Referee's Report by [Ronald Aylmer] Fisher on a paper 'A contribution to the study of animal populations. The natural control of the Knapweed Gall fly' by G C Varley Paper reference code: B.9 for 1941 [previously B.161 for 1937, withdrawn and later resubmitted] Sectional Committee: Zoology Recommends the paper for publication in Trans [Philosophical Transactions of the Royal Society]. Describes the study as 'a very resourceful and comprehensive piece of work' [Not published in Royal Society journals but in the Journal of Animal Ecology, vol. 16, number 2, pp. 139-187, 1947]. Received 29 May 1941 [28 May 1941]