842 Appendix 



Megagametophyte (meg a ga -me' to fite) (Gr. me gas, large; gamos, gametes; 



phytcn, plant), fem.ale gametophyte resulting from the development of a 



megaspore and producing female gametes (eggs). 

 Megasporangium (meg a spo -ran' ji um) (Gr. mega, large), a sporangium that 



bears megaspores which develop into megagametophytes. 

 Megaspore (meg'aspor) (Gr. mega, large; spora, spore), a large spore produced 



in a megasporangium. 

 Megasporophyll (meg a -spor' o fil), sporophyll which produces megaspores. 

 Meiosis (mi -o' sis) (Gr. meiosis, to make less) the preparation and maturation 



(reduction division) of a sex cell for fertilization in which the chromosome 



num.ber is reduced one-half. 

 Melanin (mel' a nin) (Gr. melas, black), blackish pigment. 

 Melanophore (mel' an o for) (Gr. melas, black; phoreo, to bear), chromatophore 



that contains blackish pigment. 

 Mendelism (Mendel's laws), characters are inherited as units independently of 



each other; genes separate (segregate) from one another and later recom- 



bine in various ways in the germ cells; characters are in pairs (opposites), 



one of which is dominant over the other or recessive one. These laws 



were formulated by Gregor Mendel. 

 Meninges (me -nin' jez) (Gr. meninx, membrane), three membranous coverings of 



the brain and spinal cord, outer dura mater, arachnoid, and inner pia 



mater. 

 Meristem (mer' i stem) (Gr. merizein, to divide), undifferentiated tissue of grow- 

 ing plants composed of cells actively dividing. 

 Mesencephalon (midbrain) (mes en sef a Ion) (Gr. mesos, middle; kephale, 



head), third region of vertebrate brain. 

 Mesenchyme (mes' eng kime) (Gr. mesos, middle; enchyma, infusion), middle, 



cellular layer of embryos which forms connective tissues, blood vessels, 



heart, etc. 

 Mesentery (mes'enteri) (Gr. mesos, middle; enteron, intestine), membrane to 



invest and suspend internal organs such as the intestine. 

 Mesoderm (mes' o durm) (Gr. mesos, middle; derma, skin), middle germ layer of 



cells which give rise to certain tissues and organs. 

 Mesogloea (meso-gle'a) (Gr. mesos, middle; gloios, glue), noncellular gelatinous 



substance between ectoderm and entoderm of sponges and coelenterates. 

 Mesonephros (mes o -nef ros) (Gr. mesos, middle, nephros, kidney), vertebrate 



kidney of animals from lamprey to amphibia inclusive. 

 Mesophyll (mes' o fil) (Gr. mesos, middle; phyllon, leaf), plant leaf tissues be- 

 tween upper and lower epidermis. 

 Mesophyte (mes' o fit) (Gr. mesos, middle; phyton, plant), plant requiring only 



medium moisture. 

 Mesothelium (mes o -the' li um) (Gr. m.esos, middle; thelium, lining), lining of 



the peritoneal cavity. 

 Mesothorax (mes o -thor' aks) (Gr. mesos, middle; thorax, chest) middle of three 



thoracic segments of insects. 

 Metabolism (me -tab' o lizm) (Gr. metahole, change), sum of constructive (anab- 



olism) and destructive (catabolism) phases of protoplasm. 



