GENERAL ZOOLOGY 



RECEPTOR. A region especially sensitive to changes in the environment; may be a 



sensorv cell or a complex sense organ containing many sensory cells. 

 RECESSIVE GENE. A gene that is without appreciable effect when associated with its 



dominant allelomorph. Cf. DOMINANCE. 

 RED BLOOD CELL. See ERYTHROCYTE. 

 REFLEX ACTION. An automatic response to a stimulus; the functional basis of 



nervous coordination. 

 REFLEX ARC. An afferent and efferent neuron, with or without interpolated adjustor 



neurons, so associated as to conduct impulses from a receptor to an effector; the 



functional basis of nervous coordination. 

 REGENERATION. The process of replacing a lost part. 

 RENAL. Pertaining to the kidnev. 

 REPRODUCTION. The capacity as a result of which certain cells of an organism can 



become detached and, either alone or after union with cells of another organism 



of the same kind, give rise to a new individual capable of becoming like the 



parent or parents in all essential respects; the capacity upon which continuity 



of a species depends. 

 REPRODUCTIVE ORGAN, fe GONAD. 

 RESEARCH. Continued search after facts and principles. 

 RESPIRATION. A general term which subsumes (1) external gas exchange between 



the organism and its environment; (2) transport of oxygen and carbon dioxide 



between the point of external exchange and the cells; and (3) the utilization of 



oxvgcn in cellular metabolism. See GAS EXCHANGE, METABOLISM, and CELLULAR 



RESPIRATION. 

 RESPIRATORY. Pertaining to respiration. 

 RESPIRATORY EXCHANGE. See GAS EXCHANGE. 

 RESPONSIVENESS. The capacity enai)ling living cells to respond to stimuli; the 



(apacit\- respon.sible for coordination and behavior. 

 RETRACTOR MUSCLE. A muscle that withdraws a part or pulls it backward. CJ. 



PROTRACTOR MUSCLE. 

 RHABDITE. A rod-like structure produced in certain epidermal gland cells among 



free-living turbellarians; function unknown, but may be involved in adhesion to 



the substrate. 

 RUDIMENTARY. Embryonic; not completely developed; having no function; frequently 



but not correctly used to mean vestigial. 



SAPROZOIC. A form of nutrition in which the organism requires external sources of 

 organic nutrients which are not, however, ingested in particulate form but 

 absorbed in solution through the body wall. CJ. HOLOZOIC and HOLOPHYTIC. 



SCHEMATIC. Made or done according to a fundamental plan. 



SCHIZOCOEL. A coelom formed through the development and enlargement of clefts 

 or spaces within previously solid rods or blocks of mesodermal cells, proliferated 

 from mesoblasts or pole cells. C!f. ENTEROCOEL. 



SCIENCE. Knowledge gained by systematic observation, experimentation, and reason- 

 ing; factual information, correlated and systematized. 



SECOND FILIAL GENERATION. The offspring from a mating of individuals of an F\ 

 generation; the F2 generation. 



SECRETION. Substance released from a cell, necessary for normal functions of the 

 individual; also, the process of production and release of the substance. 



SEDENTARY. Remaining in one place; not free-swimming, as a tube-dwelling animal. 

 CJ. SESSILE. 



SEGMENT. A part cut off or marked as separate from others; a natural division of 

 the body or a part of it. CJ. SOMITE. 



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