eat shield-like shell,
called technically the "carapace," ending in front in a sharp spine, on
either side of which are the curious compound eyes, set upon the ends of
stout movable stalks. Behind these, on the under side of the body, are
two pairs of long feelers, or antennae, followed by six pairs of jaws
folded against one another over the mouth, and five pairs of legs, the
foremost of these being the great pinchers, or claws, of the lobster.

It looks, at first, a little hopeless to attempt to find in this complex
mass a series of rings, each with its pair of appendages, such as I have
shown you in the abdomen, and yet it is not difficult to demonstrate
their existence. Strip off the legs, and you will find that each pair is
attached to a very definite segment of the under wall of the body; but
these segments, instead of being the lower parts of free rings, as in the
tail, are such parts of rings which are all solidly united and bound
together; and the like is true of the jaws, the feelers, and the eye-
stalks, every pair of which is borne upon its own special segment. Thus
the conclusion is gradually forced upon us, that the body of the lobster
is composed of as many rings as there are pairs of appendages, namely,
twenty in all, but that the six hindmost rings remain free and movable,
while the fourteen front rings become firmly soldered together, their
backs forming one continuous shield--the carapace.

Unity of plan, diversity in execution, is the lesson taught by the study
of the rings of the body, and the same instruction is given still more
emphatically by the appendages. If I examine the outermost jaw I find it
consists of three distinct portions, an inner, a middle, and an outer,
mounted upon a common stem; and if I compare this jaw with the legs
behind it, or the jaws in front of it, I find it quite easy to see, that,
in the legs, it is the part of the appendage which corresponds with the
inner division, which becomes modified into what we know familiarly as
the "leg," while the middle division disappears, and the outer division
is hidden under the carapace. Nor is it more difficult to discern that,
in the appendages of the tail, the middle division appears again and the
outer vanishes; while, on the other hand, in the foremost jaw, the so-
called mandible, the inner division only is left; and, in the same way,
the parts of the feelers and of the eye-stalks can be identified with
those of the legs and jaws.