68 The Dentition of British Mollusca. 



practice for its preparation, I will briefly describe the process, 

 in the hope that some of my younger readers may be induced 

 by its easiness to attempt it. 



There need be no lack of subjects for examination. Peri- 

 winkles, whelks, and limpets are to be obtained in most places, 

 even inland; but if these sea "fish" are not to be had, then 

 every ditch will yield Limncei and Planorbes in abundance, or, 

 as a last resource, the common snails and slugs of the garden 

 and the lane must serve the turn. The apparatus may be 

 the simplest possible. One or two ordinary needles and as 

 many surgical ones may be fixed into cedar pencil-sticks, or, 

 better still, into the neat little bone holders used by ladies for 

 their crochet-hooks. A few sharp pins will be required to 

 hold down the parts. A common pocket-lens must be mounted 

 so as to slide on an upright rod (a piece of soft wood stuck 

 into a flat bit of lead will answer every purpose), for the dis- 

 section necessitates some magnifying power and both hands 

 must be free. It will also be well to have a pair of small curved- 

 pointed scissors, and a pair of forceps with claw-ends. They 

 will be wanted for the larger inollusks ; but in many instances 

 the needles only can be used, on account of the great delicacy 

 of the operation. The prime requisites are patience and light 

 fingers ; and assuming that the observer possesses both, let us 

 now proceed to work. Select for a first example a good-sized 

 periwinkle. If he is alive, scald him for a second, and then 

 you will not be haunted by any qualms about vivisection ; but 

 it will not matter for the nonce if your subject has been boiled 

 and even salted. Break the shell with a smart blow, and dis- 

 engaging the animal, pin him down with his foot or walking- 

 surface underneath. Above, and in front, there will then be 

 seen a loosish flap of skin : that is the mantle, and on turning 

 it back, it will disclose the rostrum or muzzle. It has two little 

 fleshy tentacles at the sides (corresponding to the horns of a 

 snail), and a small nearly circular aperturo at the extremity, 

 which should be turned to the right. Now, cautiously insert 

 the curved point of the scissors and lay open the cavity of the 

 mouth, but take especial care not to injure its floor, where 

 it is paved with the tongue and its wondrous armaturo of teeth. 

 It' they are in thewayj pin back the cut edges, and, with the 

 needles, lift out tho lingual band. It comes away readily, and 

 as all the teeth arc rellexed it may be drawn out forwards 

 without risk of injuring them. It will probably require 

 cleaning, which is most conveniently managed under trans- 

 mitted light. In some of the. minuter examples, indeed, the 

 whole process must, he so done. To effect this, get a cigar-box; 

 t u in it on one side and make a clean hole in the upper one, 

 half an inch in diameter. A small mirror, or pieco of plain 



