Glossary
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Abdomen: In an insect, the posterior-most part of the body, behind the head and thorax.
Acceptance signal: In the Drosophila, the signal given by the adult female that she will accept the courtship of a male. She slows down, extrudes her ovipositor, and spreads her wings so that mating can occur.
Aceto-orcein: A staining solution made of 1% natural orcein in a 1:1 solution of glacial acetic acid and 85% lactic acid.
Agar: A gelatinous substance found in red algae. It can be extracted and used as a stiffening agent to produce a gel. In the laboratory, it is often used to make an agar-based culture medium. A 1.5% solution makes a solid but elastic gel when cooled to below 40ºC that will not melt again until it reaches temperatures above 85ºC. Agar is also widely used in the food industry for gelling and thickening; baking recipes may include agar instead of gelatin for thickening in making puddings, etc.
Alleles: Alternative forms of a gene that occupy a specific position, or locus, on a chromosome.
Anal plates: Sclerotized plates surrounding the anus. In male Drosophila, these are heavily bristled.
Antenna: In an insect, the segmented appendage on the head carrying sensory receptors.
Antennal lobe: Region of the brain servicing the antenna.
Antennal organ: Known as Johnston's organ, this is the special sensory apparatus of the antenna found near its base.
Anterior midgut: In Drosophila this is the region of the gut that is just posterior to the foregut and is formed in the embryo by an endodermal invagination. It will form the anterior midgut and gastric caeca of the larva.
Arista (aristae, pl): In Drosophila, a feathery extension of the antenna through which sound vibrations can be detected.
Balancer: A structure on the side of an organism that helps the organism to stabilize during flight (or swimming). In Drosophila, the balancers sit posterior to the wings and represent a modified pair of wings.
Basement membrane: The extracellular matrix (acellular) found below any epithelium. It creates a cellular barrier between the epithelium and its underlying mesenchyme and is of major importance to the differentiation and maintenance of an epithelium. It is made up primarily of type IV collagen, laminin, fibronectin, and heparan sulfate proteoglycan.
Blastoderm: The layer of cells formed in the embryo during cleavage. In Drosophila this layer is formed in the periphery of the yolky egg. In the chick, it is formed as a disc-shaped area at the animal pole of the yolky egg.
Bristles: In insects, sclerotized, stout, hairlike projections from the adult cuticle, classified as two main types, larger macrochaetae and smaller microchaetae.
Cellular blastoderm: In the Drosophila embryo, the stage at which the blastoderm has gone from being a syncytium to a being cellular. Cell membranes grow inward between the peripheral nuclei, separating off individual cells from the inner yolky cytoplasm.
Cellularization: In the Drosophila embryo, the process during early development whereby the syncytial blastoderm is turned into a cellular blastoderm. Cell membranes grow inward between the peripheral nuclei, separating off individual cells from the inner yolky cytoplasm.
Centrolecithal: Having yolk that is concentrated in the central region of the egg. Centrolecithal eggs are also macrolecithal eggs, having a large quantity of yolk. The insect egg is an example of a centrolecithal egg.
Cephalic furrow: Literally, a furrow in the head region. In the Drosophila gastrula, it is a lateral infolding that occurs toward the anterior end and extends around the circumference of the embryo; it roughly delineates the boundary of the future head.
Chitin: Made up primarily of sugars often complexed with proteins, it is the principle component of a cuticle.
Chorion: A tough, protective eggshell. In Drosophila and other terrestrial insects, it is specially designed for maximal gas exchange with minimal water loss. In fish, it is a clear, tough enveloping layer.
Chromosome: A structure in the cell nucleus made up of the genetic material, DNA, complexed with protein.
Clypeolabrum: In the Drosophila, one of the head segments that is situated anterior to the mouth parts. It is broad and flat, and hangs down in front of the mandibles.
Compound eye: The type of eye found in insects. It is made up of many individual facets, or ommatidia, each with its own corneal lens.
Corneal lens: In the compound eye, the lens that sits at the distal end of each ommatidium. In Drosophila, it is a chitinous structure, biconvex, and approximately 5µm thick at its center.
Courtship song: In the fruit fly, the courtship song is a series of sounds made by rapid movements of the male's wings which he extends and vibrates one at a time during courtship. Also called love song.
Cuticle: The hardened outer covering of flies and other arthropods, made of chitin and hardened with the tanned protein called sclerotin, forming a protective layer that prevents water loss.
Cytokinesis: Division of a cell’s cytoplasm, as opposed to karyokinesis (division of a cell’s nucleus). Typically, cytokinesis follows karyokinesis. In the early cleavage stages in Drosophila, however, nuclear division (karyokinesis) occurs many times before the cytoplasm cleaves.
Decamp: To walk away. A female Drosophila that is unreceptive to a courting male decamps as part of her rejection behavior.
Dechorionation: Removal of the chorion. The chorion is a tough extracellular coat that surrounds the eggs of many species (e.g., Drosophila, zebrafish). A chorion can usually be removed either physically with fine forceps or chemically with an enzyme capable of dissolving the chorion (e.g., Clorox, in the case of the Drosophila chorion and pronase in the case of the zebrafish chorion).
Denticle belt: On the ventral surface of the Drosophila larva, rows of small hooks found that help the larva move by gripping the substrate.
Dorsal vessel: The simple tubular heart of Drosophila.
Drosophila melanogaster: The species name for the common fruit fly.
Ecdysis: Molting; the process of shedding an old cuticle and forming a new one.
Eclosion: The emergence of the adult fly from the puparium.
Ectoderm: The germ layer in an embryo that gives rise to the epidermis and nervous system. In many cases, as in vertebrates, an anterior and posterior invagination of ectoderm gives rise to the stomodeum and proctodeum, respectively.
Endoderm: The germ layer in an embryo that gives rise to the epithelium (lining) of the gut and gut derivatives.
Epithelium: A major type of tissue in an organism, found lining body cavities and covering the outside of the body. The epidermis is an example of a specific type of epithelium.
Esophagus: A region of the foregut, just posterior to the pharynx.
Eye-antennal disc: In the fly, the imaginal disc that gives rise to both the compound eye and the antenna of the adult fly.
Fat body: A sheet of fat cells that serve in site fat storage. In Drosophila these sheets are creamy white.
First instar larva: In Drosophila, the larva that hatches from the egg. This feeding stage grows rapidly and soon molts into the second instar larva.
Flick: A rapid movement of the wings. An unreceptive female Drosophila uses flicks when rejecting the male during courtship. Males also use wing flicks directed at other males that try to court them.
Foregut: The anterior part of the gut. In vertebrates, this is formed from endoderm and includes the pharynx and esophagus-trachea regions. In insects it is formed from ectoderm and comprises the buccal (mouth) cavity, pharynx, esophagus, proventriculus and salivary glands of the larva.
Gamete: An egg or sperm.
Gastric caecae: In the Drosophila larva, a ring of four blind-ending fingerlike pouches that extend from the gastric region. They are secretory as is the rest of the gastric region and aid in digestion.
Gastrulation: The stage in embryonic development that follows cleavage. During gastrulation, cells rearrange themselves, the endoderm and mesoderm cells moving inward and the ectoderm cells spreading around the outside, with some ectoderm invaginating to form such structures as the stomodeum and proctodeum.
Genital disc: In the fly, the only imaginal disc that is unpaired, this disc gives rise to the genital ducts, accessory glands and external genitalia of the adult fly.
Germ band: In Drosophila, created during gastrulation, this is the multilayered band of germ layers on the ventral side of the embryo that curves around the embryo's posterior tip.
Germ band extension: In Drosophila, occurring during early gastrulation, this is the elongation of the germ band along the dorsal side of the embryo so that eventually the embryo's posterior end meets its head end.
Germ band retraction: In Drosophila, occurring during later gastrulation, this is the shortening and thickening of the germ band which brings the posterior end of the embryo back toward the posterior pole of the egg.
Glycerin jelly: A mounting medium used in making whole-mounts of specimens that have not been dehydrate. It contains glycerin, gelatin, and water. It is heated before use to make it liquid; when it cools, it becomes a firm gel.
Gonad: The organ that forms gametes. In males, this is the testis, a sperm-forming organ, and in females this is the ovary, an ovum-forming organ. In the embryo, the gonad begins developing in the absence of germ cells, and secondarily, becomes populated by the primordial germ cells, the cells that will become the gametes.
Haltere: In the fly, a fleshy, club-shaped organ found posterior to the wings and used for balance. Halteres are homologous to the hind wings of non-dipteran insects.
Head eversion: In the fly, marking the transition from prepupa to pupa in Drosophila, this is the turning outward of the head capsule which had previously been turned inward.
Head involution: In the fly, during gastrulation, this is the folding inward of the head region causing it to slowly disappear to the interior. Because the head involutes during development, the Drosophila larva appears superficially to be headless.
Hemolymph: The oxygen-carrying and nutritive fluid, equivalent to blood, which bathes the organs of an organism such as a fly with an open circulatory system.
Heterozygous: Having two different alleles of a particular gene.
Hindgut: The posterior part of the gut. In vertebrates, it refers to the endodermal gut posterior to the colon. In insects it is ectodermally derived, and forms the hindgut and Malpighian tubules of the larva.
Histoblasts: In the fly larva, the population of cells that will give rise to the abdominal epidermis and internal organs of the adult. They are recognizable within the larva as clumps of small cells nestled among the large differentiated cells of the larva.
Histological section: A thin slice of a tissue or organism that is typically prepared for sectioning by being fixed and embedded in a hard medium such as paraffin or plastic. Histological sections are usually stained with colored dyes.
Holometabolous: A term referring to insects that have a larval and pupal stage prior to the adult stage. Drosophila is an example of a holometabolous insect.
Homeotic gene: A gene whose expression determines the specification of a body region. In Drosophila, the expression of the homeotic gene Antennapedia, for example, specifies the identity of the second thoracic segment.
Homozygous: Having two of the same allele of a particular gene.
Humeral disc: In the fly, the imaginal disc that in the adult forms two dorsal thoracic plates, just posterior to the head, called the humerus and pronotum. In the larva this disc is found ringing the base of the anterior spiracle.
I
Imaginal discs: In the fly, these are packets of folded epithelium that eventually differentiate into many of the structures of the adult such as the wings, legs, antennae, eyes, and proboscis. They form in the embryo as epidermal invaginations. They are carried around in the larval stages, growing in size, but do not unfold and differentiate until metamorphosis.
Imago: The adult, the sexually mature stage of an insect.
Instar: Any of the larval stages in an insect separated by a molt. Drosophila goes through three instar larval stages before the onset of metamorphosis.
Involution: A type of gastrulation movement in which a sheet of cells folds inward and spreads over an inner surface.
Kaiser’s glycerin jelly: A specific recipe for glycerin jelly, containing gelatin, glycerin, water, and a mold retardant such as thymol. It is used as a mounting medium for whole-mounts.
Karyokinesis: Division of a cell’s nucleus, as opposed to cytokinesis (division of a cell’s cytoplasm). Though these two events normally both occur during cell division, there are exceptions. In the early cleavage stages in Drosophila, for example, nuclear division (karyokinesis) occurs many times before the cytoplasm cleaves.
Labial discs: The imaginal discs that will form the proboscis of the adult fly.
Labial palps: In the fly, the fleshy swollen structures on the distal end of the proboscis that make contact with the food when the adult is feeding.
Larva: Early stage or stages in the life cycle, differing significantly in morphology and ecology from the adult.
Love song: In the fruit fly, the courtship song, a series of sounds made by rapid movements of the male's wings which he extends and vibrates one at a time during courtship.
Malpighian tubules: Tubules attached to the gut having an excretory function. They form as evaginations of the hindgut.
Mandibular: Of the mandible. In insects, a mandible is one of the first pair of mouthparts, or “jaws.” In vertebrates, the mandible is the lower jaw.
Maxillary: Of the maxilla. In insects, a maxilla is one of a pair of mouthparts, lying beneath the mandible. In vertebrates, the maxilla is the upper jaw.
Melanin: A black pigment common in many animals.
Mesoderm: The germ layer in an embryo that gives rise to the muscular and circulatory systems and most of the skeletal and urogenital systems.
Metamorphosis: The transformation from the larval to the adult stage.
Microknife: A knife with a small blade, suitable for microdissection under a dissecting microscope. It can be made inexpensively from chips of razor blade, a wooden dowel, and superglue.
Microneedle: A needle that is very thin, suitable for microdissection under a dissecting microscope. It can be made inexpensively from inset pins, a wooden dowel, and superglue.
Micropyle: Found in the eggs of certain organisms such as the fruit fly, a small channel through the chorion at the anterior end of the egg that provides an entryway for sperm at fertilization.
Midgut: The region of gut between the foregut and hindgut.
Molting: Or ecdysis, is the shedding of an old cuticle and formation of a new one.
Mouth hooks: In the Drosophila larva, a pair of hooks which articulate with a chitinized H-shaped sclerite posteriorly. The mouth hooks are used to bring food to the mouth.
Ocellus (ocelli, pl.): A simple eye containing a single light-perceiving element covered by a lens. In the adult Drosophila, there are three ocelli on top of the head.
Ommatidium (ommatidia, pl.): The separate light-sensitive elements of the compound eye, each with its own corneal lens. In Drosophila each eye has approximately 750 ommatidia.
Open circulatory system: A circulatory system in which blood is not confined to vessels. Blood, after leaving the heart through major vessels, enters the hemocoel, the complex of blood-filled spaces surrounding the organs. Typical of arthropods and molluscs.
Operculum: Literally, a lid or cover. In Drosophila an operculum in the chorion at the anterior end of the egg provides an exit door for the larva at hatching. In the pupal stage, the operculum at the anterior end of the puparium is the door through which the adult fly will exit.
Optic lobes: In the brain of the fly, lateral enlargements, flanking the central brain, that service the eyes.
Ovarian follicle cells: Cells in the ovary that surround an egg, nourishing it.
Ovary: The female gonad.
Oviposition: The laying of an egg through an ovipositor.
Ovipositor: A modification at the hind end of adult female fly through which the eggs are laid. It can be extended and retracted. A female extends her ovipositor when laying an egg and also when rejecting a male during courtship.
P1-P4: In Drosophila, the prepupal stages, according to the staging series of Bainbridge and Bownes (1981).
P5-P15: In Drosophila, the pupal stages, according to the staging series of Bainbridge and Bownes (1981).
Peripodial membrane: In an imaginal disc of the Drosophila larva, the thin, smooth wall on one side of the disc. It is the unfolded region of epithelium of the vesicle that forms an imaginal disc.
Pharynx: In the Drosophila larva, the region of the digestive tract between the oral hooks of the mouth and the esophagus.
Phenotype: The detectable feature in an organism that is the manifestation of a genetic trait.
Plastron: A thin film of air maintained around a structure when submerged. It can act as a “physical gill.”
Prepupa: In Drosophila, used to refer to the stages between pupariation and head eversion, though technically, it is the stages between pupariation and the retraction of the epidermis from the previous instar cuticle. (See Ashburner, 1989, for full discussion.)
Pole cells: In Drosophila, these are the primordial germ cells that later become the gametes. They are the first cells to form in the embryo, forming posteriorly. They are brought anteriorly by germ band extension, and then sink to the interior along with the invagination of the posterior midgut.
Polyspermy: Fertilization of an egg with more than one sperm.
Polytene chromosomes: Chromosomes that replicate without separating. They occur in Drosophila larvae in most of the differentiated cells, which grow throughout the larval stages, replicating their chromosomes without dividing.
Posterior midgut: In the Drosophila this is the region of the gut that is posterior to the anterior midgut and is formed in the embryo by an endodermal invagination.
Primordial germ cells: The early population of cells that give rise to the germ cells. These are typically identifiable early in development.
Proboscis: The extensible mouth parts of the adult fly.
Proctodeum: The posterior-most region of the gut that is formed from an ectodermal invagination. The posterior opening created by the invagination is the anus.
Proventriculus: In the Drosophila larva, a heavy-walled, muscular, bulb-like region of the gut posterior to the esophagus. It’s inner intima layer is chitinous and is used for mechanical break down of food.
Ptilinum: A sac, on the front of the fly's head, which expands with blood to break the seam of the operculum when the fly exits its puparium during eclosion.
Pulse song: Part of the Drosophila male's love song. It is a purring sound created by high-amplitude motions of the wing. Intervals between pulses and qualities within a pulse in the pulse song are species-specific and contribute to sexual isolation between species.
Pupa: In Drosophila, used to refer to the stages between head eversion and eclosion. (See Ashburner, 1989, for full discussion.)
Pupariation: Formation of the puparium. In Drosophila, this process occurs at the end of the third instar larval stage and includes shortening of the body, eversion of the anterior spiracles, and tanning of the larval cuticle.
Puparium: The tanned, or hardened, larval cuticle that surrounds the organism during metamorphosis and from which the adult fly will eclose.
Pupation: Formation of the pupa.
Respiratory filaments: In the Drosophila, anterior extensions of the chorion of the egg. They have a water-repellent surface network which maintains a film of gas around them when submerged, allowing them to function as a physical gill.
Salivary glands: Glands associated with the anterior end of the digestive system that secrete saliva. In the Drosophila larva, they are large and soft, and their chromosomes are polytene (as are most of the differentiated cells of the larva), making them suitable structures for creating chromosome squashes.
Sclerotized plates: Hardened plates made of cuticular protein.
Second instar larva: The larval stage between the first and second molts. In Drosophila it is a feeding stage that lasts 24 hours.
Seminal receptacle: In the adult female Drosophila, a compactly coiled tube attached at the anterior end of the uterus that stores sperm received from the male during mating.
Sex combs: Fringes of tiny black, stout bristles on the end of the first segment of the Drosophila male's front legs. They help the male pull himself up onto the female's back during mating.
Sexually dimorphic: Having two sexes that are distinguishable from one another.
Sine song: Part of the Drosophila male's love song. It is a humming sound created by low-amplitude vibrations of the wing.
Somatic contractions: Contractions in body musculature as opposed to musculature of the gut.
Sperm: The male gamete.
Spermatheca (spermathecae, pl): A region of the female's reproductive tract of certain organisms where sperm can be stored. In Drosophila the pair of spermathecae are mushroom-shaped organs lying embedded in fat tissue and connected to the uterus by narrow ducts.
Spiracle: An external opening to a trachea. In Drosophila larvae all instars have posterior spiracles, but only the second and third instars have anterior spiracles. In the adult the spiracles, though more numerous (there are nine pairs along the thorax and abdomen), are not as obvious.
Stomodeal plate: In the embryo, the flattening and thickening of the ectoderm in the oral region in preparation for invagination to form the stomodeum.
Stomodeum: In the embryo, the invaginated ectoderm in the oral region.
Sucking pump: In the fruit fly, a muscular structure at the base of the proboscis that sucks food into the esophagus.
Superficial cleavage: A pattern of cleavage that occurs in centrolecithal eggs, in which only the peripheral cytoplasm cleaves to form individual cells, leaving the central yolky cytoplasm uncleaved. The type of cleavage found in Drosophila embryos. Also called peripheral cleavage.
Syncytium: A multinucleate tissue in which cell membranes don't completely separate the nuclei. In the Drosophila embryo, during cleavage, the blastoderm first consists of a syncytium in which many nuclei are lined up in the peripheral cytoplasm.
Telson: In the Drosophila larva, a tail-like structure that is formed from the posterior-most segments, abdominal segments 9 and 10.
Temperature-sensitive mutant: A mutant that exhibits a normal trait at a permissive temperature but fails to exhibit this trait if the temperature is shifted to a higher restrictive temperature. The wild-type displays the trait at both temperatures.
Testis: The m ale gonad in which germ cells form sperm.
Third instar larva: The larval stage following the second molt. In Drosophila the third instar larva feeds and then crawls out of the food source to pupariate. The stage lasts about two and a half days.
Thorax: In the adult fly, the region between the head and the abdomen, bearing the wings, legs, and halteres.
Trachea: In the fly, the tube-like invaginations of the body wall serving as air channels to allow internal tissues to exchange respiratory gases with the outside air. They open to the outside at the spiracles. In vertebrates, the tube that leads from the oral cavity to the lungs.
U
Uterus: The portion of a female reproductive tract lying caudal to the oviducts. In the adult female Drosophila, it is a muscular unpaired structure that receives eggs from the oviducts and moves them toward the outside.
Vaginal plates: In the adult female Drosophila, these are sclerotized plates surrounding the vulva.
Ventral furrow: In the Drosophila embryo, this is a ventral invagination that marks the onset of gastrulation and represents the inward folding of the mesoderm.
Ventral ganglion: In the Drosophila larva, it is the region of the central nervous system that is connected to the two brain hemispheres, lies ventral to them, and extends further posteriorly.
Vitelline envelope: An extracellular coat surrounding an ovum.
Vulva: In the adult female Drosophila, this is the opening of the reproductive tract to the outside, serving both as an entrance for sperm during mating and as an exit for eggs during egg laying.
White pupa: In Drosophila this is the first prepupal stage when the larval body shortens, everts its anterior spiracles, and becomes immobile.
Wing inflation: The gradual unfurling of the folded wings in the adult fly following eclosion. Blood flowing between the two epithelial layers of the wings unfurl the wings by extending and flattening them..