cated; another piece was of about the same length, but only 3 times divided. These bran- 

 ches, which proceed from the stem at a more or less acute angle, are also creeping and 

 irregularly bent, and, like the main stem, produce cells, the number of which in all on these 

 pieces of stem amounts to about 60. The stem is thus only seldom branched, and usually 

 runs to great length without producing any branch. 



The cells or tubes, which proceed from the stem by lateral budding, are of very dif- 

 ferent length, while their thickness is everywhere, and in all, about the same. The largest 

 are 67 millimetres long and V 4 Y 5 mill, thick. They are, as stated, erect, yet seldom, 

 or never perfectly straight, but always more or less bent in some part, or in the whole of their 

 length : sometimes like an S, sometimes in several bends or turns like a drawn out screw, but 

 most frequently irregularly bent, in rare instances so strongly curved that the curve is nearly 

 circular. 



From the above description it will be seen that the Polyzoarium in the Rhabdopleura 

 mirabilis is decidedly different from that of the Shetland Rh. Normanni. Firstly, the cree- 

 ping stem of the latter, of which one surface everywhere adheres to old shells or other solid 

 substances, is much more strongly branched (,,subalternately") and, like the cells, quite naked, 

 without trace of attached extraneous particles. Then the cells themselves are not, as in our 

 species, free in their whole length, but at the base for some distance, like the stem itself, 

 fixed and creeping, for which reason also the free perpendicularly rising ringed part of the 

 same is much shorter than in the Rh. mirabilis. Finally there appears some difference be- 

 tween the two species with regard to the manner of the division of the stem into chambers. 



The Polyzoarium in the Rhabdopleura does not coincide with any other species of 

 Polyzoa. The cells in their tubular form resemble most those of the Cyclostomata, but are 

 horny or chitine-like (in the Cyclostomata they are chalky) and are distinguished by their 

 surface, covered with prominent transverse folds or rings which are also foreign to the Po- 

 lyzoa, but are found in many Hydrozoa such as certain Tubulariadae and Campanulariadse. 



The Polypide. 



The individual animals or Polypides seem at first glance to resemble the ordinary Po- 

 lyzoa (see fig. 3). The body, which is only a -little over 1 millimetre long, is oblong, and 

 appears to be occupied almost entirely by the digestive system; on closer examination, we 

 find however (see pi. 2. fig. 15, 17, 18) that a thin glassy skin surrounds the digestive appa- 

 ratus, which therefore is not, as in all other Polyzoa, freely suspended in the ,,Perigastric 

 fluid", which latter, as will appear in the sequel, is entirely wanting in the Rhabdopleura. In 

 all other Polyzoa without exception there is besides the so-called Ectocyst, corresponding 

 with the Polyzoarium, also a so-called Endocyxt, which always represents a thin membrane 

 lining the interior of the Ectocyst or cavity of the cell, and, from the aperture, recurved and 

 attached round about to the Polypide under the base of the Lophophore. The interior cavity 

 of the cells in the other Polyzoa is thus actually completely closed by the endocyst and the 



