Appendix 843 



Metagenesis (met a -jen' e sis) (Gr. meta, over; genesis, origin), the alternation 



of asexual and sexual generations in the life cycle of such animals as 



Obelia and of several higher plants. 

 Metamere (met' a mere) (Gr. meta, over [repeat] ; meros, part), series of similar 



parts (segments) of a body. 

 Metamerism (me -tam' er izm), displaying metameres. 

 Metamorphosis (met a -mor' fo sis) (Gr. metamorphosis, to transform), rather 



abrupt change from one stage of embryonic development to another, as 



from larval stage to pupa in insects. 

 Metaphase (met' a faz) (Gr. meta, between; phasis, to appear), a period in 



mitosis between the prophase and anaphase stages. 

 Metaphysics (met a -fiz' iks) (Gr. meta, beyond; physics), aspects of science that 



transcend the physical world. 

 Metaplasm (met' a plazm) (Gr. meta, beyond; plassein, to mold), nonliving 



materials in living protoplasm. 

 Metathorax (met a -tho' raks) (Gr. meta, after; thorax, chest), posterior part of 



insect thorax. 

 Metazoa (met a -zo' a) (Gr. meta, later; zoa, animals), higher, multicellular ani- 

 mals (contrast with unicellular Protozoa). 

 Microgamete (mi kro ga -met') (Gr. mikros, small; gamete), smaller of two 



gametes formed by heterogamous organism. 

 Microgametophyte (mik ro ga -me' to fite) (Gr. mikros, small; gamos, gamete; 



phyton, plant), male gametophyte resulting from the development of a 



microspore. 

 Micron (mi' kron) (Gr. mikros, small), one-thousandth part of a millimeter; or 



one twenty-five thousandth of an inch. 

 Micronucleus (mi kro -nu' kle us) (Gr. mikros, small; nucleus), smaller reproduc- 

 tive nucleus of certain Protozoa in contrast to the larger nutritive macro- 

 nucleus. 

 Microorganism (mi kro -or' gan izm) (Gr. mikros, small), microscopic organism 



as a bacterium, protozoan, etc. ■ 

 Micropyle (mi' kro pile) (Gr. mikros, small; pyle, gate), small opening. 

 Microspore (mi' kro spor) (Gr. mikros, small; spora, spore), minute spore which 



grows into a male gametophyte; in seed plants it is the young pollen grain. 

 Microsporophyll (mi kro -spo' ro fil) (Gr. mikros, small; spora, spore; phyllon, 



leaf), a sporophyll-bearing microsporangium (sporophyll which bears 



microspores) . 

 Migration (mi -gra' shun) (L. migro, move), moving from one region to another. 

 Mimicry (mim' ik ri) (L. mimikos, imitate), resemblance for protective purposes. 

 Miracidium (mi ra -sid' i um) (Gr. meikakion, young), ciliated larval stage of a 



fluke. 

 Mitochondria (mit o -kon' dri a) (Gr. mitos, thread; chondros, grit or grain), 



somewhat regularly shaped bodies in cytoplasm. 

 Mitosis (mi -to' sis) (Gr. mitos, thread), indirect cell division characterized by 



nuclear division with the formation of chromosomes, spindle, etc. 

 Modification, noninheritable variation in the somatoplasm due to environmental 



causes. 

 Modifying factor, a gene which modifies others to bring about a changed trait. 



