Lydia is a bit— sexually aggressive.
In this it remains until the completion of the transformation into the sexually mature insect, which then emerges from the case, leaving the pupal integument behind.
This anomalous phenomenon is still obscure, for we do not yet know whether the second embryo is developed sexually or asexually from the first.
Through this temporary protection the active pupa, which closely resembles the mature insect, subsequently bites a way by means of its strong mandibles, and rising to the surface of the water casts the pupal integument and becomes sexually adult.
The gastrula has now become an actinula, which may be termed the distinctive larva of the Cnidaria, and doubtless represents in a transitory manner the common ancestor of the group. In no case known, however, does the actinula become the adult, sexually mature individual, but always undergoes further modifications, whereby it develops into either a polyp or a medusa.