alia 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).

MAXILLAE.--in insects, the second or lower pair of jaws, which
are composed of several joints and furnished with peculiar jointed
appendages called palpi, or feelers.

MELANISM.--The opposite of albinism; an undue development of colouring
material in the skin and its appendages.

METAMORPHIC ROCKS.--Sedimentary rocks which have undergone alteration,
generally by the action of heat, subsequently to their deposition and
consolidation.

MOLLUSCA.--One of the great divisions of the animal kingdom, including
those animals which have a soft body, usually furnished with a shell,
and in which the nervous ganglia, or centres, present no definite
general arrangement. They are generally known under the denomination of
"shellfish"; the cuttle-fish, and the common snails, whelks, oysters,
mussels, and cockles, may serve as examples of them.

MONOCOTYLEDONS, or MONOCOTYLEDONOUS PLANTS.--Plants in which the seed
sends up only a single seed-leaf (or cotyledon); characterised by the
absence of consecutive layers of wood in the stem (endogenous growth),
by the veins of the leaves being generally straight, and by the parts of
the flowers being generally in multiples of three. (Examples, grasses,
lilies, orchids, palms, etc.)

MORAINES.--The accumulations of fragments of rock brought down by
glaciers.

MORPHOLOGY.--The law of form or structure independent of function.

MYSIS-STAGE.--A stage in the development of certain crustaceans
(prawns), in which they closely resemble the adults of a genus (Mysis)
belonging to a slightly lower group.

NASCENT.--Commencing development.

NATATORY.--Adapted for the purpose of swimming.

NAUPLIUS-FORM.--The earliest stage in the development of many Crustacea,
especially belonging to the lower groups. In this stage the animal has a
short body, with indistinct indications of a division into segments,
and three pairs of fringed limbs. This form of the common fresh-water
CYCLOPS was described as a distinct genus under the name of NAUPLIUS.

NEURATION.--The arrangement of the veins or nervures in the wings of
insects.

NEUTERS.--Imperfectly developed females of certain social insects (such
as ants and bees), which perform all the labours of the community.
Hence, they are also called WORKERS.