tube or rather a gutter, open ventrally along its entire length. Upon transverse section (Plate II, Fig. 3), it is found to consist of two layers of chitin which are closely approximated all around, but form a somewhat convoluted pattern along the margins. This convolution of the two layers of chitin results in the formation of three closed tubes within each side of the labrum, giving it strength and power of penetration.

The inner surface of the labrum is perfectly smooth, but the outer one, and especially its central portion, is roughened by a peculiar pavement-like thickening of the chitin resembling long and forward pointed teeth or scales. The point of the labrum (Plate I, Fig. 2) resembles somewhat, as Nuttall expresses it, the point of a quill-pen, the tip carries six very minute teeth which are placed on chitinous thickenings, but an articulation could not be determined. A little farther back another but a trifle larger tooth is situated on the margin of either side, and still a little farther back, and just within the end of the incurved edges, two remarkable knob-like prominences* are placed, which apparently are formed by the tapering and twisting of the tube-like spaces of the chitin layers of the margins.

Compared with the description and illustrations of the quoted work of Nutall and Shipley, the labrum of the female Stegomyia presents considerable variation from that of Anopheles, a fact, which, to a lesser extent probably, is also apparent in the other mouthparts.

The mandibles, the next set of mouth elements (Plate I, Fig. 4), arise from the sides of the labrum; they do not, however, move independently, but are controlled by the muscles of the former element. In structure they are two exceedingly fine blades of chitin which, upon transverse section, seem to thicken toward the central region, their knifeblade-like margins curving slightly toward each other. The distal end of the mandible is more flattened and widened, and carries on one edge 31 exceedingly minute teeth, difficult to see or count with even a 1-12 oil immersion. In shape this distal end resembles the figure of the same organ of Anopheles given by Nuttall, as little as the labrum already described.

The next set, the maxillæ, (Plate I, Fig. 5) are structurally not

* Neither these nor the scale-like formation of the dorsal surface of the labrum epipharynx are mentioned by Nuttall and Shipley.-G. E. B.

much different from the mandibles, excepting that they are somewhat stouter and slightly longer, otherwise they resemble the blade of a bi-concave razor. The blade is rendered stouter by irregularly wavy thickenings of the chitin. The point of the maxillæ, instead of becoming wider than the blade, as is the case with the mandibles, is abruptly contracted and much narrower, tapering to an extremely fine point. The outer edge of the distal end bears thirteen knob-like blunt teeth, readily visible even under comparatively low magnification. The maxillæ arise from the inner sides. of the base of the labium. Just a little in front of the point of origin each maxilla bears a maxillary palp, which in length reaches not quite to the middle of the proboscis.

The stylet or hypopharynx (Plate II, Figs. 6 and 7) arises practically from the floor of the buccal cavity just above the base of the labium, and commences as a cone-shaped chitinous cup, the stem part of which becomes produced into the stylet, but the mouth of the cup receives the common salivary duct. In general shape the hypopharynx resembles a double-edged sword, the parallel edges of which become widened out near the distal end, and the point of which is terminated by a further knob-like dilatation. The thickened median portion of the blade is more pronounced on the lower surface than on the upper, which is nearly flat, or, at least, only slightly curved upward at the margins, which are usually in contact with the lower portion of the labrum-epipharynx, thereby converting the latter into a perfectly closed tube. The thicker ventral portion of the stylet is in a peculiar manner produced into a stout but tapering flange, which arches over so as to nearly touch the blade and becomes an extremely fine tube-like groove, styled by Annet & Dutton "the salivary gutter."

Upon cross-section of the hypopharynx the flange appears like a hook (Plate II, Fig. 7). This partially open channel, continuing to the tip of the hypopharynx, receives within the chitinous cup, already referred to, the common salivary duct, and through it the secretions of the glands are poured into the puncture made by the combined piercing elements. It is perfectly clear, therefore, that the labrum-epipharynx, being open ventrally, is closed by the dorsal surface of the hypopharynx, and is thereby converted into a perfect tube which may convey the blood or any other liquid into