Germ layer see germinal layers

germogen n. [L. germen, bud; genes, born] (MESO: Rhombo-zoa) The central part of an infusorigen in the development of an axoblast.

germovitallarium n.; pl. -vitellaria [L. germen, bud; vitellus, yolk] (PLATY) Having the ovary differentiated into yolk- and egg-producing regions.

germ plasm Genetic material which forms the physical basis of inheritance and is passed from generation to generation.

germ tract The complete detailed history of the germ cells from one generation to the next.

gerontic a. [Gr. gerontos, old man] Pertaining to decadence; old age; deteriorating.

gerontogeous a. [Gr. gerontos, old man; ge, earth] Belonging to the Old World or Eastern Hemisphere. see neogeic.

gerontology n. [Gr. gerontos, old man; logos, discourse] The study of aging.

gerontomorphosis n. [Gr. gerontos, old man; morphe, form] Evolution involving specialization and diminishing capacity for further evolutionary change.

gestation n. [L. gestare, to bear] In viviparous animals, the period from conception to birth.

geusid n. [Gr. geusis, taste] (NEMATA) Gustatory organ.

giant bud (BRYO: Gymnolaemata) Unpartitioned distal end growth in which the side walls grow faster than the internal transverse walls.

giant cell A term applied to a host response in which a multi-nucleate mass of protoplasm or cytoplasm often acts as a preferred feeding site or "nurse cell". see coenocyte, syncytium, lysigenoma, teratocyte.

giant chromosome (ARTHRO: Insecta) In Diptera, a very large chromosome bundle that arises by repeated endoreplica-tion of single chromatids.

giant fiber Enlarged nerve fibers that transmit rapid impulses in certain mollusks, crustaceans, annelids, pogonaphorans and insects; giant fibre.

gibber n. [L. gibbus, humped] A swelling or enlargement; a rounded protuberance.

gibbous, gibbose a. [L. gibbus, humped] Very convex; humpbacked; embossed; swollen; a protuberance.

Gicklhorn's organ (ARTHRO: Crustacea) In Copepods, paired photoreceptors having two cells that closely resemble retinula cells, found in proximity to the frontal eye.

gigantism n. [Gr. gigas, giant] Excessive growth of an organ or a complete organism to a large size.

gigeriate a. [L. gigerium, gizzard] (ANN) Having one or more gizzards in the digestive system.

gill n. [ME. gile, gill] 1. An external respiratory organ of various aquatic invertebrates. 2. (ARTHRO) Brachia or plastron. 3. (ECHINOD: Echinoidea) The plastron. 4. (moll) The ctenidium.

gill bailer see scaphognathite gill bar (MOLL: Bivalvia) Dorsoventral rodlike thickenings of a gill lamellae.

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