The Dawn of Reason | Page 7

edge of the mantle)--primitive eyes, it is true, yet
amply sufficient for the needs of a domestic, non-travelling, home body
like the oyster.
In most of the worms the eyes are simple ocelli--spots of pigment
supplied with nerves. These eyes can discriminate between light and
darkness, which is all that is required of them; but in the Alciope, a
small sea-worm, these organs are brought to a high degree of perfection.
This worm is exceedingly transparent, so that when observing it, it is
difficult to make out more than its large orange eyes and the violet
segmental organs of each ring. It looks like an animated string of violet
disks surmounted by a pair of orange-colored eyeglasses. The eye of
this creature is strikingly like that of a human being; it has a cornea, an
"eye-skin," a lens, vitreous humor (posterior chamber), and retina.
Another aquatic worm, Myrianida, is still more remarkable, not only on
account of its eyes, but also on account of the wonderful way in which

it reproduces its young. When seen swimming in the water it presents
the appearance of a long, many-ringed worm, which impels itself
through and by the aid of its hundreds of flat, oar-like legs. Closer
inspection reveals the startling fact that this seemingly single worm is
really a multiple worm--six or more individuals being joined together,
thus forming a living chain. This creature reproduces itself by
fissigemation; that is, when the young worms arrive at a certain age
they separate from the parent worm and begin life as individuals. These
in turn eventually become multiple worms and divide into individuals,
and so on ad infinitum. The tail worm, or that section farthest from the
head, is the oldest and is always the first to leave its comrades and take
up a separate existence. The adverb always in the above sentence is,
strictly speaking, not exactly accurate, for on one occasion I saw the
separation occur at the second head from the tail, thus producing twins.
The two sections came apart, however, in a very few seconds after their
departure from the colony. I am inclined to believe that this deviation
from the normal was due to accident; probably to manipulation. This
annelid is really "many in one" until the very moment of division; the
alimentary canal, nerves, blood-vessels, etc., extend in unbroken
continuity from the head of the parent worm to the tail of the last
section. In every fourth (sometimes fifth) ring two round, dark-colored
spots will be observed; these spots are ocelli, and some of them
eventually become the eyes of young worms. These organs even in
their embryonic state possess sight, for they have special nerves and
pigment-cells; they can differentiate between light and darkness.
The snail carries its eyes in telescopic watch-towers. This animal is, for
the most part, nocturnal in its habits, and, since prominent and
commanding view points are assigned to its organs of sight, one would
naturally expect to find a comparatively high degree of development in
them; and this supposition is correct. The eyes of the creature are in the
extreme tips of its "horns," and consist of (1) a cornea, (2) a lens, and
(3) a retina. Lubbock is rather disposed to decry the visual powers of
the snail;[10] my conclusions, drawn from personal observations, are,
however, directly the opposite. The position of the eyes at the extreme
tips of the horns naturally indicates that they subserve a very useful
purpose; otherwise they would not have attained such prominence and

such a high degree of development. Actual experimentation declares
that the garden snail can see a moving white object, such as a ball of
cotton or twine, at a distance of two feet. In my experiments I used a
pole ten feet in length, from the tip of which a white or dark ball was
suspended by a string. The ball was made to describe a pendulum-like
movement to and fro in front of the snail on a level with the tips of its
horns. Time and again I have seen a snail draw in its horns when it
perceived the white ball, to it an unknown and terror-inspiring object. I
have likewise seen it change its line of march, and proceed in another
direction, in order to avoid the mysterious white stranger dancing
athwart its pathway. Dark-colored objects are not so readily perceived;
at least, snails do not give any evidence of having seen them until they
are brought within a foot of the creatures under observation. A snail
will generally see a black ball at twelve or fourteen inches; sometimes
it will not perceive the ball, however, until it has been brought to within
six or eight inches of its eyestalks. During the season of courtship
snails easily perceive one another at