fleetness, with the quivering of their expanded
wings, remarked in the tame bird, with other
characteristics of the ostrich, making her
incapable of continuous incubation, may be
referable to the peculiar tick which infests her
far-famed feather. During the heat of night
she sits upon her eggs like a good mother, to
protect them from the effects of the diminished
temperature, but during the day, urged by
hunger to search for reptiles as food, and by the
irritation of acari—

                                        She flees,
And skims along the plain with rapid speed,
And scorns alike the hunter and his steed.

As Acarus bicaudatus infests the feathers of the
ostrich, Acarus cursor occurs in the feathers of
the owl, and there is a species called Acarus
plumiger, because it is found upon feathery hairs;
pigeons, sparrows, and grouse also have species
peculiar to themselves. There are not merely
species which affect cheese, there are kinds peculiar
to flour, to figs, to prunes, to honeycombs,
and to fungi. The itch and the mange are skin
diseases, produced by acari; and certain species
of them ulcerate and canker the feet of horses
and sheep. As the ostriches carry the acari
among the sands of the desert, the water beetles
fly with them on their shields or elyters from the
drying-pools to the ponds and streams. And
travellers say among the most curious scenes
still to be seen in the wild forests of hot
countries are the flocks of plovers which hover over
the troups of elephants, debarrassing them of
their ticks, by alighting on their backs and
pecking among their hair and wool.

Strollers on commons often observe what
looks like a red powder, lying in thick cobwebs,
entangled in furze bushes. They are the cocoons
of acari, of the genus Tetranychus, of Dufour,
of which the Acarus tellerius, of Linnæus, is
the type. They live socially on plants, weaving
webs. Lime-trees are sometimes covered by
them with a clothing of silken webs, so thick
that they look as if they were clad in glazed
satin. This mite is the redoubted red spider,
one of the greatest pests of the gardens. It is
scarcely visible to the naked eye, being about the
size, not of the head of a pin, but of the point of
a pin. Its eggs appear under the microscope like
clusters of small globules. The colour of the
mite itself is sometimes yellowish, and
sometimes brown, but generally a dull red, with a
dark spot on each side of its back. It is found all
the year round in dry and hot greenhouses, and
under the bark of lime-trees in the month of
November. In the summer-time it abounds
on the under side of the leaves of limes and
kidney beans. The mites attack also the apple,
pear, plum, and peach trees. Plants infested
by them seem scorched.

The plague of mites often breaks out where it
is least expected, unaccountably and
mysteriously. Who has not been astounded by the
apparition of the book-mite (Cheyletus eruditus)
in the best regulated libraries, and the best
preserved cabinets? The book-worms have had
the honour of giving their name to men of
learning, who, in return for a nickname, have dubbed
the mite with the title " eruditus;" as if eating
and reading books were one and the same thing!
The feelers or palpi of the book-worm are sickle-
like in their form, ending in claws. A few years
ago, some Egyptian palm-leaves having been
shut up in a dark closet of a house at Lyme
Regis, swarms of acari issued from it in
thousands, spreading from the closet through the
rooms and filling the crevices of wooden chairs,
of tables, books, paintings, and cabinets of shells.
In 1856, many dead acari were found beneath
the glass of a daguerreotype ten years old, which
was affected by what is called " fogging."
Specimens of this acarus having been submitted to
the Entomological Society, it was suggested that
this mite resembled the common paste-mite
(Cheyletus eruditus). But from a long
correspondence it appeared that the picture was
mounted in a tin tray, with the plate and glass
too tightly pressed together to permit the
insertion of the edge of a penknife, and the whole
mounted in a morocco case without either paste,
glue, or cement having been used in the mounting.
The mites themselves were common enough,
but it puzzled the learned to say how they got
beneath the glass of this daguerreotype? and
whether or no they had anything to do with the
fogging?

By far the most curious apparitions of this
group of animals, are upon other animals. The
water-beetles carry the water-mites from dry to
moist ponds. The little blue titmouse as it flits
from spray to spray, continually pugnacious and
predacious, carries about mites as large as dog-
ticks (Ixodes), besides a variety of animated
specks scarcely visible to the naked eye. The
mite of the sparrows (Sarcoptes passerinus) is
distinguished by the disproportionate and
enormous size of the third pair of legs, which, when
the mite is placed upon paper, are dragged after
it like a dead weight. Why this acarus should
be thus burthened, it would be hard to say. The
instincts of the slug-mite (Philodromus limacum)
are exceedingly curious. This mite, which is
plentiful on large slugs, the black slug
especially, lives inside the slug, in the hole at the
side which leads to the lungs. This cavity is
the residence, and the skin is the promenade of
the mite. Mr. Leonard Jenyns once confined, in
a close box, a slug apparently quite free from
mites. On opening the box a day or two
afterwards, he observed, nevertheless, very many of
these parasites crawling about upon the slug,
having apparently issued from the pulmonary
cavity, lateral foramen, or air-hole. He once
saw the mites running in and out of this cavity
at pleasure. Some of them he saw go in and
never saw them come out again, although he
watched the slug narrowly for a considerable
time. But, the most singular thing in this
whole affair is, the indifference of the slugs to
the movements of the mites, for they do not
appear to suffer the least inconvenience from the
activity of the parasites, allowing them to run
in and out without betraying the slightest
symptoms of irritation. Yet the extreme