GLOSSARY 599 



MacBride, Ernest W. English biologist; 1866- . 



Mach (makh), Ernst. Austrian physicist; 1838-1916. 



macro (mak' ro). G.; large. 



macrogamete (mSk r6 ga met'). A female sex cell, or egg cell. 



macronucleus (mSk r5 nu' kle us). The larger of two nuclei in the cells of infusoria. 



Malpighi (mdl pe' ge), Marcello. Italian anatomist; 1628-1694. 



mandible (mSn' di b'l). In invertebrates, a mouth part for chewing; in vertebrates, 



the lower jaw; adj., mandibular (man dib' u lar). 

 mandibulate (man dIb' u lat). Having mandibles. 

 mantle. A fold of the body wall which more or less envelops the body; in most 



mollusks it secretes a shell, 

 marsupium (mar su' pi um). An external pouch for carrying the young; in the fresh- 

 water mussels, a part of the gills. 

 Mast, Samuel O. American biologist, at Johns Hopkins University; 1871- . 

 maturation (mat u ra' shtin). As applied to germ cells, the final stages in gameto- 



genesis, involving chromosome reduction. 

 maxilla (mak si' la). In invertebrates, an accessory mouth part situated just back 



of the mandible and used for handling food; in vertebrates, the upper jaw; adj., 



maxillary (mak' si la rl). 

 mechanism (mek' aniz'm). The view that life phenomena are to be interpreted in 



terms of the same chemical and physical laws that govern the phenomena of 



inorganic nature. 

 medulla (me dill' a). The posterior region of the vertebrate brain, also called 



medulla oblongata; also the soft central part of a gland or other organ; adj., 



medullary (m6d' u la rl). 

 medullary. In a particular sense pertaining to the embryonic structure from which 



the nervous system of chordates develops, as the medullary groove or tube. 

 medullated (m6d' ti lat 6d). Term applied to a nerve fiber which possesses a fatty 



sheath. 

 medusa (me du' sa). A jelly fish, which is a free-swimming individual coelenterate. 

 meiosis (mi 5' sis). The reduction division in the maturation of germ cells; adj., 



meiotic (mi 6t' ik). 

 membrane (m6m' bran). A thin sheet of tissue; also a thin sheet of matter secreted 



by cells or in a cell; adj., membranous (m6m' bra nus). 

 Mendel, Gregor J. Austrian monk and botanist; 1822-1884. 

 mer (mer). G.; part. 



meridional (me rid' I 6 nal). AppUed to lines or planes running from pole to pole, 

 meroblastic (mer 6 bias' tik). The term applied to an egg cell which in cleavage is 



only partly divided into blastomeres. 

 Merriam, C. Hart. American biologist; 1855- . 

 mes (m6s). G.; middle, 

 mesencephalon (m6s 6n s6f' al6n). The third region, or midbrain, of vertebrates, 



including the optic lobes. 

 mesenchyme (m6s' 6n kim). A mesodermal mass of branched, irregular cells in the 



embryo from which arise the connective tissues generally; also written mesen- 



chyma (m6s gn'kima), a term which is also applied to the mass of connective 



tissue that occupies the center of the body in some lower forms, such as the 



planarians. 

 mesentery (mSs' 6n tgr i). A double sheet of tissue attaching the alimentary canal 



to the body wall in vertebrates; or thin sheets of tissue connecting the stomodeum 



to the body wall in sea anemones; adj., mesenteric (m6s en ter' ik). 

 mesoderm (mes' 6 diirm). The middle germ layer in embryogeny; adj., mesodermal 



(m6s 6 d<ir' mal). 



