Mechanoreception is the perception of mechanical distortion of the body caused by the external stimuli of touch and airor water-borne vibrations, or due to the internal forces generated by activities of the muscles. Mechanical stimuli are in volved in more behavioral activities than any other type of external stimulus. Among these are locomotion, posture, feeding, orientation, oviposition, and hearing. Arthropods with their rigid exoskeleton are particularly well suited for the detection of mechanical stimuli and have developed a number of specialized structures for this purpose. The sensilla for mechanoreception may be classified according to their function, such as auditory, tactile, stretch, and position receptors, or according to their structure. One structural type may have more than one function, e.g. hair sensilla, although usually tactile receptors, may also perceive air-borne vibrations. Two general groups of mechanoreceptors are known. Type I are those sensilla in which the dendrite of the bipolar neuron is associated with the cuticle or its invagi nation. Type II (commonly called stretch receptors) are sensilla with multipolar neurons which are associated with the walls of the alimentary canal, inner surface of the body wall, muscles, and connective tissues, but not the cuticle. Type I may be subdivided into (a) those sensilla which, although associated with the inner aspect of the cuticle, lack an external cuticular component, the scolopidial or chordotonal sensilla, and (b) those with an external cuticular portion, the cuticular mechanoreceptors, which are the subject of this review. For additional general information the reader is referred to Bullock & Horridge (15), Dethier (32), Hoffman (65), Sinoir (113), Slifer (114), Snodgrass (121, 122), and Schwartzkopff (110) on mechanoreceptors in general; to Howse (69) for chordo tonal organs; to Osborne (91) for stretch receptors; and to Finlayson (35), Hoffman (66), and Pringle (96) for proprioceptors. Numerous light microscope studies have determined the types and basic structure of cuticular mechanoreceptors. More recent application of electron microscopic