400 PRINCIPLES OF ANIMAL BIOLOGY 



Siphon. A passageway for currents of water; as the clefts l)etweeii the lialvcs of 



the mantle of mussels where the edges do not meet, or the tulie on tlie Aeiitnil 



side of a scjuid or cuttlefish. 

 Siphonophora {si' fo nof o ra). An order of Hydrozoa (C'oelenterata), the members 



of wliich form highly polymorphic colonies. Example, Physalia, the Portuguese 



man-of-war. 

 Siphonops {si' fo nops). A genus of caecilians (Apoda, Amphibia). 

 Siren. A genus of salamanders. 

 Skeleton. A framework of hard parts serving for support, protection, or movement, 



or a combination of these functions, in animals. 

 Slime tube. A sheath of mucous material secreted on the surface of an earthworm 



at the time of mating. 

 Small intestine. That part of the intestine of vertebrates immediately following 



the stomach, as distinguished from the large intestine. 

 Smooth muscle. Muscle composed of nonstriated, uninucleate, spindle-shaped cells. 



It is common in the intestine, bladder, and glands of vertebrates. 

 Socrates {sok' ra teez). Greek philosopher who lived about 470-399 b.c. 

 Solanum (so la' num). A genus of plants including the common potato, nightshade, 



and many others. 

 Solution. A liquid containing another substance in the form of particles not greater 



than molecules in size. 

 Soma. The body, as contrasted with the germ cells. 

 Somatic. Pertaining to the body; when applied to cells, referring to the sterile bodj- 



cells in contrast to the germ cells which are reproductive. 

 Somite. One of the segments into which the body of a worm or arthropod or othei- 



segmented animal is divided. 

 Species {pL, species). A group of animals or plants so nearly alike that, in general. 



they might have sprung from the same parents. (The term is rather arbitrarily 



used, however.) 

 Specific. Pertaining to a species. 



Sperm. One of the male germ cells in an animal or plant ; also called sperm cell. 

 Spermary. See testis. 

 Spermatheca. See seminal receptacle. 

 Spermatid. One of the two cells formed by the second division in spermatogenesis. 



By transformation in shape the spermatids become mature spermatozoa. 

 Spermatocyte {sper' ma to site'). A male germ cell between the beginning of sperma- 

 togenesis and the second division in that process. A spermatocyte is called 



primary during the growth period and prior to the first division; secondary aft(>r 



the first division but ])rior to the second. 

 Spermatogenesis {sper' iim to jen' e sife). The ripening of male germ cells. 

 Spermatogonium {sper' nia to go' ni um)^ {pi, spermatogonia!. One of the early 



germ cclis of a male animal, prior to the Ix'giiuiing of spermatog(>nesis. 

 Spermatophore {sper' ma to fore'). A mass of spermatozoa, sometimes resting upon 



a stalk or being otherwise attached, as in some salamanders. 

 Spermatozoon {sper' ma to zo' on) {pL, spermatozoa). The male germ cell in animals. 

 Sphenodon (sfen' o don). A genus of reptiles of tlie order Rhynchocephalia. Only 



on(; living species is known. 

 Spheroid. Of nearly s])lierical shape. 

 Spicule. A body of various shapes commonly of calcareous or siliceous material, 



forming part of the skeleton of a sponge. 

 Spinal cord. That part of the central nervous system of vertebrate animals lying 



behind the brain and largely enclosed in a chaiuicl in the vertebrae. 



