AbstractTwo morphological differences distinguish the membranes of the end bulb‐spherical cell synapse in rats and mice from those in guinea pigs and chinchillas. First, in freeze‐fracture replicas, the membranes of rat and mouse spherical cells lack perisynaptic aggregates which are present in the other species. Second, small gap junctions are present between the end bulb and spherical cell soma of rats and mice. These interspecies differences are not reflected in thin‐sectioned material. This observation points out the difficulty in attempting to generalize about the significance of intramembrane specializations in synaptic memb