The cells are alternate on the stem, and are curiously armed with long whip-like cilia or spines. On the back of some of the cells is a very strange appendage, the use of which is not with certainty ascertained. It is a minute body, slightly resembling a vulture’s head, with a movable lower beak. The whole head keeps up a nodding motion, and the movable beak occasionally opens widely, and then suddenly snaps to with a jerk. It has been seen to hold an animalcule between its jaws till the latter has died, but it has no power to communicate the prey to the polype in its cell or to swallow and digest it on its own account. It is certainly not an independent parasite, as has been supposed, and yet its purpose in the animal economy is a mystery. Mr. Gosse conjectures that its use may be, by holding animalcules till they die and decay, to attract by their putrescence crowds of other animalcules, which may thus be drawn within the influence of the polype’s ciliated tentacles. Fig. 7 B shows the form of one of these “birds’ heads,” and fig. 7 C, its position on the cell. FLUSTRA LINEATA. _Pl._ I. _fig._ 1. In Flustræ, the cells are placed side by side on an expanded membrane. Fig. 1 represents the general appearance of a species which at least resembles F. lineata as figured in Johnston’s work. It is spread upon a Fucus. Fig. A is an enlarged view of the cells. FLUSTRA FOLIACEA. _Pl._ I. _fig._ 2. We figure a frond or two of the common species, which has cells on both sides. It is rarely that the polypes can be seen in a state of expansion. SERIALARIA LENDIGERA. _Pl._ I. _fig._ 10. NOTAMIA BURSARIA. _Pl._ I. _fig._ 11. The “tobacco-pipe”“ appendages, fig. 11 B, are of unknown use: they are probably analogous to the birds’ heads in the Cellularæ. PLATE V. CORALS AND SEA ANEMONES. CARYOPHYLLÆA SMITHII. _Pl._ V. _fig._ 2. _Pl._ VI. _fig._ 3.