Two classes of slowly adapting mechanoreceptor fibres in reptile cutaneous nerve.

1. The myelinated fibre spectrum of the plantar nerve of reptile consists of a unimodal distribution corresponding approximately to the delta elevation in mammalian nerve and contains a variety of receptor categories similar to those of mammals except for the obvious absence of structures related to hairs.2. The various receptor types of reptilian skin do not fall into discrete groups on the basis of conduction velocity.3. Only a few thermoreceptor fibres were identified but a large proportion of slowly adapting mechanoreceptors responded to rapid temperature transients.4. Two distinct categories of slowly adapting receptors whose discharge is related to the amplitude of skin displacement have been identified and studied in detail. These two receptors can be distinguished by their patterns of discharge, and display several distinctive features including differences in resting discharge, receptive field size, threshold, response to DC polarization, etc.5. The mathematical functions describing the response to stimuli of varying magnitude for one receptor type is markedly affected by the sequence of stimulus presentation.