Abstract-Factors concerning sexual discrimination and related sensory receptors were investigated on the hermit crab Pagurus geminus. In the breeding season, male crabs of this species were observed to hold receptive females but to reject males. By using this behavior, it was examined whether males on which some operation on the sensory receptors was performed could discriminate between presented male or female crabs. Test males could not discriminate sexes of the presented crabs only when antennules were removed bilaterally. On the other hand, intact test males reacted positively to an empty shell from which "female water" exuded after passing through the chamber containing females. Thus, the factor by which the hermit crab discriminates sexes was indicated to be a water-borne chemical and that the sensory receptor related to sex-discrimination appeared to exist on the antennules. Discussions are made with respect to predicted substances taking part in sexual discrimination of this hermit crab.

Batesian mimics that show similar coloration to unpalatable models gain a fitness advantage of reduced predation. Beyond physical similarity, mimics often exhibit behaviour similar to their models, further enhancing their protection against predation by mimicking not only the model's physical appearance but also activity. In butterflies, there is a strong correlation between palatability and flight velocity, but there is only weak correlation between palatability and flight path. Little is known about how Batesian mimics fly. Here, we explored the flight behaviour of four butterfly species/morphs: unpalatable model Pachliopta aristolochiae, mimetic and non-mimetic females of female-limited mimic Papilio polytes, and palatable control Papilio xuthus. We demonstrated that the directional change (DC) generated by wingbeats and the standard deviation of directional change (SDDC) of mimetic females and their models were smaller than those of non-mimetic females and palatable controls. Furthermore, we found no significant difference in flight velocity among all species/morphs. By showing that DC and SDDC of mimetic females resemble those of models, we provide the first evidence for the existence of behavioural mimicry in flight path by a Batesian mimic butterfly.

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