HEMIPTERA.--An order or sub-order of insects, characterised by the possession of a jointed beak or rostrum, and by having the fore-wings horny in the basal portion and membranous at the extremity, where they cross each other. This group includes the various species of bugs.

HERMAPHRODITE.--Possessing the organs of both sexes.

HOMOLOGY.--That relation between parts which results from their development from corresponding embryonic parts, either in different animals, as in the case of the arm of man, the fore-leg of a quadruped, and the wing of a bird; or in the same individual, as in the case of the fore and hind legs in quadrupeds, and the segments or rings and their appendages of which the body of a worm, a centipede, etc., is composed. The latter is called serial homology. The parts which stand in such a relation to each other are said to be homologous, and one such part or organ is called the homologue of the other. In different plants the parts of the flower are homologous, and in general these parts are regarded as homologous with leaves.

HOMOPTERA.--An order or sub-order of insects having (like the Hemiptera) a jointed beak, but in which the fore-wings are either wholly membranous or wholly leathery, The Cicadae, frog-hoppers, and Aphides, are well-known examples.

HYBRID.--The offspring of the union of two distinct species.

HYMENOPTERA.--An order of insects possessing biting jaws and usually four membranous wings in which there are a few veins. Bees and wasps are familiar examples of this group.

HYPERTROPHIED.--Excessively developed.

ICHNEUMONIDAE.--A family of hymenopterous insects, the members of which lay their eggs in the bodies or eggs of other insects.

IMAGO.--The perfect (generally winged) reproductive state of an insect.

INDIGENES.--The aboriginal animal or vegetable inhabitants of a country or region.

INFLORESCENCE.--The mode of arrangement of the flowers of plants.

INFUSORIA.--A class of microscopic animalcules, so called from their having originally been observed in infusions of vegetable matters. 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. The former, including the greater part of the class, are called PLACENTAL MAMMALS; the latter, or APLACENTAL MAMMALS, include the Marsupials and Monotremes (ORNITHORHYNCHUS).

MAMMIFEROUS.--Having mammae or teats (see MAMMALIA).

MANDIBLES.--in insects, the first or uppermost pair of jaws, which are generally solid, horny, biting organs. In birds the term is applied to both jaws with their horny coverings. In quadrupeds the mandible is properly the lower jaw.

MARSUPIALS.--An order of Mammalia in which the young are born in a very incomplete state of development, and carried by the mother, while sucking, in a ventral pouch (marsupium), such as the kangaroos, opossums, etc. (see MAMMALIA).

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