332 awasAJRY 



Radicle. — The minute root of an embryo plant. 



Ramus. — One-half of the lower jaw in the Mammalia. The 

 portion which rises to articulate with the skull is called 

 the ascending ramus. 



Range. — The extent of country over which a plant or ani- 

 mal is naturally spread. Range in time expresses the 

 distribution of a species or group through the fossilifer- 

 ous beds of the earth's crust. 



Retina. — The delicate inner coat of the eye, formed by 

 nervous filaments spreading from the optic nerve, and 

 serving for the perception of the impressions produced 

 by light. 



Retrogression. — Backward development. When an ani- 

 mal, as it approaches maturity, becomes less perfectly 

 organized than might be expected from its early stages 

 and known relationships, it is said to undergo a retrograde 

 development or metamorphosis. 



Rhizopods. — A class of lowly organized animals (Protozoa), 

 having a gelatinous body, the surface of which can be 

 protruded in the form of rootlike processes or filaments, 

 which serve for locomotion and the prehension of 

 food. The most important order is that of the Foram- 

 inifera. 



Rodents. — The gnawing Mammalia, such as the Rats, Rab- 

 bits, and Squirrels. They are especially characterized 

 by the possession of a single pair of chisel-like cutting 

 teeth in each jaw, between which and the grinding teeth 

 there is a great gap. 



RuBUS.— The Bramble Genus. 



Rudimentary. — Very imperfectly developed. 



Ruminants. — The group of Quadrupeds which ruminate 

 or chew the cud, such as oxen, sheep, and deer. They 

 have divided hoofs, and are destitute of front teeth in 

 the upper jaw. 



Sacral. — Belonging to the sacrum, or the bone composed 

 usually of two or more united vertebrae to which the 

 sides of the pelvis in vertebrate animals are attached. 



