VORTICELLA. 13 



hand-lens, some of them may be found to carry minute 

 white floceulent spots or tufts which resemble spots of 

 mould. If one of these tufts be gently touched with a nee- 

 dle or a hair, it will instantly shiink back, until it is re- 

 duced to an almost invisible white spot. After the 

 disturbance ceases, it soon expands again to its former 

 size. 



Having found one of these tufts, grasp with a pair of 

 forceps the leaf or stem which canies it, and cutting out the 

 piece with a pair of scissors, transfer it to a drop of water 

 upon a glass slide ; cover it with a cover-glass, which may 

 be supported by a piece of paper, if necessary, and exam- 

 ine it with a magnifying power of about eighty diameters. 



When thus examined, the white tuft will probably 

 prove to be a colony of Voi-ticellidoB, but it may, per- 

 haps, prove to be a colony of Stentors or even of Roti- 

 fera. If the student tinds that he is unable to verify the 

 following description, he should ask his instructor to ex- 

 amine his specimen. 



Having found a colony of Vorticellidae, notice : — 



I. The bell-shaped bodies of the individuals which 

 compose the colony. 



II. The stem which projects fi-om the 

 small end of the body of each animal, and 

 joins it to the others and to the supporting 

 body (see Fig. 3). 



Fig. 3. — Diagram of a colony of Vorticellae, magni- 

 fied about fifteen diameters. Fig. 3. 



ni. The cilia around the margin of the bell. 



IV. Keeping the eye at the microscope, tap the slide 

 gently, or touch the animals with a hair, and notice their 

 rapid contraction. 



a. The edge of the bell bends inwards so that the body 

 becomes nearly spherical. 



