302 MANUAL OF ZOOLOGY. 







MEROSTOMATA (Gr. meron, thigh ; stoma, mouth). An order of Crustacea, in 

 which the appendages which are placed round the mouth and which offi- 

 ciate as jaws, have their free extremities developed into walking or pre- 

 hensile organs. 



MESENTERIES (Gr. mesos, intermediate; enteron, intestine). In a restricted 

 sense, the vertical plates which divide the somatic cavity of a Sea-anemone 

 (Actinia} into chambers. 



MESOPODIUM (G-r. mesos, middle; pous, foot). The middle portion of the 

 ' foot ' of Molluscs. 



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

 thorax in Insects. 



MESOZOIC (Gr. mesos ; and zoe, life). The Secondary period in Geology. 



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

 foot in Mollusca ; often called the ' operculigerous lobe,' because it deve- 

 lopes the operculum, when this structure is present. 



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

 mouth posteriorly in the Crustacea. 



METATHORAX (Gr. meta, after; thorax, the chest). The posterior ring of the 

 thorax in insects. 



MIMETIC (Gr. mimetiJcos, imitative). Applied to organs or animals which 

 resemble each other in external appearance but not in essential structure. 



MOLLUSCA (Lat. mollis, soft). The sub-kingdom which includes the Shell- 

 fish proper, the Polyzoa, the Tunwata, and the Lamp-shells ; so called 

 from the generally soft nature of their bodies. 



MONADS (Gr. monas, solitary). Microscopical organisms of an extremely 

 simple character, developed in organic infusions. 



MONOCULOUS. Possessed of only one eye. 



MONOECIOUS (Gr. monos, single ; oikos, house). Applied to individuals in 

 which the sexes are united. 



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

 (Lamellibranchiata) in which the shell is closed by a single adductor 

 muscle. 



MONOTHALAMOUS (Gr. monos ; and thalamos, chamber). Possessing only a 

 single chamber ; applied to the shells of Foraminifera and Mollusca. 



MULTILOCULAR (Lat. multus, many ; loculus, a little purse). Divided into 

 many chambers. 



MULTIVALVE. Applied to shells which are composed of many pieces. 



MYRIAFODA (Gr. murios, ten thousand ; poda, feet). A class of Arthro- 

 poda, 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. 



NATATORY (Lat. narc, 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 Scole- 

 cida, comprising the Round-worms, Thread- worms, &c. 



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

 Ccelcnterata. (See Cnidse.) 



NEMATOIDEA (Gr. nema, thread; eidos, form). An order of Scolecida com- 

 prising the Thread-worms, Vinegar-eels, &c. 



NKMATOPHORES (Gr. nema, thread ; phero, I carry). Csecal processes, found 

 on the ccenosarc of certain of the Sertularida, containing numerous 

 thread-cells at their extremities. 





