KHABDOPLECRA MIRABILIS. 25 



glass plate to the upper arm of my compressorium, by which 

 means the desired result was obtained far better than by the 

 use of the so-called "aquatic boxes." Moreover, most of the 

 parts of the living animal may be easily examined without 

 pressure, and without even taking the animal out of its cell. 

 A colony, or part of one, can be placed under the micro- 

 scope, and the most important parts will plainly be seen 

 through the transparent walls of the cells, even if the animal 

 has not stretched itself out of the aperture. 



Besides the outer chitine-like tube, with its off-shoots or 

 cells (poly zoarium), there may be distinguished in the animal 

 under consideration the following principal parts : — 1. The 

 polypide itself, which again shows three principal parts — (a) 

 the body ; [b) the tentacular arms ; and (c) the buccal 

 shield; 2. the contractile cord; and 3. the axial cord. I 

 shall treat each of these parts separately. 



The polyzoarium (coenoecium) in the Rhabdopleura mira- 

 bilis (see PI. I, figs. 5 and 6) has the form of a thin, elastic, 

 flexible, chitine-like, transparent, most frequently quite 

 colourless, cylindrical hollow tube, consisting of a stem, 

 which creeps along the bottom of the sea, now and then 

 attached to other bodies, irregularly winding, and only 

 seldom, here and there, forked, which at short intervals sends 

 up perpendicular, free, undivided, more or less winding 

 branches, of the same form, calibre, and nature as the stem, 

 and all terminating with a circular aperture. A difference 

 between the stem and the branches strikes the eye imme- 

 diately; the stem is always more or less thickly covered 

 with extraneous particles (sand, mud, fragments of shells, 

 Rhizopod-shells, &c.), while the branches are always, with 

 exception of the very lowest piece, quite free from such 

 particles, and consequently quite transparent, appearing in 

 their whole extent very distinctly and ornamentally ringed. 

 The rings, which are only exterior, form close, equidistant, 

 sharp, circular transverse folds, strongly prominent over the 

 surface of the tube, causing the edges everywhere to appear 

 crenulated (see fig. 5). If one can separate from the stem 

 the very closely adhering extraneous particles (which is 

 effected with no small difficulty), it will be seen that 

 this outer formation of folds is also continued on the stem 

 itself, although far less sharply marked, and also more 

 irregular, the transverse folds being often divided fork-wise, 

 or in other words, not forming completely separate rings. 

 It will also be remarked (fig. 6) that the branches of free 

 tubes are not at all sharply distinguished from the stem, but 

 that their interior cavity is prolonged immediately into, or 



