XXIV 
INTEODUCTION. 
what irregular in form. (4.) Cnidse, in greater or less 
ahundance, according to the species. As the craspedum 
flattens under pressure, these are crowded at the edges, and 
are seen to he arranged, more or less distinctly, side by 
side ; their long axes set at right angles to the axis of the 
craspedum^ and their emitting extremities either close to its 
edge, or projecting from it. The more dense their aggrega- 
tion, the more definitely is this arrangement maintained; 
doubtless because displacement of their original position is 
more readily effected by the flattening action of the com- 
pressorium, when the cnid(B are more loosely scattered in 
the fluid sarcode. The peritoneal membrane which invests 
the whole is richly ciliated on its entire surface. (Plate XI. 
fig. 3.) ^ 
The Acontia. Certain species of the Zoophytes under 
consideration have the faculty of shooting forth from the 
mouth, as well as from minute orifices scattered over the 
surface of the body, slender flexible filaments, usually of 
an opaque white hue, but sometimes, as in Adamsia 
palUata, of a brilliant lilac tint. In some instances, as in 
^agariia parasitica, 8. miniata Adamsia palliata, these 
threads are protruded in great profusion, coiled up in 
irregular spirals, and forming tangled masses that resemble 
bundles of sewing cotton. It appears to be a means of 
defence ; and any of the species just mentioned may 
readily be excited to display these weapons by a slight 
irritation of the surface of the body. The slightest touch 
is usually a sufficient stimulus to the extension, which will 
often continue to proceed for some time, the filaments 
shooting forth from various points with great force and 
rapidity. They have a strongly adhesive power, which, 
however, is not dependent on any superficial viscosity, but 
on the projectile power of the contained cnidee, of which I 
shall presently speak. 
If we carefully watch one of these threads, we shall 
perceive that after a time it is gradually withdrawn again 
into the body, by the orifice at which it was protruded. In 
the case of S. parasitica, a large species, these filaments, 
which I designate by the term acontia, sometimes extend 
six inches from the body, in a straight line. Yet in a few 
minutes the whole has disappeared. It is gradually cor- 
rugated into small irregular coils, at the end which is 
attached to the animal ; and these little coils are, one after 
