VORTICELLA. 



97 



Description. Groups of Vorticella^ or of the compound 

 form Carchesium, grow on the stems of fresh-water plants, 

 and are sometimes readily visible to the unaided eye as 

 white fringes. In Vorticella each individual suggests an 

 inverted bell with a long flexible handle. The base of the 

 stalk is moored to the water-weed, the bell swings in the 



FIG. 42. Vorticella. After Butschli. 



1. Structure. N. y Macronucleus ; ., micronucleus ; c.v. t con- 



tractile yacuole ; tn., mouth ;yCz>., food vacuole ; z>., vestibule*. 



2. Encysted individual. 3. Division. 



4. Separation of a free-swimming unit the result of a division. 



5. Formation of eight minute units (ing.). 



6. Conjugation of microzooid (ing.) with one of normal size 



water, now jerking out to the full length of its tether, and 

 again cowering down with the stalk contracted into a close 

 and delicate spiral. In Carchesium the stalk is branched, 

 and each branch terminates in a bell. Up the stalk there 

 runs, in a slightly wavy curve, a contractile filament, which, 

 in shortening, gives the non-contractile sheath a spiral form. 

 This contractile filament, under a high power, may exhibit 

 a fine striation. (A similar striated structure is seen in 



