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COLLEGE ZOOLOGY 



the partitions in the body cavity of antho- 

 zoan coelenterates. 

 Mes'o-derm (Gr. mesos, middle; derma, skin). 

 The middle layer of embryonic cells, be- 

 tween the ectoderm and endoderm. 

 Mes'o-gle"a (Gr. mesos, middle; gloia, glue). 

 Nonccllular jellylike substance lying between 

 the epidermis and gastrodermis in coelen- 

 terates such as the hydra; also other jellylike 

 layers as in the sponge. 

 Mes'o-neph"ric duct (Gr. mesos, middle; 

 nephros, kidney). Duct leading from the 

 mesonephric type of kidney to the cloaca. 

 Mes'o-neph"ros (Gr. mesos, middle; nephros, 

 kidney). A type of vertebrate kidney. It is 

 present in the embryos of most vertebrates, 

 but is replaced by another type in reptiles, 

 birds, and mammals before birth. It is the 

 functional kidney in the adult vertebrate 

 from cyclostomes to amphibians, inclusive. 

 Me-tab'o-Iism (Gr. meta, beyond; ballein, to 

 throw). The sum total of the reactions, 

 mainly chemical, that occur within the 

 protoplasm of an organism. 

 Mefa-car^pals (Gr. meta, after; L. carpus, the 



wrist). Proximal bones of the hand. 

 Met'a-gen"e-sis (Gr. meta, over; genesis, 

 origin ) . The alternation of a sexual with an 

 asexual generation in reproduction in the 

 life cycle of a coelentcrate such as Obelia. 

 Same as alternation of generations. 

 Met'a-mere (Gr. meta, over; meros, part). 

 One of a series of homologous segments in 

 a bodv; a somite. 

 Me-tam'er-ism (Gr. meta, beyond; Gr. meros, 

 part). The condition where the body of an 

 animal is made up of a succession of homolo- 

 gous parts (metameres). 

 Met'a-mor"pho-sis (Gr. meta, over; morphe, 

 form). A marked structural change or trans- 

 formation during development; for example, 

 as from the larva to the adult. 

 Met'a-phase (Gr. meta, after; phasis, appear- 

 ance). The stage of mitosis during which 

 the chromosomes are lined up in the equa- 

 torial plane of the spindle. 

 Met'a-pleu"ral folds (Gr. meta, after; pleura, 

 side). Two folds on the anterior, ventral 

 surface of the amphioxus, extending pos- 

 teriorly from the mouth to the atriopore. 

 Met'a-tar"sals (Gr. meta, after; L. tarsus, 

 ankle). Proximal bones of the foot. 



Met'a-zo"a (Gr. meta, after; zoion, animal). 

 All multicellular animals in which there is 

 a differentiation of the soma (body cells); 

 usually includes all animals but Protozoa. 



Mi'cron (Gr. mikros, small). The 34ooo P^'^^ 

 of a millimeter. 



Mi-gra'tion (L. migratio, removal from one 

 place of abode to another). Movement of a 

 part of a population of a species (usually in 

 groups) from one region to another. 



Mirii-li"ter (L. mille, one thousand; G. litra, 

 pound). The Viooo P^^t of a liter; for all 

 practical purposes, equivalent to a cubic 

 centimeter. Abbreviated ml. 



Mit'o-chon"dri-a (Gr. mitos, thread; chondros, 

 grain ) . Small, spherical or rodlike, cytoplas- 

 mic structures, associated with important 

 metabolic reactions in a cell. 



Mi-to'sis (Gr. mitos, thread). Cell division 

 during which chromosomes appear to be- 

 come doubled longitudinally, the halves of 

 each one passing into separate daughter cells. 

 Mitosis is sometimes considered, in a re- 

 stricted sense, as only nuclear division. 



Molt (M.E. mouten, from L. mutare, to 

 change). To cast off the exoskeleton. To 

 shed portions of the skin, feathers, or hair. 



Mo-noe'cious. See Hermaphrodite. 



Mon'o-hy"brid (Gr. monos, single; L. hybrida, 

 mongrel ) . A hvbrid with respect to only 

 one pair of allelic genes as Aa or Bb. 



Mon'o-ploid. See Haploid. 



Mor-phol'o-gy (Gr. morphe, form; logos, dis- 

 course). The study which deals with the 

 form and structure of organisms. 



Mu'cous (L. mucus, slime). Pertaining to 

 mucus. 



Mu'cous mem'brane (L. mucus, slime. L. 

 memhrana, membrane). Consists of an 

 epithelium with some subepithelial connec- 

 tive tissue, which lines cavities that com- 

 municate with the exterior. In some cases, 

 as in the digestive tract, the mucosa includes 

 the muscularis mucosae. 



Mu'cus (L. mucus, slime). A viscous secretion 

 containing mucin; a product of the mucous 

 glands. 



Mus"cu-Ia'ris mu-co'sae (L. musculus, muscle. 

 L. mucus, slime). Thin layer of smooth 

 muscle between the tunica propria and the 

 submucosa in the wall of the esophagus, 

 stomach, and intestine. 



