No. 7.] OSLER — FRESH-WATER POLYZOA. 403 



From beneath the crescentic lophophore the alimentary canal 

 hangs, which presents the following parts for observation : the 

 epistome, a valve-like projection overhanging the mouth, the 

 oesophagus or throat, the stomach, intestine and anus. 



The epistome is a tongue-like organ arising at the junction of 

 the inner arms of the lophophore, and serves as a valvular pro- 

 tection for the mouth. It possesses a set of muscles by which it 

 can be readily moved and jerks up and down very frequently. It 

 appears to keep materials in the throat rather than prevent the 

 entrance of anything obnoxious. Like the tentacles it is covered 

 with cilia. All the parts about the region of the espistome have 

 a dark rose-red color, and this gives a peculiar brilliancy to the 

 animals. A somewhat funnel-shaped mouth leads directly into 

 the oesophagus, a short colorless tube, which widens slightly as it 

 descends. A valve-like construction sep irates it from the 

 stomach, into which, as soon as the oesophagus is full, the food is 

 expelled by the contraction of the muscular walls. 



The stomach forms an elongated tubular cavity in which the 

 food is subject to a constant peiistaltic action during the pro- 

 cess of digestion. The lining membrane is plicated and the 

 cells upon the folds are of a brown color, containing a fluid which 

 Prof. Allman regards as a biliary secretion. The intestine or 

 coecum is a short broad cavity separated from stomach by a valve 

 and placed parallel to the oesophagus, opening by an anal orifice 

 immediately beneath the lophophore. The undigested residue 

 of the food is gradually pushed through the coecal valve and dis- 

 tends the intestine and is expelled by the contraction of the coecal 

 walls and carried away by the action of the cilia of the tentacles. 

 From the lower part of the stomach a cord-like process, the 

 funiculus, extends, and connects it with the bottom of the coe- 

 noecium. 



There is no definite circulatory system in the Polyzoa. A 

 colorless fluid bathes the interior of the coencoecium and the peri- 

 gastric cavity. By the action of the cilia which line the interior 

 of the coenoecium currents are created which .ire rendered evident 

 by the small particles carried round. 



Respiration is probably c.irried on by the cilia covering the 

 tentacles, but our knowledge of this function is extremely 

 slight. 



The nervous system of the fresh-water Polyzoa is represented 

 by a definite ganglion which lies in the neighborhood of the 



