At 20.5 h the embryo is somewhat compressed laterally because of the compressed carapace, which covers the whole body. In the Petri dish, the embryo is then situated on its side (Fig. 4C-D), slightly moving by its antennae II. The heart starts to beat. Although rudiments which generate the heart organ appear a bit earlier, the heart was defined here as organ when it started its function (by observing beating).