fulcrum D, and the flexible, curved arm being straightened, the sheath and attached lancets are projected. By an additional contraction of the muscles of C, that piece, turning on o, its only point of attachment to the lever D, tilts over the triangular piece B, on the pivot, s, causing the lancet, articulated to its movable arm at c, to slide along e, b, and thus project its point into the wound beyond the sheath. The beautiful and effective mechanism of this lever of the third class, by means of which the lancets are thrust deep into the incision first made by the point of the sheath, will, perhaps, be better understood from Fig. 10. This figure represents the levers of one side with a detached arm of the sheath and a piece of the lancet. The form of the lever, D, is shown by the line, k, o, n, m, this lever being articulated to the arm at n. The broad lever, C, whose outline is denoted by x, i, o, k, with its anterior side beyond k, o, overlapping D, is articulated by a ligament to D, at the point o, and turning on this point, changes its position to that denoted by the dotted line of the same form, strikes its angle, i, against the triangular piece, which is also articulated to D, near o, and throws its movable arm, which curves over the arm of the sheath to its attachment with the lancet at e, to the position denoted by the dotted outline of that piece moving the end of the lancet, a to a'. Fig. 1, E E, are two pieces attached to the levers, D D, and resembling, in every respect, the organs of sense appended to the head of many insects, and called palpi, or feelers. That they here serve the same purpose is shown by the fact that they are always protruded in advance of a thrust made by the sting, as if to ascertain the location or character of an object of attack. The name sheath, applied to the principal piece used for making an incision, is a somewhat misleading term, for it can hardly be said to enclose the lancets in any part of its course, as may plainly be seen by inspecting the transverse sections; but I have deemed it best to adopt the English name by which it is most generally described. "Gorgeret" or Gorget applied to this piece by Lacaze Duthiers from its resemblance to the surgical instrument of that name, is much more appropriate, but would necessarily lead to the adoption of the entire nomenclature of that author, which, though unquestionably more in accordance with the principles and plan of scientific description, would introduce a number of terms not yet familiar to our language, a proceeding foreign to the purpose of this paper. The remarkable mechanical action described in connection with the valve attached to the lancets may be corroborated by any one skilled in the manipulation of small objects, by forcing a fluid through the opening in front of the valve and out of the small canals. I found no difficulty in doing this, but it might be inferred, a priori, that some such action was necessary, for, to make these pieces project only one-fiftieth of an inch deeper into the wound than the sheath, without any provision to introduce the poison, would produce no sensible effect upon the nervous system of any of the higher animals, much less on that of another insect. The venomous effect of a wound made by the sting is entirely due to the poison introduced by it, but to construct a complicated mechanism for thrusting into the skin a pair of spicules the one five-hundredth part of an inch in diameter to the depth of one-fiftieth of an inch, without any other provision for producing an effect upon the nervous system, would be worse than arming soldiers with Gatling guns without ammunition, and a provision no naturalist would expect to find. The following micrometric measurements will afford some idea of the dimensions of this formidable weapon. Whole length of sheath, about... Length of penetrating part.... ... 2.5 mm. 1.2 mm. Length of that part of lancets projecting beyond the sheath..... Diameter of lancets... .4 mm. .04 mm. DEMODEX FOLLICULORUM.—In Vol. V. of the Bulletin of the Museum Comp. Zoology, at Cambridge, Mr. Walter Faxon gives a description of this parasite, as found in some cow-hides from the west. Leather made from these hides appeared disfigured with pits, which often penetrated almost entirely through it. These cavities were seen in sections to be enlarged and diseased hair follicles. A full description of the characters of the species found is given as far as they could be made out in their imperfect condition when examined, and a valuable series of references to the literature of the subject. DESCRIPTION OF NEW SPECIES OF DIATOMS. BY PROF. H. L. SMITH, LL.D. Homoeocladia capitata, n. sp. H. L. S. Hab. Black Rock, Cal. Mr. C. Febiger. Frond membranaceous, umbellately branched; branches elongated, and with corymbose capitate apex. Frustules linear, valves lanceolate with acute and very slightly constricted apices; frustules densely packed, but not in series, or fascicles; marginal punctæ faint, 35 in .001. Length of frustule .0008 in, breadth, .0002 in.; Frond 1.5" to 2". Plate III, fig. 1. I received the material containing this well-marked species from Mr. C. Febiger, who procured it in California as a gathering containing his Biddulphia Edwardsi. In this gathering I found the fronds of the present species. The well marked peculiarity of corymbose apices, and the close resemblance to Kutzing's Schizonema capitatum suggested the name, possibly it may be Kutzing's species, though he states that the frustules are arranged in rows, but the outline figure which he gives of the frustules agrees, as also the size, with the present form. It is not, however, a Schizonema (Micromega) since the frustules are unmistakably Nitzschioid. The walls of the filaments are dense, and the frustules so closely packed as to appear opaque even after prolonged burning at a full red heat. Meridion intermedium, n. sp. H. L. S. Hab. Knoxville, Tenn. Josiah Curtis, M. D. Frustules sessile, cuneate, margins nearly smooth, valves with very faint pervious costæ in f. v. which are scarcely discernable in s. v., cuneate, rounded at the larger extremity. Length .00166 to .003. Plate III, fig. 2. This curious modification of M. circulare was found growing DESCRIPTION OF PLATE III. Fig. 1. Homoeocladia capitata, n. sp. H. L. S. Fig. 3. Navicula Kutzingiana, n. sp. H. L. S. |