CRUSTACEA. IAr 
nature is shown most obviously in the hindmost pairs of these 
jaws, which are so little altered from ordinary legs that they 
are known as ‘‘foot-jaws” (fig. 63, 3). The last five segments 
of the thorax carry five pairs of walking-legs, hence the name 
Decapoda applied to the order. Of these legs, the first three 
pairs have their extremities converted into nipping-claws or 
“chelz,” and the first pair is much larger than the others, 
and constitutes the well-known great claws of the lobster. 
The last two pairs of legs simply terminate in pointed extremi- 
ties, and not in pincers. The segments of the abdomen, with 
the exception of the hindmost, carry each a pair of paddle-like 
appendages, which are used in swimming, and are called the 
“swimmerets” (fig. 63, 2). The last pair of swimmerets are 
attached to the last segment but one, and are very greatly ex- 
panded, so as to form a very powerful tail-fin. The last seg- 
ment of all is known as the “telson” (fig. 63, 1 2), and is not 
provided with any lateral appendages, 
The mouth in the lobster leads by a short gullet into a globu- 
lar stomach, which is furnished with a calcareous apparatus for 
grinding down the food, commonly called the “lady in the lob- 
ster.” The intestine is continued backwards from the stomach 
without convolutions, and opens by a distinct anus placed in 
front of the telson. A well-developed liver is also present. 
The heart is placed dorsally, and is filled with aerated blood 
derived from the gills, which it propels through every part of 
the body. The gills, or branchiz (fig. 63, 3), are pyramidal 
bodies attached to the bases of the legs, and placed in a kind of 
chamber formed beneath the great shield, or carapace, on each 
side of the body. They consist each of a central stem support- 
ing numerous lateral branches, and they are richly supplied 
with blood. The water which fills the gill-chambers is constantly 
renewed by the movements of the legs, and thus the gills are 
kept constantly supplied with fresh water. The nervous system 
is placed along the ventral surface of the body, and has its 
usual form. The organs of sense are the two pairs of feelers 
or antenne, the compound eyes, and two organs of hearing. 
B. Anomura.—The most familiar members of this tribe are 
the hermit-crabs (Paguride) which occur so commonly on 
every shore. They are distinguished by the fact that the abdo- 
men is quite soft, and is not protected by a chitinous crust. 
The animal, therefore, is compelled to protect the defenceless 
