INFUSORIA 65 



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

 16 genera. 



Key to the genera of Vorticellidae here described : 



Oj Animals not sessile and without a stalk ; parasites or commensals on Hydra 



and other animals 1. TBICHODINA 



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



animals. 



&! Body not enclosed in a cup. 

 <?! Stalk long or short and not branched ; animals solitary. 



di Stalk long and contractile 2. VOBTICELLA 



d 2 Stalk short and not contractile. 

 6i Oral disc acts like a cover (operculum) which may close the opening of 



the cup 3. PYXIDIUM 



e z No such cover 4. RHABDOSTYLA 



c 2 Stalk branched ; animals colonial. 

 dt Stalk contractile. 

 6j Each individual of the colony can contract independently. 



5. CABCHESIUM 



2 The colony contracts as a whole 6. ZOOTHAMNIUM 



d 2 Stalk not retractile, but rigid. 



e No operculum 7. EPISTYLIS 



e 2 Operculum present 8. OPEBCULABIA 



& 2 Body enclosed in a transparent cup 9. COTHUB^IA 



1. TEICHODINA 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 moving 

 over the surface of the body ; sometimes entopara- 



sitic in the urinary bladder or intestine of fish or 

 amphibians; several species. 



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

 mm. : often common on Hydra. 



2. VORTICELLA L. Body more or less bell- 

 shaped with the oral groove extending inwards Fig. 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. 



