460 



SUPPLEMENT. 



culated and act as lateral jaws. In Mglrus the mouth is also furnished with 

 membranous fringes (A. and H. PI. XVII. fig. 14). Ancula cristata has 

 a formidable spinous collar (PI. XVII. fig. 7). 



Fig. 260, a 



b 



c. 



a, mandible ; x, dental sac : 



Mouth of JEgirus ptmctilucens. 

 Horny upper mandible detached. 

 Prehensile collar of Ancula. 

 . b, insertion-plate of mandible ; c, passage of mouth. 



Note on the preparation of the Lingual Teeth as microscopic objects ■ bv 

 J. W. Wilton, Esq. The mollusk when taken from its shell must be pinned 

 down m the dissecting trough, with needle-points passed through the sides 

 of the muscular foot (fig. 251, and note). Water is then to be poured in 

 till the ammal is covered, and should be changed as often as the condition of 

 the object renders it turbid. It is convenient to make these examinations 

 under a simple lens, attached to an upright rod with a rack and screw so 

 that both hands may be free. A good light is necessary, and with lamp- 

 light a bull's-eye condenser is useful. The lower point of the scissors should 

 be passed into the mouth of the animal, and kept close to the upper side, 

 Avhich is to be cut open so as to expose the floor of the mouth, or tongue, with 

 Its teeth. When the cut edges have been pinned back, the whole length of 

 the dental sack or canal may be carefuUy worked out with a lancet or other 

 suitable instrument. Experience in this process may be gained bv examining 

 the pernvinkle and whelk, or any others of which a number may be easily 

 procured. The lingual ribbon, when detached, should be placed in a watch- 

 glass of distilled water, and cleaned by repeated washings with a camel's-hair 

 brush, and then placed in pure alcohol till wanted for mounting. If there is 

 much difficulty in getting the membrane clean, it may be put for a time in 

 hquor potassce, care being taken to wash it in frequent change of water after- 

 wards. Before mounting in balsam the preparation requires to be saturated 

 with spirits of turpentine, which will more readily enter its structure if it be 

 first soaked in chloroform. The slide is prepared by dropping a little Canada 

 balsam on its centre, the quantity varying with the size and thickness of the 

 object. The dental membrane is placed on the balsam with the side from 

 which the teeth project upwards, and guided into the desired position; it is 



