VI. VORTICELLA 



Vorticella is another interesting example of a ciliated, uni- 

 cellular animal belonging to the Infusoria. It exhibits a number of 

 important structural features some of which are quite different from 

 those in Paramecium. Thus the cilia, instead of forming a uniform 

 covering, are, in general, restricted to a definite anterior region 

 where they function in the capture of food particles. Vorticella 

 has a distinctive bell-shaped body and is often referred to as the 

 'bell-animalcule.' It is usually found attached to some solid ma- 

 terial in the water. This attachment is by a long contractile 

 stalk. Our interest in Vorticella lies chiefly in the unusually high 

 development of its various structural features as is shown, for ex- 

 ample, by the presence of definite contractile fibers in the stalk 

 which are suggestive of the specialized contractile elements, the 

 muscle tissue, of the higher animals. Another point of interest is 

 the development, in closely related species, of colonial types with 

 several functionally independent individuals attached to a common 

 stalk — a condition essentially similar to that already noted in 

 Volvox. 



A. Structure of Vorticella 



Projecting from the large, flaring bottom (peristome) of the 

 bell-shaped body is a circular structure, the disc. The edge of the 

 disc (epistome) is in close contact with the peristome around most 

 of its circumference. At one point, however, the epistome and 

 peristome are separated, and a considerable space is left between 

 them, which is known as the vestirule. In this vestibule, the 

 food particles are first collected and then passed from it through 

 a mouth opening into the gullet. The comparatively long, con- 

 tractile stalk, which continues from the apex of the body, is an 

 extraordinary bit of protoplasm, as will be seen from the descrip- 

 tion given below. ( W. f. 18, C.) 



The body of Vorticella is made up of an outer layer of ectoplasm 

 and an inner portion of endoplasm. There is a comparatively 

 heavy secreted pellicle which encloses the entire body and stalk 



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