Johnston's organ

Johnston's organ is a collection of sensory cells found in the pedicel (the second segment) of the antennae in the class Insecta. Johnston's organ detects motion in the flagellum (third and typically final antennal segment). It consists of scolopidia arrayed in a bowl shape, each of which contains a mechanosensory chordotonal neuron. The number of scolopidia varies between species. In homopterans, the Johnston's organs contain 25 - 79 scolopidia. The presence of Johnston's organ is a defining characteristic which separates the class Insecta from the other hexapods belonging to the group Entognatha. Johnston's organ was named after the physician Christopher Johnston, father of the physician and Assyriologist Christopher Johnston.