--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 flower stem and spread out like the wires of an
umbrella, so as to bring all the flowers in the same head (UMBEL) nearly to
the same level. (Examples, parsley and carrot.)
UNGULATA.--Hoofed quadrupeds.
UNICELLULAR.--Consisting of a single cell.
VASCULAR.--Containing blood-vessels.
VERMIFORM.--Like a worm.
VERTEBRATA or VERTEBRATE ANIMALS.--The highest division of the animal
kingdom, so called from the presence in most cases of a backbone composed
of numerous joints or VERTEBRAE, which constitutes the centre of the
skeleton and at the same time supports and protects the central parts of
the nervous system.
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