PUPAE).--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 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.

SCUTELLAE.--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 ordi