Hook hooklets see hamulus uncus

hoplochaetellin a. [Gr. hoplon, implement; chaite, hair] (ANN: Oligochaeta) Denoting earthworm male terminalia in which one pair of sperm ducts open together with the prostatic ducts of segment xvii or close to the prostatic pores, the other pair of sperm ducts similarly associated with the prostates of segment xix.

horiodimorphism n. [Gr. horios, in season; dis, twice; mor-phe, form] Seasonal dimorphism.

horismology n. [Gr. horos, boundry; logos, discourse] (ARTHRO: Insecta) Scientific description of the neuration of insects wings. see orismology.

horizontal a. [Gr. horizon, bounding] Laying in a plane at right angles to a primary axis; parallel with the horizon.

horizontal classification Classification focusing on grouping species in a similar stage of evolution, rather than location on the same phyletic line. see vertical classification.

horme n. [Gr. horme, impulse, impetus] 1. Behavioral activity directed toward a goal. 2. In living cells or organisms a purposive behavior, urge or drive.

hormone n. [Gr. hormao, instigate] A chemical regulator or coordinator secretion having some specific effect on me tabolism, development, or response of the organism or some particular part of it.

horn n. [A.S. horn] 1. A stiff, pointed, unbranched cuticular process. 2. (ARTHRO: Insecta) a. A long handlelike process of the first gastric tergite of Innostemman wasps, that curves up and over the mesoscutum and houses the retracted ovipositor. b. In the plural sometimes refers to antennae.

horny a. [A.S. horn] Thickened or hardened.

horny corals (CNID: Anthozoa) In the order Gorgonacea, commonly called sea fans or sea whips, with extensive skeleton composed of a horny protein material, gorgonin.

horotelic a. [Gr. horos, boundry; telos, completion] Pertaining to evolution proceeding at the standard rate. see tachytelic, bradytelic.

host n. [L. hospes, guest or host] Any living organism in or on which a parasite lives, and/or feeds.

host selection principle A theoretical hypothesis that female organisms that breed on two or more hosts will return to the host on which she was reared to reproduce.

host specificity The degree to which a parasite is able to mature in one or more host species.

Hoyle's organ (MOLL: Cephalopoda) In embryonic Sepia, a distinct set of cells in an anchor-shaped complex at the site of the shell sac closure; a hatching gland that produces a proteolytic enzyme that dissolves the chorion and surrounding envelope.

humeral a. [L. humerus, shoulder] 1. Pertaining to or situated on the shoulder. 2. (ARTHRO: Insecta) The anterior basal portion of an insect wing.

humeral angle (ARTHRO: Insecta) 1. The basal anterior angle or portion of a wing. 2. The outer anterior angle of the ely-trum of beetles.

humeral bristles (ARTHRO: Insecta) In Diptera, the bristles on the humeral callus.

humeral callus (ARTHRO: Insecta) In Diptera, a more or less rounded tuberculate anterior lateral angle of the thoracic notum.

humeral carina (ARTHRO: Insecta) In Coleoptera, an elevated keel-like ridge on the outer anterior angle of an elytron.

humeral cross vein A cross vein between the base of a wing and the apex of the subcosta.

humeral lobe (ARTHRO: Insecta) The base of the costal margin of the hind wing that overlaps the fore wing in some primitive forms that serves to prevent the wings from moving out of phase.

humeral nerve (ARTHRO: Insecta) A transverse nerve in the wing between the costal and subcostal veins.

humeral plate (ARTHRO: Insecta) 1. In Odonata, a large plate hinged to the tergum and supported by an arm from the pleural wing process. 2. In Hymenoptera (wasps and honey bees), a small plate separated from the metanotum anteriorly and laterally which bears the anterior notal wing process of the hind wing. 3. In mosquitoes, an anterior preaxil-lary sclerite of the wing base supporting the costa.

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