88 ELEMENTARY BIOLOGY. [iX. 



edge of the peristome to be curved in and shut against it, so 

 as to give the body a more globular form. At the same time, 

 the stem is thrown into a spiral, and the body is thus 

 drawn back towards the point of attachment. If the dis- 

 turbing influence be continued, this state of retraction per- 

 sists ; but if it be withdrawn, the spirally coiled stem slowly 

 straightens, the peristome expands, and the cilia resume 

 their activity. 



In the interior of the body, immediately below the disc, 

 a space, occupied by a clear watery fluid, is seen to make 

 its appearance at regular intervals slowly enlarging until 

 it attains its full size and then suddenly and rapidly dis- 

 appearing by the approximation of its walls. This is the 

 contractile vesicle. Whether it has any communication with 

 the exterior or not and what is its function, are still open 

 questions. If the Bell-animalcule is well fed, one or more 

 watery vesicles of a spheroidal form, each containing a certain 

 portion of the ingested food, will be seen in the soft central 

 mass of the body. And by mixing a small quantity of 

 finely divided carmine or indigo with the water in which 

 the Vorticellm live, the manner in which these food-vesicles 

 are formed may be observed. The coloured particles are 

 driven into the vestibule by the action of the cilia of the 

 peristome and the adjacent parts and gradually accumulate 

 at the inner end of the gullet. After a time the mass here 

 heaped together projects into the central substance of the 

 body, surrounded by an envelope of the accompanying water ; 

 and then suddenly breaks off, as a spheroidal drop, hence- 

 forward free in the soft central substance. In some Bell- 

 animalcules, the food-vesicles thus formed undergo a move- 

 ment of circulation, passing up one side of the body, then 

 crossing over below the disc and descending on the other 

 side. Sooner or later the contents of these vesicles are 

 digested, and the refuse is thrown into the vestibule by an 



