xxviii GLOSSARY OF TECHNICAL TERMS 



MEGASPORANGIUM (Gr. jue'ya?, large ; o-no^os, seed ; ayyt'iov, vessel), 

 a large sporangium, in cases where the latter are differentiated 

 into two sizes. 



MEGASPORE (Gr. /xeyas, large ; O-TTO/JOS, seed), a large spore, in cases 

 where large and small are produced. 



MEIOSIS (Gr. /^etWis, reduction), the reduction of the chromo- 

 somes which takes place in the maturation of germ cells. 



MERISTEM (Gr. /ute/no-rrjj, a divider), an un differentiated tissue 

 in which cell-division is going on actively (in plants). 



MERISTIC (Gr. jue/Horrj?, a divider), numerical (variation). 



MEROGONY (Gr. pepos, part ; yoVos, reproduction), the develop- 

 ment of enucleated eggs, after fertilization. 



MESENTERY (Gr. //eVoj, middle ; tvrcpov, intestines), the mem- 

 brane which supports the intestines in the body cavity. 



MESOBLAST (Gr. pea-os, middle ; /3Aaoro's, germ), the middle one of 

 the three layers of cells of which the body of a ccelomate 

 embryo is made up. 



MESODERM (Gr. /ueW, middle; 8e/>jma, skin), that part of the 

 body which is derived from the embryonic mesoblast. 



MESOGLCEA (Gr. /ueVo?, middle ; yAoia, glue), the gelatinous 

 supporting layer between ectoderm and endoderm in 

 coalenterates. 



MESOPHYLL (Gr. /ueo-oy, middle ; tyvXkov, leaf), the middle layer of 

 a leaf. 



MESOZOIC (Gr. /xeVo?, middle ; C<ov, life), one of the primary divi- 

 sions of the earth's history. 



METABOLISM (Gr. juera/3oA?i, change), the sum total of the chemical 

 processes which go on in the living body. 



METACARPALS (Gr. juera, next after ; Kopiros, wrist), the bones in 

 the palm of the hand. 



METAGENESIS (Gr. //era-, expressing change ; yeVe<m, birth), the 

 alternation of sexual and asexual generations. 



METAMERIC (Gr. /uera, next after ; |ue>os, portion), a term applied to 

 a type of segmentation in which the similar parts (metameres) 

 of which the body is composed follow after one another in 

 longitudinal series. 



METAMORPHIC (Gr. /xcra-, expressing change ; MP< 7 ?, form), a 

 term applied to rocks which have undergone extensive 

 changes since they were laid down. 



METAMORPHOSIS (Gr. /mera/xop^axrij, transformation), a more or 

 less abrupt change from one stage of development to another 



