Genera of the Xorth American Palaeozoic Bryozoa. 421 



of very rare occurrence. Within this sac is suspended the ali- 

 nientary canal, consisting of oesophagus, stomach and the intestine 

 bent upon itself so that the anus is in close proximity to the 

 mouth, as shown in fig. 1 and in the figures on Plates A and B. 

 Around the mouth is a fringe of ciliated tentacles, which serve 

 as respiratory organs and as a means of conveying food. In all 

 the marine species and in the fresh- water genus Paludicella, 

 the tentacles are arranged in a circle around the mouth, but in 

 the other fresh-water genera they are bilateral, the arrangement 

 being in the form of a horseshoe, from which fact this group of 

 Bryozoa is called Hijppocrepian. 



The mouth and tentacles are protruded from and contracted into 

 the cell by the action of occlusor and retractor muscles. From the 

 fund as of the stomach to the base of the cell is a cord known as 

 the funiculus. This cord extends through the cell, forming a means 

 of communication with the other cells composing the colony. 

 This cord frequently gives off filaments which extend through 

 the walls of the cell, being continuous with similar filaments from 

 adjacent cells (Plate A, tig. Ir). The testis is formed on the funi- 

 culus, the ovaries being situated on the endocyst much nearer 

 the mouth of the cell (fig. 1, 6», and plate A, figs. 1, 2). The 

 space between the alimentary canal and wall of the cell is 

 filled with a perigastric fluid. There is a single nerve ganglion, 

 on the side of the oesophagus, near the mouth (tig. 1, g), from 

 which filaments proceed in different directions, but principally to 

 the lophophore and tentacular crown. In some forms, as in 

 Bowerhankia densa^ the ectocyst is chitinous and beautifully 

 transparent, so that all the parts of the animal can be 

 distinguished through it. In most of the forms the ectocyst 

 is calcareous and opaque. Some portions of the cell are fre- 

 quently more fragile than others. These are usually absent in 

 the fossil stage, the more calcareous portions alone remaining 

 and giving a very false impression as to the original form of the 

 cell. Some species which when living had an ampullate or cucul- 

 late cell, with opercula, appear in a fossil state as having poly- 

 gonal cells, as in a thin section ol a Favosite. This condition may 

 also be observed in some of the forms adhering to shells. In the 

 Membranipora, a large group of incrusting Bryozoa, the cells 

 are surrounded by a well-marked and elevated border. The 



