. Carnegie Institution di Washington la pubblicazione. 48 zanzare DI AMERICA DEL NORD del terzo segmento palpar, dentellatura sul suo margine interno in corrispondenza della punta e meglio sviluppata rispetto a quelle della maggior parte JSTematocera; e una coppia di corti mandibole, ampio, sottile, e debolmente chitinized. Come in altre nematocerous mosche, vi è un sistema ben sviluppato labrum-epipharynx e un elemento allungato ipofaringe appiattita. Nei maschi le mandibole sono insufficienti. " Nella larva la bocca è del tipo pungente, con breve dentato ed heavy mandibole, breve, jawlike mascella con distinti uno-palpus segmentata, e un piccolo, fortemente chitini

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. Carnegie Institution of Washington publication. 48 MOSQUITOES OF NORTH AMERICA of the third palpar segment, serrate on its inner margin at the tip and better developed than in most JSTematocera; and a pair of short mandibles, broad, thin, and weakly chitinized. As in other nematocerous flies, there is a well-developed labrum-epipharynx and an elongate flattened hypopharynx. In the males the mandibles are wanting. " In the larva the mouth is of the biting type, with short-toothed and heavy mandibles, short, jawlike maxilla with distinct one-segmented palpus, and a small, strongly chitinized labium or labial plate. In addition, labrum, epi- pharynx, and hypopharynx are all well developed. "The head of the larva having a thoroughly opaque, strongly chitinized cuticle.. hnxp. mx. ihyp.! tmc/. ^ i.md. Fig. 2.—Frontal section through tJie head of old larva of SiinuUum sp., show- ing forming imaginal parts. I.e., larval cuticle ; i.d., imaginal derm ; I.md., larval mandible; i.md., imaginal mandible ; l.mx., larval maxilla ; i.mx., imaginal maxilla ; l.mx.p., larval maxillary palpus; l.hyp., hypopharynx. it was impossible to clear whole heads sufficiently to make visible the develop- ing imaginal head and its parts, so that the method of sections had to be relied on to reveal the internal conditions. These sections of heads of larvae of various ages show plainly that the general method of development of the imaginal parts within the larval head, and the correspondence between forming imaginal parts and the corresponding larval parts already noted in the other orders of holo- metabolous insects, hold good in the Diptera. Fig. 1 shows in sagittal longitud- inal section the forming imaginal head parts within the larval head. This sec- tion shows particularly well the relation of the forming imaginal antenna to the larval antenna. In the larva the antennse are very small compared with their size in the imago, and the imaginal antenna is thus forced, in its develo