Vocabulary

Amacrine Cells: carries information across the retina to integrate the signals from the ganglion and bipolar cells (vertebrate eye); this structure in cephalopods is located in the optic lobe, however it has yet to be determined if it has the same function.

Analogous Structures: similarity of structure between two species that are not closely related and attributable to convergent evolution.

Anlage: The initial clustering of embryonic cells from which a part or an organ develops.

Axon: a long extension from a neuron, that carries nerve impulses away from the cell body toward target cells.

Bipolar Cells: each bipolar cell receives signals from multiple rods and cones, and then transmits these signals to several ganglion cells (vertebrate eye); this structure in cephalopods is located in the optic lobe, however it has yet to be determined if it has the same function.

Ciliary Body: produces the clear, watery aqueous humor that fills the anterior cavity of the eye.

Ciliary Muscles: muscles that change the shape of the lens based on contraction or relaxation.

Compound Eye: the eye type of insects and crustaceans, which can have up to 1000 or more light-detecting, focusing ommatidia.

Cone: one of the two photoreceptors in the vertebrate eye that detects color during the day.

Convergent Evolution: the independent development of similar traits between species as a result of their having the similar ecological roles and selection pressures.

Cornea: transparent structure, which lets light into the eye and acts as a fixed lens.

Cupula: a gelatinous cap into which hair cells project into, in the semicircular canal.

Ectoderm: the outermost of the three primary germ layers in animal embryos.

Epithelial Tissue: sheets of tightly packed cells that line organs and body cavities.

Forebrain: The most anterior part of the three regions of the embryonic brain.

Ganglion Cells: synapse with bipolar cells and send the signal they receive to the optic nerve.

Hair Cells: cells that detect motion.

Homologous Structures: structures in different species that are similar because of common ancestry.

Iris: structure that regulates the amount of light entering the pupil by changing shapes.

Lens: Structure that bends light and focuses it on to the retina.

Mesoderm: the middle primary germ layer of an early embryo.

Optic Nerve: nerves that arise from the retina and carry action potentials to the brain, or optic lobe.

Organogenesis: an early period of rapid embryonic development in which the organs take form from the primary germ layers.

Photopsins: visual pigment in the cone; known as red cone, blue cone, and green cone.

Pupil: the hole in the center of the iris.

Retina: the innermost layer of the eye, containing photoreceptor cells and neurons; transmits images formed by the lens to the brain via the optic nerve.

Retinochrome: secondary pigment of a cephalopod which is located toward the basement membrane of the outer segment of the retina and assists in light collection.

Rhabdome: the functional unit of the retina, made up of four rhabdomeres.

Rhabdomers: the individual retinal cells, that are the photoreceptors of the cephalopod eye.

Rhodopsin: the main visual pigment in both vertebrate and cephalopod eyes; the amino acid structure is different between the rhodopsin of the cephalopod eye and the rhodopsin of the vertebrate eye.

Rod: one of the two photoreceptors in the vertebrate eye that is responsible for night vision and black and white vision.

Saccule: one of the structures in the inner ear responsible for keeping vertebrates orientated with respect to gravity and movement.

Sclera: a white outer layer of connective tissue.

Semicircular canals: arranged in three spatial planes, with hair cells located at the bottom of each one.

Single-lens Eye: eye type that works on a camera-like principle, by changing the amount of light that is allowed to enter into the eye and by focusing this incoming light with a lens.

Statocysts: the balance and orientation organ of the cephalopod.

Utricle: contain hair cells that let the brain know which way is up and inform it of changes in space.

Vestibule: structure in the inner ear that encompasses the utricle and the saccule.

All vocabulary taken from: Campbell, N., Mitchell, L. and Reece, J. Biology. 5th Edition. Addison Wesley Longman, Inc., 1999.

Exceptions: Anlage, Forebrain (www.Dictionary.com); Rhabdome, Rhabdomere, Statocyst (Young 1971).

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