geographical isolation/barriers A population or group of populations prevented by geographic barriers from free gene exchange with other populations of the same species; a geographic isolate. see climatic isolation.
geographic race A geographically delimited race; usually a subspecies.
geographic variation The differences between spatially segregated populations of a species.
geology n.; pl. -gies [Gr. ge, earth; logos, discourse] The science which treats of the structure and history of the earth.
geometrid a. [Gr. ge, earth; metron, measure] (ARTHRO: In-secta) A larva whose movements resemble a looping motion moving tail to head, such as the geometrid moth larva (Geometridae) "measuring worms"; geometroid. see recti-grade.
geophagous a. [Gr. ge, earth; phagein, to eat] Feeding on earth.
geophilous a. [Gr. ge, earth; philein, to love] Living in or on the ground; ground loving, as land snails.
geotaxis n.; pl. -taxes [Gr. ge, earth; taxis, arrangement] A tactic response with the force of gravitation as the stimulus. a. Positive geotaxis : toward the force of gravitation. b. Negative geotaxis : away from the force of gravitation.
geotropism n. [Gr. ge, earth; tropos, turn] Movement determined by the direction of gravitational force. geotropic a. see tropism.
geoxenes n. [Gr. ge, earth; xenos, stranger] Organism occurring only occasionally in the soil showing little effect on the soil structure. see geobionts.
geratology n. [Gr. geras, old age; logos, discourse] Study of degeneration and decadence of species with age. see gerontology.
germarium n. [L. germen, bud] 1. The distal chamber of an ovarial or testicular tube containing the oogonia or spermatogonia. 2. An ovary. 3. An egg or sperm producing part of a gonad. see insect ovary types.
germ-balls 1. (ARTHRO: Insecta) Reproductive cells in some larvae from which other young larvae may be produced. 2. (PLATY: Trematoda) Embryos in the redial stage.
germ band (ARTHRO) In egg, the thickened area from which the embryo is produced; embryonic rudiment; germ disc;
germ cells A reproductive cell in a multicellular organism. see somatic cells.
germiduct n. [L. germen, bud; ducere, to lead] (PLATY: Tre-matoda) The oviduct.
germigen n. [L. germen, bud; Gr. genos, offspring] (PLATY: Trematoda) The ovary.
germinal a. [L. germen, bud] Pertaining to a germ cell or embryonic structure. see soma.
germinal cell Cells which produce gametes through meiosis, i.e., oocytes in females, spermatocytes in males; products of the germinal primordium.
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