nary 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 CORD.--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 (pl. TARSI).--The jointed 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.

TENTACULA or TENTACLES.--Delicate fleshy organs of prehension or touch
possessed by many of the lower animals.

TERTIARY.--The latest geological epoch, immediately preceding the
establishment of the present order of things.

TRACHEA.--The windpipe or passage for the admission of air to the lungs.

TRIDACTYLE.--Three-fingered, or composed of three movable parts attached
to a common base.

TRILOBITES.--A peculiar group of extinct crustaceans, somewhat
resembling the woodlice in external form, and, like some of them,
capable of rolling themselves up into a ball. Their remains are found
only in the Palaeozoic rocks, and most abundantly in those of Silurian
age.

TRIMORPHIC.--Presenting three distinct forms.

UMBELLIFERAE.--An order of plants in which the flowers, which contain
five stamens and a pistil with two styles, are supported upon footstalks
which spring from the top of the f