that, wonderful pearly play of light which is so
indescribably lovely in these creatures. Many
other fishes have these specula within their
scales, but none are so brilliant as those of the
gold and silver fish.

When the microscopist examined the blood
on that murderer's knife, what did he see? An
infinite number of small round bodies of a clear
yellowish colour, called blood globules, or blood
disks, which, when, the blood is fresh and living,
are seen floating in a colourless fluid, but when
the blood is dead, or coagulated, are heaped
together like rolls of money, and quite stationary.
It is only when thus heaped together that their
rich red colour can be seen, only when the
light passes through a number of them, amassed
in heaps, that their hue is determinable. Alone,
they are simply of a light yellowish tinge, in a
mass they are a deep bright scarlet. It is these
disks which give its "blood-red" colour to
blood; for blood is pale or high coloured
according to the smaller or larger number of them
which it contains. All vertebrate blood
contains these disks, which in the mammalia are
circular, or nearly so, and slightly concave on
both surfaces, while in birds, fishes, or reptiles
they are elliptical, and flat, or slightly convex
on the surface. Men, monkeys, seals, whales,
elephants, and kangaroos have them of about
the same size; all other animals have them much
smaller—the smallest being found in the
ruminating animals. The little musk-deer of Java
has disks not more than one-fourth as large as
the human. But these are the smallest known
among the mammalia, and quite out of the ordinary
rule. Oxen have them about three-fourths,
and sheep little more than one-half, the human
average. Speaking broadly, fish and birds have
them nearly equal in size, but of a more elongated
ellipse in birds than in fishes; compared
to the human blood disks they average the same
diameter, but are rather more than half as long
again in length. The largest of all are found
in reptiles; especially in the naked-skinned
frogs and newts. A large American species—
the Sirena lacertina—has them the extraordinary
size of 1-400th of an inch long by 1-800th
broad, or about eight times the size of those of
man. Our own common newts, though
possessing the largest known among us, are not
above half the size of the tremendous fellow's
just quoted.

One of the most interesting microscopic
experiments is the circulation in the foot of a
living frog. It is an experiment easy to be made,
owing to the extreme fineness and tenuity of the
membrane which connects the toes; and is
perfectly satisfactory in all its aspects excepting
perhaps to the frog himself. We will give it
in Mr. Gosse's own words:

"There is an area of clear colourless tissue filling
the field, marked all over with delicate angular
lines, something like scales; this is the tesselated
epithalium of the surface. Our attention is caught
by a number of black spots, often taking fantastic
forms, but generally somewhat star-like; these are
pigment cells, on which the colour of the animal's
skin is dependent; but the most prominent feature
is the blood. Wide rivers, with tortuous course
roll across the area, with many smaller streams,
meandering among them, some pursuing an independent
course below the layer, and others branching
out of them, or joining them at different angles. The
larger rivers are of a deep orange-red hue, the smaller
faintly tinged with reddish-yellow. In some of
these channels the stream rolls with a majestic
evenness, in others it shoots along with headlong
impetuosity; and in some it is almost, or even quite,
stagnant. By looking with a steady gaze we see
that in all cases the stream is made up of a multitude
of thin reddish disks, of exactly the same
dimensions and appearance as those we saw just now
in the frog's blood, only that here, being in motion,
we see very distinctly, as they are rolled over each
other, that they are disks and not spherules, for they
forcibly remind us of counters, such as are used for
play, supposing they were made out of pale red
glass."

Blood disks are not always red coloured. In
some invertebrate animals they are quite pale
and hueless; indeed, scarcely to be called blood
disks at all, save by analogy, as belonging to the
fluid evidently serving to keep up the life of the
creature. We are obliged to content ourselves
with analogy in many other things connected
with the lower organisms, and call that a heart,
those lungs, this a brain, and yonder a nerve,
which are as unlike their antitypes in humanity
as a cuttlefish is unlike a man.

The microscope shows us some very pretty
facts connected with the cuttlefish, and chiefly
about his bone, or shell. In the first place,
then, this bone, or shell, does not enclose
the animal, as is the normal condition, of shells
and their fishes, but is enclosed by it, "being
contained within a cavity in the substance
of the fleshy mantle." Cut the mantle and
the shell drops out. The cuttlefish is a rapid
swimmer in the open sea; wherefore it needs a
shell at once light and strong, buoyant and
protective. A solid limestone shell would sink it
to the bottom like a stone. Accordingly we
find this bone, or shell, to be not only light, but
an actual float both in shape and substance. It
swims like a cork when thrown on the water.
The microscope shows us why. Under a high
power, a small cube cut out of the "pounce"
reveals itself to us as a collection of the most
wonderfully beautiful stalactites ranged in
stages—inconceivably thin crystal laminæ
grouped in columns and edgeway plates,
supported on corrugated limestone floors. It is a
fairy cavern, of stalactites ranged one upon the
other in infinite succession, and of bewildering
beauty of form and colour; and as all the
interstices of this most lovely dome of crystal
columns are filled with air, we have thus a
combination of strength and lightness as wonderful as
the result is beautiful. The microscope is never
so bewitching as when it shows us the minute
geometry of Nature. Her living mechanism is
beautiful too, and strangely prophetic of the
mechanical contrivances of man. Take the
periwinkle: would you expect to find a mower,
an Irish reaper, or a patent reaping-machine in