SECTION A 



1. Multicellular organisms with or without a sheath or unicellular organisms arranged 



in chains and surrounded by a sheath 2 



Unicellular organisms 18 



2. Multicellular organisms not in a sheath 3 



Organisms in a sheath 11 



3. Both trichomes and abstricted cells are non -motile and are not flagellated 4 



Either trichomes or abstricted cells or both are motile. Motility may be either by glid- 

 ing on solid surfaces (non-flagellated) or by means of flagella. (Apparently non- 

 motile but flagellated cells are included in this section.) 5 



4. Trichomes up to 5,000 microns in length attached basally by means of a globular hold- 



fast; endospores produced in any or all cells within the trichome and obliquely sit- 

 uated; recorded from the alimentary canal of millipeds, cockroaches and toads 



Arthromitus p. 835 



Trichomes long and attached by means of a holdfast which may be distinct or rela- 

 tively inconspicuous; globular sulfur deposited internally when growing in the 

 presence of hydrogen sulfide Thiothrix p. 84^ 



Long trichomes arranged in bundles; each cell contains one or more gas vacuoles 

 which gleam reddish in transmitted light; do not deposit sulfur internally 



Peloploca p. 270 



Trichomes limited to four cells, the end ones being rounded; may be arranged in chains; 

 recorded from the buccal cavity Simonsiella p. 833 



5. Trichomes flagellated, peritrichous 6 



Trichomes or abstricted cells not flagellated; motility of a gliding type on solid sur- 

 faces or along adjacent cells 7 



6. Cells approximately 5 microns in width and straight to curved; develop a large endo- 



spore apparently by fusion of several cells within the trichome. The spore is nor- 

 mally centrally located. Division is preceded by formation of biconcave discs within 

 the trichome somewhat similar to those produced by Oscillator ia; found in large 



numbers in the cecum of the guinea pig Oscillospira p. 834 



Cells 3 or more microns wide; actively motile; do not produce endospores; common in 

 fresh dung Caryophanon p. 831 



7. Spiral cells Thiospirillopsis p. 840 



No spirals 8 



8. Entire trichomes are motile 9 



Entire trichomes are not motile; attached by means of a holdfast; taper from the base 



to the tip; single cells formed by abstriction from the tip are motile by a gliding 

 motion on a solid surface; trichomes characteristically arranged in rosettes but may 

 occur singly Leucothrix p. 850 



9. Elemental sulfur is deposited in a globular form in the cells when growing in waters 



containing hydrogen sulfide Beggiatoa p. 838 



Elemental sulfur is not deposited internally 10 



10. Cells within the trichomes contain one or more gas vacuoles which gleam bluish or 



reddish in transmitted light; described from surface films in pond waters 



Pelonema p. 271 

 Note: Pelonema is described as having a thin sheath and as being possibly 

 motile. It seems unlikely that floating motile filaments would be ensheathed, 

 and for this reason Pelonema is included here. 

 Not as above Vitreoscilla p. 845 



11. Width of sheath increases from base to tip; cells within the sheath divide trans- 



991 



