Commons, J.R., McCracken, H.L. & Zeuch, W.E. (1922). Secular trends and business cycles: a classification of theories. Rev. Econom. Stat. 4, 244-263: 244.
If one transfers a few fruit flies from a pint bottle in which the population cycle is well advanced to another bottle, and then deals with the two bottles as a single population, one would expect a composite growth curve, one cycle added to another.
Wright, S. (1926). Review: The Biology of Population Growth (1925), by Raymond Pearl; The Natural Increase of Mankind, by J. Shirley Sween (1926). J. Amer. Stat. Assoc. 21, 493-497: 495.
The internal factor determining the population cycle is alleged to be the normal life cycle of the germ cells themselves.
Lundberg, G.A. (1931). The biology of population cycles. Social Forces 9, 401-408: 403.
population cycle The more or less regularfluctuation in abundance of a species or population.
Lincoln, R.J., Boxshall, G.A. & Clark, P.F. (1982). A Dictionary of Ecology, Evolution and Systematics: 200.