THE PRINCIPLES OF CLASSIFICATION 79 



(6) Lamprocystis.— -Fami\\es at first forming a solid mass, 



later forming a reticulated hollow sphere. 



c. Division in two directions of space. 



(7) Thiopedia. — Families in plates, cells arranged sym- 



metrically in fours, and capable of motion. 



d. Division of cells in one direction of space. 



(8) Amoshobacter. — Families amoeboid and motile. Cells 



connected by plasma threads. 



(9) Thiothece. — Families with thick slime cysts. Cells 



motile and loosely enclosed in a common envelope 

 of slime. 



(10) Thiodictyon. — Families made up of rods arranged net- 



wise. 



(11) Thiopolycoccus. — Families compact. Cells non-motile, 



small and closely pressed together. 



(B) Cells free, and capable of movement. 



(12) Chromatinm. — Cells cylindrical-elliptical. 



(13) Rhabdochromatium. — Cells rod- or spindle-shaped. 



(14) Thiospirillum. — Cells spirally twisted. 



Remarks on Winogradsky's Classification. 



The attributes selected for the grouping are simple, and for 

 the most part easily ascertainable. The most serious fault 

 of this system lies in the inconstancy of the characters used 

 in the grouping, and this applies in particular to the partition 

 of these organisms according to the number of dimensions in 

 space in which they divide. Motility or its absence is also 

 an uncertain factor. 



The following features in the species are constant : — • 



[a) The division into coloured and uncoloured forms. 



[b) The division into free cells and aggregates of cells 



(families). 



[c) The shape of the cell (rod, globular, etc.) 



As Winogradsky discounted the facts of pleomorphism, and 

 in consequence magnified the importance of variants into 

 species and even into genera, the value of his system is 



