Effect of Unilateral Ovariectomy on Twinning Frequency in the Marmoset

The marmosets, small New World primates of the family Callithricidae, were reported by Wislocki (1939) to have a high frequency of fraternal twinning. On the basis of information obtained from an examination of nineteen pregnant specimens and observations on an additional twenty-one cases reported by others, Wislocki (1939) calculated an 87·5% incidence of twinning. Breeding data obtained in our colony over the past 5 years have substantiated this twinning phenomenon. In 261 recorded deliveries, there have been 77% twins, 5% triplets, and 18% single births (Gengozian, 1970), and the sexes of the twins approximate to those expected for fraternal twinning, i.e. 1 (mm) : 2 (mf) : 1 (ff). Another unique facet of the marmoset's physiology is the extensive placental vascular connection which invariably exists between the twin foetuses; Hill & Hill (1927) noted this briefly and