464 THE ORIGIN OF SPECIES 



Processes. — Projecting portions of bones, usually for the attachment 



of muscles, ligaments, etc. 

 Propolis. — A resinous material collected by the Hive-Bees from the 



opening buds of various trees. 

 Protean. — Exceedingly variable. 

 Protozoa. — The lowest great division of the Animal Kingdom. These 



animals are composed of a gelatinous material and show scarcely 



any trace of distinct organs. The Infusoria, Foraminifera and 



Sponges, with some other forms, belong to this division. 

 Pupa (pi. Pup^e). — The second stage in the development of an Insect, 



from which it emerges in the perfect (winged) reproductive form. 



In most insects the pupal stage is passed in perfect repose. The 



chrysalis is the pupal state of Butterflies. 



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

 which rises to articulate with the skull is called the ascending 

 ramus. 



Radicle. — The minute root of an embryo plant. 



Range. — The extent of coimtry over which a plant or animal is natu- 

 rally spread. Range in time expresses the distribution of a species 

 or group through the fossiliferous beds of the earth's crust. 



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

 ments spreading from the optic nerve and serving for the percep- 

 tion of the impressions produced by light. 



Retrogression. — Backward development. When an animal, as it ap- 

 proaches 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 root-like processes or filaments, which serve for locomotion and 

 the prehension of food. The most important order is that of the 

 Foraminifera. 



Rodents. — The gnawing Mammalia, such as the Rats, Rabbits 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. 



