INFUSORIA 65 



edge of the cup; body very contractile; animals frequently colonial: 

 16 genera. 



Key to the genera of Vorticellidae here described: 



Oi Animals not sessile and without a stalk ; parasites or commensals on Bydra 



and other animals 1. Trichodina 



Oo Animals sessile and stalked and not parasitic, although often attached to other 

 animals. 

 6i Body not enclosed in a cup. 

 Ci Stalk long or short and not branched ; animals solitary. 



di Stalk long and contractile 2. Vorticella 



dz Stalk short and not contractile. 

 Ci Oral disc acts like a cover (operculum) which may close the opening of 



the cup 3. Pyxidium 



62 No such cover 4. Rhabdostyla 



C2 Stalk branched ; animals colonial. 

 dx Stalk contractile. 

 61 Each individual of the colony can contract independently. 



5. Carchesium 



€2 The colony contracts as a whole 6. Zoothamnium 



do Stalk not retractile, but rigid. 



61 No operculum 7. Epistylis 



€n Operculum present 8. Opekcularia 



^2 Body enclosed in a transparent cup 9. Cothurnia 



1. Trichodina Ehrenberg. Body short, cylindrical or disc-shaped 

 with a ring of cilia around the circular flat base ; oral end also flat : 

 parasites or commensals on Hydra, planarians, and other small animals, 

 also on the gills of fishes, attaching itself by the sucker-like base or mo^dng 

 over the surface of the body ; sometimes entopara- 

 sitic in the urinary bladder or intestine of fish or . ttumirHiuiiiiiiiiiiiim/ 

 amphibians; several species. 



T. pediculus Ehr. (Fig. 119). Length .08 

 mm. : often common on Hydra. 



2. Vorticella L. Body more or less bell- ^^■"^^■' mM^^ 

 shaped with the oral groove extending inwards rig. 119 — Trichodina 

 from the rim and with a long stalk ; nucleus horse- 

 shoe-shaped; colorless or green or blue: many species; in salt and fresh 

 water, on plants and animals. 



V. nebulifera Ehrenberg (Fig. 120). Body campanulate, some- 

 times green in color, .07 mm. long with a stalk 4 times as long: in clear 

 water. 



V. campanula Ehr. The largest Vorticella, with a body .2 mm. 

 long or less, bluish in color, and a stalk several times as long, not 

 annulated: in fresh water, often in clumps on water plants. 



V. convallaria L. Body annulated, .1 mm. long, with a long stalk: 

 in infusions. This animal is interesting because it was the first micro- 

 scopic animal discovered by Leeuwenhoek. who first saw it in April, 1675. 



