NATURAL SCIENCES OF PHILADELPHIA. 14] 
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 esophagus. 
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 buecal 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 aspirit 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 
