222 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 
sionally found detached from the animal and adhering to the glass 
in which the Limas have been placed. Again, observations have 
often been made on the characteristic motion of the tentacles and 
their power of retaining vitality long after being broken off from 
the animal. But none of the recorded observations seem to throw 
light on the part these curious organs play in the economy of the 
animal. Landsborough has suggested that they may be for 
catching the prey on which the animal feeds, doubtless having in 
his mind the somewhat similar tentacles in Actinia and the part 
these play in catching and drawing the prey into the mouth of 
this anima]. There is no further reason for this supposition, and 
much against it. The question also naturally suggests itself here 
as to whether the adhesion of the tentacles is due to the same 
cause as in the Celenterates, viz., stinging cells. 
Some light will be thrown on these points by a minuter examina- 
tion of the tentacles. If a tentacle be cut off and laid on a slide 
under the microscope, the process of fixing may be observed. It 
will be seen that a quantity of mucus is slowly given out at the little 
ring-like swellings that occur at intervals on the tentacles. After 
a time this adheres so firmly to the glass as to prevent further 
motion of the tentacle. This, and not the presence of stinging 
cells, is, no doubt, the cause of the adhesiveness. We can further 
examine the nature of the cellular elements by means of sections. 
It is then seen that the main shaft of the tentacle is composed of 
well-developed muscular elements, and that the swellings which 
occur at intervals are composed of glandular cells secreting the 
mucus, and of the characteristic sensory cells which Fleming first 
discovered in the tentacles of Helix, viz., cells provided with sensory 
hairs or bristles. All the tentacles are not, however, alike as to the 
proportion of sensory and glandular cells present. The longer and 
more central tentacles have a preponderance of glandular cells, 
while the shorter and more laterally placed have a preponderance 
of sensory cells. This is quite in keeping with the observed facts, 
for the longer tentacles show little or no reaction to stimuli, 
while there is an immediate shrinking and closure of the shell on 
irritation of the shorter. 
These shorter tentacles are in immediate contact with the walls 
of the nest, so that by them the animal is at once made aware of 
any disturbance that may threaten encroachment on its premises, 
and by the sudden contraction to be afterwards described can at 
