The social interactions of 12 adult Lemur catta were observed under standard conditions over a 20‐month period. Descriptions of the behavioural repertoire and of vaginal cytology throughout two breeding seasons provided the basis for a preliminary analysis of hormonal influences on social behaviour in a“lower”primate. Both long and short term fluctuations in gonadal activity were associated with changes in the frequency of expression of several non‐sexual patterns, particularly of the species‐characteristic and sexually differentiated displays of males. The latter appear to be predominantly olfactory gestures and serve to distribute skin‐gland secretions, thereby integrating much social activity. In contrast to the extended receptivity characteristic of some monkeys and apes, mating in the Ring‐tail is restricted to a brief period during the 51/2‐week cycle, being invariably coincident with vaginal oestrus. Hormonal factors alone are probably sufficient to determine the appearance of full behavioural oestrus. Patterns (other than fighting) tentatively associated with territoriality and/or dominance appear the least sensitive to influence by gonadal secretions.

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Accessory olfaction is defined as the chemoreceptive system that employs the vomeronasal complex (VNC) and its distinct central projections to the accessory olfactory bulb (AOB) and limbic/cortical systems. Comparisons of the structural and functional features of primate accessory olfaction can now be made at many levels. Advances in the understanding of molecular mechanisms of odorant transfer and detection, physiological analyses of signal processing, and appreciation of ontogenetic timetables have clarified the contribution of accessory chemoreception to the sensory map. Two principal functions dominate: the decoding of social information through the uptake of signals (often fluid-borne), and the provision of an essential pathway for the "migration" of presumptive neurocrine (GnRH) cells from the olfactory placode to the hypothalamus. VN "smelling" (vomerolfaction) is now seen to overlap with primary olfaction. Both systems detect signal compounds along the spectrum of volatility/molecular weight, and neither is an exclusive sensor. Both main and accessory chemoreception seem to require collaborative molecular devices to assist in odorant transfer (binding proteins) and (for the VNO) signal recognition (MHC1 proteins). Most adaptive-selective features of primate chemocommunication variously resemble those of other terrestrial mammals. VN function, along with its genome, has been maintained within the Strepsirrhines and tarsiers, reduced in Platyrrhines, and nearly extinguished at the Catarrhine up to hominin levels. It persists as an intriguing ancient sense that retains key features of past evolutionary events.