[73] Rathke has described ('Acta Nova,' 1839, p. 147), in some siphonostomatous crustaceans, a pair of curious organs, which serve to secrete a substance that holds the eggs attached together in a mass to the parent's body: these organs Rathke has designated by a similar name to that which I have used, namely, the cementing organs or receptacles; they are distinct from the oviducts, but enter them near their external orifices. As in Cirripedes, the cement-glands and ducts are certainly continuous with an ovarian tube; and as they occupy a quite different position in the animal's body, these organs of Rathke, though in some degree analogous in function, must be homologically distinct. _Affinities, Classification, Variation._ Under the Order it has been stated that the Balanidæ, are, on the cirripedial type, the highest in the class; that is, they are the most complicated, but not (to use Professor Owen's term) by mere vegetative repetition. Amongst the Balanidæ, the first section of the genus Balanus may be taken as typical; here we have the structure of the shell extremely complicated, yet beautifully adapted for strength, and for the protection of the included body. The cementing apparatus is here, also, most complicated. I have divided the Balanidæ into two natural sub-families, the Balaninæ and Chthamalinæ, in accordance with certain differences in the structure of the shell and of the animal's body: that this division is natural, might almost be inferred from the one fact, that all the characters by which the Chthamalinæ differ from the Balaninæ, are those by which the former approaches the family of the Lepadidæ; moreover, certain anomalous characters in the Chthamalinæ, as the supplemental whorls of compartments in Catophragmus, and the presence of caudal appendages in this same genus and in Pachylasma, reveal this same affinity. The only objection which I can see to the separation of the sixteen genera into the above two sub-families, may be drawn from the degree to which they blend together; thus, as far as the shell is concerned, Chelonobia, in one important internal point of structure, tends to assume the character of the Chthamalinæ; and on the other hand, Pachylasma, a member of the Chthamalinæ, has a shell, which if not examined during its earliest growth, would be placed without doubt amongst the Balaninæ. But it fortunately so happens, that in no one character of the body does Pachylasma approach the Balaninæ more nearly, than do the other members of its sub-family; or Chelonobia approach, in the same respects, the Chthamalinæ. It is only in Chthamalus, of which the shell clearly places it in the sub-family bearing its name, that in some of the species, the less bullate labrum,--the larger palpi,--the lower teeth of the mandibles being laterally double,--and the lower segments of the third pair of cirri being thickly clothed, like the lower segments