=Met-a-dis-coi´dal= [Gr. _meta_, after; _diskos_, disk; _eidos_, appearance.] Resembling a discoidal form. =Met-a-mor´pho-sis= [Gr. _meta_, over; _morphe_, form.] The series of pronounced external changes through which an animal passes after leaving the egg-envelopes and before reaching sexual maturity. =Met-a-phy´ta= [Gr. _meta_, above, higher; _phyton_, plant.] =Met´a-plasm= [Gr. _metaplasmos_, transformation.] =Met-a-zo´a= [Gr. _meta_, after, higher; _zoon_, animal.] =Met-en-ceph´a-lon= [Gr. _meta_, after; _enkephalos_, brain.] A fundamental segment of the brain. =Mi-cro-ceph-a´li-a= [Gr. _mikrokephalos_, small-headed.] Imperfect development of the cranium. =Mi-cren-ceph-a´li-a= [Gr. _mikros_, small; _enkephalos_, brain.] Small-brained. =Mi´cro-cosm= [Gr. _mikros_, small; _kosmos_, world.] =Micro-gro´mi-a so-ci-al´is= [Gr. _mikros_, small; _gromia_; Lat. _socialis_ < _socius_, companion.] =Mi-cro-les´tes.= =Mi´das.= A wealthy king of Phrygia. =Mi-o-hip´pus= [Miocene; Gr. _hippos_, horse.] =Mi´o-cene= [Gr. _meion_, less; _kainos_, recent.] =Mi-to´sis= [Gr. _mitos_, thread.] =Mol-lus´ca= [Lat. _mollis_, soft.] =Mon-o-cot-y-le´don-es= [Gr. _monos_, single; _kotyledon_, cup-shaped cavity.] A group of flowering plants in which the first leaves of the embryo are alternate, for which reason they are said to have one seed-leaf or cotyledon. =Mon-o-del´phi-a= [Gr. _monos_, single; _delphys_, womb.] A sub-class of mammals having a single vagina and uterus; embryo attached by a placenta; brain has a corpus callosum. Includes all animals above Monotremes and Marsupials. =Mon´o-tremes= [Gr. _monos_, single; _trema_, hole.] An order of ornithodelphians. =Mor´u-la= [Lat. dim. of _morum_, mulberry.] =Mul-ti-tu-ber-cu-la´ta= [Lat. _multus_, many; _tuberculum_, tubercle.] =My-ce´tes= [Gr. _myketes_, bellower.] =Myr-i-ap´o-da= [Gr. _myrios_, numberless; _pous_, foot.] Insects with numerous pairs of legs, as centipedes. =Nau´ti-loids= [Gr. _nautilos_, sailor; _eidos_, like.] A group of cephalopods. =Nau´ti-lus= [Gr. _nautilos_, sailor.] A cephalopod. =Nem-a-thel-min´thes= [Gr. _nema_, thread; _helmins_, worm.] =Nem-er-ti´na= [Gr. _nemertes_, unerring.] Worms with skin ciliated, proboscis retractile, and nervous, muscular, and vascular systems characteristically developed. =Ne-o-lith´ic= [Gr. _neos_, new; _lithos_, stone.] =Noc-ti-lu´ca mi-li-a´ris= [Lat. _nox_, night; _luceo_, shine; _miliarius_, < _milium_, millet.] =No´to-chord= [Gr. _notos_, the back; _chorda_, a chord.] A cartilaginous rod found in the young chordate embryo in a situation that is later on occupied by the centers of the bodies of the vertebræ. It separates a dorsal nervous system from a ventral alimentary (digestive) canal. The notochord is persistent in its entirety in Leptocardians and Marsipobranchs and also in some pisces, as the sturgeon. =O-don-tor´ni-thes= [Gr. _odous_, a tooth; _ornis_, bird.] Including all those extinct birds having teeth.