animals. This circulation is still more evident in the mantes than in the genera that we have described. The air taken in by the branches of the arterial tracheæ in the stigmata, is spread, by means of their common trunks, into the branches of the pulmonary tracheæ which carry it to their principal trunks, where it is taken up by other ramifications, and distributed in all parts of the body. When the decarbonization of the blood is effected, the remaining oxygen, the azote, and the carbonic acid, are driven out by the contraction of the elastic tracheæ. These gases may either take the road by which the air entered, or a different one. All parts, then, enjoy the impression of air; and the pulmonary tracheæ are destined to serve as a reservoir, that this impression may be for some time independent of the inspirations and expirations. The locusta exhibits likewise two orders of tracheæ, but their situation is different from what we described as that of the mantes. The pulmonary tracheæ extend in a straight line from one extremity of the body to the other, always keeping towards the middle and upper part of the body. They originate above the cerebrum, give some branches to that organ, then proceed to the eyes, sending different branches to the organs situated in the head. These tracheæ penetrate into the corcelet through the foramen occipitale, approach each other by degrees, and become gradually parallel, giving out a branch to the first pair of legs. When they come to the thorax they give out different branches, some of which go to the two last pair of legs, and others to the muscles of the thorax. When they reach the abdomen their diameter diminishes, though they receive nine branches from each side, furnished them by the arterial tracheæ. These tracheæ then extend to the extremity of the body, giving out a certain number of ramifications to the dorsal vessel. The pulmonary tracheæ are very conspicuous in this genus; but the contrary is the case with the arterial. Originating below the cerebriform ganglion, they distribute themselves to different parts of the head, giving in particular numerous branches to the muscles of the head. They extend in the corcelet by two common trunks, which go along the side of the body. But when they reach as far as the first pair of legs, they become considerably larger, form a sort of tubular cavity, and take air immediately by a large oval opening or stigma situated in that part. This tracheæ, the diameter of which is very considerable, extends to the extremity of these legs. Besides this great branch, the arterial tracheæ furnish other ramifications to the muscles, and which bring air to the trunk of the pulmonary tracheæ. The arterial tracheæ continuing in the thorax and abdomen by two common trunks, send branches to the legs, the pulmonary tracheæ, and the muscles of the thorax. The arterial tracheæ become very complicated in the abdomen. By their internal side they give off 16 principal branches, 12 of which proceed in pairs, while the other four are simple. The first branch is simple: at first very small; it increases suddenly, giving M.Longmire on Rents 3.1 Engraved for D. Thomson's Annals._ for Baldwin Gradock & Joy. Paternoster Row. July 1.1815. different ramifications to the abdominal muscles and the pulmonary trachee. The second branch sets out simple, but speedily divides into two branches, each much larger than the common trunk. Near the point where these tracheæ unite to furnish a single branch to the pulmonary tracheæ, they send off two branches, the superior of which goes to the superior branch, and the inferior to the inferior. Thus on each side of the abdomen are disposed the five other common trunks which open into the stigmata, so that these six orders of tracheæ correspond to the openings of these parts. As there are in all 16 branches on each side of the abdomen, the arterial tracheæ give on each side three large simple branches, which go to the pulmonary. They communicate with each other by means of small ramifications which they send to each other. All these principal branches have constantly a transverse direction. The bundle of tracheæ that go to the organs of generation proceeds from the first double branch. What is remarkable in this respiratory apparatus is the great diameter of all the abdominal tracheæ, especially those with double branches. These tracheæ are so large, and so close together, that they form a kind of envelope round the organs contained in the abdomen. ARTICLE VIII. i An Essay on the Shapes, Dimensions, and Positions of the Spaces, in the Earth which are called Rents, and the Arrangement of the Matter in them. By Mr. John B. Longmire. (Continued from vol. v. p. 281.) The junctions of bended-tabular Rents. The horizontal direction of any rent is not parallel to this direction of all the other rents in a formation; and as the lengths of rents in general are much greater than the distance between any two contiguous rents, many rents must be joined to others. Two of the junctions of bended-tabular rents I am now to describe. Bended-tabular rents, according to the difference in their positions, are joined together in their horizontal directions, and in those which are at right angles to them, whether angular or perpendicular. The junctions of these rents, in common language, are called crossings: and one rent is said to intersect and to cross another; and to disturb it by throwing or heaving it, either upwards o downwards, in horizontal junctions, and either to the right or left hand, in angular junctions. 1. Of horizontal Junctions. When the sides of one rent, say the rent A. fig. 1, Plate XXXV., are joined to those of another, BB, in a direction cd, which is horizontal, they are joined together in their horizontal directions. If a miner, in travelling downwards in the angular direction, ab, of a rent, B, meet with another rent, A, having a reverse position, and whose upper side, fg, is horizontally joined to both sides of that part of the rent in which he is standing, then the part of the latter rent which is joined to the under side of the former rent, will join it, as at c, above the place where the part ab joins it on the opposite side. Let it be remembered that the strata are always lower on the upper side than on the under side of every rent of this shape, then this separation of the rent B into parts will be easily accounted for. The lowest extremities of any one rent are generally situated in one stratum; hence, as the matter of the formation contracted, these extremities of both parts of the separated rent would necessarily sink with the stratum that contains them; but this stratum, as well as those above it, sunk a greater distance on the upper side, than on the under side of the unseparated rent, and brought down the part of the separated rent which lies on the former side as much lower than that part of this rent on the latter side of the unseparated rent, as the strata are lower on this than on that side of the last rent. This want of opposition," therefore, in the two parts of one of the joining rents which lie on opposite sides of the other is the effect of that unequal contraction of the matter which produced the rents, and is not caused by the action of a newer rent on an older, as has been generally supposed. 66 In every junction where the unseparated rent is the larger, it is as old as, if not older than, the separated rent; but when it is the smaller, it is always the newer of the two joining rents. I would in both instances, however, be understood to mean, that the formation of these rents took place during the process of the matter's consolidation; and when I say one is older than the other rent, I only mean that the commencement of the formation of the older happened before that of the newer rent; and, not that any one rent was completely formed and filled before the formation of any other had commenced. 2. Of angular Junctions. When two rents are joined together in their angular directions, they exhibit the appearance of fig. 3, Plate XXXV.; in which the parts, bg, hd, of one rent, A, are joined to another rent, BB, in a direction, bfg, which is parallel, or nearly so, to the angular direction of both rents. I will at present only describe the horizontal junctions of two rents that meet each other at nearly right angles; one of which, the unseparated rent, contains both kinds of the earthy tabular masses, and the other, or the separated rent, contains both of the earthy associated with the metallic tabular masses. If a miner, in travelling in the horizontal direction of a rent, ab, fig. 2, (which figure is a horizontal view of an angular junction of |