscular system, have already been described ; and in 

 the class before us, these parts of their economy offer no peculiarities 

 worthy of special notice. 



(1006.) Throughout all the Crustacean families the alimentary canal 

 exhibits great simplicity of arrangement, and consists of a short but 

 capacious oesophagus, a stomachal dilatation or cavity in which is con- 

 tained a singular masticatory apparatus, and a straight and simple in- 

 testinal tube, which passes in a direct line from the stomach to the last 

 segment of the abdomen, where it terminates. 



(1007.) The description of these parts as they exist in the Lobster, 

 will give the reader a sufficiently correct idea of their general disposition 

 and structure ; nor are we acquainted with any class of animals in which 

 so little variety in the conformation of this portion of the system is to 

 be met with. 



(1008.) The oesophagus is covered at its origin by the several pairs 

 of foot-jaws already alluded to, the most internal of which forms a 

 decided cutting apparatus, resembling a pair of strong shears, while the 

 rest are only instruments of prehension, or, perhaps, of sensation also. 



having been drawn out from them as the finger from a glove ; and no fissure of the 

 shell or rupture of the ligaments connecting the joints was anywhere visible in these 

 portions of the skeleton. The auditory tubercles, and the membrane stretched over 

 the orifice of the ear, occupied the same position as in the living Cray-fish. The jaws, 

 foot-jaws, and ambulatory feet retained their original connexions, with the exception 

 of the right chela, which had been thrown off before the moult began ; and the seg- 

 ments of the abdomen, false feet, and tail-fin exactly resembled those of the perfect 

 creature. Even the internal processes derived from the thoracic segments (apode- 

 matd) rather seemed to have had the flesh most carefully picked out from among 

 them, than to have been cast away from a living animal. But perhaps the most 

 curious circumstance observable was, that attached to the base of each leg was the 

 skin which had formerly covered the branchial tufts, and which, when floated in 

 water, spread out into accurate representations of those exquisitely delicate organs. 

 No fissure was perceptible in any of the articulations of the small claws ; but in the 

 chela each segment was split in the neighbourhood of the joints, and the articulating 

 ligaments ruptured. The lining membrane of the stomach was found in the thorax, 

 having the stomachal teeth connected with it : from its position, it would seem that 

 the animal had dropped it into the place where it lay, before the extrication of its 

 limbs was quite accomplished. The internal tendons were all attached to the move- 

 able joint of each pair of forceps, both in the chela and in the two anterior pairs of 

 smaller ambulatory legs. 



On examining the animal which had extricated itself from the exuviae described 

 above, the shell was found to be soft and flexible, but contained a sufficiency of cal- 

 careous matter to give it some firmness, especially in the claws. The tendons of the 

 forceps were still perfectly membranous, presenting a very decided contrast when 

 compared with the old ones affixed to the discarded shell. The stump of the lost 

 chela had not as yet begun to sprout, and the extremity was covered by a soft black 

 membrane. The jaws were quite hard and calcified, as likewise were the teeth con- 

 tained in the stomach. 



