[Illustration: FIG. 54.--Illustrates the genus Microspira. It is (though the photograph does not prove it) a short spiral with one flagellum at the end.] [Illustration: FIG. 55.--Illustrates the genus Spirillum. Spiral bacteria with more than three, in this case four, flagella at the end.] [Illustration: FIG. 56.--Illustrates the genus Spirochæta.] [Illustration: FIG. 57.--Illustrates the genus Chlamydothrix. Fine threads with a delicate sheath.] [Illustration: FIG. 58.--Illustrates the genus Crenothrix. The thickness of the cell walls is due to deposits of iron hydroxide. (After Lafar.)] [Illustration: FIG. 59.--Illustrates the genus Beggiatoa. The filament _A_ is so full of sulphur granules that the individual cells are not visible. _B_ has fewer sulphur granules. In _C_ the granules are nearly absent and the separate cells of the filament are seen. (After Winogradsky, from Lafar.)] ORDER I. Eubacteria. Cells without nuclei, free from sulphur granules and from bacteriopurpurin (p. 112); colorless, or slightly colored. 1. Family: COCCACEÆ (Zopf) Migula, all cocci. {Genus 1. _Streptococcus_ Billroth: { division in one plane only (Fig. 49). Non-flagellated, { „ 2. _Micrococcus_ (Hallier) Cohn: Non-motile { division in two planes only (Fig. 50). { „ 3. _Sarcina_ Goodsir: { division in three planes only (Fig. 51). { „ 4. _Planococcus_ Migula: Flagellated, { division in two planes only. motile { „ 5. _Planosarcina_ Migula: { division in three planes only. 2. Family: BACTERIACEÆ Migula, all bacilli. Genus 1. _Bacterium_ (Ehrenberg) Migula: no flagella; non-motile. „ 2. _Bacillus_ (Cohn) Migula: flagella peritrichic (Fig. 52). „ 3. _Pseudomonas_ Migula: flagella at the end: monotrichic, lophotrichic, amphitrichic (Fig. 53). 3. Family: SPIRILLACEÆ Migula, all spirilla. {Genus 1. _Spirosoma_ Migula: { non flagellated; non-motile. { „ 2. _Microspira_ (Schrœter) Migula: Cells stiff { flagella one to three at the end (Fig. 54). { „ 3. _Spirillum_ (Ehrenberg) Migula: { flagella more than three { at the end (Fig. 55). Cell flexible { „ 4. _Spirochæta_ Ehrenberg: { motile; no flagella (Fig. 56). 4. Family: CHLAMYDOBACTERIACEÆ. Cells cylindrical in long threads and surrounded by a sheath. Reproduction also by gonidia formed from an entire cell. Genus 1. _Chlamydothrix_ Migula (Fig. 57). „ 2. _Crenothrix_ Colin (Fig. 58). „ 3. _Pragmidiothrix_ Engler. „ 4. _Spherotilus_ (including Cladothrix). ORDER II. THIOBACTERIA: SULPHUR BACTERIA.