Freshwater Bryozoa, with descriptions of new Species. 1 77 



in some points of view the angles formed by this flattening have 

 not a little the appearance of rudimentary arms just sprouting. 



The oesophagus descends at once in a straight line from the 

 oral opening. In Fredericella, PL II. figs. 1 / & 2 b, it is rather 

 short and wide, and the walls, which are thick and fleshy, 

 are parallel throughout, except at the commencement, where 

 they are a little bulged, forming a sort of pharynx which is lined 

 with vibratile cilia : the other extremity communicates with the 

 stomach by a distinct valvular orifice, PI. II. figs. 1 g & 2 c, — 

 the cardiac, projecting downwards. The whole surface is covered 

 with minute circular cells resembling very much the peculiar 

 structure observed in the marine species, and pointed out by 

 Dr. Farre in his valuable paper on the Marine Ascidian Polypes 

 published in the ' Philosophical Transactions' for 1837. 



The stomach, figs. 1 h & 2 d, is more than twice the length 

 of the oesophagus, tapering slightly downwards and truncate 

 above ; the lower extremity being obtuse : the walls, like those of 

 the oesophagus, are thick and fleshy, and are covered with nu- 

 merous, minute, close-set cells of a glandular character. The 

 pyloric orifice is circular and well marked, and has the appearance 

 of being guarded by a sphincter muscle ; it is likewise supplied 

 with vibratile cilia which extend some little way into the stomach. 

 This orifice is situated above, at one side and a little below the 

 cardiac opening. The intestine, figs. 1 & 2 i, e, is straight, and 

 a little longer than and nearly as wide as the oesophagus, with 

 which it lies in contact and to which it is apparently attached ; 

 the pyloric extremity is obtusely pointed, and communicates by 

 the side with the stomach ; from thence the intestine tapers a 

 little upwards towards the anal extremity, which, turning out- 

 wards, passes through the tentacular sheath just below its attach- 

 ment to the disc supporting the tentacles, and there terminates 

 in an obtuse perforated point, figs. 1 & 2j &/, which can be 

 either protruded or retracted to a considerable extent at the will 

 of the animal. The whole of the alimentary canal is highly irri- 

 table, particularly the oesophagus and stomach, in the walls of 

 both of which, minute, transverse striae are distinctly visible, pro- 

 bably indicating the presence of muscles. The stomach is per- 

 petually in motion when the animal is displayed, contracting in 

 an undulating or vermicular manner from above downwards. 

 The contractions of the oesophagus, too, are very decided on re- 

 ceiving food, which for a second or two rests in the pharyngeal 

 enlargement, and is then hurried to the stomach with great 

 rapidity. 



The alimentary canal of Plumatella and Alcyonella does not 

 vary in any important manner from that of Fredericella. In the 



Ann. % Mag. N. Hist. Ser. 2. Vol. v. 12 



