Sex problems are treated by Clarke, _Sex in Education_ (Boston, 1873), who is criticised in the works of Brackett, Howe, and Greene; Geddes, _Evolution of Sex and Sex in Education_ (1899-1900); Maudsley, _Sex in Mind and Education_ (New York, 1884); Ames, _Sex in Industry_ (Boston, 1875); Lyttelton, _Training of the Young in the Laws of Sex_ (London and New York, 1900); Blackwell, _The Human Element in Sex_ (new ed., London, 1894); Brown, _Gunethics_ (New York and London, 1887); Trall, _Sexual Physiology and Hygiene_ (Glasgow and London, 1897); Gardner, _The Conjugal Relations_ (Glasgow and London, 1898); Walker, _Intermarriage_ (Birmingham, 1897); Heinzen, _The Rights of Women and the Sexual Relations_ (Chicago, 1898); Tait, _Magdalenism_ (2d ed., Edinburgh, 1842); Lecour, _La prostitution à Paris et à Londres, 1789-1877_ (Paris, 1882); Guyot, _La prostitution_ (Paris, 1882); Parents-Duchatelet, _De la prostitution dans la ville de Paris_ (Paris, 1837); Dühren, _Das Geschlechtsleben in England_ (Charlottenburg and Berlin, 1901-3); Klebs, _Verhältniss des männ. und weib. Geschlechts in der Natur_ (Jena, 1894); Herman, _Sexualismus und Aetiologie_ (Leipzig, 1899); Lindwurm, _Geschlechtsliebe_ (Leipzig, 1879); Debay, _Philosophie des Ehelebens_ (Berlin, 1895); Mantegazza, _Hygiene der Liebe_ (3d ed., n. p., n. d.); Nemmersdorf, _Der Kampf der Geschlechter_ (Leipzig, 1891); Daalen, _Die Ehe und die geschlecht. Stellung der Frau_ (Berlin, 1896); Gardener, "A Battle for Sound Morality, or the Hist. of Recent Age-of-Consent Legislation in the U. S.," in _Arena_, XIII, XIV (Boston, 1895); Flower, "Wellsprings of Immorality," _ibid._, XI, XII (Boston, 1894-95); _idem_, "Social Conditions as Feeders of Immorality," _ibid._, XII (Boston, 1895); _idem_, "Prostitution within the Marriage Bond," _ibid._, XIII (Boston, 1895); Pearson, "Socialism and Sex," in his _Ethic of Free Thought_ (London, 1888). Early German works of interest are _Der rechte Gebrauch und Missbrauch des Ehe-Bettes_ (Leipzig, 1734); being a translation of Defoe's _Use and Abuse of the Marriage Bed_ (London, 1727); Hencke, _Volles entdecktes Geheimniss der Natur_ (Braunschweig, 1786); Josephi, _Ueber die Ehe und physische Erziehung_ (Göttingen, 1788); Heydenreich, _Mann und Weib: ein Beytrag zur Philosophie über die Geschlechter_ (Leipzig, 1798); Butte, _Die Biotomie des Menschen_ (Bonn, 1829). See also the works of Stetson, Caird, Bebel, and Schreiner above mentioned.