M.R.C. Unit of Reproductive Biology, 2 Forrest Road, Edinburgh, and Department of Animal Genetics, University of Edinburgh, Edinburgh
(Received 25th September 1974)
The marmosets (F. Callithricidae), in common with other South American primates, do not menstruate. This is a major disadvantage in animals which otherwise have many attributes as experimental models for studies in reproductive physiology. The conventional methods of determining the stage of the ovarian cycle by means of vaginal smear cytology do not work for the common marmoset (Callithrix jacchus). The presence of spermatozoa in the vaginal smear is no indication of oestrus because marmosets mate frequently and apparently indiscriminately throughout the cycle and early pregnancy (Hearn & Lunn, 1974). The patterns of LH, oestradiol and progesterone in the peripheral plasma of the common marmoset show that this species has a clearly defined ovarian cycle of 16·4± 1·7 days (Hearn & Lunn, 1974), and it seemed possible that
