RECESSIVE CHARACTER (L. _recessus_, a going back), a character from one parent which remains undeveloped in offspring when associated with the corresponding dominant character from the other parent. REDUCTION DIVISION, a division of the maturing germ-cells in which the dual or somatic (diploid) number of chromosomes is reduced to the single (haploid) number. REFLEX ACTION (L. _re_, back; _flectere_, bend), an automatic response of the nervous and motor mechanism of the body. RESTRICTIVE (or negative) EUGENICS, a system of improving the human race by preventing reproduction of the unfit. REVERSION (L. _re_, back; _verto_, turn), the reappearance of ancestral traits which have for some generations been in abeyance. RHEOTROPISM (Gr. _rheo_, to flow; _trope_, turning), defined, p. 198. SALPINGECTOMY (Gr. _salpinx_, trumpet; _ectome_, cutting out), removal of part or all of a Fallopian tube (oviduct). SEGREGATION (L. _se_, aside; _grex_, flock), separation. SEX CHROMOSOME, a special chromosome which is supposed to be concerned in the determination of sex. SEX-LINKED CHARACTERS, defined, p. 60. SIMIAN (L. _simia_, ape), ape-like. SIMPLEX (L. _sim_, same; _plico_, fold), the condition in which a character is represented by a determiner from only one of the two parents. SOMA (Gr. _soma_, body), the body considered apart from the germ-cells. SPERMATID (Gr. _sperma_, seed), a cell resulting from the last division of the germ-cell in spermatogenesis. It transforms into the spermatozoon. SPERMATOCYTES (Gr. _sperma_, seed; _kytos_, cell), cells concerned in the maturation divisions of the male germ-cells. SPERMATOGENESIS (Gr. _sperma_, seed; _genesis_, origin), the development of spermatozoa from primitive sex-cells. SPERMATOGONIUM (Gr. _sperma_, seed; _gonos_, generation), a primordial sperm-cell. SPERMATOZOON (Gr. _sperma_, seed; _zoon_, animal), the functional male sex-cell. SPINDLE, a fibrous organ formed in indirect cell-division. SPIREME (L. _spira_, coil), a characteristic stage preliminary to indirect cell-division in which the chromatin material of the nucleus appears in the form of a skein of filaments. STEREOTROPISM (Gr. _stereos_, solid; _trope_, turning), defined, p. 198. STERILIZATION (L. _sterilis_, barren), deprivation of reproductive power. For methods, see p. 322. SYNAPSE (Gr. _syn_, together; _hapto_, unite), the coming in contact of the processes of one nerve cell with the processes or body of another. SYNAPSIS (Gr. _syn_, together; _hapto_, unite), union of the chromosomes in pairs preliminary to the reduction division. TELEGONY (Gr. _telegonos_, born far away), the supposed influence of an earlier sire on offspring born later of the same mother to a different sire. THERMOTROPISM (Gr. _thero_, heat; _trope_, turning), defined, p. 198. THIGMOTROPISM (Gr. _thigmo_, touch; _trope_, turning), defined, p. 198. TOXIN (Gr. _toxicon_, poison), poisonous compounds of animal, vegetable, or bacterial origin.