GLOSSARY 



AUDITORY. Pertaining to hearing or to the organs related to hearing. 



AURICLE. The external ear of mammals or something that resembles such a projec- 

 tion; more specifically, a thin-walled, laterally expanded part of the heart that 

 receives blood from the veins. 



AUTOSOMES. Chromosomes that occur in pairs of similar size and shape and in 

 equal numbers in both males and females of a species; chromosomes other than 

 the sex chromosomes. Cf. SEX CHROMOSOMES. 



AUTOTROPHIC. See HOLOPHYTIC. 



AXIAL. Pertaining to the central line, or axis, of any symmetrical body; for example, 

 the axial skeleton of vertebrates is composed of the skull and vertebral column. 



BACKBONE. The vertebral column. 



BACK-CROSS. A cross between a hybrid of the F^ or F2 generations and either of the 

 parent types; a back-cross with the recessive parent type is used to distinguish 

 heterozygous and homozygous individuals showing the dominant characteristics 

 in an F., generation. 



BACTERIA {smg. BACTERIUM). Microscopic, colorless, unicellular plants without dis- 

 crete nuclei. 



BALEEN. "Whalebone"; the material making up the feeding filters of several kinds 

 of whales. Cetaceans may be divided into the toothed whales and the whale- 

 bone whales. 



BARRIER. Any obstruction that prevents migration. 



BEHAVIOR. The total reactions of an organism to its external environment. 



BI-. Combining form, meaning "two"; same as DI-. 



BILATERAL SYMAAETRY. The symmetry of right and left halves of the body. 



BINOMIAL NOMENCLATURE. System of naming animals, introduced by Linnaeus, in 

 which each kind of organism is given two names, that of the genus and that 

 referred to as the specific or trivial name. 



BIOGENESIS. The production of living things from living things, not from non-living 

 things; opposed to abiogenesis, or spontaneous generation; includes both re- 

 production and organic evolution. 



BIOLOGY. The science of living things, both plants and animals; derived from bios, 

 meaning life. 



BIOTIC. Conditions in an environment related to, or dependent on, the living organ- 

 isms inhabiting the environment; usually implies contrast wiUi the physico- 

 chemical conditions. 



BIRADIAL SYMMETRY. A simple bilateral symmetry obviously derived from radial 

 symmetry; sometimes termed radiobilateral symmetry. 



BLASTODERM. The developing part of the egg of a fish, reptile, or bird in which 

 partial cleavage occurs; it gives rise to both the embryo and the embryonic 

 membranes. 



BLASTODISK. That part of the egg of a fish, reptile, or bird in which the nucleus is 

 located and in which cleavage will occur. 



BLASTOPORE. The opening of the gastrula cavity (archenteron) which is surrounded 

 b\- the lips of the blastopore, or the germ ring. 



BLASTULA. A developing individual characterized by a monoblastic structure. 



BLASTULA CAVITY. The cavity of the blastula; cleavage cavity, or blast ocoel. 



BODY CAVITY. Any extensive cavity lying between the wall of the digestive tract 

 and the body wall. See COELOM and PSEUDOCOEL. 



BODY PLAN. The fundamental plan of organization of tissues, cavities, organs, and 

 organ systems in animals. 



BRANCHIAL. Pertaining to branchiae, or gills. 



BRANCHIATE. Having gills (branchiae) as organs of external gas exchange. CJ. 

 PULMONATE. 



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