Cuar. II] INFLECTION INDIRECTLY CAUSED. a 
few of the tentacles moved. ‘Those which were not affected 
were left for about half an hour, and the particles were then 
disturbed or tilted up several times with a fine needle under 
the microscope, the glands not being touched. And now in 
the course of a few minutes almost all the hitherto motion- 
less tentacles began to move; and this, no doubt, was caused 
by one end or some prominence of the particles having come 
into contact with the surface of the glands. But, as the 
particles were unusually minute, the movement was small. 
Lastly, some dark blue glass pounded into fine splinters 
was used, in order that the points of the particles might be 
better distinguished when immersed in the secretion; and 
thirteen such particles were placed in contact with the 
depending and therefore thicker part of the drops round so 
many glands. Five of the tentacles began moving after an 
interval of a few minutes, and in these cases I clearly saw 
that the particles touched the lower surface of the gland. A 
sixth tentacle moved after 1 hr. 45 m., and the particle was 
now in contact with the gland, which was not the case at 
first. So it was with the seventh tentacle, but its movement 
did not begin until 3 hrs. 45 m. had elapsed. The remaining 
six tentacles never moved as long as they were observed ; 
and the particles apparently never came into contact with 
the surfaces of the glands. 
From these experiments we learn that particles not con- 
taining soluble matter, when placed on glands, often cause 
the tentacles to begin bending in the course of from one to 
five minutes ; and that in such cases the particles have been 
from the first in contact with the surfaces of the glands. 
When the tentacles do not begin moving for a much longer 
time, namely, from half an hour to three or four hours, the 
particles have been slowly brought into contact with the 
glands either by the secretion being absorbed by the particles 
or by its gradual spreading over them, together with its 
consequent quicker evaporation. When the tentacles do not 
move at all, the particles have never come into contact with 
the glands, or in some cases the tentacles may not have been 
in an active condition. In order to excite movement, 1t 1s 
indispensable that the particles should actually rest on the 
glands; for a touch once, twice, or even thrice repeated by 
any hard body, is not sufficient to excite movement. 
Another experiment, showing that extremely minute par- 
ticles act on the glands when immersed in water, may here 
