I will now make a few remarks on these larvæ in the first stage, before and after the first moult, supplemental to those in my former volume. Their shape is oval, and the whole dorsal surface is evidently covered by a carapace. It is remarkable that the body exhibits no distinct articulations; those given by Goodsir[52] being certainly erroneous. Commencing at the anterior extremity, the eye varies considerably in the state of its development; in _Platylepas decorata_ it is nearly circular, and in most of the specimens very distinct; whereas in the allied _Coronula balænaris_, before the first moult, it is very imperfect, but afterwards square and of considerable size. In _Balanus galeatus_, in the immature larvæ dissected out of the egg, the cellular matter which was in process of conversion into the eye, formed a transverse band, obscurely divided into two portions, and this seems to indicate that the single eye is in fact formed by the confluence of two eyes. In _Scalpellum vulgare_, this heart-shaped eye lies between a V-shaped muscle, the nature of which I cannot understand, and which has not been represented in (Pl. 29, fig. 8, _a_). I need only further add, that in _Chthamalus stellatus_, after the first moult, the eye exhibits, in specimens sent me by Mr. Bate, some appearance of tending to become double. [52] 'Edinburgh New Philosophical Journal,' July, 1843, Pl. 3, 4. Arising posteriorly to the eye, we see, in _Scalpellum vulgare_, a pair of minute curved horns (_b′_), directed backwards; and within these horns I distinctly saw an articulated organ. These horns are difficult to be distinguished, and probably could not be made out previously to the first moult, in any larva of less size than that of _Scalpellum vulgare_. But after the first moult, Mr. Bate has seen, in two species of Balanus, in Verruca and in Chthamalus (fig. 10, _b_), a pair of articulated organs, in this same position, evidently now forming antennæ, and directed anteriorly, and free from any envelope. It is somewhat important, as we shall presently see, to bear in mind that these antennæ first appear within an envelope or horn; and that I detected that they included an articulated organ, before I had heard of Mr. Bate's observations. These antennæ, from their small size, from being seated internally with respect to the horns containing the other pair of antennæ, and from the position which the latter assume in the later stages of the larva, I believe to be the first or anterior pair. Their position in appearance posteriorly to the large lateral horns, containing the second pair of antennæ, is probably due to the anterior cephalic segments having been driven inwards, the truncated outline of the front of the head, and likewise, probably, the position of the mouth between the bases of the natatory legs being thus caused.