Length of Gestation Period and Menstrual Cycle in the Chimpanzee

Abstract

THIS note should have been written a year ago, but during the preceding two years I was working at the Anthropoid Experiment Station of Yale University, in Orange Park, Florida, U.S.A., in a rather isolated place without adequate library facilities, and therefore had no opportunity to read Dr. R. C. Clarke's notes on the birth of a chimpanzee¹, in which he states: ” Although the preconceived idea is that the period of gestation [in the chimpanzee] is nine months I cannot help feeling that it is five months, at any rate all the evidence points to it in this case” (1, p. 732). Dr. Clarke does not give either the menstrual history of his female preceding the time (December 1, 1933) when she was ” properly served” or the date of the infant's birth. On the basis of information given in the article by J. M. Wyatt and G. M. Vevers² and the time of acceptance of Dr. Clarke's publication one can surmise that the infant was born in the first half of May, 1934. The parents of the infant had lived together for a period prior to the first observation of proper mating, during which time there was a ” certain amount of sexual play”. Because of this fact there is a possibility that the date of conception assumed by Dr. Clarke is not correct. The female may have been fertilised during one of sexual play. The December swelling and acceptance of the male do not preclude this possibility, for there are records proving that chimpanzee females may have swellings of the sex skin and be receptive during the gestation period⁴.