572 GLOSSARY 



mesoglea (mgsogle'a). A layer, mostly noncellular, between the ectoderm and 



entoderm in coelenterates; if it contains scattered cells, these do not have the 



character of a mesoderm. 

 mesonephros (m6s 6 n6f ' r6s). The kidney of the lower vertebrates, from the lamprey 



to the amphibians; adj., mesonephric. 

 mesothelium (m6s 6 the' II um). A mesodermal sheet of cells in the embryo from 



which arise particularly the epithelia lining coelomic cavities and the striated 



muscles; adj., mesothelial. 

 meta- (mCf a). G.; after, behind. 

 metabolism (me tab' 6 liz'm). The sum of the chemical changes in a living organism, 



accompanied also by physical changes; adj., metabolic (met a b6l' ik). 

 metagenesis (m6t a j6n' esis). The regular alternation of sexual and asexual types 



of reproduction in a given species of animal. 

 metamere (mgf amer). One of a lineal series of sections into which the bodies of 



the higher invertebrates and the vertebrates are divided; adj., metameric 



(met amgr'Ik). 

 metamerism (me tftm' er iz'm). The existence of metameres in the body of an 



animal. 

 metamorphosis (m6t amor' fo sis). A pronounced change in appearance during the 



development of an animal. 

 metanephros (m6t a ngf r6s). The kidney of reptiles, birds, and mammals; adj., 



metanephric. 

 metaphase (mgt'afaz). That period in mitosis when the chromosomes, having 



become lined up on the equator of the spindle, are divided into two, or, if splitting 



has previously occurred, when they become so arranged. 

 metaplasm (mgf a plSz'm). Nonliving matter in the cytoplasm of a cell, 

 metencephalon (m6t 6n s6f' a I6n). The fourth region of the vertebrate brain, includ- 

 ing the cerebellum and pons, 

 micro (ml' cro). G.; small. 



microgamete (ml kr6 ga met'). A male sex cell, or sperm cell, 

 micronucleus (ml kro nu' kle us). The smaller of two nuclei in an infusorian. 

 micropyle (ml' kro pll). The minute opening in the covering of an egg of any one of 



certain types of animals through which a sperm cell enters. 

 migration (mi gra' shun), periodic. A periodic movement shared by all animals of 



a species, or all of those occupying a certain area, from that area to another on 



the earth's surface. 

 milt. The spermatic fluid of a male fish. 

 mimicry (mim' Ik rl). A resemblance of one organism to another organism of a very 



different character. 

 miracidium (mir a sId' I lun). The first larval stage in flukes. 

 mit (mit). G.; thread. 

 mitochondria (mit 6 k6n' dri jI). Structures in a cell which seem to be normally 



present but the significance of which is unknown. 

 mitosis (mi to' sis). Normal cell division; adj., mitotic (ml t6t' Ik). 

 molt. To cast off an outer covering, such as a cuticula, scales, or feathers. 

 mon- (m5n). G.; single. 

 monecious (mo ne' shus). A species of animal having both male and female gonads 



in the same individual. 

 monoblastic (m6n 6 bias' tik). Having one germ layer — the blastoderm. 

 monohybrid (m6n 6 hi' brid). An offspring of parents differing by one character. 

 Morgan, Thomas H. American zoologist, at California Institute of Technology; 



186(>-. 

 morph (morf). G.; form, structure. 



