GLOSSARY 



successive generations; pure lines can be sorted out of a population by selec- 

 tion. CJ. PURE LINE. 



POSTERIOR. Pertaining to or situated near the end away from the head; the hind 

 part of an animal or part; opposite to anterior. 



PREDATORY. Capturing other animals for food. 



PREHENSILE. Fitted for grasping or holding. 



PREHUMAN. Existing before the appearance of man upon the earth. 



PRIMATE. A member of the order Primates, which includes all kinds of monkeys, 

 the lemurs, and man. 



PRIMORDIAL. First in order; primitive. 



PRIMORDIUM (/;/. PRIMORDIA) A beginning. 



PROCTODEUM {pi. PROCTODEA). The ectodermal invagination which forms the most 

 l)ostcrior part of the digestive tract during development. CJ. STOMODEUM. 



PRONUCLEUS {pi. PRONUCLEI). The nucleus of a gamete; contains the haploid 

 number of chromosomes. 



PROPAGATION. The increase in numbers resulting from reproduction. 



PROTONEPHRIDIUM. A flame bulb or solenocyte, in which a tuft of cilia or a single 

 llagellum, respectively, creates currents in an intracellular duct system moving 

 fluids from lymph spaces or a pseudocoel to the exterior. Classically in- 

 terpreted as functioning in excretion, but mav be involved rather in salt and 

 water balance. 



PROTOPLASM. The contents of livins^ cells. 



PROTOZOA {smo. PROTOZOON or PROTOZOAN). The phvlum of the unicellular ani- 

 mals; unicellular animals. Cf. METAZOA. 



PROTOZOOLOGY. Fhe science of Proto/oa. 



PROTRACTOR MUSCLE. A muscle that extends a part or draws it forward. CJ. RE- 

 TRACTOR MUSCLE. 



PROXIMAL. Situated toward the center or place of attachment. Cf. DISTAL. 



PSEUDOCOEL. A body cavity that lacks a continuous peritoneal lining and does not 

 develop in mesoderm; may represent remnants of the blastocoel, and may be 

 partially occupied by mesenchyme and structures of mesodermal origin. CJ. 

 COELOM. 



PSEUDOPODIUM {pi. PSEUDOPODIA). A temporary protrusion of a cell by means of 

 whic h locomotion is etiected or extracellular material engulfed. 



PULMONARY. Pertaining to the lungs. 



PULMONATE. Having lungs or lung-like structures as specialized organs of respir- 

 atory exchange. CJ. BRANCHIATE. 



PURE LINE. A group of individuals of the same species that are homozygous for 

 some particular character or characters and consequently breed true; varia- 

 tions in a pure line are usually fluctuations. Cf. POPULATION. 



PYLORIC. Pertaining to the opening between the stomach and intestine. 



PYRAMID OF NUMBERS. Concept derived from the numerical relationships existing 

 between organisms in a community. In a food chain the basal herbivorous 

 animals are extremely numerous; at each succeeding step in the chain, numbers 

 become smaller, until the final type at the end of the chain is represented in the 

 community by only a relatively few individuals. 



RADIAL SYMMETRY. Symmetry in all planes pa.ssing through a longitudinal axis, 

 as in a cylinder, or in which parts are arranged around an axis like the spokes 

 of a wheel. 



REASSOCIATION. The coming together of parts that previously have been artificially 

 separated. 



RECEPTION. The process that occurs in a receptor; the initial response to a stimulus. 



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