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COLLEGE ZOOLOGY 



O-cel'lus (L., little eye). A simple type of eye 

 as in many invertebrates, especially in in- 

 sects or other arthropods. 



Oc'u-lar (L. oculus, eye). Eyepiece of the 

 microscope; pertaining to the eye. 



Ol-fac'to-ry (L. olfacere, to smell). Pertaining 

 to the sense of smell. 



Om-ma-tid'i-um (Gr. omna, eye). One of the 

 elongated rodlike units of a compound eye 

 of an arthropod. 



Om-niv'o-rous (L. omnis, all; yorare, to de- 

 vour). Eating all kinds of food, both plants 

 and animals. 



On-tog'e-ny (Gr. onto, being; genos, birth). 

 The entire developmental history of the in- 

 dividual organism. 



O'o-cyte (Gr. con, egg; kytos, cell). The egg 

 mother cell from which are produced, by 

 the first maturation division, the secondary 

 oocyte and the first polar body. 



0'o-gen"e-sis (Gr. con, egg; genesis, origin). 

 The process of formation of ova. 



0'o-gon"i-um (Gr. con, egg; gonos, offspring). 

 In animals, the primordial egg cell prior to 

 the process of maturation (meiosis); it is 

 the cell from which primary oocytes are pro- 

 duced. 



O-per'cii-lum (L., lid). The structure covering 

 the gills of fishes and tadpoles; also the plate 

 ser\ing to cover the opening of some snail 

 shells. 



Oph-thaFmic (L. ophthalmia, eye). Pertaining 

 to the eye. 



Op'tic (Gr. optikos, sight). Pertaining to the 

 eye or to sight. 



Op'tic lobes (Gr. optikos, pertaining to sight. 

 L. lobus). Thickenings on the dorsal surface 

 of the midbrain (mesencephalon). 



Op'tic nerves (Gr. optikos, pertaining to sight. 

 L. nervus, nerve) . Nerves from the eye to the 

 brain. 



O'ral (L. OS, mouth) . Pertaining to the mouth. 



O'ral groove. A groove having ciliated ridges, 

 which starts at the anterior end and runs 

 posteriorly to the cell mouth (cytostome) 

 in some ciliated protozoans, such as the 

 Paramecium. 



Or'bit (L. orbis, circle). The region of the 

 skull of the vertebrate surrounding the eye. 



Or'gan (Gr. organon, instrument). Any part 

 of an animal performing a definite function, 

 a group of cells or tissues that are associated 



in the body to perform one or more func- 

 tions. 



Or'gan-elle" (Gr. dim, from organon). A spe- 

 cialized part within a single-celled animal, 

 differentiated to perform a certain function, 

 and comparable to an organ of a metazoan. 

 Compare with Organ. 



Or-gan'ic com'pound (Gr. organon, imple- 

 plcment. L. componere, to put together). A 

 molecule containing the element carbon. A 

 few simple carbon compounds such as car- 

 bon dioxide are considered by some as inor- 

 ganic. 



Or'gan-ism (Gr. organon, instrument). Any 

 living individual, either plant or animal. 



Or'ga-nog"e-ny (Gr. organon, an instrument, 

 implement; genesis, origin). The process of 

 the formation of specialized tissues and or- 

 gan svstems during embrvonic development. 



Or'i-gin (L. orior, rise, become visible). End 

 of a muscle which remains relatively fixed 

 during contraction of the muscle. 



Or'tho-gen"e-sis (Gr. orthos, straight; genesis, 

 descent). A term usually applied to a tend- 

 encv to evolve consistently in the same direc- 

 tion, or to the concept of "predetermined" 

 evolution toward a definite goal. 



Os'cu-lum (L., little mouth). The relatively 

 large external opening of the central cavity 

 (spongocoel) through which water leaves a 

 sponge. 



Os-mo'sis (Gr. osmos, pushing). In a narrow 

 biologic sense it may be defined as diffusion 

 of a solvent through a semipermeable mem- 

 brane. In biologic processes the solvent is 

 almost universally water. 



Os'se-ous (L. osseus, bony). Pertaining to the 

 bone. 



Os'te-oI"o-gy (Gr. osteon, bone; Zogos, study). 

 Study of bones. 



Os'ti-um (L., door). A small mouthlike open- 

 ing such as the anterior end of the oviduct 

 in the frog and other vertebrates; in general, 

 an opening in both invertebrates and verte- 

 brates, usually guarded by a valve or circular 

 muscle. 



O'to-lith (Gr. ous, ear; lithos, stone). A limy 

 particle in the inner ear of vertebrates or in 

 the auditory organ of some invertebrates. 



O'va-ry (L. ovarium, ovary) . The female gonad 

 in which the eggs (ova) multiply and de- 

 velop. 



