GLOSSARY. 413 



PROTEAN. Exceedingly variable. 



PROTOZOA. The lowest great division of the Animal Kingdom. These 

 animals are composed ot 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.B). 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. 



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 rarnus. 



RANGE. The extent of country over which a plant or animal is naturally 

 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 filaments 

 spreading from the optic nerve, and serving for the perception of the 

 impressions produced by light. 



RETROGRESSION. Backward development. When an animal, as it approaches 

 maturity, becomes less perfectly organised 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 organised animals (Protozoa), having a gela- 

 tinous 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 characterised 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. 



Ruuus. The Bramble Genus. 



RUDIMENTARY. Very imperfectly developed. 



RVMINANTS. 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. 

 SARCODE. The gelatinous material of which the bodies of the lowest animals 



(Protozoa) are composed. 

 SCUTELLJE. The horny plates with which the feet of birds are generally more 



or less covered, especially in front. 



SEDIMENTARY FORMATIONS. Rocks deposited as sediments from water. 

 SEGMENTS. The transverse rings of which the body of an articulate animal 



or Annelid is composed. 

 SEPALS. The leaves or segments of the calyx, or outermost envelope of an 



ordinary flower. They are usually green, out sometimes brightly coloured. 

 SERRATURES. Teeth like those of a saw. 

 SESSILE. Not supported on a stem or footstalk. 

 SILVRIAN SYSTEM. A very ancient system of fossiliferous rocks belonging to 



the earlier part of the Palicozoic series. 

 SPECIALISATION. The setting apart of a particular organ for the performance 



of a particular function. 

 SPINAL CHORD. The central portion of the nervous system in the Vertebrata, 



