The animal’s body is included within the capitulum, within what I call the _sack_ (see Pl. IV, figs. 2 and 8´ _a_, and Pl. IX, fig. 4). The body consists of the _thorax_ supporting the cirri, and of an especial enlargement, or downward prolongation of the thorax, which includes the stomach, and which I have called the _prosoma_. (Pl. IX, fig. 4 _n_). The cirri are composed of two arms or _rami_, supported on a common segment or support, which I call the _pedicel_. The _caudal appendages_ are two little projections, either uni-or multi-articulate (Pl. IV, fig. 8´ _a_), on each side of the anus, and just above the long proboscis-like penis. On the thorax and prosoma, or on the pedicels of the cirri, there are in several genera, long, thin, tapering filaments, which have generally been supposed to serve as branchiæ; these I call simply _filaments_, or _filamentary appendages_ (Pl. IX, fig. 4 _g-l_). The mouth (fig. 4 _b_) is prominent, and consists of _palpi_ soldered to the _labrum_; _mandibles_, _maxillæ_, and _outer maxillæ_, these latter serve as an under lip; to these several organs I sometimes apply the title used by Entomologists, of “trophi.” Beneath the outer maxillæ, there are either two simple orifices or tubular projections; these, I believe, serve as organs of smell, and have hence called them the _olfactory orifices_. Within the sack, there are often two sheets of ova (Pl. IV, fig. 2 _b_), these I call (after Steenstrup, and other authors) the _ovigerous Lamellæ_; they are united to two little folds of skin (Pl. IV, fig. 2 _f_), which I call the _ovigerous Fræna_. From the peculiar curved position which the animal’s body occupies within the capitulum, I have found it far more convenient (not to mention the confusion of nomenclature already existing) to apply the term Rostral instead of ventral, and Carinal instead of dorsal, to almost all the external and internal parts of the animal. Cirripedes have generally been figured with their surfaces of attachment downwards, hence I speak of the lower or Basal margins and angles, and of those pointing in an opposite direction as the Upper; strictly speaking, as we shall presently see, the exact centre of the usually broad and flat surface of attachment is the anterior end of the animal, and the upper tips of the Terga, the posterior end of that part of the animal which is externally visible; but in some cases, for instance in Coronula, where the base is _deeply concave_, and where the width of the shell far exceeds the depth, it seemed almost ridiculous to call this, the anterior extremity; as likewise does it in Balanus to call the united tips of the Terga, lying deeply within the shell, the most posterior point of the animal, as seen externally. I have followed the example of Botanists, and added the interjection [!] to synonyms, when I have seen an authentic specimen bearing the name in question.