CLASSIFICATION OF OBJECTh OF lislJiRirfT. 4o0 



separated from the cartilage to which it is attached ; after a 

 slight washing, or even maceration in water, it should be laid 

 on a slide, with its spiny side uppermost, and pressed quite 

 flat, so that in drying it may adhere to the glass ; it should 

 then be surrounded, with a cell of paper or card-board, and 

 the cover cemented down either with sealing-wax or the 

 electrical cement ; if required for polarized light, a specimen 

 mounted in balsam will answer. A power of forty diameters 

 is sufficient for examining this remarkable organ, which can 

 be viewed either as a transparent or as an opaque object. 



The tongue of the Patella or limpet, though not so beau- 

 tiful a structure as that of the whelk, is, nevertheless, a very 

 interesting object ; it is remarkable, also, for its length, being 

 often three times that of the body; it is supported on two 

 cartilaginous pieces, placed on each side of its root; from 

 these arise strong and short muscular bands, which move the 

 organ. The surface, like that of the whelk, is covered with 

 spines, or teeth, placed in transverse rows, and arranged in 

 three series; each central group has three or four spines, 

 but those on the sides contain only two; the anterior part 

 should be selected for examination, as there the teeth are the 

 firmest. On opening the body of the animal, the tongue is 

 seen doubled up upon itself, from which situation it can 

 readily be detached.* In consequence of its length, this 

 tongue cannot be mounted in the same manner as that of the 

 whelk ; the best plan to adopt is to coil it up in a tubular cell 

 and mount it in fluid ; short lengths may be dried, in order to 

 display the structure of the teeth. The tongues of the peri- 

 winkle, nassa, &c., require similar treatment. 



Some of the Gasteropods are provided with a muscular 

 gizzard, armed with gastric teeth of stony hardness; these 

 are also interesting subjects for examination ; the larger kinds 

 may be ground down thin and viewed as transparent objects, 

 whilst the smaller can be mounted as opaque objects and 

 examined in situ. The principal genera in which the gastric 

 teeth may be seen, are Bulla, Scyllaea, and Aplysia ; but the 

 most remarkable forms occur in the last mentioned genus. 

 * Cydopcedia of Anatomy and Physiology, vol. ii. ; article, Gasteropoda. 



