146 THE FIXED MOLLUSCA. 



are fixed by a short ligament ;* while the Ligula anatina is 

 raised and supported on a cylindrical cartilaginous peduncle, 

 a few inches long, and capable, apparently, of a certain 

 degree of contraction and elongation. 



Very similar in this respect to the Ligula is the mode of 

 attachment exhibited in the Boltenia and Clavelina, genera 

 of the tunicated mollusca that rise up on a slender stalk, 

 which serves them for a cable, and is fixed to its stay by 

 fibrous radicles, not unlike those of some sea-weeds. The 

 greater number, however, of the Tunicata are sessile, ad- 

 hering by a broad basis, or spread out in the manner of 

 a crust. Thus the Distoma, Aplidium, Polyclinum, Bo- 

 tryllus, &;c., envelope the stems and leaves of sea-weeds in a 

 jelly-like mass, studded over with stellated figures; while 

 the Cynthise and Ascidia? grow from them, and from rocks, 

 like morbid warts or tumours, the more like from their 

 being covered with a rovigh, sometimes granular, coriaceous 

 skin. The adhesion of all of them is permanent and very 

 strong ; so that when you attempt their removal, it must 

 be made cautiously, and with a knife ; otherwise their body, 

 tough as it is, will certainly be torn. These mollusca, how- 

 ever, are born free, and in their veriest infancy even swim at 

 large ; but, unapt to roam, and careless of liberty, they soon 

 voluntarily root themselves beside their parents, never again 

 to remove from the natal rock. 



A few Gasteropods have the same permanent fixation as 

 the footless moUuscans I have been bringing under your 

 notice. When Rang asserts that the genus Hijjponyx, and 

 perhaps the Capulus, are the only Gasteropods in this con- 

 dition, f he forgets the Vermetus of Adanson, and the Le- 

 mentina of Risso. You may, perhaps, hint to me that I 

 am likely to forget the limpets (Patellae) ; but although these 

 creatures are assuredly sedentary to a high degree, — the 

 same individual having been seen for days, nay, even years, 

 attached to the same spot, yet this is from choice, not 

 necessity. " This singular attachment to a particular spot 

 having commenced during their young state, they seldom 

 seek another, but accommodate their shell, in its after- 

 growth, to all the irregularities of the rocks." You know, 



on the surface : " Elles ont en outre la faculte de se detacher, suivant le 

 besoin, pour allcr nager sur la surface de I'eau." — Enci/clap. Method, i. 70. 



* The plug of the Anomia appears to he closely allied to the byssus of the 

 Monomyaires. It passes out of a similar notch, and not of a hole as it is 

 often said ; it is not solid like shell, but formed of numerous parallel laminae 

 placed side by side, somewhat like the lamellar beard or foot of the Area, 

 e. g. A. noffi. J. E. Gray, MS. t Man. p. 28. 



