GLOSSARY 519 



Mesothelium (mes 6 tlie'li um), the mesodermic, membranous lining of the peri-" 

 toneal cavity. 



Mesovarium (mes 6 va'rium), the mesentery in which the ovary is suspended. 



Metabolism (me tab'6 liz'm), the building up of living protoplasm and its con- 

 current oxidation. 



Metagenesis (met a.ien'e sis), an alternation of sexual and asexual generation 

 in the life cycle of an organism, 



Metameres (met'a mers), one oi a series of similar parts that follow one another 

 in a vertebrate or articulate animal. 



Metamerism (me tam'er iz'm), serial symmetry or succession of segments. 



Metamorphosis (met a mor'fo sis), the transformation of one developmental stage 

 into another without intermediate steps. 



Metaphase (met'a faz), the phase of mitosis involving the longitudinal splitting 

 of the chromosomes on the equatorial plate. 



Metazoa (met'a z5 a), animals whose bodies consist of few or many cells func- 

 tioning as a unit. 



Micronucleus (mi kro nu kle us), the small nucleus of certain protozoans sup- 

 posed to control reproduction. 



Micropyle (mi'kropil), the small opening in the egg where sperm enter in cer- 

 tain forms of animals. 



Milt (milt), the light-colored spermatic fluid of male fisli. 



Miracldium (mi ra sid'i fim), the early larval stages in the flukes. 



Mitochondria (mit 6 kon'dri a), small structures in the cytoplasm of animal 

 cells; their significance is not entirel}^ understood. 



Mitosis (mito'sis), indirect cell division, involving the formation and splitting 

 of chromosomes and their equal distribution to daughter cells. 



Molt (molt), a complete or gradual shedding of the outer covering. 



Monodelphia (mon 6 del'fi a), having a placenta. 



Monoecious (mone'shiis). (See Hermaphroditic.) 



Monohybrid (mon 6 hi'brid), an offspring of parents which differ by only one 

 character. 



Morphology (mor fol'o ji), the science that treats of the form and structure of 

 the bodies of animals. 



Morula (mor'ula), a type of blastula characterized by the absence of a seg- 

 mentation cavity. 



Mucosa (miiko'sa), a cellular membrane lining such cavities as those of the 

 digestive tract. 



Mucus (mii'kus), a viscous secretion which contains mucin (mu'sin). Mucous 

 is the adjective form. 



Mutation (muta'shun), a heritable change in an organism due to changes in 

 one or more genes of germ cells. 



Mutualism (mu'tii al iz'm), animals of different species associating together for 

 the mutual advantage of each. 



Myelencephalon (mi e len sef'alon), the fifth or most posterior division of the 

 vertebrate brain; the medulla oblongata of the adult. 



Myelin (mi'elin), fatty substance surrounding the axone in medullated nerve. 



Myoneme (mi'onem), contractile fiber or strand in the cytoplasm of certain 

 protozoans. 



Myotomes (mi'otoms), segmental divisions of the muscles. 



Nares (ua'rez), the openings into the nasal cliambers in vertebrate animals. 



Nauplius (no'plins), a larval stage of certain Crustacea. 



Nekton (nek'ton), the pelagic aquatic animals which are independent of the 



effect of wind and waves. 

 Nematocysts (nem'a to sists), stinging bodies found in the tentacles of certain 



coelenterates. 

 Nematode (nem'a tod), a roundworm belonging to class Nematoda of phylum 



Nemathelminthes. 

 Neoteny (neot'eni), the indefinite persistence of the immature condition of an 



animal. 



