sels of the breathing organs, from which it returns directly to the
heart.
The mode in which the breathing organs of this animal are sup- plied with water, makes it evident. in Mr. Home’s opinion, that all, similar animals which have no cavity for the reception of sea Water, must have their breathing organs placed externally; and he thinks that the beautiful membranous expansions displayed by those species of Actiniae, called in the West Indies animal flowers, are, in fact, the breathing organs of those animals; and not, as their appearance formerly led Mr. Home to believe, tentacula for catching food.
The Teredo gigantea, when arrived at its full growth, closes up its shell; so also does the Teredo Navalis. Hence Sellius Was led to suppose that the animal, by this act, formed its own tomb. This, however, is not thecase; since, in some specimens in Mr. Grifliths’s possession, the animal appears to have receded from its first inclosure, and to have formed a second, three inches up the tube, and after- wards a third, two inches further on. These facts show that the Teredo gigantea, when arrived at its full growth, closes up its shell, and lives a long time afterwards, being furnished with food from the sea by means of its tenmcula. The Teredo Navalis closes up its shell in the same manner; it must therefore, after that period, be supplied with food through the medium of the sea water; and it is probable that the small tentacula, before described, are for the pur- pose of catching food.
As the Teredo gigantca bores in mud, from which it cannot be supposed to receive any part of its nutriment, it may be questioned whether the Teredo IVavalis receives its support from the wood it destroys, or is wholly supplied with food from the sea. The latter opinion appears to Mr. Home the most probable. The quantity of wood taken into its stomach is, he thinks, by no means sufficient for the support of an animal which has red blood and very perfect organs. He also remarks, that the saw-dust already spoken of did not appear to Mr. Hatchett to have undergone any change.
These animals, having only a slight connexion with their shell at one particular spot, are capable of turning themselves round in their shell; this facility of motion seems evidently to be intended for the purpose of boring.
On the inverted Action of the alburnous Vessels of Trees. By Thomas Andrew Knight, Esq. F.R.S. In a Letter to the Right Hon. Sir Joseph Banks, K.B. P.R.S. Read May 15, 1806. [Fill Trans. 1806, p. 293.]
Mr. Knight, in the papers formerly communicated by him to the Royal Society, endeavoured to prove that the fluid by which the various parts added to trees, &c. are generated, has previously circulated through their leaves, either in the same or in the preceding season, and has subsequently descended through their barks. There is, however, a circumstancc stated by Hales and by Du Hamel, which
