DECAl'ODA. 17 



passage of water. Sometimesj — see Dorippe — the posterior 

 and inferior extremity of the thorax has two peculiar aper- 

 tures for that purpose. The branchiae are situated at the 

 origin of the last four foot-jaws and feet; the four anterior ones 

 have less extent. The six foot-jaws are 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 pe- 

 dicle, and a setaceous and pluri-articulate stem — it has been 

 compared to a whip, palpus flagelUformis{\). The two an- 

 terior feet, and sometimes the two or four following ones, are 

 in the form of claws. The penultimate joint is dilated, com- 

 pressed, and in the form of a liand ; its inferior extremity is 

 lengthened into a conical point, representing a sort of finger, 

 opposed to another formed by the last joint, or the tarsus 

 proper. This one(2) is movable, 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 sim- 

 ple tooth ; in this case the other is bent underneath. The 

 hand with the fingers constitutes our forceps properly so 

 called. The preceding, or antepenultimate joint is termed 

 carpus. 



The respective proportions and the direction of the organs 

 of locomotion are such, that these animals can walk sideways 

 or backwards. 



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

 of the tail(3), 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, sup- 



(1) There is a long, tendinous and hairy lamina at its base. 



(2) The hand being placed on its edge, the finger is uppermost. 



(3) This suite 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 termed the post-abdomen. The appellation of tail usually affixed to 

 it, and which, in order to accommodate ourselves to common parlance, we have 

 retained, is very improper; it can only apply to the posterior terminal appendages 

 of the body which extend considerably beyond it. See my Fam. Nat. du Regne 

 Anim., p. 255, et seq. 



Vol. III.— C 



