Peripheral synapses in Limulus chemoreceptors.

1. Contact chemoreceptors on spines of Limulus prosomal appendages responded to stimulation by amino acid solutions with slowly adapting activity. 2. Mixtures of amino acids elicited stronger responses than equal concentrations of single amino acids. 3. Single unit responses consisted of irregularly timed, intermittent, bursts of action potentials recorded from the axons of the primary chemoreceptor neurons. 4. These axons send collateral branches to neural plexuses located at points peripheral to the recording sites. 5. Putative chemical synapses among the collaterals are seen and suggested as the site for implementing the second order nature of the responses.