IX.] THE BELL- ANIMALCULE. 91 



stome ; the vestibule gaping widely and the cilia working 

 vigorously. But the least shock causes the disc to be re- 

 tracted, and the 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 disturbing influence be continued, this state of retrac- 

 tion persists ; but if it be withdrawn, the spirally coiled stem 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 cer- 

 tain 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 Vorticelliz 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, 

 henceforward free in the soft central substance. In some 

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

 movement of circulation, passing up one side of the body, 



