Cuar. III] THE PROCESS OF AGGREGATION. 33 
process of aggregation has been partly effected than before. 
The purple fluid which exudes from a crushed tentacle is 
somewhat coherent, and does not mingle with the surrounding 
water; it contains much flocculent or granular matter. But 
this matter may have been generated by the cells having 
been crushed ; some degree of aggregation having been thus 
almost instantly caused. 
If a tentacle is examined some hours after the gland has 
been excited by repeated touches, or by an inorganic 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 colourless or almost colourless fluid. The change is so 
conspicuous that it is visible through a weak lens, and even 
sometimes with 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 becomes as homogeneous 
and transparent as it was at first. The process of redissolu- 
tion travels upwards from the bases of the tentacles to the 
glands, and therefore in a reversed direction to that of 
aggregation. ‘l'entacles 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. 
The little masses of aggregated matter are of the most 
diversified shapes, often spherical or oval, sometimes much 
elongated, or quite irregular with thread- or necklace-like or 
club-formed projections. They consist of thick, apparently 
viscid matter, which in the exterior tentacles is of a purplish, 
and in the short discal tentacles of a greenish, colour. These 
D 
