1891 - 92 .] Dr Griffiths on the Olfactory Organs of Helix. 199 
and it was this irritation or sense of pain which caused both the 
excised and non-excised animals to retract their steps, The vapours 
of bromine, ammonia, and other irritating liquids act in a similar 
manner; consequently, we are justified in rejecting Sochaezewer’s 
suggestion that the pedal gland of Helix performs among other 
functions that of an olfactory organ. As the pedal gland is a highly 
cellular organ which secretes mucus, it may he stated that the 
vapours of irritating liquids cause a much more rapid secretion of 
this fluid, which is due to the stimulation or excitation of the 
secreting cells. For it is known that {a) every action that modifies 
the normal condition of a cell is an irritant of that cell ; (h) every 
external force, provided it has a certain intensity, is capable of in- 
ducing cellular irritability ; and there is no doubt the action of the 
vapours of turpentine, bromine, and ammonia on snails (either with 
or without their tentacula) cause them to retract their steps from 
such irritating vapours. 
Now, as a matter of fact, the tentacula are the seat of the olfactory 
organs in Helix 'pomatla. Near the end of each tentaculum there is 
a ganglion from which nerve-fibres pass to the epithelium in which 
are sensory bulbs. To prove that the tentacula are the seat of the 
olfactory organs in Helix pomatia and Helix aspersa, the author 
placed a number of these animals on flat slabs, the edges of which 
were smeared with eau de Cologne, methyl alcohol, ether, and ethyl 
acetate. The vapours of these liquids do not act as irritants, for the 
secretion of mucus appeared to be perfectly normal. Those animals 
whose tentacula had been removed, gradually approached to the 
edges of the slabs ; but those animals whose tentacula had been left 
intact did not approach, but turned away from the edges. This 
proves that the tentacula are the seat of the olfactory organs in 
Helix; because in these experiments excitation, due to irritating 
vapours, was reduced to nil. It will also be seen that non-irritating 
substances alone in the state of vapours, or of fine particles sus- 
pended in the atmosphere, can provoke olfactory sensations, not 
only in the higher animals, but also in the Pulmog aster op)oda, and 
other Invertebrates. 
