Vibrionia.'] THE infusoria. 135 



clusters of these creatures. Found in vegetable infusions 

 in fetid water. Length l-200th. Thickness 1-I7200th. 



Genus XXVIII. Spirochaeta. The twisting Animal- 

 cules. — This genus is characterized by its members being 

 developed in filiform and flexible chains, of a spiral descrip- 

 tion, which are elongated by the imperfect or incomplete 

 mode of the creatures' self- division. The details of their 

 organization are at present unknown to us. 



98. Spirochaeta plicatilis {V. set'pens, M.) The 

 ivorm-like or writhing Spirochaeta. — Chain constituted of 

 very delicate bodies, of nearly a globular shape, connected 

 together in a long filiform spiral form, having numerous 

 and closely arranged coils ; colourless. Group 62 shews 

 three clusters. Found at Tilbury Fort. Length of chain 

 1-1 70th to 1 -440th. Thickness 1-1 2000th. 



Genus XXIX. Spirillum. The cylinder spiral Animal- 

 cules. — This genus is characterized by its members deve- 

 loping themselves in tortuous chains, or inflexible and 

 cylindrical spirals. These are elongated in the same 

 manner as before described, by the incomplete self- divi- 

 sion of the creatures, which takes place in an oblique 

 direction. Their brisk, energetic, and voluntary motion, 

 and the increase of the chain by division, are the only- 

 animal properties which have been hitherto observed as 

 characterizing the creature. 



99. Spirillum tenue. The slender Spirillum. — Spiral 

 consists of three or four coils, constituted of very slender, 

 slightly bent, and colourless fibres ; articulations distinct. 

 Found in vegetable infusions. Length about 1 -900th. 

 Thickness 1-1 2000th. 



100. Spirillum undida {V. undula, M.) The wavy 



