DECAPODA. 



all of a different form, are applied to the mouth, and divided into two 

 branches, the exterior of which resembles a small antenna, formed of 

 a pedicle, and a setaceous and pluri-articulate stem it has been com- 

 pared to a whip, palpus jlagelliformis *. The two anterior feet, and 

 sometimes the two or four following ones, are in the form of claws. 

 The penultimate joint is dilated, compressed, and in the form of a 

 hand ; its inferior extremity is lengthened into a conical point, repre- 

 senting a sort of finger, opposed to another formed by the last joint, or 

 the tarsus proper. This onef is moveable, and has received the name 

 of thumb -pollex ; the other is fixed, and considered as the index 

 index. These two fingers are also called mordaces. The last is 

 sometimes very short, and has the form of a simple tooth ; in this 

 case tin- other is bent underneath. The hand with the fingers con- 

 stitutes our forceps properly so called. The preceding, or antepenul- 

 timate joint is termed carpus. 



The respective proportions and the direction of the organs of 

 locomotion are such, that these animals can walk sideways or back- 

 wards. 



With the exception of the rectum, which opens at the end of the 

 tailj, all the viscera are contained in the thorax, so that this portion 

 of the body represents the thorax and the greater part of the abdomen 

 of insects. The stomach, supported by a cartilaginous skeleton, is 

 in i ued internally with five bony and notched appendages, which com- 

 pletes the tritunition of the aliment. In it, in the moulting season, 

 whirl i arrives near the end of the spring, we observe two calcareous 

 bodies, round on one side and flat on the other, commonly called 

 crabs 9 eyes, that disappear after the change is completed, thereby 

 inducing us to believe that they furnish the material for the renewal 

 of the shell. The liver consists of two large clusters of blind vessels, 

 filled with a bilious humour, which they pour into the intestine, near 

 the pylorus. The alimentary canal is short and straight. The flanks 

 nt a range of holes situated immediately at the insertion of the 

 branchiae, but which can only be seen by removing those organs. The 

 under shell, viewed internally, at least in several large species exhi- 



* There it a long, tendinous and hairy lamina at its base. 



|- Tlu h;m.l in ing placed on 10 finger is uppermost. 



; This suit of segments which, in the Crustacea of the first orders, imme- 

 diately succeed those to which the five last pairs of feet are attached, compose what 

 I have UTuu-'l the posl-abihincn. The appellation of tail usually affixed to it, and 

 \\lmh, in onU-r to accommodate ourselves to common parlance, we have retained 

 Is very improper ; it can only apply to the posterior terminal appendages of the 

 bopy which extend considerably beyond it. See my Fam. Nat, du Regue Anim., 

 p. 265, et seq. 



