236 



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 the case ; since, in some specimens in Mr. Griffiths'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 tentacula. 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 gigantea bores in mud, from which it cannot be 

 supposed to receive any part of its nutriment, it may be questioned 

 whether the Teredo Navalis 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. [Phil. 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 va- 

 rious parts added to trees, &c. are generated, has previously circu- 

 lated through their leaves, either in the same or in the preceding 

 season, and has subsequently descended through their barks. There 

 is, however, a circumstance stated by Hales and by Du Hamel, which 



