38 



Tvitli a vieli ruby-coloured matter, thereby adding to the beauty 

 of the Polyzoa by the contrast of colours, and beautifully dis- 

 playing the action of digestion. By referring to the diagram, 

 you wUl see that the mouth is surrounded by a number of tenta- 

 cula, arising from a sort of stage or disc, termed the Lophophore. 

 These tentacles are covered with vil)ratile cilia, which when in 

 motion have the appearance of passing upon the one side of each 

 tentacle, and down the opposite, the rapid motion of which 

 causes a current of water to set in, in the direction of the mouth, 

 bearing with it the food requisite for the support of the animal. 

 The whole eoiu-se of the alimentary matter thus obtained, from 

 the moment of its prehension to its final ejection, may be easily 

 witnessed in many of the fresh-water polyzoa. If a polyjnde of 

 Plumatella repens be watched while in an exerted state, different 

 kinds of Infusoria and other minute organic bodies may be ob- 

 served to be whirled along in the vortices caused by the action 

 of the tentacular cilia, and conveyed to the mouth, where many 

 of them are at once seized and swallowed, and others rejected. 

 The food having once entered the oesophagus experiences in this 

 tube no delay, but is rapidly conveyed downwards b}- a kind of 

 peristaltic action, and delivered to the stomach. In the stomach 

 the food is destined to experience considerable delay ; it is here 

 rapidly moved up and down by a strong peristaltic action, which 

 first takes place from above downwards, and then inverting 

 itself, propels the contents in an opposite direction Every now 

 and then the fundus of the stomach seems to perform some func- 

 tion distinct from the rest of the organ, in that it seizes a portion 

 of the alimentary mass, and retains it for a moment by an hour- 

 glass restriction separate from the remainder, and then power- 

 fully contracting on it, forces it back among the other contents 

 . of the stomach. All this time the food is becoming imbued with 

 the peculiar secretion of the gastric walls, and soon assumes a 

 rich brown colour. After having thus imdergone for some time 

 the action of the stomach, the alamentary matter is delivered by 

 degrees into the intestine, where it accmnulates in the wide 

 pyloric extremity of this tube. After continuing here for a 

 while in a state of rest, and probably jielding to the absorbent 

 tissues its remaining nutritious elements, portions, in the fonn of 

 oval shaped pellets, become separated at intervals from the mass, 

 and are slowly propelled along the tube towards the vent, where 

 having arrived, they are suddenly ejected into the surrounding 

 water and rapidlj- whiided away by the tentacular cm-rents. In 

 all the fresh polj-zoa, bodies of a very peculiar nature occur at 

 seasons lying loose in the perigastric space ; to these are given 

 the name of statoblasts. From the earliest period that the fresh- 

 water polyzoa became an object of study, the statoblasts attrac- 



