VII.] THE BELL-ANIMALCULE. 361 



In the undisturbed condition of the Bell-animalcule, 

 the stem is completely straightened out; the peristome is 

 everted, and the edges of the disc separated from the peri- 

 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 tion persists; but if it be withdrawn, the spirally coiled stem 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 or vacuole. It communicates with the ex- 

 terior at the moment of contraction, and in all probability 

 performs an excretory function. 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 Vorticellce 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, 



