downward (page 25, figs. a, b), and is thus well disposed for the operation of the tongue in removing the operculum, which is of an oval figure, and surrounded with a prominent margin. The microscope shows the case of the egg to be shagreened in squares, or impressed longitudinally and transversely with delicate striæ. When the larva or grub is hatched from the egg it is a small active worm, long in proportion to its thickness; but as its growth advances it becomes proportionably thicker and broader, and beset with bristles. These larvæ are very frequent in horses that have been at grass, and are in general found adhering to the white insensible tissue or coat which comes from the lining of the oesophagus, and extends over the upper part of the stomach. They make small, deep, round holes wherever they adhere to this white tissue, and sometimes so deep as to pass through it, but not through the other layers or coats of the stomach.

The larvæ usually hang in dense clusters from the lining of the stomach, and maintain their hold by means of two dark brown hooks; between these a longitudinal slit or fissure is seen, which is the mouth of the larva. When the larvæ are removed from the stomach with a sudden jerk so as not to injure them, they will, if fresh and healthy, attach themselves to any flaccid membrane, and even to the skin of the hand. For this purpose they sheath or draw back the hooks almost entirely within the skin, till the two points come close to each other; they then present them to the membrane, and keeping them parallel till it is pierced through, they expand them in a lateral direction, and afterwards, by bringing the points downwards towards themselves, they include a sufficient piece of the membrane to enable them to remain firmly fixed for any length of time as at anchor, without requiring any further exertion. The body of the larva is of a whitish red colour, and ap

pears to be composed of eleven segments, surrounded with a double row of horny bristles, a longer and a shorter series, and placed alternately: the two last segments appear to be naked or destitute of them. These spines are of a reddish colour, except the points, which are black, and are directed towards the tail or large end of the larva.

The larva, when matured, quits the stomach of the animal and falls to the ground, and finding a convenient place of retreat, undergoes its change to a chrysalis, the skin then losing its organization, and changing in colour to a reddish brown. After remaining torpid in the chrysalis state a few weeks, the superfluous moisture being removed and the parts of the future insect hardened by drying, it bursts from its confinement, and the fly makes its exit at the small end of the case. A few hours after quitting their shell they become dry, take wing, and seek their mates.

A second species of breeze-fly has a still more wonderful history its eggs are laid in the nostrils of sheep, from one to seven or eight in each individual, and these on becoming larvæ, enter the frontal and maxillary sinuses, and even the horns, and feed on their secretions: when the larvæ are young they are perfectly white and transparent, except two small, black, horny plates: as they increase in size the upper surface becomes marked with two transverse brown lines on each segment, the anterior being shorter and narrower than the posterior; and some spots are also observable on the sides. The body consists of twelve segments besides the head. These larvæ move with considerable activity, holding with their tentacula to a fixed point and drawing up the body. When full grown the larvæ fall through the nostrils of the sheep, and change to the pupa state lying on the earth or adhering to the side of a blade of grass: in about two months the case of the chrysalis opens, and the fly makes its appearance.

Sheep are exceedingly annoyed by these flies, and to

dable than either of those previously described: its eggs are laid on the backs and sides of cows and oxen, and the larvæ hatched from them enter the hide, producing tumours as large as pigeons' eggs. The larva itself is of an oblong figure, larger at one extremity than at the other: the body is divided into ten or twelve segments by transverse bands, and these are again intersected by six longitudinal lines, which purse up the skin, and produce along the sides a series of mammiform protuberances, each possessing at its extremity a respiratory pore: on each segment of the body may be observed ridges, or dotted prominent lines, interrupted however by the longitudinal lines already noticed there are in pairs a narrower and broader line of minute dots or points; the narrower line is found, under a lens, to be formed of hooks bent towards the posterior extremity of the insect; the broader lines consist of smaller hooks bent in an opposite direction, or towards its head: it is probably by the aid of these hooks that the animal raises or depresses itself in the tumour, and finally, when mature, effects its escape.

The food of the larva appears to be the pus or matter surrounding it in the tumour in which it exists: regards the period of its continuing to feed we have little

as

satisfactory information. Its colour when young is white, but as it advances towards maturity it becomes browner, and finally of a deep dark brown approaching to black: having attained its full size it presses itself against the upper part of the tumour, and by some unknown process makes an aperture in the hide of about sufficient size to admit a pea; through this the larva wriggles itself a segment at a time until it comes quite out, and falling to the ground seeks a convenient retreat in which to become a chrysalis.

The chrysalis is of a dark brown colour, and in figure somewhat resembles the half of a walnut-shell, being narrower at one end than the other, flat on one side, and very rounded and convex on the other: after lying on the ground for some weeks a portion of the indurated skin or cover, of a triangular shape, is forced up at the smaller end, and through the aperture thus occasioned the fly emerges.

The fly is large and handsomely coloured; although the presence of the larva in the backs of cattle is frequently observable, the insect in its perfect state is rarely met with, and very few of our cabinets possess good specimens: it flies with rapidity, but apparently without noise, and never

ventures over water.

The act of oviposition appears to be attended with severe suffering, or apprehension at least, which makes the cattle run wild and furious, and gad or stray from the pastures, and hence the ancient epithet of gad-fly. When oxen are yoked to the plough, the attack of this fly is attended with real danger, since they become perfectly uncontrollable, and often run directly forwards through the hedges, or whatever obstructs their way. On this account many ploughs are provided with a contrivance for setting the oxen immediately at liberty. When the cattle are attacked by this fly it is easily known by the extreme terror

and agitation of the whole herd; the unfortunate object of the attack runs bellowing from among them, and seeks a refuge in the nearest water; the tail becomes rigid, and is brandished aloft or held straight out from the body.

Its frightened companions follow in the rear of the animal attacked, and a wild and apparently unmeaning chase takes place, which, from the inelegant gallop of the cows, has often a very ludicrous effect.