Sworm 



A dense aggregation of minute aquatic organisms, or of 

 certain insects such as bees and midges. 



Sweep-net Method 



A technique for determining an evaluation of the density 

 of insects and other invertebrates in an area by making a 

 certain number of swings of a standard entomological sweep 

 net. 



Sweepstakes Bridge 



The accidental transportation of organisms across a bar- 

 rier from one area to another, usually where no land connec- 

 tion occurs, e. g., the migration of a few kinds of animals 

 from Africa to Madagascar, cf. Filter bridge, Corridor. 



Symbiont 



In a broad sense an organism that lives in close associa- 

 tion with another, cf. Symbiosis. 



Symbiosis 



In a broad sense the living together of two or more or- 

 ganisms of different species; including Parasitism, Mutual- 

 ism, and Commensalism (q. v.). cf. Coaction. In a narrow 

 sense synonymous with mutualism. 



Symmetry 



The condition of similarity in form or structure in the 

 parts of an organism on each side of an axis dividing it. 

 cf. Bilateral symmetry, Zygomorphy. 



Sympatric 



Refers to the origin or area of occupation of two or more 

 closely related species in the same geographical area. cf. 

 Allopatric. 



Synapse 



One of the places in the nervous system of animals where 



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