or MICROSCOPIC OBJECTS. 171 



" As to preserving the animals till wanted, they should 

 simply be dropped alive into glycerine or alcohol. Glycerine 

 is perhaps best where only the tongues are wanted ; but it 

 leaves the animals very soft ; and as it does not harden 

 their mucus at all, they are very slippery and difficult to 

 work upon when so preserved. 



" Then as to the apparatus required for dissection. In the 

 first place, all the work is to be done under water, and a 

 common saucer is generally the most convenient vessel 

 to use. ETo kind of fastening down or pinning out of the 

 animal is needed; and, in fact, it is much better to have 

 it quite free, that you may turn it about any way you wish. 

 The necessary instruments are a needle-point, a pair of 

 fine-pointed scissors, and small forceps ; the forceps should 

 have their points slightly turned in towards each other. 



" A word or two on the lingual apparatus generally, and 

 on its special characters in a few different animals, will con- 

 clude what I have to say. 



" The mode of using the tongue can be easily seen in any 

 of the common water-snails, when they are crawling on the 

 glass sides of an aquarium ; it may then be observed that 

 from between the fleshy lips a thick mass is protruded, with 

 a motion forwards and upwards, and afterwards withdrawn, 

 these movements being almost continually repeated. The 

 action has the appearance of licking ; but when the light 

 falls suitably on the protruded structure, it is seen to be 

 armed with a number of bright points, which are the lingual 

 teeth, so arranged as to give the organ the character and 

 action of a rasp. 



" If you proceed to dissection, and open the head of one 

 of these mollusca (say, for instance, a common limpet), you 

 will find the cavity of the mouth almost filled with the thick 

 fleshy mass, the front of which is protruded in the act of 

 feeding ; and on its upper surface, extending along the 

 middle line from back to front, is seen the strong membranous 

 band upon which the teeth are set. The mass itself consists 

 of a cartilaginous frame, surrounded by strong muscles ; and 



