Fine structure of the egg of Trichoprosopon digitatum (Diptera: Culicidae) and its relationship to egg raft formation

Eggs of Trichoprosopon digitatum (Rondani) occur in rafts; the anterior polesare submerged, and the posterior two-thirds float above the water surface. Each egg isapproximately 1,060 µm long and 270 µm wide. The hydrophilic end is more curved dorsallythan ventrally and is covered with flattened, anteriorly pointed, scalelike tubercles exceptfor a small area around the micropyle. The hydrophobic portion is clad in a layer of closelyarrayed, small, round tubercles among which are positioned much larger, flattened, anteriorlydirected tubercles with deeply fissured surfaces. At three positions equidistant around theperiphery of the egg, narrow, tongue-shaped extensions (the embrasures) from the anteriorhydrophilic region project posteriorly into the hydrophobic region. Along these embrasures,progressing posteriorly, the tubercles change in form from flattened and bladelike to finelytapered, then, at the extension's posterior two-thirds, to long filaments with well-developedterminal hooks. Eggs in rafts are maintained in polygonal rosettes by the interlocking ofthese filaments and hooks and the surface tension of menisci between contiguous embrasures.