GLOSSARY-INDEX 409 



molecule. The smallest particle of a chemical compound which can exist 

 without the compound being chemically destroyed. 



Monocystis, 241. 



monoecious (Gr. monos = one + oikos = house). With both sexes in the 

 same individual; applied to plants, 251. 



monogamous (Gr. monos = one + gamos = marriage) . The sexual asso- 

 ciation of one male with one female. 



monotrichic (Gr. monos one + thrix = hair). With a single flagellum, 

 81. 



morphology (Gr. morphe = form + logos = discourse). The study of the 

 structure of organisms in all relations, 19. 



morula (Lat. morum = a mulberry). The stage in the egg development 

 after the egg has become a sphere of cells. 



motion, in plants, 136, 218; in the earthworm, 167; in the frog, 211. 



motor cells. The neurons which send impulses over their axons to the 

 muscles to produce motion, 172, 213. 



motor ocularis. The third cerebral nerve supplying the eye muscles, 194. 



Mucor, 97, 247. 



mucous membrane. The lining of the alimentary canal, 187. 



mucous. -Applied to glands secreting mucus. 



mucus. A thick, viscid secretion from the mucous membrane. 



multicellular organisms (Lat. multus = many + cellular). Organisms 

 made of many cells which show a differentiation among themselves, 

 90,95. 



muscles, 219. 



mutations (Lat. mutare = to change). Sudden departures from the race 

 character which have a tendency to remain fixed, 358. 



mutation theory (Lat. mutare = to change). The theory of evolution that 

 assumes that progress has taken place by mutations rather than by 

 individual diversities, 357. 



mutualism. An associating of organisms for mutual benefit, 228. 



mycelium (Gr. mykes = fungus + helos = a nail). The thread-like fila- 

 ments of which fungi are composed, 96. 



myosin (Gr. mus = muscle). A proteid in lean meat, 8. 



nares. See nostrils. 



nasal bones, 180. 



natural selection. The law by which the best fitted organisms survive, 

 353. 



NEEDHAM, 13. 



nematocysts (Gr. nema = a thread + cystis = sac). Special cells in Cce- 

 lenterata which have a coiled poison thread capable of extrusion; net- 

 tling cells, 143. 



