The Polyzoarium.- 



The Polyzoarium (co?rio3cium) in the Rhabdopleura mirabilis (see tig. 1. -2. & 3.) has 

 the form of a thin, elastic flexible, chitine-like, transparent, most frequently quite colorless 

 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 aud there, forked, 

 which at short intervals sends up perpendicular, free, undivided, more or less winding branches 

 or continuations, 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. 3). If one can sepa- 

 rate from the stem the very closely adhering extraneous particles, (which is connected with 

 no small difficulty) it will be seen (fig. 9) that this outer formation of folds is also continued 

 on the stem itself, although far less sharply marked aud 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. 10) that the branches or free tubes are not at all sharply dis- 

 tinguished from the stem, but that their interior cavity is prolonged immediately into, or 

 continuously with, the cavity of the stem. This latter, the interior walls of which, like those 

 of the tubes, are quite smooth, is divided at certain intervals, by tolerably thick transverse 

 lamellae, or septa, into several successive cylindrical chambers, which do not communicate 

 with each other, but each one of which is continued immediately in one of the perpendicular 

 tubes proceeding upwards from the stem. Through the whole of the creeping stem, exten- 

 ding along through all its chambers, runs a thin cylindrical chitinous cord (the axial cord) very 

 remarkable from its dark nearly black color, of which more hereafter. This cord is never 

 continued up through the free tubes, but may now & then, rarely, divide itself fork-wise, 

 namely when the creeping stem divides itself in this manner. 



Every one of the perpendicular branches or fubes contains an animal, which is connected 

 by a long cylindrical fleshy cord (the contractile .cord) near the bottom of the corresponding 

 chamber in the stem, with the axial cord, which thus unites all the individuals of the colony 

 with each other. 



The creeping stem in the Kh. .mirabilis may indeed attain a very considerable length; 

 but it is very difficult to get the whole separated from the substances which adhere to it. 

 One can usually therefore only get up small pieces of the colony, and seldom more connected 

 portions. The largest connected piece of stem (fig. 1) which I succeeded in getting loose from 



its attachment, was about 40 millimetres long, and was at irregular distances 4 times bifur-. 



1* 



