Appendix 847 



Organelle (or gan -el' ), a special part of a single cell serving a specific function. 



Organicism (or -gan' i sizm), a theory stressing the importance of the organiza- 

 tion of the entire living thing rather than the importance of the parts of 

 which that thing is composed. 



Organism (or' gan izm) (Gr. organon, implement), an independent living being. 



Organismal theory, a theory that an organism is a unit with its unity consist- 

 ing of centralized control of one dominant region over all subordinate 

 regions (contrast with Elemental theory). 



Organogeny (or gan -og' a ni), formation and development of organs. 



Orientation (o ri en -ta' shun) (L. orient, rise), change in location or position by 

 organs or their parts due to environmental influences; may also be applied 

 to an entire organism. 



Orthogenesis (or tho -jen' e sis) (Gr. orthos, straight; genesis, descent), develop- 

 ment or evolution in a definite direction. 



Orthoptera (or -thop' ter a) (Gr. orthos, straight; ptera, wings), order of insects, 

 such as grasshopper, whose wings meet in a straight line down the back. 



Osculum (os'kulum) (L. osculum, little mouth), an excurrent opening as in a 

 sponge. 



Osmosis (os-mo'sis) (Gr. osmos, pushing), diffusion of substances through a 

 semipermeable membrane. 



Osmotic pressure, pressure exerted by substances in solution due to molecular 

 activity. 



Osseous (os' e us) (L. os, bone), pertaining to bone. 



Osteology (os te -ol' o ji), study of bones. 



Ostium (os' ti um) (L. ostium, little opening), m.outhlike opening. 



Otolith (o'tolith) (Gr. ous, ear; lithos, stone), a limy particle in the auditory 

 organ of certain animals. 



Outbreeding, crossing of unrelated or distantly related individuals. 



Ovary (o' va ri) (L. ovarium, ovary), female reproductive organ in which the egg 

 cells develop; the enlarged, basal part of a pistil (female) within which 

 seeds develop. 



Oviduct (o'vidukt) (L. ovum, egg; ducere, to lead), tube to carry eggs from 

 ovary (to exterior). 



Oviparous (o -vip' a rus) (L. ovum, egg; parere, bring forth), producing eggs 

 that hatch after being excluded from the body. 



Ovipositor (o vi -poz' i ter) (L. ovum, egg; ponere, to place), specialized tip 

 of abdomen in certain insects for depositing eggs. 



Ovoviviparous (o vo vi -vip' a rus) (Gr. ovum, egg; F. vivipare, produce), form- 

 ing eggs, with a well-developed covering, which develop within the body 

 of the parent. 



Ovulation (o vu -la' shun) (L. ovum, egg), discharging mature eggs from the 

 ovary. 



Ovule (ov' ule) (L. ovum, egg), structure consisting of a female gametophyte, 

 nucellus, and integuments, which, after fertilization, develops into a seed. 



Oxidation (ox i -da' shun) (Gr. oxys, acid), combining oxygen with a substance. 



Oxyhemoglobin (ok si he mo -glo' bin) (Gr. oxys, acid; haema, blood; L. globus, 

 globe), temporary union of oxygen with the hemoglobin of the blood. 



