_Mouth._--This is seated in exactly the same position as in the mature Cirripede, on a slight prominence, fronting the thoracic limbs, and so far within the carapace, that it was obviously quite unfitted for the seizure of prey; and it was equally obvious, that the limbs were natatory, and incapable of carrying food to the mouth. This enigma was at once explained by an examination of the mouth, which was found to be in a rudimentary condition and absolutely closed, so that there would be no use in prey being seized. Underneath this slightly prominent and closed mouth, I found all the masticatory organs of a Cirripede, in an immature condition. The state of the mouth will be at once understood, if we suppose very fluid matter to be poured over the protuberant mouth of a Cirripede, so as to run a little way down, in the shape of internal crests, between the different parts, and in the shape of a short, shrivelled, certainly closed tube, a little way (.008 of an inch in _L. australis_) down the oesophagus. Hence, the larva in this, its last stage, cannot eat; it may be called a _locomotive Pupa_;[11] its whole organisation is apparently adapted for the one great end of finding a proper site for its attachment and final metamorphosis. [11] M. Dujardin has lately (‘Comptes Rendus,’ Feb. 5, 1850, as cited in ‘Annals of Nat. History,’ vol. v, p. 318,) discovered that the “Hypopi are Acari with eight feet, without either mouth or intestine, and which, being deprived of all means of alimentation, fix themselves at will, so as to undergo a final metamorphosis, and they become Gamasi or Uropodi.” Here, then, we have an almost exactly analogous case. M. Dujardin asks--“Ought, therefore, the Hypopi to be called larvæ, when, under that denomination, have hitherto been comprised animals capable of nourishing themselves?”