The perineal organ of male red colobus: its structure and possible social function as a mimic of female genitalia.

The perineal organ of male red colobus monkeys (Piliocolobus tephrosceles) is illustrated with photographs. I discuss its possible role as a mimic of female genitalia and how thereby it may play a role in social relations between adult and juvenile males and ultimately in the reproductive success of males. This is one of the few examples of a monkey species in which the male perineal anatomy appears to mimic the female external genitalia, contrary to the pattern in many New World monkey species that have hypertrophied clitorises possibly mimicking a penis or scrotum. Furthermore, I emphasize that when one can recognize this organ and distinguish it from the external genitalia of females, more refined demographic data are obtained, particularly so as it relates to when age-related changes in sex ratio occur.