The Mechanism of the Pupal Gin Trap

Abstract

ABSTRACT The sensilla inside the gin trap are connected with an intemeurone in the ipsilateral connective above the ganglion in which their axons terminate. This cell is driven by the combined input of many fibres in the afferent bundle; it receives an inhibitory input driven by the contralateral muscle receptor organ and another driven by the contralateral trap sensilla. There is an inhibitory relation between efferent activity on opposite sides of the nervous system. A model is proposed which enhances contrast between the two halves of the nervous system by an inhibitory cross-connexion. The closure mechanism of the gin trap does not fit this model but can be derived from it by a small change in the properties of the ipsilateral junction of triggering sensilla and second-order neurones. A consequence of this theory is that the terminals of the triggering sensilla need not be identified within the central nervous system.