452 ELEMENTS OF BIOLOGY 



subdivision of the body into ring-like compartments or metameres, 

 each resembUng adjacent compartments. 



Metamorphosis. The transformation of larval forms in the development 

 of animals. 



Metanephros. The kidney of reptiles, birds, and mammals. 



Metaphase. An arbitrary stage in the process of mitotic cell division 

 characterized by the longitudinal splitting of each chromosome 

 aligned on the equatorial plate of the mitotic spindle. 



Metaphyta. Plants consisting of many cells in which specialization of 

 structure and of function is well defined. 



Metazoa. Animals consisting of more than one cell in which the cells 

 show appreciable specialization of function and of structure. 



MiCRONUCLEUS. The smaller member of two nuclei that are found in 

 some types of Protozoa. 



Microspore. Spores of flowering plants that develop into the sperm- 

 producing gametophyte generations. Commonly known as pollen. 



Mimicry. The imitation by the organism of some other living form or 

 of some inanimate object. 



Mitochondria. Rod-like structures occurring in the cell cytoplasm. 



Mitosis. The usual process of cell division, involving an equal division 

 and distribution of the chromosomes to daughter cells. 



Molecule. A combination of atoms that forms a complete and more or 

 less stable chemical unit. 



Monoblastic. An animal consisting of a single layer of cells or its 

 derivatives would be described as monoblastic. No adult monoblastic 

 Metazoa occur. The blastula stage of the embryo might be de- 

 scribed as monoblastic. 



MoNO-HYBRiD. The progeny of two individuals who differ in a single 

 alternative character. 



Myopia. Near-sightedness, 



Nares. Air passages of the nose. 



Natural selection. The effect of environmental conditions serves to 

 eliminate living forms which are not fitted to survive and thus acts 

 to select the fittest for survival. 



Nematocyst. a barbed coiled fibre in the cnidoblast cell of the Ccelen- 

 terata. When discharged together with a poison it serves as a de- 

 fensive weapon, but more especially serves in the capture of food 

 by the tentacles. 



Nephridia. The excretory tubules of Annelida. 



