[61] Quoted by Dana, 'Crustacea of United States Exploring Expedition,' p. 1264. _Antennæ._--These, from their present position, and from standing, in their earlier stages whilst within their envelopes or horns, exteriorly to the small medial pair (since aborted), I believe to be the second pair; and this is Mr. Dana's opinion. In my former description of these very singular and important organs (Pl. 30, figs. 4 and 8), I have fallen into some considerable mistakes: the two plates or segments (fig. 4, N), of which the posterior margins are inflected as apodemes (_n_), carrying the eyes, are certainly, as may be clearly seen in the pupa of Alcippe, Pl. 23, fig. 16, and as affirmed by Burmeister,[62] the basal segments of the antennæ. The second or main segment (formerly called by me the basal segment) has in some species an upper portion of the membrane of which it is composed, next to the body, excessively thin, and separated from the rest of the membrane composing the segment, by an oblique line (fig. 8, _o_), which I mistook for its articulation with the body.[63] We then come to the disc or third segment; and lastly to the fourth, or ultimate segment. This ultimate segment, generally, has its external corner projecting up, as a step; and this sometimes, as in _Dichelaspis Warwickii_, gives the appearance of its consisting of two segments; but a careful examination of this part in Ibla, in which the step-like structure is carried to an extreme, makes me believe that there is only one segment.[64] The prehensile antennæ, therefore, like the natatory legs, are formed of four consecutive segments, of which the basal segments give rise to the singular apodemes, presently to be noticed (fig. 7), that carry the great compound eyes. This basal segment, in all Cirripedes, is moulted with the eyes, the three other segments invariably remaining cemented to the surface of attachment. [62] 'Beiträge zur Naturgeschichte der Rankenfüsser,' p. 19. In tab. 1 of this work there are good drawings of the general structure of the pupa of a species of Lepas, probably _L. australis_. I believe this author was the first who made out the structure of the abdomen of the pupa. [63] In the table of measurements of the antennæ of the several genera and species of the Lepadidæ (p. 286) of my former volume, the articulation, called by me _basal_, I now know to be really the articulation between the basal and second segment. In the fourth column, headed "Length from end of the disc to the inner margin of the basal articulation," the term inner margin really applies to the oblique curved line separating the thin and scarcely visible membrane from the thicker membrane of that segment. These corrections do not in the least affect the object for which the table was given.