From starfish and frogs to mice and humans, many embryos have a common spherical geometry. ButDrosophila embryos kick it ellipsoidal style. Why? For flies, the size of the embryo when the egg is laid is the same size of the larvae when it hatches, since it must fully develop inside the egg shell. This ellipsoidal shape is important because it allows a relatively large egg that can still fit through ovipositor of fly.
Image: Collage of wildtype and transgenic Drosophila embryos at blastoderm stage and the onset of gastrulation. Embryos are immunolabeled for the transcription factors Dorsal and Twist and co-stained by fluorescent in situ hybridization for the developmental transcription factors snail, single-minded, and twist. Individual embryo images were taken on a Leica SP confocal microscope at 20x magnification.