apex of this cone is prolonged into an exceedingly small tube, that
enters a striped spindle-like body called the striated spindle; the
entire structure is called a visual rod. Nerve-fibrils emanating from
the optic nerve enter the striated spindle at its lower extremity, and
in this way nervously energize the visual rod. There is a deposit of
pigment about the visual rod which arrests all rays of light save those
which strike the cornea parallel to the long axis of the crystalline
cone. We see from this that the visual picture formed by a crayfish's
eye must be made up of many parts; it is, in fact, a mosaic of hundreds
of little pictured sections, which, when united, form the picture as a
whole. Each visual rod receives its impression from the ray or rays of
light reflected from the object viewed which strike it in the line of
its long axis; the other rays are stopped by the layer of pigment-cells.
When the impressions of all the visual rods are added together, the sum
will be a mosaic of the object, but such a perfect one that the junction
of its many portions will be absolutely imperceptible.

The crayfish can see quite well. It has been thought that this creature
uses its sense of smell more than its sense of sight in the procurement
of its food. This is undoubtedly true where the animal is surrounded by
water that is muddy, or that is otherwise rendered opaque. The
odoriferous particles coming from the food being carried to the creature
by the water, it follows them until it arrives at this source.

It is different, however, in clear water and on land. I have seen
crayfish rush down stream after bits of meat thrown to them, thus showing
that here, at least, the sense of sight directed them. Again, I have
enticed crayfish from clear streams by slowly dragging a baited hook in
front of them. Moreover, when high and dry on land, I have seen them
follow with their eyes and bodies the tempting morsel as it waved to and
fro in the air above their heads.

The female crayfish carries her eggs beneath her tail, and, when they
have hatched out, the young find this sheltering member a safe and cosey
dwelling-place until they have grown strong enough to enter life's
struggle. At such times, the mother crayfish is quite brave, and will do
battle with any foe. With her eyestalks protruded to their utmost extent,
she vigilantly watches her enemy. Her eyes follow his movements, and her
sharp nipper is held in readiness for imme