38 JOURNAL OF THE TRINIDAD 



One species is known, Crenothrix kuhniana. It occurs as 

 little whitish or brownish tufts in wells and drain-pipes. It fouls 

 the water and may stop up the narrower pipes. 



2. Beggiatoa. In this genus the threads are not articulated ; 

 the cells contain sulphur granules ; the habitat is water. 



Three species are described, the best known of which is 

 Beggiatoa roseo-persicina, which has been already mentioned as 

 furnishing the material from a study of which Lankester formu- 

 lated his doctrine of pleomorphism. 



The cocci form at first solid families bound together by 

 gelatinous substance. Then the} 7 become larger, ovoid or globular 

 and hollow, containing watery fluid. These hollow families are 

 often perforated, presenting a reticulated appearance. Finally 

 they may become broken up into irregular structures. In the 

 cocci of the older vesicles dark granules of sulphur occur. These 

 micro-organisms occur sometimes in such quantity that whole 

 marshes or ponds may be coloured red by them. 



3. Phragmidiothrix. In this genus the threads are without 

 joints ; successive sub-division of cells is continuous ; the cells are 

 without sulphur ; the habitat is water. 



One species is known, Phragmidiothrix multiseptata. It 

 consists of cocci and threads. The latter are separated by 

 transverse partitions into discs. Repeated transverse and longitu- 

 dinal division takes place in these discs, resulting in the formation 

 of cocci. These cocci develop in situ into slender threads. 



Phragmidiothrix is especially characterized by this constant 

 sub-division, but it also differs from beggiatoa in the absence of 

 sulphur and from crenothrix by the absence of a sheath. It 

 occurs in sea water attached to crabs. 



4. Leptothrix. In this genus the threads are articulated or 

 not articulated \ successive sub-division of cells is not continuous ; 

 the cells are without sulphur. 



The threads are composed of long rods, short rods, and cocci. 

 The threads may break up into spiral, vibrio, and spirochete 

 forms. They occur in large numbers in the mouth in man and 

 animals, and are believed to be connected with dental caries. 

 Two species are described. 



Group IV. — Cladstrichea?. 



This group possesses cocci, rods, threads and spirals. The 

 thread forms have false branchings. 



The group contains only one genus. 



1. Cladsthrix. This has aheady been mentioned as the 

 micro-organism on which Zopf worked when establishing his 

 classification of bacteria founded on the theory of pleomorphism. 

 Its development can be traced from cocci to rods and threads. 



