Glossary of "Life (9th ed.)" by Sadava et al. (2011)
- A chemical signal produced in minute amounts at one site in a multicellular organism and transported to another site where it acts on target cells.
Glossary of "Principles of Behavioral Genetics" by Anholt & Mackay (2010)
- A chemical substance secreted by one tissue, an endocrine gland, that produces a specific physiological response on some remote target tissue or system.
- Anholt, R. R. H. & Mackay, T. F. C. 2010. Principles of Behavioral Genetics. x + 334 pp. Academic Press, San Diego.
- Sadava, D., Hillis, D. M., Heller, H. C. & Berenbaum, M. R. 2011. Life: The Science of Biology, 9th ed. -xliv + 1266 pp. Sinauer Associates, Inc., Sunderland.