THE JAW AND LINGUAL MEMBRANE. 43 



watch crystal'^fuU of a strong solution of caustic potash. Allowing it 

 to remain for several hours, the potash will destroy all of the buccal 

 mass, and leave the jaw and lingual membrane perfectly clean and 

 ready for examination. They remain attached, if the solution is not 

 too strong, showing a connection between the two. They must be well 

 rinsed in clean w^ater, in another watch crystal, before examination. 

 Another more expeditious process is to place the whole buccal mass in 

 a test-tube, with the solution of potash, and boil it for a few seponds 

 over a spirit lamp. Pouring the contents of the test-tube into a watch 

 crystal, the lingual membrane attached to the jaw will be readily seen 

 by a pocket lens. If the species be very small, as Patula striatella for 

 instance, its whole body may be thrown into the solution. Still more 

 minute species, as Zonites milium for instance, may be treated in this 

 way : crush the whole shell between two glass slides, wash away the 

 particles of the broken shell in a few drops of water, still keeping the 

 body of the animal on the slide ; w^hen clean, drop on it the caustic 

 potash and boil it by holding the slide itself over the spirit lamp. 



On Mounting. * 



For the purpose of examination, the jaw and lingual membrane may 

 be simply mounted in water and covered with thin glass. One must 

 be sure to spread out the lingual membrane, not have its upper side 

 down, and it will be well to cut it transversely in several places, as 

 the teeth are beautifully shown, and often stand detached, on the edges 

 of the cut. 



For preservation for future study I hesitate to recommend any 

 process, as I know of none which has been tried for a sufficiently long 

 time. I have myself lost many specimens by imperfect mounting. 

 Canada balsam, formerly used, ruins the membrane by rendering it too 

 transparent. The glycerine mounting fluids, now in use, certainly pre- 

 serve a membrane for several years, but they have not been tried many 

 years, and have the great disadvantage of deliquescing in warm weather. 



On the Jaw. 



The jaw and lingual membrane, having been mounted, must now be 

 examined under the microscope. 



The jaw will be found to vary greatly in its characters in the different 

 genera. It is either in one single piece ; in one single piece with an 



