Ouap. ITI. THE PROCESS OF AGGREGATION. 39 
If a tentacle is examined some hours after the gland 
has been excited by repeated touches, or by an in- 
organic or organic particle placed on it, or by the 
absorption of certain fluids, it presents a wholly 
changed appearance. The cells, instead of being filled 
with homogeneous purple fluid, now contain variously 
shaped masses of purple matter, suspended in a colour- 
less or almost colourless fluid. The change is so 
conspicuous that it is visible through a weak lens, 
and even sometimes by the naked eye; the tentacles 
now have a mottled appearance, so that one thus 
affected can be picked out with ease from all the 
others. The same result follows if the glands on the 
disc are irritated in any manner, so that the exterior 
tentacles become inflected; for their contents will 
then be found in an aggregated condition, although 
their glands- have not as yet touched any object. But 
aggregation may occur independently of inflection, . 
as we shall presently see. By whatever cause the 
process may have been excited, it commences within 
the glands, and‘then travels down the tentacles. It 
can be observed much more distinctly in the upper 
cells of the pedicels than within the glands, as these 
are somewhat opaque. Shortly after the tentacles have 
re-expanded, the little masses of protoplasm are all 
redissolved, and the purple fluid within the cells be- 
comes as homogeneous and transparent as it was at 
first. The process of redissolution travels upwards 
from the bases of the tentacles to the glands, and 
therefore in a reversed direction to that of aggre- 
gation. Tentacles in an aggregated condition were 
shown to Prof. Huxley, Dr. Hooker, and Dr. Burdon 
Sanderson, who observed the changes under the 
microscope, and were much struck with the whole 
phenomenon. 
4 
