Definition of puberty:
- "Manual of Surgery Volume Second: Extremities--Head--Neck. Sixth Edition.", Alexander Miles Alexis Thomson.
Birds differ from Mammals, firstly, in the difficulty of carrying out complete castration, and secondly, in the fact that the occurrence of puberty is not so definite, and that immature birds are so small and delicate that it is almost impossible to operate upon them successfully.- "Hormones and Heredity", J. T. Cunningham.
- "The Truth About Woman", C. Gasquoine Hartley.