The microfiber texture in a specialized plastic cuticle area within a sensillum field on the cockroach maxillary palp as revealed by freeze fracturing.

A field of sensilla extends across the ventral surface of the terminal segment of the maxillary palps of Periplaneta americana. The sensilla project from a sheet of pliable cuticle. Ultrathin sections of the cuticle in this area reveal a clear-cut parabolic microfiber pattern. Microfibers can also be seen from freeze fracture faces running parallel to the cuticular surface. These microfibers have a diameter of 80 A and may consist of chitin crystallites surrounded by a matrix coat. The number of straight parallel microfibers visible in a fracture face increases the more closely parallel to the surface the fracture runs. This result suggests a helicoidal texture, as the model of Bouligand would demand. The layer-to-layer rotational displacement of the microfibers is about 12 degrees. This texture can be regarded as typical for flexible cuticles in general. Other structural properties such as the continuation of the epicuticular dense layer into deeper cuticular layers around the enveloping cells of sensilla can be interpreted as specializations connected with the function of the sensillum field.