It is further to be remarked that the Zoëæ of the Crabs, as also of the _Porcellanæ,_ of the Tatuira and of the Shrimps and Prawns, are enveloped, on escaping from the egg, by a membrane veiling the spinous processes of the carapace, the setæ of the feet, and the antennæ, and that they cast this in a few hours. In _Achæus_ I have observed that the tail of this earliest larval skin resembles that of the larvæ of Shrimps and Prawns, and the same appears to be the case in _Maia_ (see Bell, ‘Brit. Stalk-eyed Crust.’ p. 44). Widely as they seem to differ from them at the first glance, the Zoëæ of the _ Porcellanæ_ (Fig. 24) approach those of the true Crabs very closely. The antennæ, organs of the mouth, and natatory feet, exhibit the same structure. But the tail bears _five_ pairs of setæ, and the dorsal spine is wanting, whilst, on the contrary, the frontal process and the lateral spines are of extraordinary length, and directed straight forward and backward. Fig. 24. Zoëa of Porcellana stellicola, F. Müll. Magnified. Fig. 25. Zoëa of the Tatuira (Hippa emerita), magnified. Fig. 26. Zoëa of a small Hermit Crab, magnified . Fig. 24. Zoëa of _Porcellana stellicola,_ F. Müll., magnified. Fig. 25. Zoëa of the Tatuira (_Hippa emerita_), magnified. Fig. 26. Zoëa of a small Hermit Crab, magnified. The Zoëa of the Tatuira (Fig. 25) also appears to differ but little from those of the true Crabs, which it likewise resembles in its mode of locomotion. The carapace possesses only a short, broad frontal process; the posterior margin of the tail is edged with numerous short setæ. The Zoëa of the Hermit Crabs (Fig. 26) possesses the simple inner antennæ of the Zoëa of the true Crabs; the outer antennæ bear upon the outside on a short stalk a lamella of considerable size analogous to the scale of the antennæ of the Prawns; on the inside, a short, spine-like process; and between the two the flagellum, still short, but already furnished with two apical setæ. As in the Crabs, there are only two pairs of well-developed natatory feet (maxillipedes), but the third pair is also present in the form of a two-jointed stump of considerable size, although still destitute of setæ. The tail bears five pairs of setæ. The little animal usually holds itself extended straight in the water, with the head directed downwards.