[4] The most various opinions prevail as to the position of the Cirripedia. Some ascribe to them a very subordinate position among the Copepoda; as Milne-Edwards (1852). In direct opposition to this notion of his father’s, Alph. Milne-Edwards places them (as _Basinotes_) opposite to all the other Crustacea (_Eleuthéronotes_). Darwin regards them as forming a peculiar sub-class equivalent to the Podophthalma, Edriophthalma, etc. This appears to me to be most convenient. I would not combine the Rhizocephala with the Cirripedia, as Liljeborg has done, but place them in opposition as equivalent, like the Amphipoda and Isopoda. The near relationship of the Cirripedia to the Ostracoda is also spoken of, but the similarity of the so-called “_Cypris_-like larvæ,” or Cirriped-pupæ as Darwin calls them, to _Cypris_ is so purely external, even as regards the shell, that the relationship appears to me to be scarcely greater than that of _Peltogaster socialis_ (Fig. 59) with the family of the sausages. [5] In connexion with this it may be mentioned that, in the females of Brachyscelus, in which the posterior antennæ are deficient, the conical processes with the canal permeating them are nevertheless retained. [6] Compare the figure given by Darwin (Balanidæ Pl. xxx fig. 5) of the first natatory foot of the pupa of _Lepas australis,_ with that of _Lernæodiscus Porcellanæ_ published in the ‘Archiv für Naturgeschichte’ (1863, Taf. iii, fig. 5). The sole distinction, that in the latter there are only 3 setæ at the end of the outer branch, whilst in the Cirripedia there are 4 on the first and 5 on the following natatory feet, may be due to an error on my part. [7] Darwin describes as “acoustic orifices” small apertures in the shell of the pupæ of the Cirripedia, which, frequently surrounded by a border, are situated, in _Lepas pectinata,_ upon short, horn-like processes. I feel scarcely any hesitation in regarding the apertures as those of the “shell-glands,” and the horn-like processes as remains of the frontal horns. [8] The roots of _Sacculina purpurea_ (Fig. 60) which is parasitic upon a small Hermit Crab, are made use of by two parasitic Isopods, namely a Bopyrus and the before mentioned _Cryptoniscus planarioides_ (Fig. 42). These take up their abode beneath the _Sacculina_ and cause it to die away by intercepting the nourishment conveyed by the roots; the roots, however, continue to grow, even without the _Sacculina,_ and frequently attain an extraordinary extension, especially when a _Bopyrus_ obtains its nourishment from them.