Vibrionia.'] THE INFUSORIA. 135 



clusters of these creatures. Found in vegetable infusions 

 in fetid water. Length 1 -200th. Thickness 1-1 7200th. 



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 plicatllis (V. serpens, M.) The 

 worm-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 60 shews 

 three clusters. Found at Tilbury Fort. Length of chain 

 l-l?0th to l-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 l-12000th. 



100. SPIRILLUM undula (V. undula, M.) The wavy 



