Glossary 339 



HO-MO-ZY'-GOTES. Pure-breds resulting from the union of gametes which 

 are hereditarily similar. 



HY'-BRID. The offspring of parents which differ in one or more characters. 



IDENTICAL TWINS. Twins which have come from a single egg and which 

 show identical hereditary characters. 



ID'-I-O-PLASM. The germ-plasm or inheritance material. 



INDUCTION. A modification of the first filial generation caused by the 

 action of environment on the germ cells of the parental generation. 

 (Woltereck.) 



INHERITED CHARACTER. A character the differential cause of which is in 

 the germ. 



INSTINCTS. Complex reflexes involving nerve centers. 



INVERSE SYMMETRY. Having the right half of one asymmetrical individual 

 equivalent to the left of another; mirrored symmetry. 



IRRITABILITY. Capacity of receiving and responding to stimuli. 



KAR-Y-O-KI-NE'-SIS. See Mitosis. 



LA-MARCK'-ISM. The doctrine that evolution takes place through the in- 

 heritance of acquired characters. 



LETHAL FACTORS. Factors which cause the early death of gametes or zy- 

 gotes. 



LINKAGE. Inheritance of characters in groups, probably due to the link- 

 age of genes in a chromosome. 



LOCALIZATION. The gathering together of particular substances in definite 

 parts of an egg or embryo. 



LOL'-I-GO. The squid, a genus of cephalopod mollusks. 



MAR-SU'-PI-ALS. A primitive group of mammals, including opossums and 

 kangaroos, which carry the young in a pouch. 



MAT-U-RA'-TION. The final stages in the formation of sex cells, charac- 

 terized by two peculiar cell divisions. 



ME-RIS'-TIC VARIATION. Variation in the number of parts. 



MES'-EN-CHYME. Loosely scattered cells of the mesoderm. 



MES'-O-DERM. A layer or group of embryonic cells lying between ectoderm 

 and endoderm. 



ME-TAB'-O-LISM. Transformation of matter and energy within a living 

 thing. 



MI'-CRO-PYLE. The minute opening in an egg membrane through which 

 the spermatozoon enters. 



MI-TO'-SIS. Indirect nuclear division in which the nucleus is transformed 

 into a spindle and chromosomes ; the latter split and the halves move 

 to the poles of the spindle where they form the daughter nuclei. 



MODIFYING FACTORS. Factors whose principal influence is seen in modifying 

 other factors or the characters to which they give rise. 



