422 GLOSSARY 



M 



Macronu'cleus (Gr. makros, large) : the large nucleus, as opposed to the micro- 

 nucleus, or small nucleus. 



Mam'mary glands (Lat. mamma, breast) : milk-secreting glands found in mam- 

 mals. 



Man'dible (Lat. viandere, to chew) : in insects, a hard cutting jaw. 



Man'tle (Lat. mantellum, a cloak) : the soft outer fold of skin in mollusks which 

 secretes the outer shell. 



Maxilla (Lat. mxixilla, a jaw) : an appendage near the mouth of arthropods, 

 modified in insects to form an organ for getting food. 



Maxiriiped (Lat. maxilla, jaw; pes, foot) : an appendage next posterior to the 

 maxilla in arthropods. Foot jaw. 



Medulla oblonga'ta (Lat. medulla, pith) : the most posterior part of the brain. 



Med'uUary rays (Lat. medulla, pith) : thin plates of pith which separate the 

 wood of dicotyledonous stems into wedge-shaped masses. 



Mes'oderm (Gr. mesos, middle ; dermxi, skin) : the middle layer of cells in a 

 young animal embryo. 



Metab'olism (Gr. metaholos, changeable) : changes taking place continually in 

 living cells which may result in either building up or breaking down the 

 cells. 



Metamor'phosis (Gr. meta, after ; morphe, form) : change of form undergone 

 from egg to adult, as in insects. 



Mic'ropyle (Gr. micropyle, a Httle gate) : the hole where the pollen tube enters 

 the embryo sac. 



Mid'rib : central vein of a leaf. 



Mi'grant : an animal which moves from one place to another and back regularly 

 at stated seasons of the year. Many birds migrate to warmer regions 

 for the winter. 



Mimicry (Gr. mimikos, imitative) : the imitation in form or color of a harm- 

 ful insect by a harmless one which is protected thereby. 



Mol'ecules : units of a chemical substance. 



Monocotyle'don : a plant that bears seeds having but one cotyledon. 



Monohy'brid : Mendelian term for a cross between organisms which differ 

 in one pair of alternative characters. 



Mu'cous membrane (Lat. mucus, slime ; memhrana, skin) : a delicate, moist 

 membrane lining all body passages which have an external opening. 



Mus'cle (Lat. musculus, muscle) : a contractile tissue capable of bringing 

 about movement. 



Muta'tion : a heritable modification arising from internal causes in an organism. 



Myce'lium : the threadlike body of a mold, or other fungus, the individual 

 threads being called hyphse. 



N 



Narcotic (Gr. narkotikos, making dumb) : a substance which blunts the senses 

 and in large quantities causes insensibility. 



