to live, by means of its strong legs; or
swimming by powerful strokes of its great tail, the appendages of whose
sixth joint are spread out into a broad fan-like propeller: seize
it, and it will show you that its great claws are no mean weapons
of offence; suspend a piece of carrion among its haunts, and it will
greedily devour it, tearing and crushing the flesh by means of its
multitudinous jaws.

Suppose that we had known nothing of the lobster but as an inert mass,
an organic crystal, if I may use the phrase, and that we could suddenly
see it exerting all these powers, what wonderful new ideas and new
questions would arise in our minds! The great new question would be,
"How does all this take place?" the chief new idea would be, the idea
of adaptation to purpose,--the notion, that the constituents of animal
bodies are not mere unconnected parts, but organs working together to
an end. Let us consider the tail of the lobster again from this point of
view. Morphology has taught us that it is a series of segments composed
of homologous parts, which undergo various modifications--beneath and
through which a common plan of formation is discernible. But if I look
at the same part physiologically, I see that it is a most beautifully
constructed organ of locomotion, by means of which the animal can
swiftly propel itself either backwards or forwards.

But how is this remarkable propulsive machine made to perform its
functions? If I were suddenly to kill one of these animals and to take
out all the soft parts, I should find the shell to be perfectly
inert, to have no more power of moving itself than is possessed by
the machinery of a mill when disconnected from its steam-engine or
water-wheel. But if I were to open it, and take out the viscera only,
leaving the white flesh, I should perceive that the lobster could bend
and extend its tail as well as before. If I were to cut off the tail, I
should cease to find any spontaneous motion in it; but on pinching any
portion of the flesh, I should observe that it underwent a very
curious change--each fibre becoming shorter and thicker. By this act of
contraction, as it is termed, the parts to which the ends of the
fibre are attached are, of course, approximated; and according to the
relations of their points of attachment to the centres of motions of the
different rings, the bending or the extension of the tail results. Close
observation of the newly-opened lobster would soon show tha