Terrestrial pulmonates can learn olfactory-aversion tasks and retain them in their long-term memory. To elucidate the cellular mechanisms underlying learning and memory, researchers have focused on both the peripheral and central components of olfaction: two pairs of tentacles (the superior and inferior tentacles) and a pair of procerebra, respectively. Data from tentacle-amputation experiments showed that either pair of tentacles is sufficient for olfactory learning. Results of procerebrum lesion experiments showed that the procerebra are necessary for olfactory learning but that either one of the two procerebra, rather than both, is used for each olfactory learning event. Together, these data suggest that there is a redundancy in the structures of terrestrial pulmonates necessary for olfactory learning. In our commentary we exemplify and discuss functional optimization and structural redundancy in the sensory and central organs involved in olfactory learning and memory in terrestrial pulmonates.