14 PROTOZOA. 



VORTICELLA. 



Place a number of individuals on a slide and cover loosely 

 to avoid crushing. As usual, study first with the low power and 

 then with the high. 



1. Notice that the body of Vorticella has the general shape 

 of an inverted bell. The covering of the body is a very thin 

 transparent layer, the cuticle, underneath which is the periphe- 

 ral layer of ectoplasm enveloping the more fluid and granular 

 endoplasm. 



2. The peristome is the rounded rim about the base of the bell. 



3. The elevated and inclined area included within the peri- 

 stome, and ciliated around the edge, is the disk. It is some- 

 what convex. 



4. The marked depression between the disk and the peri- 

 stome is the vestibule. It is also lined with cilia. The vestibule 

 defines the ventral surface of the animal. 



5. The gullet, a slender canal, leads from the vestibule toward 

 the center of the body. 



6. The feces escape from the body by the side of the vestibule. 

 The opening is temporary. 



7. Within the endoplasm are situated the clear contractile 

 vacuole, several gastric vacuoles, the long U-shaped macronucleus, 

 and the small round micronucleus. The macronucleus may be 

 made more distinct by treating with methyl-green. 



8. The stalk is composed of a sheath, which is continuous with 

 the cuticle of the body, and, within the sheath, the contractile 

 axis or myoneme, which is continuous with the body ectoplasm. 

 Notice that this myoneme is situated within the sheath in a 

 very loose spiral, and that the stalk quickly contracts into a 

 close spiral when the animal is stimulated. Observe also the 

 manner in which the peristome folds over simultaneously with 

 the contraction of the stalk. What purpose does the contrac- 

 tion of the stalk serve? 



Vorticella is distinguished from its allied genera by its sim- 

 ple unbranched stalk and also by the spiral form assumed by the 

 contracted stalk. In which order of the Ciliata does the cilia- 

 tion of Vorticella place it? Compare with Zoothamnium. 



