Ultrastructural study of the development of the auditory tympana in the cricket Teleogryllus commodus (Walker)

The cuticle in the tympanal area of immature crickets, Teleogryllus commodus (Walker), is ultrastructurally indistinguishable from that elsewhere on the prothoracic leg. It is only in the pharate adult that changes associated with development of the tympana first appear. In pharate adults and adults the external layer of the tympana consists of a layer of electron-dense material overlying a layer where the electron-dense material is interspersed with cuticle in which the bundles of microfibrils are coarser and more loosely arranged than elsewhere in the leg. The innermost portion of the tympana consists of this same type of cuticle without the electron-dense material. Associated with the appearance of the electron-dense material in the tympana of the pharate adult is a change in the toluidine blue staining properties from blue to deep purple. The reaction of the tympana in acid and base is consistent with their being composed of chitin. There are no major deposits of resilin in the tympana. In the first few days following the imaginal ecdysis the posterior tympanum and underlying trachea come into tight apposition due to the withdrawal of the epidermal cells. The epidermal cells do not withdraw from beneath the anterior tympanum. The surrounding non-tympanal cuticle continues to thicken for several weeks with the result that in the mature adult the posterior tympanum serves as an acoustic window in the thick cuticle of the leg. The functional significance of the anterior tympanum has not been established.