Figure 13

Origin of the paired pilidial imaginal discs with respect to the larval ciliated band. This simplified diagram depicts a pilidium larva as a sphere, with the apical tuft pointing up and the subequatorial larval ciliated band represented by a dash line. The cephalic imaginal discs (cd) invaginate from the larval episphere, i.e. above the larval ciliated band, and have been shown experimentally to be derived from the first-quartet micromeres (1q cells). The trunk discs (td) and the cerebral organ discs (cod) invaginate from the hyposphere, i.e. below the larval ciliated band, and therefore are derived either from the second-quartet (2q cells), or the third-quartet micromeres (3q cells).