THE LEUCO-THIOBACTERIA 105 



The threads are 5/x — 6/x thick, and are divided into cellular 

 segments by transverse bands of clear protoplasm placed at 

 regular intervals. They form in the mass, thin, chalky-white 

 slimy layers, of the texture of a spider's web. The segments 

 are either as broad as they are long, or half as long as they 

 are broad. 



Habitat. — Found originally in the sulphur springs at 

 Karlsbad. It occurs in waters, both fresh and salt, containing 

 mud rich in HgS. 



Beggiatoa leptomitiformis (Meneghini), Trevisan (i), 

 1842. 



Literature. — Meneghini (2), 1844 ; Massart, 1902. 



Description. — This species is found in great numbers in 

 various sulphur springs. The threads are not segmented. 



They measure i-8 — 2-5/n in thickness and form a chalky- 

 white covering to the objects on which they settle. 



Habitat. — Sulphur springs. 



Genus 2. — Thiothrix (Winogradsky), 188S. 

 Founded by Winogradsky to designate a group of organisms 

 very similar to, and frequently in association with, Beggiatoa. 

 The genus differs from Beggiatoa in the following respects : — 



1. Absence of free miovement. 



2. Presence of an anchoring slimy organ of attachment. 



3. Development of a slime sheath. 



4. Formation of " conidia " at the free end of the threads. 



These are thrust out of the sheath, and after a slow, 

 creeping, independent movement, attach themselves 

 to objects in the water, w^here they form new threads. 



It is not always possible to distinguish these two general 

 for Beggiatoa alba sometimes develops excessive slime, when it 

 becomes stationary, and resembles Thiothrix. Again, another 

 species, Beggiatoa arachnoidea, possesses an anchoring organ 

 of attachment, and thus also resembles Thiothrix. But slime 

 development resulting in an enveloping hollow sheath is a 

 normal feature in the life-history of Thiothrix. This sheath 



