XXIV INTRODUCTION. 



what irregular in form. (4.) Cnidse, in greater or less 

 abundance, according to the species. As the craspedum 

 flattens under pressure, these are crowded at the edges, and 

 are seen to be 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 cnida are more loosely scattered in 

 the fluid sarcode. The peritoneal membrane which invests 

 the whole is richly ciliated on its entire surface. (Plate XI. 

 tig. 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 

 palliata, of a brilliant lilac tint. In some instances, as in 

 ^agartia parasitica, S. miniata and 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 cniclce, 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 perceive that after a time it is gradually withdrawn again 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 



