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 
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Fic. 42.— Vorticella.—After Biitschli. 
2. Structure. JV., Macronucleus; ., micronucleus; ¢.v., con- 
tractile vacuole ; 7z., mouth; /v., food vacuole; v., vestibule. 
2. Encysted individual. 3. Division. 
4. Separation of a free-swimming unit—the result of a division. 
5. Formation of eight minute units (#g-). 
6. Conjugation of microzooid (#zg.) 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 Carchestum 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 
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