THE PROTOZOA 



13 



to be found in most elementarj? text-books of zoology,^ and any 

 further account of it will be omitted here, since Vorticella, the 

 next unicellular form to be 



studied, amply illustrates the 'noutti 



complexity of diflferentiation 

 and life- history possible in 

 these simple forms ; also it 

 is so vei'y commonly met 

 with by the student of pond- 

 life that a study of it is in- 

 evitable. " 



Tyiie : Vorticella, tlie Bell 

 Animalcule. 



Habitat, I'^ examining 



General water -weeds or 

 Appearance, other o li j c c t s 

 taken from a pond, there are 

 very frequently to be seen 

 with the naked ej-e, minute, 

 colourless, bell-shaped bodies, 

 that constantly seem to float 

 away from the surface of the 

 weed, and then, on the 

 slightest vibration of the 

 water, to be suddenlj' drawn 

 back again by a delicate 

 thread which contracts into 

 a thick, .spirally-coiled stalk. 

 Bell Animalcule. 



There are three chief points in which Vorticella is seen at 

 once to differ from Amoeba : — it is permanently fixed by 

 this contractile stalk ; the body does not exhibit the same 

 curious irregularchanges of shape as in Amoeba, for although the 

 protoplasm contracts and expands, it never sends o>it irregular 

 pseudopodia Init keeps its definite shape ; and, finally, round 

 the free margin of the "bell," there is a circle of fine cilia, 

 which by their vibrations keep the surrounding water in con- 

 stant motion. 



1 See FJemenlanj Biology, by T. Jefl'ery Parker. 



Fig. 4. 



Vorticella, attacheil to a Water-weed. 



A, An extended bell; Ji, a contracted 

 beU ; C, a bell dividing by simple 

 fission; 7i((, macro-nucleus ; ion. cor, 

 contractile vacuole ; /. vaf, food 

 vacuoles; con. fibre, contractile iiiire 

 of stem. 



This organism is Vorticella, the 



