They consist of a gelatinous material enclosed in a delicate membrane, the whole or part of which is furnished with short vibrating hairs (called cilia), by means of which the animalcules swim through the water or convey the minute particles of their food to the orifice of the mouth.
INSECTIVOROUS .-- Feeding on insects.
INVERTEBRATA, or INVERTEBRATE ANIMALS .-- Those animals which do not possess a backbone or spinal column.
LACUNAE .-- Spaces left among the tissues in some of the lower animals and serving in place of vessels for the circulation of the fluids of the body.
LAMELLATED .-- Furnished with lamellae or little plates.
LARVA (pl.LARVAE) .-- The first condition of an insect at its issuing from the egg, when it is usually in the form of a grub, caterpillar, or maggot.
LARYNX .-- The upper part of the windpipe opening into the gullet.
LAURENTIAN .-- A group of greatly altered and very ancient rocks, which is greatly developed along the course of the St.Laurence, whence the name.
It is in these that the earliest known traces of organic bodies have been found.
LEGUMINOSAE .-- An order of plants represented by the common peas and beans, having an irregular flower in which one petal stands up like a wing, and the stamens and pistil are enclosed in a sheath formed by two other petals.

The fruit is a pod (or legume).
LEMURIDAE .-- A group of four-handed animals, distinct from the monkeys and approaching the insectivorous quadrupeds in some of their characters and habits.

Its members have the nostrils curved or twisted, and a claw instead of a nail upon the first finger of the hind hands.
LEPIDOPTERA .-- An order of insects, characterised by the possession of a spiral proboscis, and of four large more or less scaly wings.

It includes the well-known butterflies and moths.
LITTORAL .-- Inhabiting the seashore.
LOESS .-- A marly deposit of recent (Post-Tertiary) date, which occupies a great part of the valley of the Rhine.
MALACOSTRACA .-- The higher division of the Crustacea, including the ordinary crabs, lobsters, shrimps, etc., together with the woodlice and sand-hoppers.
MAMMALIA .-- The highest class of animals, including the ordinary hairy quadrupeds, the whales and man, and characterised by the production of living young which are nourished after birth by milk from the teats (MAMMAE, MAMMARY GLANDS) of the mother.

A striking difference in embryonic development has led to the division of this class into two great groups; in one of these, when the embryo has attained a certain stage, a vascular connection, called the PLACENTA, is formed between the embryo and the mother; in the other this is wanting, and the young are produced in a very incomplete state.