THE PRINCIPLES OF CLASSIFICATION 89 



for purposes of uniformity. It has been found necessary to 

 discard some hitherto famihar names. The best known of 

 these is Lamprocystis. It has been shown already (p. 18) 

 that the organisms known by this name are forms of growth 

 of one or other of several organisms, and not independent 

 species. It is considered that the attributes by which this 

 genus is known, namely, that division is at first in " three 

 directions of space " and subsequently in " two directions of 

 space," is a fugitive character, and due in all probability to 

 some change in the constitution of the sHme which envelops 

 the cells. The validity of this alleged distinctive feature of 

 Lamprocystis has never been confirmed by any subsequent 

 writer. 



The following genera are discarded for reasons given be- 

 low : — Thiosphcera, Thiosphcerion, Thiothece, Thiopoly coccus, 

 and Hillhousia. Of these the first four are discarded because 

 it is considered that they represent merely phases in the life- 

 histories of various pleomorphic bacteria. Zoogloea struc- 

 tures, when they occur in organisms other than the sulphur 

 bacteria, have not been regarded as other than forms of growth, 

 not as separate organisms. There is still some doubt whether 

 the genus Hillhousia is specifically distinct from Achromatium. 

 The balance of evidence supports the view that they are 

 identical. 



Ellis's Classification. 

 The sulphur bacteria arc divided into two groups : — 



A. Leuco-Thiobacteria. — Colourless sulphur bacteria. 



B. Rhodo-Thiohacteria. — Coloured sulphur bacteria. 

 A. Leuco-Thiobacteria. — Four families. 



Family i. Beggiatoacece. — Normally straight filaments, but 

 may show spiral or globular forms ; normally motile ; 

 occasionally enters zoogloea condition. 



Genus i. Beggiatoa. — Normally straight, motile, 



filaments. 

 Genus 2. Thiothrix. — Filaments attached, and often 



enclosed in sheath of hardened slime. 

 Genus 3. Thioploca. — Aggregates of threads in har- 

 dened slime. 



