labium
(L. a lip). The lower lip of
the insect formed by fusion of the second
pair of maxillae.
labrum
(L. a lip). The upper lip of
insects and crustaceans situated above or in
front of the mandibles; also refers to the
outer lip of a gastropod shell.
labyrinth
(L. labyrinthus, labyrinth).
Vertebrate internal ear, composed of a
series of fluid-filled sacs and tubules
(membranous labyrinth) suspended within
bone cavities (osseous labyrinth).
labyrinthodont
(Gr. labyrinthos, labyrinth, + odous, odontos,
tooth). A group of Paleozoic amphibians
containing the temnospondyls and the
anthracosaurs.
lachrymal
(L. lacrimia, tear).
Secreting or relating to tears.
lacteal
(L. lacteus, of milk). Noun,
one of the lymph vessels in the villus of the
intestine. Adj., relating to milk.
lacuna
, pl. lacunae (L. pit, cavity).
A sinus; a space between cells; a cavity in
cartilage or bone.
lagena
(L. large flask). Portion of the
primitive ear in which sound is translated
into nerve impulses; evolutionary beginning
of cochlea.
Lamarckism
Hypothesis, as expounded by
Jean Baptiste de Lamarck, of evolution by
the acquisition during an organism's lifetime
of characteristics that are transmitted to
offspring.
lamella
(L. dim. of lamina, plate).
One of the two plates forming a gill in a
bivalve mollusc. One of the thin layers of
bone laid concentrically around an osteon
(Haversian canal). Any thin, platelike
structure.
lappets
Lobes around the margin of
scyphozoan medusae (phylum Cnidaria).
larva
, pl. larvae (L. a ghost). An
immature stage that is quite different from
the adult.
larynx
(Gr., the larynx, gullet).
Modified upper portion of respiratory tract
of air-breathing vertebrates, bounded by the
glottis above and the trachea below; voice
box; adj.,
laryngeal, relating
to the larynx.
lateral
(L. latus, the side, flank). Of or
pertaining to the side of an animal; a bilateral animal has two sides.
laterite
(L. later, brick). Group of
hard, red soils from topical areas that show
intense weathering and leaching of bases
and silica, leaving aluminum hydroxides and
iron oxides; adj. lateritic
lecithotrophy
(Gr. lekithos,
yolk of egg, + trophos, one who feeds).
Nutrition of an embryo directly from the
yolk of an ovum.
lek
(Sw. play, game). An area where
animals assemble for communal courtship
display and mating.
lemniscus
(L. ribbon). One of a
pair of internal projections of the epidermis
from the neck region of Acanthocephala,
which functions in fluid control in the
protrusion and invagination of the proboscis.
lentic
(L. lentus, slow). Of or relating to
standing water such as swamp, pond, or lake.
lepidosaurs
(L. lepidos, scale,+ sauros, lizard). A lineage of diapsid
reptiles that appeared in the Permian and
that includes the modern snakes, lizards,
amphisbaenids, and tuataras, and the extinct
ichthyosaurs.
lepospondyls
(Gr. lepos,
scale, + spondylos, vertebra). A group of
Paleozoic amphibians distinguished by the
possession of spool-shaped vertebral centra.
leptocephalus
pl. leptocephali (Gr. leptos, thin, + kephale,
head). Transparent, ribbonlike migratory
larva of the European or American eel.
leukemism
(Gr. leukos, white, + ismos, condition of). Presence of white
pelage or plumage in animals with normally
pigmented eyes and skin.
leukocyte
(Gr. leukos, white, + kytos, hollow vessel). Any of several kinds
of white blood cells (for example,
granulocytes, lymphocytes, monocytes), so
called because they bear no hemoglobin, as
do red blood cells.
library
In molecular biology, a set of clones
containing recombinant DNA. Obtained
from and representing the genome of the
organism.
ligament
(L. ligamentum,
bandage). A tough, dense band of connective
tissue connecting one bone to another.
ligand
(L. ligo, to bind). A molecule
that specifically binds to a receptor; for
example, a hormone (ligand) binds
specifically to its receptor on the cell surface.
limax form
(L. limax, slug). Form of
pseudopodial movement in which entire
organism moves without extending a
discrete pseudopodium.
lipase
(Gr. lipos, fat, + ase, enzyme
suffix). An enzyme that accelerates the
hydrolysis or synthesis of fats.
lipid, lipoid
(Gr. lipos, fat). Certain
fatlike substances, often containing other
groups such as phosphoric acid; lipids
combine with proteins and carbohydrates to
form principal structural components
of cells.
lithosphere
(Gr. lithos, rock, + sphaira, ball). The rocky component of the
earth's surface layers.
littoral
(L. litoralis, seashore). Adj.,
pertaining to the shore. Noun, that portion
of the sea floor between the extent of high
and low tides, intertidal; in lakes, the
shallow part from the shore to the lakeward
limit of aquatic plants.
lobopodium
(Gr. lobos,
lobe, + pous, podos, foot). Blunt, lobelike
pseudopodium.
locus
, pl. loci (lo´sï) (L. place).
Position of a gene in a chromosome.
logistic equation
A mathematical expression
describing an idealized sigmoid curve of
population growth.
lophocyte
(Gr. lophos, crest, + kytos, hollow vessel). Type of sponge
amebocyte that secretes bundles of fibrils.
lophophore
(Gr. lophos, crest, + phoros, bearing). Tentacle-bearing ridge
or arm within which is an extension of the
coelomic cavity in lophophorate animals
(ectoprocts, brachiopods, and phoronids).
lorica
(L. corselet). Protective
external case found in some protozoa,
rotifers, and others.
lotic
(L. lotus, action of washing or
bathing). Of or pertaining to running water,
such as a brook or river.
lumbar
(L. lumbus, loin). Relating to
or near the loins or lower back.
lumen
(L. light). The cavity of a tube
or organ.
lymph
(limf) (L. lympha, water). The
interstitial (intercellular) fluid in the body,
also the fluid in the lymphatic system.
lymphocyte
(L. lympha, water,
goddess of water, + Gr. kytos, hollow
vessel). Cell in blood and lymph that has
central role in immune responses. See
T cell and B cell
lymphokine
(L. lympha, water, + Gr. kinein, to move). A molecule secreted
by an activated or stimulated lymphocyte
that causes physiological changes in certain
other cells.
lysosome
(Gr. lysis, loosing, + soma, body). Intracellular organelle
consisting of a membrane enclosing several
digestive enzymes that are released when
the lysosome ruptures.
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