a special organ, occurring only in the Lepadidæ; the digestive organs are very simple, from not having any distinct liver; the generative system is very low, for both sexes are generally united in the same individual; and the testes and ovaria closely resemble each other. On the other hand, the thoracic limbs are, to a considerable extent, specialised in their structure and functions; only the three posterior pairs strictly resembling each other. Lastly, the dermal and muscular systems are complicated, and not, to use Professor Owen's term, by mere vegetative repetition, as will be obvious to any one who will study the beautifully constructed and modified carapace--that is the operculum, shell and basis--of a Balanus. On the whole, I look at a Cirripede as a being of a low type, which has undergone much morphological differentiation, and which has, in some few lines of structure, arrived at considerable perfection,--meaning, by the terms perfection and lowness, some vague resemblance to animals universally considered of a higher rank. [17] English Translation, in 'Scientific Memoirs,' 1853, vol. i, p. 228. * * * * * It has been seen that I divide the Cirripedia into three orders,--the Thoracica, Abdominalia, and Apoda; between which the fundamental difference consists in the limbs or cirri being thoracic in the first, abdominal in the second; and entirely absent in the third. For the sake of showing the range of character in Cirripedes, to which allusion has been made, I will briefly indicate the leading differences in each order. In the Thoracica, three families are included,--the Balanidæ, or sessile Cirripedes, the Verrucidæ, remarkable from their quite asymmetrical shell, and the Lepadidæ, or pedunculated Cirripedes. The great difference in external appearance between these three families is known to all naturalists. Even within the one family of Lepadidæ there are great differences in external appearance, as will be admitted on comparison of Lepas, Pollicipes, Conchoderma, &c.; but we have also important internal differences, as in the case of Anelasma, in which the cirri are barely articulated, and are not capable of seizing prey, whilst the mouth is almost probosciformed, with the outer maxillæ and palpi rudimentary: still more important are the differences in Alcippe, in which the cirri of the first pair act as brushes; the second, third, and fourth pairs being quite aborted; and the fifth and sixth pairs consist only of four segments, with one of the two normal rami converted into a crenated, button-like projection, for the sake apparently of triturating food; Alcippe, also, is very remarkable in being destitute of a rectum and anus. In this same genus Alcippe, in Ibla and Scalpellum, there are either separate males or Complemental males, some of which are so utterly abnormal in their characters, that by no definition which I could frame, could they be included even in