On the Study of Zoology | Page 8

establish a complete body of
zoological morphology.
Again, we investigated the distribution of our type in space and in time,
and, if the like had been done with every animal, the sciences of
geographical and geological distribution would have attained their
limit.
But you will observe one remarkable circumstance, that, up to this
point, the question of the life of these organisms has not come under
consideration. Morphology and distribution might be studied almost as
well, if animals and plants were a peculiar kind of crystals, and
possessed none of those functions which distinguish living beings so
remarkably. But the facts of morphology and distribution have to be
accounted for, and the science, whose aim it is to account for them, is
Physiology.
Let us return to our lobster once more. If we watched the creature in its
native element, we should see it climbing actively the submerged rocks,
among which it delights 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 that all its movements are due
to the same cause--the shortening and thickening of these fleshy fibres,
which are technically called muscles.
Here, then, is a capital fact. The movements of the lobster are due to
muscular contractility. But why does a muscle contract at one time and
not at another? Why does one whole group of muscles contract when
the lobster wishes to extend his tail, and another group when he desires
to bend it? What is it originates, directs, and controls the motive
power?
Experiment, the great instrument for the ascertainment of truth in

physical science, answers this question for us. In the head of the lobster
there lies a small mass of that peculiar tissue which is known as
nervous substance. Cords of similar matter connect this brain of the
lobster, directly or indirectly, with the muscles. Now, if these
communicating cords are cut, the brain remaining entire, the power of
exerting what we call voluntary motion in the parts below the section is
destroyed; and on the other hand, if, the cords remaining entire, the
brain mass be destroyed, the same voluntary mobility is equally lost.
Whence the inevitable conclusion is, that the power of originating these
motions resides in the brain, and is propagated along the