BLASTOPHTHORIA (Gr. _blastos_, germ; _phtheiro_, destroy), deterioration of the germ as the result of direct pathogenic or other disturbing agents. BLENDING INHERITANCE, inheritance in which the characters of the parents seem to blend in the offspring. CACOGENIC (Gr. _kakos_, bad; _genesis_, origin), pertaining to genetically undesirable human strains. CELL, the fundamental unit of structure in plants and animals. CENTROSOME (Gr. _kentron_, center; _soma_, body), a small body which functions in indirect cell-division. CHARACTER, any distinguishing feature, trait or property of an organism. CHEMOTROPISM (chemical and tropism), defined, p. 198. CHROMATIN (Gr. _chroma_, color), deeply staining substance of the cell-nucleus. CHROMOSOMES (Gr. _chroma_, color; _soma_, body), characteristic deeply staining bodies, typically constant in number and appearance in each species of animal or plant, which appear in the cell during indirect division. CHROMOTROPISM (Gr. _chroma_, color; _trope_, turning), defined, p. 198. CLEAVAGE, the division of the egg-cell into many cells. CONGENITAL (L. _con_, together; _gigno_, bear), present at birth. CONJUGATION (L. _con_, together; _jugum_, yolk), the union of germ-cells or unicellular individuals for reproduction. CONSTRUCTIVE (or positive) EUGENICS, a system of securing a superior race through propagation of the fittest individuals. CORTEX (L. _cortex_, bark), the outer or investing layer of the brain. CYTOPLASM (Gr. _kytos_, cell; _plasso_, form), the protoplasm of the cell outside of the nucleus. DALTONISM, the commonest form of color-blindness in which the affected individual is unable to discriminate between red and green. DENDRITES (Gr. _dendron_, tree), branching processes which spring from nerve-cells. DETERMINER (L. _determinare_, to determine), the distinctive cause or unit in a germ-cell which determines the development of a particular character in the individual derived from that cell. The terms _gene_ and _factor_ are sometimes used as synonyms of determiner. DIHYBRIDS (L. _di_, two; _hybrida_, mongrel), the offspring of parents differing in two characters. DIPLOID (Gr. _diploos_, double; _eidos_, form), the dual or somatic number of chromosomes. DOMINANT CHARACTER (L. _dominare_, to be a master), a character from one parent which manifests itself in offspring to the exclusion of a contrasted character from the other parent. DROSOPHILA, a genus of fruit-flies of which there are several species. DUPLEX (L. _duo_, two; _plico_, fold), the condition in which a character is represented by two determiners, one from each parent. ELECTROTROPISM (Gr. _electron_, amber; _trope_, turning), defined, p. 198. EMBRYO (Gr. _embryon_), the young organism in its earliest stages of development. EMBRYOGENY (Gr. _embryon_; _genesis_, generation), the development of the embryo. EUGENICS (Gr. _eugenes_, well-born), the science relating to improvement of the human race through good breeding.