Morphology and ontogeny of single-walled multiporous sensilla of hemimetabolous insects

Comparative morphological investigations were made to determine the common organization plan of single-walled multiporous sensilla. The development of multiporous chemoreceptive sensilla of Gryllus, Oncopeltus and Lepisma follows the same path. Each chemoreceptive sensillum is associated with four types of enveloping cell. During ontogeny, enveloping cell 1 secretes the dendritic sheath. Enveloping cell 4 builds the connection of the hair base with the antennal cuticle. In Gryllus and Oncopehus, enveloping cells 2 and 3 build the hair shaft, the wall pores and pore tubules in nearly equal parts. Enveloping cells 2 and 3 lie side by side in the hair process, in which enveloping cell 2 produces the inner part, enveloping cell 3 the outer part of the hair shaft. In Lepisma the predominant part of the hair shaft with the wall pores is formed by the doubled enveloping cells 3. Interpreting our findings and the literature data, a new proposal is given for the homology of the enveloping cells. In singlewalled chemoreceptors, enveloping cell 1 is considered as thecogen and enveloping cell 4 as tormogen cell. Enveloping cell 2 is interpreted as inner trichogcn cell and enveloping cell 3 as outer trichogen cell.