a young frog before it has disengaged itself from the membranes that envelop it in its first stage of life.

TENIA, in zoology; a genus of animals belonging to the class of vermes, and order of intestina. The body is long, depressed, and jointed like a chain, and contains a mouth and viscera in each joint. According to Gmelin, there are 92 species; all which inhabit the intestines of various animals, particularly of quadrupeds.

Seven species of tenia are peculiar to man. 1. The tief-cerealis, which is inclosed in a vesicle, broad in the fore-part, and pointed in the hinder part, inhabits the liver, the placenta uterina, and the falc which contains the superfluous fluid of droppings. 2. The celluloïs, which is inclosed in a cartilaginous vesicle, inhabits the cellular substance of the muscles; is about an inch long, half an inch broad, and one-fourth of an inch thick, and is very tenacious of life. 3. The dentata, has a pointed head; the large joints are streaked transversely, and the small joints are all dilated; the oculum or opening in the middle of both margins is somewhat raised. It is narrow, 10 or 12 feet long, and broad in the fore-parts; its ovaria are not visible to the naked eye; and the head underneath resembles a heart in shape. It inhabits the intestines. 4. The lata, is white, with joints very short and knotty in the middle; the oculum is solitary. It is from 18 to 120 feet long; its joints are streaked transversely; its ovaria are disposed like the petals of a rose. 5. The vulgaris, or common tape-worm, has two lateral mouths in each joint; it attaches itself so firmly to the intestines, that it can scarcely be removed by the most violent medicines; it is slender, and has the appearance of being membranaceous; it is somewhat pellucid, from 10 to 16 feet long, and about four and a half lines broad at one end. 6. The trutta, which chiefly inhabits the liver of the trout, but is also to be found in the intestines of the human species. 7. The folium, has a marginal mouth, one on each joint.

The structure and physiology of the tenia is curious, and it may be amusing as well as instructive to consider it with more attention. As the tenia is often the occasion of dif-

Vol. XVIII. Part I. opening at its extremity, which is considered to be its mouth. See Plate D1, fig. 1, 2. This opening is continued by a short duct into two canals; these canals pass round every joint of the animal's body, and convey the aliment (fig. 3.). Surrounding the opening of the mouth are placed a number of projecting radii, which are of a fibrous texture, whose direction is longitudinal. These radii appear to serve the purpose of tentacles for fixing the orifice of the mouth, as well as that of muscles to expand the cavity of the mouth, from their being inserted along the brim of that opening: (See fig. 1.) After the rounded extremity or head has been narrowed into the neck, as is represented in fig. 2, the lower part becomes flattened, and has two small tubercles placed upon each flattened side; the tubercles are concave in the middle, and appear destined to serve the purpose of suckers for attaching the head more effectually. The internal structure of the joints composing the body of this animal is partly vascular and partly cellular; the substance itself is white, and somewhat resembles in its texture the coagulated lymph of the human blood. The alimentary canal passes along each side of the animal, forming a cross canal over the bottom of each joint, which connects the two lateral canals together. See fig. 3.

Mr Carlile, who gives the best account of the structure and economy of the tenia which we have seen, injected with a coloured fluid by a single puff with a small syringe three feet in length of these canals, in the direction from the mouth downwards. He tried the injection the contrary way, but it seemed to be slopped by valves. The alimentary canal is impervious at the extreme joint, where it terminates without any opening analogous to an anus. Each joint has a vascular joint occupying the middle part, which is composed of a longitudinal canal, from which a great number of lateral canals branch off at right angles. These canals contain a fluid like milk.

The tenia seems to be one of the simplest vascular animals in nature. The way in which it is nourished is singular; the food being taken in by the mouth, passes into the alimentary canal, and is thus made to visit in a general way the different parts of the animal. As it has no excretory ducts, it would appear that the whole of its alimentary fluid is fit for nourishment; the decayed parts probably dissolve into a fluid which transudes through the skin, which is extremely porous.

This animal has nothing resembling a brain or nerves, and seems to have no organs of sense but that of touch. It is most probably propagated by ova, which may easily pass along the circulating vessels of other animals. We cannot otherwise explain the phenomena of worms being found in the eggs of fowls, and in the intestines of a fetus before birth, except by supposing their ova to have passed through the circulating vessels of the mother, and by this means been conveyed to the fetus.

The chance of an ovum being placed in a situation where it will be hatched, and the young find convenient subsistence, must be very small; hence the necessity for their being very prolific. If they had the same powers of being prolific which they now have, and their ova were afterwards very readily hatched, then the multiplication of these animals would be immense, and become a nuisance to the other parts of the creation.

Another mode of increase allowed to tenia (if we may call it increase) is by an addition to the number of their joints. If we consider the individual joints as distinct beings, it is so; and when we reflect upon the power of generation given to each joint, it makes this conjecture the more probable. We can hardly suppose that an ovum of a tenia, which at its full growth is 30 feet long, and composed of 400 joints, contained a young tenia composed of this number of pieces; but we have seen young tenia not half a foot long, and not possessed of 50 joints, which fill were entire worms. We have also many reasons to believe, that when a part of this animal is broken off from the rest, it is capable of forming a head for itself, and becomes an independent being. The simple construction of the head makes its regeneration a much more easy operation than that of the tails and feet of lizards, which are composed of bones and complicated vessels; but this last operation has been proved by the experiments of Spallanzani and many other naturalists.

When intestinal worms produce a diseased state of the animal's body which they inhabit, various remedies are advised for removing them; many of which are ineffectual, and others very injurious by the violence of their operation. Draught purges seem to operate upon tenia, partly by irritating the external surface of their bodies, so as to make them quit their holds, and partly by the violent contractions produced in the intestine, which may sometimes divide the bodies of tenia, and even kill them by bruising. Mr Carlile proposes the trial of a simple remedy, which (a priori) promises to be successful; namely, small shocks of electricity passed frequently through the regions of the abdomen; the lives of the lower orders of animals seeming to be easily destroyed by such shocks of electricity as do not injure the larger and more perfect animals.

Plate D1, fig. 1, shows the head of the tenia magnified; the mouth is in the middle of the circular plane, where the body becomes flattened and broad; there are two hollow tubercles represented by the dark shaded spots. Fig. 2, is the same head, of its natural size, and which belonged to a tenia 20 feet in length. Fig. 3, shows the alimentary canals, in a portion of the same tenia, of their natural size. The dark shaded undulating lines are the alimentary canals, which are seen to their full extent in this portion of the worm. Fig. 4, shows the middle system of vessels, in two joints, which are represented by the dark lines. Fig. 5, shows two joints, from one side of which a slip was torn down to show the vessels underneath, and also the direction of the fibres in the slip, which are accumulated into little fasciculi like muscular fibres. Fig. 6, exhibits three joints, having the ducts leading from the lateral ocula injected; the dark transverse lines leading from each oculum show the size, direction, and extent of these ducts. Fig. 7, shows the edge of two joints turned forwards, and the appearance of the ocula in this point of view. Fig. 8, represents the whole of these canals in their relative situations.

For a more complete account of the tenia, we must refer to Mr Carlile's ingenious paper in the Linnaean Transactions.

TAFETY or TAFFETA, in commerce, a fine smooth silk-like stuff, remarkably glossy. There are taffeties of all colours, some plain, and others striped with gold, silver, &c., others chequered, others flowered, &c., according to the fancy of the workmen.