mountainous places in the East Indies, and yield- | rendered obvious by their phosphorescent propering, by decoction from its unripe pods and inner wood, one of the kinds of catechu used in medicine as a powerful astringent, and which, from its containing much tannin, is used for tanning. The gum arabic tree, A. arabica, is another species of this division; a tree thirteen or fourteen feet high, of rather inelegant appearance, and growing in the East Indies, Arabia, and Abyssinia. The bark when wounded gives out a sap which hardens upon exposure to the air into transparent lumps, and is known in commerce as Gum Arabic. A tree called the Mezquite tree, and said to be a kind of Acacia, has lately been discovered in the north of Texas, towards Arkansas, and in the state of New Mexico, from which gum has been procured equal to that imported from the East. It exudes spontaneously in a semi-fluid state from the bark of the trunk and branches, soon becoming hard, and it may be collected in inexhaustible quantities. The wattle of Australia, A. discolor, belongs here also, the bark of which is very astringent, and an extract from it is brought to this country for the purpose of tanning. Other species of acacia have the leaves pinnate only when young, and are remarkable for the petiole or leaf-stalk being developed into the form of what is called a phyllodium when they are old. Of these about 100 species are known, most of them natives of Australia. Many are ornamental shrube, but are not useful in commerce. The flowers of a species of acacia are used by the Chinese in making that yellow which we see bears washing so well, in their silks and stuffs, and which appears with so much elegance in their paintings on paper. The flowers, before they are fully open, are exposed to a gentle heat over a fire for some time; they are then boiled with a little water till it becomes thick and yellow. To this liquor, coarsely strained, some alum and finely powdered oyster shells are added, and all well mixed together.

ties. They are surrounded by a very delicate epidermis; and on the arms, tentacles, and other parts of the body, there exist peculiar organs, which produce, when handled, a stinging sensation like that of nettles. These nettling organs, as they have been called, are generally composed of an oval capsule, containing a spirally coiled filament, which is suddenly thrown out upon the least disturbance. This has been compared to the lasso, used by the natives of South America to catch wild horses, &c. Upon this lasso-like filament a number of barbules are arranged in regular spiral rows, extending to the very extremity, and all pointing backwards, when it is projected. From this stinging property possessed by them, they have derived the name of Sea Nettle. The acalephæ possess a muscular system, a nervous system, and a distinct digestive apparatus. Their food consists of small fishes and marine animals. Their circulatory system is less distinct, but it exists, though the system is not regular, but depends upon the irregular contraction of various parts of the body. Their respiratory system is more distinct, however, as the whole body is traversed with canals lined with a delicate ciliated epithelium. Some of the acalephæ are hermaphrodite or bisexual, while others are of one sex alone. They are propagated by eggs, and according to the plan of the alternation of generations. The eggs produce a series of young which at first resemble infusoria. These become fixed and assume a polype-like form, which give birth by gemmation to a new progeny, which ultimately assumes the original form. See ALTERNATION OF GENERATIONS. They also multiply their kind by gemmation alone, little ones springing out almost ready made from the substance of their parents, chiefly from the walls of the peduncle, or from the surface of the ovaries, and closely resembling the parent animal from which they spring. A great Acalephæ (axaλn@n, a nettle). Sea Nettles. portion, if not all, of the acalephæ possess the -A class of marine invertebrate animals, of power of emitting a phosphorescent light in the which the medusa may be taken as the type. The dark-the smaller species giving out bright sparks body of the acalephæ is composed of a trans- of light, while the larger medusæ appear like parent gelatinous substance composed of poly-globes of fire. They are now generally arranged hedral cells. The quantity of solid matter in them is very small, for if we take a medusa out of the water, and lay it on a board or dry stone, it deliquesces very rapidly. An animal, weighing fifty ounces when taken out of the sea, has been found in no great length of time to leave nothing behind but a little dry cellular tissue, weighing no more than five or six grains. They are from this structure often called Jelly fishes. Their organs are arranged in ray-like processes, radiating from a common centre or a longitudinal axis, in which are lodged the digestive organs. They are elegant pellucid beings, floating on or near the surface of the water, of varied hues and diverse forms; frequently of considerable dimensions, but more often of minute size, and only

in four orders; the classification being based upon the mode of locomotion peculiar to the different tribes. The first order is that of the Discophora, or Pulmograda. The motion of these animals is effected by means of a powerful contraction of the body, by which the water contained in its hollow is expelled. By such alternate contractions and dilatations of the body they are enabled to propel themselves with tolerable rapidity. The species properly termed medus, and generally known by that name, are contained in this order. See MEDUSA. The second order is that of the Ctenophora, or Ciliograda. The motion of the animals of this order is effected by means of numerous small vibratile cilia, disposed in rows upon the sides of the body. The family of beroes

Acanthochites (axarla, a thorn; xairn, a bristle).-A genus of mollusca. See CHITONIDE. Acanthodium.-A genus of plants. See ACANTHACEÆ.

common to all poisonous snakes, has a double row of sharp curved teeth. The tail is terminated by a little spur or horny excrescence, which has given the name to the genus. There are several species. They are all of small size, are viviparous, reside on dry land, secreting themselves in rat-holes or beneath the roots of trees, and feed on small lizards, frogs, &c. One of the species found in Australia is considered to be the most venomous reptile of that country. Acanthopleura («zavba, a spine; wλsuga, the side). A genus of mollusca. See CHTONIDE.

is contained in it. See BEROE. Here belongs | also the curious genus Cestum, which consists of a very short, free, gelatinous body, which is prolonged on each side into a long riband-like appendage, having one of the sides furnished with Acanthomys (unasta, a spine; μvs, a rat). two rows of vibratile cilia. It is generally called A genus of mice. See MURIDE. the girdle of Venus, C. veneris, and is found in the Acanthophis (axavda, a thorn; opis, a snake). Mediterranean. It is highly phosphorescent, five-A genus of serpents remarkable for their venomor six feet in length, and appears, in a calm dark ous qualities. The mouth is capable of great night, like a long luminous snake, as it is seen float-extension, and besides the retractile poison fangs ing along the surface of the water. The third order is the Cirrhigrada. The body in these animals is almost membranous, oval, or circular in shape, supported by an internal, sub-cartilaginous part; and their organs of locomotion consist of numerous extensile tentacular cirrhi, pendent from the whole of the under surface. The Velella have on the upper surface of their membranous body a vertical, oblique crest, which acts like a little lateen sail. Some of the species are of a lovely blue colour, and are often met with far at sea, huddled together, young and old, in considerable masses. The Porpita are circular in shape; the membranous body is concave below, and its lower Acanthopterygii (unavba, a thorn; rigu, surface is furnished with numerous cirrhi, the a wing).—An order of bony fishes in which the external of which are provided with short cilia first dorsal fin, where there are two, or the first The P. gigantea, from the Mediterranean and portion of the fin, where there is only one, has other warmer seas, is of a beautiful blue colour, always spiny rays. In the anal fin, and generally with its tentacula purple. The P. Linneana, with in the ventral also, one of the rays is spiny likeits numerous suctorial tentacula, is described as wise. This order contains by far the greater a wonderfully beautiful animal, which is found number of the ordinary fishes, many of them useswimming, or rather floating, on the serene sur-ful to man as articles of food, and of considerable face of the Carribean sea in calm weather, and seizing its prey by suddenly extending downwards some of its arms and embracing its victims. The fourth order is the Physograda, which are characterized by their possessing one or more vessels filled with air, by means of which they keep themselves suspended in the water, and by their being furnished with more or less numerous cirrhiform tentacula. See PHYSALIA and DIPHYIDE.

Acanthacea (axava, a thorn).-An order of plants belonging to the monopetalous dicotyledones. There are many genera, and about 750 species are described, but few that are very interesting; some are mere weeds, but others are handsome greenhouse plants; and a few possess medicinal qualities, as emollients or diuretics. They are herbaceous plants, or shrubs, and abound in most tropical countries. Some of the species of the genera Justicia, Ruellia, and Aphelandra, are cultivated in cur hothouses for their showy flowers. The seeds of Acanthodium spicatum are remarkable for the beautiful spiral cells they have in their episperms or coats, and the style of Ruellia anisophylla exhibits a peculiar degree of irritability. The type of the order is ACANTHUS. which see.

Acanthocephala (axava, a spine; head). A genus of intestinal worms.

TOZOA.

value in a commercial point of view; such as the mackerel, &c. See SCOMBERIDÆ.

Acanthotheca.-A genus of intestinal worms. See ENTOZOA.

Acanthuris (~zavla, a thorn; ovęœ, a tail). — A genus of acanthopterygious fishes, remarkable for the sharp and lancet-like spines which are placed on each side of the tail (hence the name of the genus), and which when the fish is handled incautiously inflict serious wounds. There are several species, natives of the sea, of both East and West Indies, distinguished by the beauty of their colours and variety of form, and living entirely on vegetable matters, such as sea-weeds, &c. The colonists and sailors call them surgeon fishes, lancet fishes, &c.

Acanthus (navla, a thorn).-A genus of dicotyledonous plants belonging to the nat. ord. Acanthacea. The species are herbaceous, and are found in the south of Europe, Asia Minor and India. One of the species, A. spinosus, with prickly pinnate leaves, and flowers tinged with pink, is found growing on the borders of cultivated fields or gardens in Greece. This is the plant which is now considered to have given Callimachus his first idea of the Corinthian capital. Vitruvius relates that the nurse of a young girl who died at Corinth, carried her cherished pan, playthings to her tomb, and having left the basket See EN-containing them, covered with a tile, over the root of a plant, it was encompassed all round by

the leaves of the acanthus, till meeting with the | the skin. Amongst the parasitic acari one has tile they curled back in a kind of scroll. The tile constitutes the abacus, the leaves the volutes, and the basket the capital.

Acarida.—A division of the tracheary Aracknida containing the minute animals generally known as Mites, Ticks, &c. They are a numerous tribe of little creatures, some of which are free and live a wandering life, while others are fixed and live parasitic upon other animals. Those which are free have a mouth with distinct mandibles, and are what are properly called Mites. Of these there are,-1st, the true mites, Acarida, one species of which, Acaras domesticus, is found on all kinds of dry provisions, as old cheese, for instance, the powder of which consists entirely of these little animals with their eggs and excrement; also on flour, brown sugar, &c.; while another species, A. destructor, is exceedingly annoying to entomologists and zoologists, feeding upon dried insects, stuffed animals, &c. 2d, The garden mites, Trombidiida, living upon the leaves, flowers, fruit, and bark of trees. One species, common in spring, is of a blood-red colour. 3d, The spider mites, Gamasida, amongst which is the red spider of hothouses, Gamasus telarius, which, though exceedingly small, is a great pest to nurserymen, from its forming upon the leaves of plants a very fine web which causes them very much injury. 4th, The wood mites, Oribatida, which are found creeping slowly upon stones and trees amongst moss. Those which live a parasitic life have the mouth in form of a sucker, and are the Ticks. Of these there are,-1st, the true ticks, Ixodida, which are found in thick woods, attached to low plants, and are ready to fasten upon dogs, cows, horses, and other quadrupeds which approach them. They bury their suckers so deep in the skin of these animals that it is almost impossible to detach them without tearing away the skin to which they are fastened. They multiply so rapidly that oxen and horses attacked by them have been known to perish from mere exhaustion. The Ixodes ricinus, or tick of the dog, is at first very much flattened, but it soon begins to acquire a large size, and at last appears swollen out like a bladder. The I. reticulatus, or tick of the ox, is often when thus swollen out half an inch long. 2d, The plant ticks, Bdellida, which live parasitic upon plants. 3d, The water ticks, Hydrachnidæ, which live in the water and are very numerous. They vary in form and colour, and when young undergo a regular metamorphosis during their progress to maturity. The larvæ have only six legs, and when they assume the pupa state they become inactive and attach themselves to the bodies of other aquatic insects, as the Dytisci or water beetle, the Nepæ or water scorpions, &c. 4th, The harvest ticks, Leptide, one species of which, the Leptus autumnalis, well known as the harvest bug, is common in autumn in grass and herbage, from which it gets on to our bodies, and though exceedingly small, produces extreme irritation in

been found to live entirely in the skin of man, the Sarcoptes galei, producing the disease called the itch. It is very minute, scarcely visible to the

Sarcoptes galei-Itch insect.

naked eye, but when examined by the microscope is found possessed of a peculiar suctorial apparatus at the extremities of the four anterior feet, by which it is enabled to adhere to the most polished surface. Another curious microscopic animal has also lately been found inhabiting the sebaceous sacs and hair follicles of the human skin, the Demodex folliculorum. Its body is elongated, with eight short legs, and its chief residence appears to be the sebaceous follicles of the nose, where it may be recognized by a minute dark coloured speck, or raised point in the skin. This curious little animal has by some naturalists been referred to the Acarida, but by more recent zoologists it is considered to be more nearly related to the Rotifera, its parasitic habits causing it to resemble some of the numerous forms of the Crustacea.

Acasta (A sea nymph).-A genus of cirripedian crustacea. See BALANUS.

Acaules (a, priv.; and caulis, a stem). Plants which have either a very indistinct stem, or none at all; such as the Lichens, Fungi, Algæ, &c.

Accipiter. The Hawk genus.--See ACCIPITRINE.

Accipitres.-An order of birds, also called Raptatores and Rapaces. They are distinguished by having powerful hooked beaks and talons; great strength and extent of wing, adapting them for rapid flight, and a general organization suitable for preying upon other animals. They are among birds what the carnivora are amongst mammalia. The females are generally larger than the males, and they only lay a few eggs, which are hatched in an artificial nest usually built upon inaccessible rocks or high trees. Some

of these birds of prey exercise their calling during | the day, and are called diurnal birds of prey. They have the eyes directed sideways, the plumage close, and the quills strong. The young undergo no change of feather till their second autumn, being during their first period of life densely clad in short soft down. This division contains the vultures and falcons. See VULTURIDE and FALCONIDE. Others only exercise their calling during the evening, and are called nocturnal birds of prey. These have large eyes directed forwards, and their plumage is soft and downy. This division contains the owls. See STRI

is not much used, as it is readily attacked by insects; and yet the tree is in great request. It furnishes a copious supply of excellent sugar. The trunk is tapped in the spring, and it is said that as much as thirty-three lbs. of sugar are obtained from the sap which flows from a single tree. Several other species afford useful wood for turning purposes.

Acephala («, priv.; and estaλn, a head). | by its changing leaves. The wood is hard, but -A sub-class of molluscous animals, principally characterized by having a headless body, and a very large mantle which envelops the body so that there is a spacious and more or less closed cavity in which the oral and anal orifices are often concealed. Some have the body wholly asymetrical, and so enclosed in the mantle, that there are only two narrow openings. This section contains the ascidians. See TUNICATA. Others are symmetrical in form or divided into right and left sides, and provided with two shelly valves, and their mantle, which is more or less closed, contains within it two pairs of lamelliform tentacles and branchiæ. This section contains the mollusca generally known by the name of bivalve shells. See CONCHIFERA.

Acephalocysts (a, priv.; x:paλn, head; Ern, a cyst).-In various parts of the body of man and other animals, as the liver, cavity of the abdomen, &c., are often found simple sacs filled with a transparent liquid, and generally described by pathologists under the name of Hydatids. They used to be considered parasitic animals, but recent observations prove them to be the cysts of a genus of intestinal worms (Entozoa), called Echinococcus. These sacs are oval or approaching to spherical, and vary in size from a pin's head to that of a child's. They appear to increase by gemmation, developing smaller cysts between the lamina of the parent which are discharged from its inner or outer surface. They are composed of a homogeneous substance resembling albumen in properties. The number of these cysts developed in the liver, &c., is sometimes astonishing, amounting to many hundreds. In general, when they are discovered, the Echinococci have either disappeared by death and dissolution, or they have not yet been formed. From the observations very recently made, it is most probable the Echinococci which inhabit these cysts are only a particular state of existence of other entozoa, such as Tæniæ or tape worms, and that their development takes place in the manner described in ALTERNATION OF GENERATIONS.

Acherontia.-A genus of lepidopterous insects belonging to the family Sphingidæ. A species of this genus is found in this country, and from the remarkable appearance on the back of the thorax of the representation of a human skull, is called the Death's-head moth. The moth itself is from four to more than five inches in expanse of wing, and is a very handsome insect. When disturbed or handled it emits a peculiar squeaking noise. It attacks bee-hives, devouring the honey and scattering the bees. Amongst the ignorant and superstitious, it is looked upon with dread, and its appearance is considered ominous. The well armed and numerous inhabitants of the beehive too, seem to fear its approach, as though unarmed itself, when it attacks the colony, it is always successful. The larva or caterpillar, is a handsome, beautifully marked and large creature, measuring about five inches in length. It feeds upon the leaves of the potato and jessamine; changes into a chrysalis in the month of September, retiring for that purpose deep under the surface of the earth, and emerges a complete insect in the following June or July.

Achetidæ. The Cricket family.—A family of saltatorial Orthoptera, containing those insects which are familiarly known to us by the name of crickets. The French entomologists apply to those insects the name Gryllida, which English authors on the contrary apply to the grasshoppers. See GRYLLIDE. The English name cricket, and the French name cri-cri, given to those insects, is derived from the stridulous sound produced by the males, and resembling the word "cris-cris." This peculiar sound is produced by their rubbing the inner edges of the wing-covers Acer. A genus of plants belonging to the together. They are solitary animals, each innat. ord. Aceraceae. The species are numerous, dividual forming for itself a burrow in which it and widely diffused throughout the north of Eu- passes the day, coming out only in the evening rope, Asia, America, and India. Amongst the to seek for its food. At the mouth of his burrow European species are the maple, A. campestre, the male takes up his abode, and commences his and the sycamore, A. pseudo-platanus, which strong and rapid chirp in order to attract the afford wood valuable to the turner. The polished female. Some live upon animal food, others upon maple of Nepaul, A. lævigatum, is used by the vegetable matters; and children in France capnatives for building purposes. The Tartarean ture them by introducing an ant tied to the end maple of the southern provinces of Asiatic Russia, of a string, or a long straw, into their burrows, A. tartaricum, affords a hard white wood, and the which, being seized by the cricket, it is drawn Calmucs obtain from the keys or seed-vessels, out. They seem to like heat, as their burrows boiled in water, an astringent beverage, which, are constructed with a southern aspect. They mixed with milk and butter, forms a favourite are very timid, at the least alarm ceasing their article of their diet. In North America the stridulous noise, and taking refuge in their holes. sugar maple, A. saccharinum, is very abundant, The females, which are mute, are very prolific, and often reaches the height of eighty feet. In each one laying about 300 eggs towards the the autumn the woods are dyed of a crimson hue | middle of summer. The larvæ are like their