11 



The lanceolate auxiliary valves, which are affixed to the 

 exterior end of the animal, clofe upon the interior, or inner- 

 moii pair of lamina, and ferve not only as a fecurity againft 

 the intrufion of larger infefts that might injure the delicate 

 body of the animal, but alfo ferve to regulate the furround-. 

 ing fluid in the cell ; for. by this apparatus the whole cir-. 

 cumambiant water may be difcharged through the exterior ^ 



fyphons at pleafure. 



As the laminated part of the tube is even with the liirface 

 of the timber perforated, the fyphons of the animal may he 

 obferved to be exerted when in its natural element, in fearch 

 of food like other teflaceous Afcidia; and like them the 

 powers and propenfities afligned for the purpofe of deiliroy- 

 ing ufelels matter by fome folvent meiiflruum, or other 

 myfterious means, is equally evident, but with this differ- 

 ence ; tlie Teredo navalis is only deflined for the redudlion 

 of ligneous matter, whereas the Pho/ade?, and fome others, 

 are capable of reducing Rone as well as timber. Whatever 

 may be the means by which this great oj^eration of nature 

 is effe6ted, it is evidently performed by all, with that part 

 which is enclofed within the j^rlncipal valves, and, that it is 

 by the oppofite or exterior end that they, receive, all their 

 nutriment by means of their fyphons, the only part of ihefe 

 animals not ablolutely imprifoned. It is therefore evident 

 that the deftru6lion made by this, and all other teflaceous 

 animals of a fimilar nature, is not for the purpofe of food, 

 but for a fecure lodgement : confequently it is moft reafon- 

 able to conclude that the diflblution of the wood or ftonein 



B 2 which. 



