VORTICELLA. 13 



2. Note the highly refractive, long, band-like (moniliform) 

 macronucleus. In another species of Spirostomum the macro- 

 nucleus is similar to that of Paramsecium. It is desirable to 

 examine stained specimens of the two species of Spirostomum. 



3. Note the sudden contractions of the body. When these 

 occur spiral lines appear on the surface. Can you distinguish 

 these lines when the animal is extended? These are primitive 

 structures (myonemes) functioning as muscles. 



Make a drawing of the extended animal and a diagram show- 

 ing the form when contracted. (See Doflein, p. 968.) 



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 anus occurs at the side of the vestibule. It is a tem- 

 porary opening from which the undigested products are passed 

 into the vestibule and so to the exterior. 



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. 



