Embryogenesis of the connective chordotonal organ in the pedicel of the American cockroach: cell lineage and morphological differentiation.

The ontogenesis of single scolopidia of the chordotonal organ of the American cockroach, Periplaneta americana, takes about 4 days. At 23% embryogenesis (100%=30 d) the first anlagen of scolopidia were identified within the eipithelium by staining with anti-horseradish peroxidase. Reconstruction of the cell lineage of the scolopidial cells was facilitated by two facts: (i) the arrangement of the cells throughout ontogenesis follows a strict pattern, and (ii) daughter cells are recognizable for several hours after mitosis by the cytoplasmic bridge and midbody joining them. When they separate, the midbody undergoes lysosomal degeneration in one of these cells. The earliest recognizable stage is a pair of cells, one of which (cell 1) encloses the other (cell 2) apically. The enclosing cell becomes the accessory cell. Cell 2 divides, yielding the mother cell (cell 3) of two sensory cells which degenerate later, and cell 2'. Cell 2' gives rise to the attachment cell and to cell 2'', which in turn produces the scolopale cell and the mother cell (cell 2'' 2''') of a second pair of sensory cells; the latter are the definitive sensory cells. The end result is the total of 5 cells characteristic of the adult scolopidium. Secretion of the scolopale and cap together with the migration of the sensory cell perikarya into the antennal lumen complete development.