GENERAL ZOOLOGY 



SPERMIOGENESIS. The cytosomal differentiation of a spermatozoon; the transfor- 

 mation of a spermatid into a spermatozoon. 



SPINAL. Pertaining to the vertebral column. 



SPONGOCOEL. The characteristic major internal cavity of a sponge, either lined by 

 choanocytes (as in the simplest sponges) or lined by endopinacocytes and re- 

 ceiving currents of water from radially disposed flagellated chambers. 



SPORULATION. Reproduction by multiple fission. 



STERNAL. Pertaining to the ventral midregion of arthropods; pertaining to the 

 breastbone, or sternum, of vertebrates. 



STIMULUS {pi. STIMULI). An effective change in the environment that provokes a 

 response on the part of an organism. 



STOMODEUM {pi. STOMODEA). The ectodermal invagination which forms the mouth 

 cavity during development. CJ. PROCTODEUM. 



STROBILIZATION. A method of reproduction by linear budding. 



STRUCTURE. The arrangement or organization of parts of an organism. 



SUB-. Combining form, meaning "under" or "below." 



SUBSTRATUM {pi. SUBSTRATA). Anything which underlies or supports; a substrate. 



SUPER-. Combining form, meaning "over"; same as HYPER-; opposite to SUB-. 



SUPERFICIAL. Lying on or near the surface. 



SUPRA-. Combining form, meaning "above"; same as SUPER-. 



SYMBIOSIS. Any biotic situation in which two or more individuals of different species 

 arc mutually interdependent or otherwise closely related. See PARASITISM, 

 MUTUALISM, and COMMENSALISM. 



SYMMETRY. The reversed repetition of parts around an axis or on opposite sides 

 of any plane, so that mirrored halves result from a separation along the axis 

 or plane of symmetry. 



SYNAPSE. The place of contact between two nerve fibers. 



SYNAPSIS. The temporary pairing of homologous chromosomes which precedes the 

 first meiotic division; occurs during the growth period. 



SYNGAMY. See FERTILIZATION. 



SYNTHESIS. The building-up of a chemical compound from simpler compounds or 

 molecules. 



SYNTHETIC TYPE. A species that represents an intermediate condition between well- 

 recognized groups of organisms; a primitive ancestral type from which more 

 highly specialized types have arisen. 



SYSTEM. A group of structurally related organs which perform some general 

 function. 



TACTILE. Pertaining to the sense of touch. 



TAXIS. See TROPISM. 



TAXONOMY. The science of classification. 



TELOLECITHAL EGG. An egg in which the yolk is abundant and concentrated in or 

 toward the vegetal hemisphere. Cf. ISOLECITHAL EGG. 



TENTACLE. An elongated, flexible, cellular process of the bodv. 



TERRESTRIAL. Living on land. 



TESTIS {pi. TESTES). A gonad in which spermatozoa undergo differentiation. CJ. 

 OVARY. 



THEORY. A conception of how something has been brought about; an explanation 

 or correlation of observed facts; theories may be disproved, because they are 

 the products of man's thinking. 



THERMAL. Pertaining to heat. 



THORAX {pi. THORACES). A part of the body between the head and abdomen. 



TISSUE. A group of somatic cells differentiated in the same way for the perform- 

 ance of the same function. 



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