Dominant: a character more constant and conspicuous than any other: a type or series occurring in large numbers both as to genera, species and individuals and in which differentiation is yet active. Dorsad: extending or directed toward the upper side. Dorsal: of or belonging to the upper surface: in Diptera, that face of the laterally extended legs visible from above. Dorsal bristles: see dorso-central. Dorsal diaphragm: the wings of the heart, or the very thin membrane upon which these muscles rest: = pericardial diaphragm, q.v. Dorsal gland orifices: in Diaspinae, oval orifices arranged in more or less distinct rows on the surface of the pygidium, through which is discharged the material of which the dorsal scale is formed. Dorsal glands: see last preceding title. Dorsal line: in caterpillars, extends longitudinally on the middle of the back or dorsal. Dorsal scale: that part of the covering scale of the Diaspinae that lies above the insect, as opposed to the ventral scale, which lies below. Dorsal space: in slug-caterpillars is the area between the sub-dorsal ridges. Dorsal vessel: the heart; q.v. Dorsi-meson: the middle of the upper surface. Dorso-alar region: Diptera; between the transverse suture and the scutellum on one side and the root of the wing and the dorso-central region on the other. Dorso-central bristles: Diptera; two or four longitudinal rows on the inner part of the dorsal. Dorso-central region: Diptera; bounded by two imaginary lines drawn from the scutellar bridges forward, and coinciding with a space free from bristles that exists on the outer side of the dorsal rows and is often occupied by a dorsal thoracic stripe. Dorso-humeral region: Diptera; bounded by the anterior end of thorax and transverse suture on two sides and by the dorsopleural suture and dorsocentral region on the two others. Dorsolum: the mesoscutum. Dorsopleural suture: Diptera; the lateral suture between dorsal and pleurum from the humeri through the base of the wing: separates the mesonotum from the pleura. Dorso-ventral: in a line from the upper to the lower surface. Dorsulum: the mesonotum before the scutellum, with the wing sockets: also, specifically, the meso-scutellum. Dorsum: the upper surface: in Coleoptera; often confined to meso- and meta-thorax: Odonata; includes mesepisterna and meso- and meta-thoracic terga: Diptera; upper surface of thorax, limited by the dorsopleural sutures laterally, the scutellum posteriorly and the neck anteriorly: Lepidoptera; the lower or inner margin of the wing. Draw-thread: the silk-producing gland. Drone: in Hymenoptera; the male bee. Duct: a channel, tube or canal for carrying a secretion from a gland to the point of discharge. Ductus ejaculatorius: the single duct or tube formed by the union of the vasa deferentia from each side, through which the seminal fluid is ejected into the vagina.