Myelon

(Gr. muelos, marrow). The spinal cord of Vertebrates.

Myriapoda or Myriopoda

(Gr. murios, ten thousand; podes, feet). A class of Arthropoda comprising the Centipedes and their allies, characterised by their numerous feet.

Nacreous

(Fr. nacre, mother-of-pearl, originally Oriental). Pearly; of the texture of mother-of-pearl.

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.

Nectocalyx

(Gr. necho, I swim; kalux, cup). The swimming-bell or "disc" of a Medusa or Jelly-fish.

Nematelmia

(Gr. nema, thread ; helmins, a worm). The division of Scolecida comprising the Round-worms, Thread-worms, etc.

Nematocysts

(Gr. nema, thread; kustis, a bag). The thread-cells of the Coelenterata. (See Cnidae.)

Nematoidea

(Gr. nema, thread; eidos, form). An order of Scolecida comprising the Thread-worms, Vinegar-eels, etc.

Nematophores

(Gr. nema, thread; phero, I carry). Caecal processes found on the coenosarc of certain of the Sertularida, containing numerous thread-cells at their extremities.

Nemertida

(Gr. Nemertes, proper name). A division of the Turbellarian Worms, commonly called " Ribbon-worms."

Nervures

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

Neural

(Gr. neuron, a nerve). Connected with the nervous system.

Neurapophysis

(Gr. neuron, a nerve; apophusis, a projecting part). The " spinous process" of a vertebra, or the process formed at the point of junction of the neural arches.

Neuropodium

(Gr. neuron, a nerve; pous, the foot). The ventral or inferior division of the "foot-tubercle" of an Annelide; often called the "ventral oar."

Neuroptera

(Gr. neuron; and pteron, a wing). An order of insects characterised by four membranous wings with numerous reticulated nervures (e.g., Dragon-flies).

Neuter

(Lat. neither the one nor the other). Having no fully developed sex.

Nidification

(Lat. nidus, a nest; facio, I make). The building of a nest.

Nocturnal

(Lat. nox, night). Applied to animals which are active by night.

Normal

(Lat. norma, a rule). Conforming to the ordinary standard.

Notobranchiata

(Gr. notos, the back ; and bragchia, gill). Carrying the gills upon the back ; applied to a division of the Annelida.

Notochord

(Gr. notos, the back; chorde, string). A cellular rod which is developed in the embryo of Vertebrates immediately beneath the spinal cord, and which is usually replaced in the adult by the vertebral column. Often it is spoken of as the "chorda dorsalis."

Notopodium

(Gr. notos, the back; and pous, the foot). The dorsal division of one of the foot-tubercles or parapodia of an Annelide; often called the " dorsal oar."