Marmosets (hapiladae): breeding seasons, twinning, and sex of offspring.

Our records on marmosets, primarily Oedipomidas oedipus, plus data from the literature, confirm that these animals customarily have twins. Demonstrated chimerism for several tissues is significant, for virtually all twins are of biovular origin. Furthermore, a single birth may often be a survivor of twins. Births occur during any month, but springtime appears to be the most common period. An average interval of 240 days between births predicts the production level of a captive colony. A gestation period of about 140 days appears to be a valid estimate.