↑K. J. Betteridge (1981). “An historical look at embryo transfer”, Reproduction. The Journal of the Society for Reproduction and Fertility62, p. 1–13. “Three years later, the Estonian, Karl Ernst von Baer, finally found the true mammalian egg in a pet dog (von Baer, 1827).”.
↑Hodgson, Geoffrey M.. (2001) How economics forgot history: the problem of historical specificity in social science. Nov-Jorko: Routledge, p. 331. ISBN 0-415-25717-4.
↑Barbieri, Marcello. (2007) Biosemiotics: Information, Codes and Signs in Living Systems. Nova Publishers, p. 6. ISBN 9781600216121.
↑Lockwood, Michael. (2005) The labyrinth of time: introducing the universe. Oxford [Oxfordshire]: Oxford University Press, p. 374. ISBN 0-19-924995-4.
↑Herrmann, Debra S.. (2003) Lonely Planet Estonia Latvia & Lithuania (Lonely Planet Estonia, Latvia and Lithuania). Hawthorn, Vic., Australia: Lonely Planet Publications. ISBN 1-74059-132-1.