NATURAL SCIENCES OF PHILADELPHIA. 141 



eye the two organs here treated of. Above the external opening 

 of the mouth, through the transparent tissue of the head, is seen 

 a small, arched, reddish, free instrument, which appears to rise 

 and fall as if used in cutting off morsels of food. This is the jaw. 



On the floor of the mouth is the lingual membrane, occupying 

 about the position of the human tongue. Its color is too nearly 

 the same as that of the head to afford any strong contrast, but, 

 with close attention, it will be detected by its glistening silvery 

 appearance, as it works backward and forward. 



The use of the tongue seems to be to rasp the food and also to 

 force it back into the oesophagus. 



More detailed description, fully illustrated by figures, of the 

 position of these two organs, will be found in the chapters on 

 Special Anatomy in the first volume of the " Terrestrial Air-breath- 

 ing Mollusks of the United States." 



Method of Extraction. 



On opening the head of Helix thyroides from above, one readily 

 notices at the extreme anterior part, close against the outer integu- 

 ment, a prominent oval body. This is called the buccal mass. It 

 is easily cut away from the animal, and will be found to contain 

 both jaw and lingual membrane. They can be removed by fine 

 scissors or knives from the buccal mass in the larger species, but 

 in the smaller species, the method usually employed is putting 

 the whole buccal mass in a watch crystal full 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 first be well rinsed in 

 clean water, 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 seconds 

 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 

 Paluta 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 



