Morphology of identified cercal afferents and giant interneurones in the hatchling cockroach Periplaneta americana

Cobalt backfills from the thoracic connectives of the hatchling Periplaneta americana allowed identification of giant interneurones in the terminal abdominal ganglion, morphologically comparable to GI 1, 2 and 3 in the adult. The bipolar neurone innervating each cercal filiform wind receptor hair is ultrastructurally similar to the adult cell and possesses an individually identifiable afferent axon, four of which provide the behaviourally functional escape response system with a simplified sensory input. Both pre- and postsynaptic neurones can be identified and may provide a good preparation for the study of cholinergic synapses.