Glossary 



abdomen an animal's major body region occurring be- 

 hind the thorax and containing the viscera. 



abiotic devoid of life. 



aboral opposite the mouth. 



abrasion process or result of rubbing away by friction. 



absolute humidity the grams of water vapor per cubic 

 meter of air. 



absorption the taking up of fluids or other substances as a 

 sponge takes up water. 



acellular without cells; pertaining to body organization in 

 which the organism appears unicellular or its nuclei 

 are not separated by cell membranes. 



acid a substance that releases hydrogen ions in water; 

 with a pH less than 7. 



acoelomate without a body cavity; the basis for defining 

 Acoelomata, animals without a body cavity but with 

 organs and organ systems, the Platyhelminthes and 

 Nemertea. 



Actuoiistic Phase that portion of earth history having an 

 over-all environment, especially an atmosphere, similar 

 to that of the present ; about the last two billion years. 



adaptation the fitness of structure, function, or behavior 

 of an organism or taxon for its environment; also, the 

 process of becoming so fitted; specialization and ad- 

 justment. 



adaptive radiation the evolution of several distinct or- 

 ganisms with unique adaptations from a single an- 

 cestor; an evolutionary process generally involved 

 in the formation of large taxa. 



adjustment an adaptation that is primarily due to an 

 organism living within and being modified by an 

 environment . 



adsorption the adhesion of a very thin layer of gaseous, 

 liquid, dissolved, or suspended substances to the sur- 

 face of a solid. 



advanced pertaining to a relatively recent or complex 

 stage in the life cycle of an organism; generally im- 

 plies complex, rather than simple, and specialized, 

 rather than generalized, features; assumed to denote 

 features developed during a period remote from the 

 origin of life; not primitive. 



aerobe an organism requiring oxygen for respiration. 



aestival pertaining to the summer season. 



aestivation summer dormancy in an organism 



Age a geological time unit of variable meaning: (1) the 

 precise time unit represented by a rock stage; 



(2) the loose time unit represented by a conspicuous 

 group of organisms, e.g., Ages of Monera, Algae, 

 Amphibians, etc. 



air mass a large moving body of air, generally recognized 

 by uniform conditions of temperature and moisture. 



alkali a substance that releases more hydroxyl than hy- 

 drogen ions in water; with a pH more than 7. 



alluvium materials carried or deposited by a stream. 



alternate leaves or buds an arrangement in which either 

 or both occur singly at a node. 



alternation of generations the occurrence of two or more 

 distinctive types of adult individuals during the life 

 cycle of a single species, each adult being produced in 

 a difTerent manner; generally, an alternation of two 

 unlike-appearing, sexual and asexual, generations. 



amensalism symbiosis in which one organism is harmed 

 and the other unaflTected. 



amitosis cell division involving direct division of a 

 nucleus or nuclear material without the appearance of 

 chromosomes. 



amoeboid pertaining to the putting forth of protoplasmic 

 extensions as does Amoeba (Sarcodina); often related 

 to movement, as in amoeboid movement. 



anaerobe an organism living in the absence of free 

 oxygen and not using oxygen for respiration. 



anatomy the study of life organization, particularly of 

 visible striictures. 



ondesite a fine-grained, intermediate-colored (often dark 

 grayish); igneous rock rich in feldspar; generally any 

 intermediate-colored lava. 



angiosperm any flowering plant, Class Angiospermae. 



annual an organism that completes its life cycle, from 

 origin to death, in one year. 



antenna a movable sense organ found in many arthro- 

 pods and certain other animals. 



anterior toward the front. 



anticline an elongated, archlike fold in the land. 



anticyclone a localized atmospheric pressure distribu- 

 tion or area in which pressure decreases and winds 

 travel away from the center; a "High." 



aphelion the point on a solar system body's orbit that is 

 farthest from the sun; also applies to any body orbiting 

 about another. 



appendage any part of an organism that projects from 

 the main body mass and has a free end; in animals, 

 generally confined to movable parts. 



403 



