576 GLOSSARY. 



MESOPODIUM (Or. metot, middle ; pout, foot). The middle portion of the 

 "foot "of Molluscs. 



MESOSTERNUM (Or. mesos, intermediate ; sternon, the breast-bone). The 

 middle portion of the sternum, intervening between* the attachment of the 

 second pair of ribs and the xiphoid cartilage (xiphitternum). 



MESOTHOHAX (Gr. mesos; and thorax, the chest). The middle ring of the 

 thorax in Insects. 



MKSOZOIC (Gr. mesox; and zoe, life). The Secondary period in Geology. 



METACARPUS (Gr. meta, after ; karpos, the wrist). The bones which form the 

 " root of the hand," and intervene between the wrist and the fingers. 



METAMORPHOSIS (Gr. met a, implying change ; morplte, shape). The changes 

 of form which certain animals undergo in passing from their younger to 

 their fully-grown condition. 



METAPODIUM (Gr. meta, after ; pous, the foot). The posterior lobe of the foot 

 in Mollufca ; often called the " operculigerous lobe," because it develops 

 the operculum when this structure is present. 



METASTOMA (Gr. meta, after ; stoma, mouth). The plate which closes the 

 mouth posteriorly in the Crustacea. 



METATARSUS (Gr. meta, after ; tarsot, the instep). The bones which inter- 

 vene between the bones of the ankle (tarsus) and the digits in the hind-foot 

 of the higher Vertebrates. 



METATHORAX (Gr. meta, after ; t/iorax, the chest). The posterior ring of the 

 thorax in Insects. 



MIMETIC (Gr. mimetikos, imitative). Applied to organs or animals which re- 

 semble each other in external appearance, but not in essential structure. 



MOLARS (Lat. mo/a, a mill). The "grinders" in man, or the teeth in diphyo- 

 dont Mammals which are not preceded by milk-teeth. 



MoLLOSCA (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 Molliuca, 

 comprising the Polyzoa, Tunicata, and Brachiopoda. 



MONODELPHIA (Gr. monos, single; delphus, womb). The division of Mammalia 

 in which the uterus is single. 



MONOMYARY (Gr. mono*, single ; muon, muscle). Applied to those bivalves 

 (Lamelliliranchiata) in which the shell is closed by a single adductor muscle. 



MONOPHYODOXT (Gr. monos ; phuo, I generate ; odous, tooth). Applied to 

 those Mammals in which only a single set of teeth is ever developed. 



MONOTHALAMOUS (Gr. moiios ; and tkalamos, chamber). Possessing only * 

 single chamber. Applied to the shells of Foraminifera and Mollusca. 



MONOTREMATA (Gr. monos ; trema, aperture). The order of Mammals com- 

 prising the Duck-mole and Echidna, in which the intestinal canal opens 

 into a " cloaca" common to the ducts of the urinary and generative organs. 



MOLTILOCULAR (Lat. multus, many; loculns, a little purse). Divided into 

 many chambers. 



MuLTl VALVE. Applied to shells which are composed of many pieces. 



MULTDXOULA (Lat. multus, many ; ungula, hoof). The division of Perisso- 

 dactyle Ungulates, in which each fool has more than a single hoof. 



MYRIAPODA or MYRIOPODA (Gr. mvriot, 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 Xautilus in shape. 

 NERVURES (Lat. ncrvus, a sinew). The ribs which support the membranous 



wings of insects. 



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

 NKURAPOPHY8IS (Gr. neuron, a nerve ; apophtuit, a projecting part). The 



