Vannus see vannal region

variance n. [L. variare, to change] A sampling statistic relating to deviations from the mean.

variate n. [L. variare, to change] A variable quantity or character.

variation n. [L. variare, to change] Differences resulting from nongenetic responses of the phenotype to immediate environmental conditions; ecophenotype.

varicellate a. [L. varix, dilation] Having small or indistinct varices.

varices pl. of varix varicose a. [L. varix, dilation] Bearing a varix or varices.

variegated a. [L. variegatus, of different sorts] Marked by different shades or colors.

variety n. [L. variare, to change] An ambiguous taxonomic term for a heterogeneous group of phenomena including nongenetic variations of the phenotype, morphs, domestic breeds, and geographic races.

variole n. [F. variole, smallpox] A pock-like mark; fovea; fossa. variolate a.

varix n.; pl. varices [L. varix, dilation] (MOLL: Gastropoda) Transverse elevations that occur on the outer shell surface; more prominent than the costa and generally spaced more widely; result of growth halt in which a thickened outer lip developed.

vas n.; pl. vasa [L. vas, vessel] A small tubular vessel, duct or canal, especially leading from the testis.

vascula n.pl.; sing. -um [L. dim. vas, vessel] (BRACHIO) Branches of the mantle canal system.

vascular a. [L. dim. vas, vessel] Pertaining to vessels adapted for transmission or circulation of fluids.

vascular markings (BRACHIO) Impressions of the mantle canals on the inside of the shell; pallial markings.

vas deferens sing.; pl. vasa deferentia 1. A sperm duct leading away from a testis. 2. (ANN: Oligochaeta) A duct carrying sperm from the male funnel to the male pore.

vas efferens sing.; pl. vasa efferentia Tubule leading from the testis to the vas deferens.

vasiform a. [L. vas, vessel; forma, shape] Vessel-shaped.

vector n. [L. vehere, to carry] 1. Any carrier, particularly an animal that transmits a disease organism from one host to another. 2. In helminthic disease, an intermediate host that seeks out the definitive host; as a mosquito.

vegetal pole In an early embryo, a region with large cells with much yolk; portion of egg or zygote with more yolk than opposite end.

vegetative functions All natural functions of living organisms that maintain life.

vegetative reproduction The development of a new individual from a group of cells in the absence of any sexual process.

veins n.pl. [L. vena, vein] 1. Vessels conducting blood toward the heart. 2. (ARTHRO: Insecta) The heavily sclerotized portion of wings that usually enclose small central tracheae.

velarium n. [L. velarium, awning] (CNID) A velum-like structure having canals lined with endoderm; flaps on the edge of the bell.

veliconch n. [L. velum, curtain; concha, shell] (MOLL: Bivalvia) The shell of the veliger larva; prodissoconch.

veliger n. [L. velum, curtain; gerere, to bear] (MOLL) A larval stage with a ciliated swimming membrane or membranes; a free-swimming young bearing a velum.

velum n.; pl. vela [L. velum, curtain] 1. A thin membranous covering. 2. (ANN: Hirudinoidea) A membrane separating the buccal cavity from the cavity of the oral opening. 3. (ARTHRO: Crustacea) In Ostracoda, a ventral ridge, flange, or frill that may extend around part or all of the anterior and posterior ends. 4. (ARTHRO: Insecta) The membrane forming part of the apical and marginal areas of a pa-ramere. 5. (CNID) A shelf of tissue extending inward near the margin of the bell of medusae. 6. (MOLL) a. In Bivalvia, the large, ciliated swimming disc of larval oysters. b. In Gastropoda, the swimming membrane consisting of two large semicircular folds bearing cilia. 7. (NEMATA) The ventral membranous winglike extensions on the spicule of some male nematodes. 8. (platy: Cestoda) The membranous posterior margin of a proglottid overlapping the anterior of the following one.

velutinous a. [NL. vellutum, velvet] Clothed with very dense, upright short hairs.

venation n. [L. vena, vein] The complete system of veins.

venom n. [L. venenum, poison] The secretion of the accessory venom, or poison gland. venomous a.

venom apparatus 1. (ARTHRO: Insecta) The sting apparatus or accessory glands. 2. (ANN: Polychaeta) The seta or venomous jaws.

venom gland 1. A gland secreting an irritating or lethal substance. 2. (ARTHRO: Chelicerata) In true spiders, a pair of glands situated in the cephalothorax; in others, on the che-licerae with ducts traversing each claw with an oval slit opening near the tip. 3. (ARTHRO: Insecta) In Hymenop-tera, the largest sting gland situated between the rectum and vagina and ending in the aculeus. see apid venom gland, braconid venom gland, vespid venom gland.

venose a. [L. vena, vein] Having veins or lines that branch like veins.

venous a. [L. venosus, full of veins] Having numerous veins.

venter n. [L. venter, belly] The ventral side; the entire under surface of an animal.

ventilation tracheae (ARTHRO: Insecta) Tracheae, that are subject to collapse, that respond to varying surrounding pressure. see diffusion tracheae.

ventrad adv. [L. venter, belly; -ad, toward] Toward the venter, or underside of the body. see dorsad.

ventral a. [L. venter, belly] 1. The lower or underside of the body. 2. (MOLL: Bivalvia) The edge remote from the hinge; opposite the umbones.

ventral brush (ARTHRO: Insecta) In culicid larvae, a linear series of irregularly paired setae, often divided into two groups, posteroventrally on the midline of abdominal segment 10.

ventral cardo (ARTHRO: Crustacea) In Ostracoda, that portion of the peniferum that serves as a hinge by which it articulates with the zygum.

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