THE LEUCO-THIOBACTERIA 103 



Description. — This remarkable organism is composed of 

 threads varying in thickness from 15 to 45/.t. In spite of its 

 large size it has the same simple structure of cell as Beggiatoa 

 alba. It differs, however, from that species in possessing a 

 sharplv defined external membrane and transverse walls similar 

 to those of the genus Bacillus. Cohn depicts transverse walls 

 and their existence has been confirmed by Hinze, who has de- 

 scribed their structure in detail. Warming, however, depicts a 



Fig. S. — Beggiatoa mirahilis (Cohn), 1865, and Beggiatoa mirabilis (Warming). 



a and b show parts of filaments of the organism which Warming described 

 under this name. Transverse walls are not formed, x 500. 



c-f show parts of filaments of the Beggiatoa mirahilis as figured by Cohn 

 and Hinze. 



c. — Shows the outer walls, the transverse membranes, the vacuoles and the 

 sulphur globules, x 1200. 



d (after Hinze) . — Two cells separated by a delicate transverse wall : sulphur 

 globules and bodies alleged by Hinze to be chromatin (see p. 182^. 

 X 1200. 



e (after Hinze) . — The first phase in the development of the transverse wall : 

 formation of an annular ring. Seen in section at a^. X 1200. 



/. — Diagrammatic representation of the annular ring, shown in section in 

 the preceding diagram. 



g.- — Photomicrograph of Beggiatoa mirahilis as described by Warming. From 

 material from the South of England. X 500. 



h. — Beggiatoa mirahilis of Warming.— K diagrammatic representation of 

 the internal structure of a thread preserved in formalin. The plasma 

 appears as an irregularly reticulate knotted mass. The nucleus is 

 absent, and there are no transverse walls. At the time of writing 

 living threads have not been obtainable, but there seems little doubt 

 that in the living condition the structure of the plasma conforms to 

 that shown in Fig. 6b. x 1200. 



species by the name of Beggiatoa mirahilis (Fig. 8 a and h) which 

 is essentially different from the organism figured by Cohn, in 

 the complete absence of transverse w'alls. The thread appears 

 to be roughly segmented, but this is not really the case, the 

 fictitious appearance being caused by the occurrence of trans- 

 verse bands of plasma at more or less regular intervals. In 

 Fig. 8g is shown a photomicrograph of an organism found in 

 the South of England (in material kindly sent to the author 

 by Miss Nellie Carter) which corresponds in all essentials to 

 the organism described by Warming. Viewed with a low 



