.A'CANUS, a fossil genus of fishes, from Clarks. (AgaRsiz.) ACA'IllatE, a division of A rad ida [A RACHN I nA], which compre hends the small spider-like animals popularly termed Mites (Acart), as well as Water-Mites and Ticks. Solna of these are wanderers COI land or in water ; others are fixed upon various animals, whose blood or humours they suck, and even insinuate themselves beneath the skin, and often multiply prodigiously.
These minute animals are not considered by modern naturalists to rank among insects, on account of their structure being very different, and from their having, in most cases, like spiders, eight feet, while no insect has more than six feet. Their mouths, iu some, are furnished with jawa (mandibuhe), either having piucers or clawa, but concealed in a projection of the breast-plate (sternum) in form of a lip ; in others it is in tho form of a syphon or sucker ; and in others it presents a simple cavity. M. Latreille makes four diviaiona of the Acarithe : 1, Mites (Trombidites); 2, Ticka (Riciniics); 3, Water-Mites (11gd rads ndle) ; and 4, Flesh-Worma (if icruplithira).
All the creatures now embraced in this family were included by Lin mews under his genus Acarus, and the whole of the species are popularly called Mites, or Acari. They are all very minute, some being alienist microscopical. They are very generally distributed. Some are whilst others are free. The itch is now well known to owe its exist ence to a creature of this tribe. Others live naturally in tho human skin, whilst beetles and other insects are very liable to lie attacked by them. They are found on the leaves, fruit, flowers, and bark of plants; and on all kinds of provisions, as flour, dried meat, dried cheese, and putrid animal matters.
Amongst the true Mites (Trouibiditcs, Latreille), the following com mon forms are placed: The Domestic Mite (Acarus domesticus, De Geer), is very commonly found in collectiona of insects aud stuffed birds, and is exceedingly destructive to cabinets. Camphor hail some effect in destroying this but is not powerful enough to prevent it altogether. Moistening the specimens with a weak solution of corrosive sublimate, is said to prove an effectual preventative. The species found in flour and on food is called A. tarine.
The Itch Mite (A cares Scabiei, Fabricius, &resides Galri, L) is a microscopic animal, found under the human skin in the pustules of a well-known cutaneous disease. It has a remarkable auctorial appa ratus, by means of which it secures its hold under the epidermis of the skin, into which it has the power of penetrating. This animal is most effectually destroyed by aulphur ; and indeed this is a specific for the disease which the A citrus produce's.
The Sugar Mite (Acarus saccharinitm) is found in the brown sugar of commerce. Thirty-five out of thirty-Rix apecimens examines] by
the analytical commissioners of "I'lm Lancet,' bought in the shops of London, in 1850, were found to contain these creatures.
The Bed Spider of the hot-houses is the Acarus tellarius. It is the pest of hot-houses and greenhouses. Though so mall as scarcely to be seen by the naked eye, its effect's on plants are very obvioue. These creatures live upon the juices of the plant which they attack, and also prevent the function of the leaves from being properly performed. They are best destroyed by sulphur. The mode of applying it is to sprinkle tho sulphur on the hot pipes or on plates ; afterwards, the plants should be Other species, as A. horteneis, A. holoscriceus, A. genica hew, attack various plants, and the best way of treating them is the same the above.
The Sparrow Mite (A cares passerines, Fabricius) is distinguished by the remark able size of its third pair of legs. Geoffroy called it the Bat Tick, and Latreille formerly placed it in his genus Sarcoptes.
A very interesting form of these crea tures is that first described by Dr. Simon, of Berlin, as inhabiting the sebaceous sacs and hair-follicles of the human skin.
He called it an Acarus, but Professor Owen regards it as a lower form of one of the higher divisions of A rachnida. He names it Demodex Folliculoruni. It has also been described in this country by Mr. Erasmus Wilson, under the name of Entozoon Folliculorum. It has an elongated body, with eight short legs, and is found very commonly in the sebaceous follicles of the nose. In its parasitical habit it resembles some of the lower forms of the Crustaxea, as the Cyntothoe and Bopyrus ; and, perhaps, through the Tardigrada, it has a relation with the Rotifera.
The Ticks (Rieinites, Latreille) are, some of them free, some para sitic. The latter have no eyes. They embrace the genus Ixedes, which are well known from attacking cows, horses, dogs, and even tortoises. They bury their suckers so deeply in the skin, that they frequently cannot be taken away without tearing the flesh. They deposit a prodigious quantity of eggs, which are discharged from the mouth. The genus Argas is found on pigeons and other birds. The A. Pcrsicus is the venomous bug of Miana.
The Water Mites (II ydrachnellm) live only in the water. They are often parasitic or aquatic insects. Duges has recently made some important observations on the development of these mites, in which he shows that in their earlier stages of growth they have but six legs. If this be correct, it will probably lead to the rejection of Latreille's fourth division, the Jf icrophthira, which are characterised by possessing six legs, as they are probably only earlier stages of some of the higher forms.