o one of the pairs of jaws in _Crustacea_
and Spiders, to the beak of Cephalopods, the lower jaw of
Vertebrates, &c.

MANTLE. The external integument of most of the Mollusca, which
is largely developed, and forms a cloak in which the viscera
are protected. Technically called the "pallium."

MANUS (Lat. the hand). The hand of the higher Vertebrates.

MARSIPOBRANCHII (Gr. _marsipos_, a pouch; _bragchia_, gill).
The order of Fishes comprising the Hag-fishes and Lampreys, with
pouch-like gills.

MARSUPIALIA (Lat. _marsupium_, a pouch). An order of Mammals in
which the females mostly have an abdominal pouch in which the
young are carried.

MASTODON (Gr. _mastos_, nipple; _odous_, tooth). An extinct genus
of Elephantine Mammals.

MEGALONYX (Gr. _megas_, great; _onux_, nail). An extinct genus
of Edentate Mammals.

MEGALOSAURUS (Gr. _megas_, great; _saura_, lizard). A genus of
Deinosaurian Reptiles.

MEGATHERIUM (Gr. _megas_, great; _therion_, beast). An extinct
genus of Edentata.

MESOZOIC (Gr. _mesos_, middle; and _zoe_, life). The Secondary
period in Geology.

MICROLESTES (Gr. _mikros_, little; _lestes_, thief). An extinct
genus of Triassic Mammals.

MILLEPORA (Lat. _mille_, one thousand; _porus_, a pore). A genus
of "Tabulate Corals."

MIOCENE (Gr. _meion_, less; _kainol_, new). The Middle Tertiary
period.

MOLARS (Lat. _mola_, a mill). The "grinders" in man, or the teeth
in diphyodont Mammals which are not preceded by milk-teeth.

MOLLUSCA (Lat. _mollis_, soft). The sub-kingdom which includes
the Shell-fish proper, the _Polyzoa_, the _Tunicata_, and the
Lamp-shells; so called from the generally soft nature of their
bodies.

MOLLUSCOIDA (_Mollusca_; Gr. _eidos_, form). The lower division
of the _Mollusca_, comprising the _Polyzoa, Tunicata_, and
_Brachiopoda_.

MONOGRAPTUS (Gr. _monos_, single; _grapho_, I write). A genus
of Graptolites.

MYLODON (Gr. _mulos_, a mill; _odous_, tooth). An extinct genus
of Edentate Mammals.

MYRIAPODA or MYRIOPODA (Gr. _murios_, ten thousand; _podes_,
feet). A class of _Arthropoda_ comprising the Centipedes and their
allies, characterised by their numerous feet.

NATATORES (Lat. _nare_, to swim). The order of the Swimming Birds.

NATATORY (Lat. _nare_, to swim). Formed for swimming.

NAUTILOID. Resembling the shell of the _Nautilus_ in shape.

NERVURES (Lat. _nervus_, a sinew). The ribs which support the
membranous wings of insects.

NEUROPTERA (Gr. _neur