intracristal space Space enclosed by cristae in the mitochondrion.
intracuticular skeleton (BRYO: Gymnolaemata) In Cheilostomata, skeletal layers between noncellular organic sheets or within organic networks of cuticles of the exterior walls.
intrados n. [L. intra, within; F. dos, the back] The interior curve of an arch. see extrados.
intrahemocoelic a. [L. intra, within; Gr. haima, blood; koilos, hollow] Within the hemocoel or perivisceral cavity of an invertebrate.
intralecithal cleavage Cleavage where the nuclei undergo several divisions within the yolk without concurrent cytokinesis; common in arthropods.
intraparies n.; pl. intraparietes [L. intra, within; paries, wall] (ARTHRO: Crustacea) In Lepadomorpha, the secondary lateral margin of the carina.
intrapetalous a. [L. intra, within; Gr. petalon, leaf] (ECHINOD) Within the area of the tube feet.
intrapulmonary respiration Type of respiration that does not involve movements of the outer body wall and is confined to the respiratory organs.
intrasegmental a. [L. intra, within; segmen, piece] Within a segment.
intraspicular a. [L. intra, within; spicula, little point] (PORIF) Pertains to spicules completely embedded in spongin.
intratentacular budding (CNID: Anthozoa) A zoantharian colony growing by asexual reproduction, through the formation of new mouths on the oral disk, resulting in branching, or in linear groups of polyps bearing tentacles mainly on the outer edges of the row.
intrauterine a. [L. intra, within; uterus, womb] 1. Within the uterus. 2. Applied to developing offspring hatching within the uterus of the mother. see matricidal hatching.
intra vitam Applied to certain stains having the property of tinting cells of living organisms without killing them.
intrazooidal budding (BRYO: Stenolaemata) Budding within the living chamber of a single zooid.
intrazooidal polymorphism (BRYO: Stenolaemata) Two different types of zooids developed in the same living chamber.
intrinsic a. [L. intrinsecus, inward] 1. Inherent or within. 2. Cycles of species in a population. 3. Rate of natural increase in a stabilized population. see extrinsic.
intrinsic articulation A type of articulation where sclerotic prolongations within the articular membrane make contact. see extrinsic articulation.
intrinsic body wall muscles (BRYO) Circular and longitudinal muscle layers in the body walls.
intrinsic muscles Muscles which move an organ (leg, etc.) that originate within the segment. see extrinsic muscles.
introduced a. [L. intro, within; ducere, to lead] Not native but brought into an area by man.
introitus n. [L. introitus, entered] Opening or orifice.
intromittent a. [L. intro, within; mettere, to send] Designed for entering or inserting.
intromittent organ A male organ for transfer of seminal fluid into the female.
introrse a. [L. intro, within; versus, turn] Facing or directed inward toward the axis. see extrorse.
introvert n. [L. intro, within; versus, turn] (BRYO/SIPUN) A cavity which accepts retractable appendages, e.g., the anterior cavity that accepts the anterior tentacles.
intumescent n. [L. in, in; tumescere, to swell up] A swelling; being swollen or expanded.
intussusception n. [L. intus, within; suscipere, to take up] Deposition of new particles of formative material among those already present in a tissue or structure. see apposition, accretion.
invagination n. [L. in, into; vagina, sheath] An infolding, or ingrowth of a sheet or layer of cells forming a pouch or sac, especially in embryos. see emboly.
invalid a. [L. invalidus, not strong] Dismissing; without standing in zoological nomenclature.
inverse eyes Eyes in which the distal ends of the retinal cells face the interior of the cup or vesicle. see converse eyes.
invertase n. [L. invertere, to turn around; -asis, ending signifying an enzyme] An enzyme found in many plants and animal intestines that causes the hydrolysis of sucrose and converts it into a mixture of glucose and fructose.
invertebrate n. [L. in, not; vertebrata, with backbones] Any animal without a backbone or vertebral column.
investment n. [L. investire, to clothe] An outer covering of a cell, part, or organism.
in vitro [L. in, in; vitrum, glass] In the test tube or other artificial environment.
in vivo [L. in, in; vivere, to live] Occurring within a living organism.
involucrum n. [L. involucrum, sheath] (ARTHRO: Insecta) A sheath of cerumen around the brood chamber of stingless bees.
involute a. [L. in, in; volute, spiral] 1. Rolled inwards at margins or edges. 2. (MOLL) The last whorl of a shell enveloping earlier ones and concealing, or nearly so, the axis or earlier volutions. see convolute, revolute.
involution n. [L. in, in; volute, spiral] 1. Act of involving or infolding. 2. Deterioration or retrograde evolution.
ipsilateral a. [L. ipse, same; latus, side] Pertaining to or situated on the same side. see contralateral.
iridescence n. [L. iris, rainbow] A rainbow-like display of interference colors that change with variations of the angle of view, due to diffraction of light reflected from ribbed or finely striated surfaces. iridescent a.
iridophore n. [L. iris, rainbow; Gr. phoreus, bearer] An iridescent chromatophore; an iridocyte.
iris n.; pl. irises, irides [L. iris, rainbow] Dark pigment surrounding the compound eyes of arthropods and the camera-type eyes of cephalopods.
irregular n. [L. in, not; regularis, according to rule] Unequal, curved, bent; not regular.
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