538 GLOSSARY 



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

 rises to articulate with the skull is called the ascending ramus. 



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 organized than might be expected 

 from its early stages and known relationships, it is said to undergo 

 a retrograde development or metamorphosis. 



Rhisopods — A class of lowly organized animals (Protozoa), having a gelat- 

 inous 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. 



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. 

 Scutella — ^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 traverse 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, but sometimes brightly 



coloured. 

 Serratures — Teeth like those of a saw. 

 Sessile — Not supported on a stem or footstalk. 

 Silurian System — A very ancient system of fossiliferous rocks belonging to 



the earlier part of the Palaeozoic 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, 



which descends from the brain through the arches of the vertebrae, 



and gives off nearly all the nerves to the various organs of the body. 

 Stamens—The male organs of flowering plants, standing in a circle within 



the petals. They usually consist of a filament and an anther, the 



anther being the essential part in which the pollen, or fecundating 



dust, is formed. 

 Sternum — The breast-bone. 



Stigma — ^The apical portion of the pistil in flowering plants. 

 Stipules — Small leafy organs placed at the base of the footstalks of the 



leaves in many plants. 

 Style — The middle portion of the perfect pistil, which rises like a column 



from the ovary and supports the stigma at its summit. 

 Subcutaneous—Situated beneath the skin. 

 Suctorial — Adapted for sucking. 

 Sutures (in the skull) — ^The lines of junction of the bones of which the 



skull is composed. 



Tarsus (pi. Tarsi) — The pointed feet of articulate animals, such as Insects. 



Teleostean Fishes — Fishes of the kind familiar to us in the present day, 



having the skeleton usually completely ossified and the scales horny. 



