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 s.e.x-cells.

SPERMATOGONIUM (Gr. _sperma_, seed; _gonos_, generation), a primordial sperm-cell.

SPERMATOZOON (Gr. _sperma_, seed; _zoon_, animal), the functional male s.e.x-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.

TROPISM (Gr. _trope_, turning), the automatic directing of an organism toward or away from a source of stimulus.

UNIT-CHARACTER, a character which behaves as an indivisible unit in heredity.

VASECTOMY (L. _vas_, vessel; _ektome_, cutting out), removal of a portion of the vas deferens (duct for conveying spermatozoa).

VESTIGEAL (L. _vestigium_, footstep), representing organs which existed once in a more developed condition.

VOLVOX (L. _volvo_, roll), a small fresh-water organism occurring in spherical colonies.

Wa.s.sERMAN REACTION, a test for syphilis, see p. 188.

X-ELEMENT, same as s.e.x-chromosome.

ZYGOTE (Gr. _zygon_, yolk), the product of the union of two gametes.

REFERENCES FOR FURTHER READING AND STUDY

BATESON, W., 1909. _Mendel's Principles of Heredity._ Cambridge, The University Press. The best technical account of Mendelism. It contains also a translation of the original papers of Mendel.

CASTLE, WILLIAM E., 1911. _Heredity._ New York, D. Appleton and Company.

CASTLE, WILLIAM E.; COULTER, JOHN M.; DAVENPORT, CHARLES B.; EAST, EDWARD M.; TOWER, WILLIAM L., 1912. _Heredity and Eugenics._ Chicago, The University of Chicago Press.

CONKLIN, EDWIN GRANT, 1915. _Heredity and Environment in the Development of Men._ Princeton, Princeton University Press.

DAVENPORT, CHARLES B., 1911. _Heredity in Relation to Eugenics._ New York, Henry Holt and Company.

DONCASTER, L., 1911. _Heredity in the Light of Recent Research._ Cambridge, The University Press.

DONCASTER, L., 1915. _The Determination of s.e.x._ Cambridge, The University Press.

ELLIS, HAVELOCK, 1912. _The Task of Social Hygiene._ New York, Houghton Mifflin Company.

GALTON, FRANCIS, 1869. _Hereditary Genius: an Inquiry Into Its Laws and Consequences._ London, Macmillan and Company.

GALTON, FRANCIS, 1889. _Natural Inheritance._ New York, The Macmillan Company.

GALTON, FRANCIS, 1895. _English Men of Science; Their Nature and Nurture._ New York, D. Appleton and Company.

GALTON, FRANCIS, and SCHUSTER, EDGAR, 1906. _Noteworthy Families_ (Modern Science). London, J. Murray.

G.o.dDARD, HENRY HERBERT, 1912. _The Kallikak Family; a Study in the Heredity of Feeble-mindedness._ New York, The Macmillan Company.

G.o.dDARD, HENRY HERBERT, 1914. _Feeble-mindedness; Its Causes and Consequences._ New York, The Macmillan Company.

HEALY, WILLIAM, 1915. _The Individual Delinquent._ Boston, Little, Brown and Company.

KELLICOTT, WILLIAM E., 1911. _The Social Direction of Human Evolution; an Outline of the Science of Eugenics._ New York, D. Appleton and Company.

MORGAN, THOMAS HUNT, 1913. _Heredity and s.e.x._ New York, Columbia University Press.

PUNNETT, R. C., 1911. _Mendelism._ New York, The Macmillan Company. The best popular account of Mendelism.

SALEEBY, CALEB WILLIAM, 1909. _Parenthood and Race Culture; an Outline of Eugenics._ London, Ca.s.sell and Company.

SCHUSTER, EDGAR, 1912. _Eugenics._ London, Collins Clear-Type Press.

THOMSON, J. ARTHUR, 1908. _Heredity._ London, John Murray.

WALTER, HERBERT EUGENE, 1913. _Genetics._ New York, The Macmillan Company.