694 



GLOSSARY 



like tissue enclosing soft structures of 

 an animal, such as a moUusk. 

 Ma-nu'bri-um (L. maniis, hand). The up- 

 permost part of the sternum; also the 

 structure bearing the mouth in the me- 

 dusa. 

 Ma-rine' (L. marinus, from mare, the sea). 



Pertaining to the sea. 

 Mas'ti-ca"tion (L. masticare, to chew). Re- 

 ferring to chewing. 

 Ma-ter'nal (L. maternus, of a mother). Re- 

 ferring to the mother. 

 Mat'u-ra"tion (L. maturus, ripe). The final 

 stages in the production of gametes in 

 which the number of chromosomes is 

 reduced to one-half (diploid to hap- 

 loid) the number characteristic of the 

 species. 

 Me'di-an (L. mediiis, middle). Pertaining 



to the mid-line. 

 Me-dul'la (L. medulla, marrow). The dis- 

 tinct inner portion of a structure. 

 Me-dul'la ob-lon-ga'ta (L. oblong medulla). 

 The most posterior portion of the brain. 

 Med'ul-la-ry plate, groove, or tube ( L. me- 

 dtdlaris, narrow). Neural plate, groove, 

 or tube found in the embryonic devel- 

 opment of the vertebrate nervous sys- 

 tem. 

 Med'ul-lat-ed. A nerve fiber with a myehn 



covering or sheath. 

 Mei-o'sis (Gr. to make smaller). See Matu- 

 ration. 

 Mem'brane (L. membrana, membrane). 



Any thin cellular sheet or layer. 

 Me-nin'ges (Gr. meninx, membrane). The 

 three membranes enveloping the brain 

 and the spinal cord. 

 Mes'en-chyme (Gr. mesos, middle; eng- 

 chein, to pour in). A loose embryonic 

 connective tissue derived chiefly from 

 mesoderm. 

 Mes'en-ter-y (Gr. mesos, middle; enteron, 

 intestine). A membrane supporting an 

 organ in the abdominal cavity; also a 

 partition found in certain coelenterates. 

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

 skin). The mid-layer of embry.onic 



cells found between the ectoderm and 

 the endoderm. 

 Mes'o-gle"a (mesogloea) (Gr. mesos, mid- 

 dle; gloia, glue). A non-cellular, jelly- 

 like substance found in coelenterates. 

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

 ros, kidney). A kind of vertebrate kid- 

 ney found in all embryos and in certain 

 adult fish and amphibians. 

 Me-tab'o-lism (Gr. meta, beyond; hallein, 

 to throw). The sum total of the chem- 

 ical and physical processes occurring in 

 protoplasm. 

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

 origin ) . Alternation of sexual and asex- 

 ual generations. 

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



Homologous segment of the body. 

 Me-tam'er-ism. The possession of a succes- 

 sion of homologous parts. 

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

 form). The structiu-al changes taking 

 place in the transformation of a larva 

 to an adult. 

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

 pearance). The midstage of mitosis 

 during which there is a lengthwise sep- 

 aration of chromosomes at the equa- 

 torial plate. 

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

 The multicellular animals in which 

 there is a differentiation of the somatic 

 cells. 

 Mi'cron (Gr. mikros, small). One thou- 

 sandth part of a millimeter. 

 Mi'cro-nu"cle-us (Gr. mikros, small; L. nu- 

 cleus, kernel). The small reproductive 

 nucleus of certain Protozoa. 

 Mi-gra'tion (L. migratio). Moving from 



place to place. 

 Mirii-li"ter (L. mUle, one thousand; Fr. 

 litre, liter). Thousandth part of a li- 

 ter. 

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

 dros, grain). Small granules or rod- 

 shaped structures found in the cyto- 

 plasm, thought to contain enzymes. 

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



