398 PRINCIPLES OF ANIMAL BIOLOGY 



Reptilia. A class of vertebrate animals including the snakes, lizards, crocodiles, 



turtles, and some others. For definition see Chap. 19. 

 Respiration. The gaseous metabolism of protoplasm, including elimination of carbon 



dioxide, usually absorption of oxygen, and, according to some physiologists, the 



chemical reactions which consume oxygen or produce carbon dioxide. 

 Retina {ret' i no). The sensitive inner layer of the eye of vertebrates and some other 



animals. 

 Retractile. Capable of being withdrawn. 

 Rhabdocoele {rab' do seel). A flatworm (Platyhelminthes) of the order Rhabdo- 



coelida. 

 Rhinozoa (ri' no zo' a). A group of animals (literally, nose animals) in Oken's early 



classification. It comprised the reptiles. 

 Rhizopoda (n zop' o da). A class of Protozoa having a form that is changeable 



through the production of pseudopodia; example. Amoeba. 

 Rhynchocephalia (ring' ko se fa' U a) . An order of Reptiha, comprising only one 



living form, Sphenodon, of the New Zealand region. 

 Riboflavin (ri' bo fla' vin). Vitamin B2, the preventive of scaliness of skin, tendency 



to cataract, etc. 

 Rodent. A gnawing mammal, a member of the order Rodentia (rats, mice, squirrels, 



etc.). 

 Rodentia. The order of mammals including the rodents (rats, mice, squirrels, etc.). 

 Rotifera (ro tif er a). A group of animals (the rotifers) usually regarded as a separate 



phylum, but of uncertain position in the animal kingdom. For definition see 



Chap. 19. 



Sacculina (sak' ku W na). A degenerate crustacean, related to the barnacles, para- 

 sitic on crabs. 



Sacral. Pertaining to the sacrum, the region between the hips. 



Sacrum. A group of vertebrae, more or less fused, in the region between the hips. 



Sagitta (so jit' ta). A marine animal of small size, sometimes called the arrowworm, 

 but not a true worm at all. Its relationship to other animals is obscure. 



Salientia (sa' li en' shi a). An order of Amphibia including the tailless forms (frogs, 

 toads). 



Saliva. The fluid secreted by the salivary glands about the mouth. 



Salivary. Pertaining to saliva, the fluid secreted into the mouth in mammals. 



Salt. A compound, other than an acid or base, which in solution produces ions. 



Sarcolemma. The membrane surrotmding a striated muscle cell. 



Sarcoplasm. The protoplasm of a striated muscle cell, as distinguished from the 

 enclosed myofibrils. 



Sargasso sea. A great eddy in an ocean, enclosing masses of seaweeds; with capital- 

 ized initials the name may be limited to the eddy of the North Atlantic Ocean. 



Sargassum. A genus of seaweeds. 



Scaphiopus (ska fi' pus). A genus of spadefoot toads. 



Scaphites (.skaf i' ieez). A genus of extinct cepliMlopods of the ammonitic form. 



Scaphopoda (skaf op' da). A class of MoUusca in which the shell and mantle are 

 tubular, as in Dentalium. 



Scapula. The shoulder blade; a bone of the pectoral girdle, located on or near the 

 dorsal side of the body. 



Schleiden, Matthias (shli' den). German botanist, 1804-1881. 



Schultze, Max (shooW sa). German biologist and anatomist, 1825-1874. 



Schwann, Theodor (shvahn). German physiologist and anatomist, 1810-1882. 



