408 BIOLOGY 



mesoblast. The mesoderm of the developing embryo. 



mesoderm (Gr. mesos = middle + derma = skin). The middle layer in 



a developing embryo, 283. 



mesoglcea (Gr. mesos = middle -f- glows = glue). The middle, non-cellu- 

 lar layer of Hydra and allied animals, 143. 

 mesophyll cells (Gr. mesos = middle + phyllon = leaf) . The irregular, 



loosely packed, chlorophyll cells in the middle of a leaf, 117. 

 mesophytes (Gr. mesos = middle + phyton = plant). Plants living in a 



moderately moist habitat. 

 metabolism (Gr. meta = beyond + ballein = to throw) . A name given 



to the series of chemical changes going on in organisms, 138, 210. 

 metacarpals, 182. 

 metameres (Gr. meta = beyond + meros = a part) . Segments of animals 



like the earthworm, 155. 

 metamorphosis (Gr. meta = beyond -j- morphe = form) . A life history in 



which an organism passes through several unlike stages, more or less 



independent, 72, 289; of frog, 280, 286. 

 metaphase. The second step in karyokinesis, 87. 

 Metaphyta (Gr. meta = beyond -f- phyton = plant). Plants made of 



many cells, 223. 

 metastasis (Gr. meta = beyond + histanai = to place.) The process of 



using foods, 132, 135, 300. 

 metatarsals, 182. 

 Metazoa (Gr. meta = beyond + zoon = animal) . Animals made of many 



cells, 223. 



mice, breeding of, 361. 

 micronucleus (Gr. mikros = small + nucleus). The small nucleus in a 



cell containing two nuclei, 62. 



microorganism. Any organism of microscopic size, 

 microsomata (Gr. mikros = small + soma = body). Extremely minute 



bodies in the protoplasm which frequently show motion, 32. 

 microspores (Gr. mikros = small + spore). The small spores in a plant, 



which develop into male gametophytes, 122, 273. 

 mid-brain. The middle part of the brain, consisting of the optic lobes 



(called corpora quadrigemina in man), 193. 

 migration. The act of changing one's dwelling place from one locality to 



another, 379. 

 mimicry. Resemblances which some organisms show to other objects, for 



protective purposes. 



mitosis (Gr. mitos = a thread). See karyokinesis. 

 mitral valve. The valve between the left auricle and ventricle, 

 molds, 96, 99, 235. 





