CUTICULAR PROTUBERANCE OF INSECTS

Studies, especially with transmission electron microscopy of developmental stages, show that the many superficially different spines, bristles, hairs, etc. can be classified into 4 major types: (1) multicellular with cells similar to those of the general epidermis (spines); (2) multicellular with differentiation of a segregated trichoid complex (setae); (3) unicellular (acanthae); and (4) subcellular in the sense of several or many per cell (microtrichia). Except for eversible pouches, there are no flaccid projections because the cuticle of setae and other projections is always sclerotized. Spines, as the term is used above, occur primarily on external surfaces, except for comparable structures in the proventriculi of some insects. Setae are on external surfaces only, and most of them retain a sensory function. Acanthae are best known on internal surfaces of foregut and reproductive ducts but can be found on external surfaces also. Microtrichia occur mostly on external surfaces but occasionally on the taenidia of tracheae. Only the socketed setae include one or more sense cells, and hence only setae are sensory (but spines can bear setae). Several or numerous subtypes can be recognized for each of these types. All of the types can have the cells withdraw; they then usually become filled with cuticle and even commonly become underlaid by cuticle; the producing cells may or may not persist. Such solid hairs commonly cannot be identified as to type without knowledge of their development. © 1979.