DECAPODA. 
159 
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, oi)posed 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 the other is bent underneath. The hand with the fingers con- 
stitutes our forceps properly so called. The preceding, or antepenul- 
timate joint is termed caipus. 
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 
tail J, 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 
armed internally with five bony and notched apjxmdages, Avhich com- 
pletes the trituration of the aliment. In it, in the moulting season, 
which arrives near the end of the spring, we observe two calcareous 
bodies, round on one side and flat on the other, commonly called 
crabs’ eyes, that disai^pear 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 
present 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 is a long, teiidiuous and hairy lamina at its base, 
f The hand being placed on its edge, the finger is uppermost. 
J 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 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 
bopy which extend considerably beyond it. See my Fam. Nat. du Kegne Anim., 
p. 255, et seq. 
