to 



-cretion ; ift this cafe the invaded feems to retreat, and for 

 -better feciirity throws an arched f4ptum acrofs the gallery 

 at the part where the flielly tube had terminated, and thus 

 fecurelyenclofes iffelf within a wall of its own preparing, 

 which is i-JTOof againft further ii^ftrufion. 



Some of thefe tubular cafes we have obferved are defti- 

 tute of the thickened laminated ftru6lure at the fmaller, or 

 exterior end, and only furniflied with an oblo^ig perforation 

 for protruding the animal's fyphons. Thofe alfo that are 

 furniflied with lamince differ materially in number, without 

 any regard to the fize of the tubes, varying from four to 

 twenty. One in particular we examined had no lefs than 

 twenty-nine, fix of which on each fide were furniflied with 

 a mid-rib ftanding above the plain of the lamince in a cari- 

 nated ridge. 



This fpecirtien Was not of an uftufual fize, but was an 

 •inch and a half in length at that part. 



For what particular purpofe this fingular ftru(5lure is de- 

 figned, is difficult to determine, fmce we find fome deflitute 

 of it ; but we may infer it has its ule, as few, comparatively 

 fl)caking, are without it. 



Probably it is intended to infnare the fmaller marine ani- 

 makuli on which the animal undoubtedly preys, and in this 

 labyrinth are readily colle6];ed and drawn in by the tubular 

 extremity of the Afcidia, 



The 



