The Infusoria, Foraminifera, and Sponges, with some other forms, belong to this division. PUPA(pl PUPÆ). 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 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 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 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 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. 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 vertebræ 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. SCUTELLÆ The horny plates with which the feet of birds are generally more or less covered, especially in front. SEDIMENTARYFORMATIONS 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, but sometimes brightly coloured. SERRATURES Teeth like those of a saw. SESSILE Not supported on a stem or footstalk. SILURIANSYSTEM A Very ancient system of fossiliferous rocks belonging to the earlier part of the Palæozoic series. SPECIALISATION The setting apart of a particular organ for the performance of a particular function. SPINALCHORD The central portion of the nervous system in the Vertebrata, which descends from the brain through the arches of the vertebræ, 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.
