1. HAVELOCK ELLIS, Studies in the Psychology of Sex, Vol. II, Sexual Inversion.
2. F. A. E. CREW, Art. “Sex” in Outline of Modern Knowledge.
3. G. MARAÑÓN, The Evolution of Sex and Inter-sexual Conditions.
4. “The Sex Life of College Men,”;PECK;Journal of Nervous and Mental Diseases,1925
5. G. V. HAMILTON, A Research in Marriage.