Vibrionia.] THE INFUSORIA. 131 



discover these is a task not to be fully accomplished, 

 even with the greatest assiduity, attended by the most 

 effective optical means which we at present possess. The 

 traces of organization in the members of this family are 

 so few, and those so indefinite, that a question might arise 

 whether or not they are to be considered as belonging to 

 the animal portion of the creation. The answer to this is, 

 that they possess a very powerful writhing, and evidently 

 voluntary state of locomotion ; and in one genus (Bac- 

 terium), a single vibratory proboscis is present as the 

 organ of motion. In it the individual forms are strung 

 more slightly together, the filiform cluster not being able 

 to exert the writhing movement seen in the true Vibrios, a 

 direct movement in swimming being alone practicable. In 

 Spirillum the constrictions or articulations are oblique, so 

 that increase in length by division engenders a spiral chain. 

 This family is distributed among five genera, as follows : 



Articulated threads (clusters). Inflexible Bacterium. 



Straight, the divisions being 

 rectangular and transverse V Flexible, like a snake Vibrio. 



Articulated threads spirally twisted 

 (like a bell-spring or cork-screw) the - 

 transverse divisions being oblique 



Flexible Spirochoeta. 



with a cylindrically \ 



extended j- Spirillum, 



spiral form ) 

 Inflexible ^ 



with a disc-like \ 



compressed spiral [ Spirodiscus. 

 form 



Genus XXVI. BACTERIUM. The jointed- wand Animal- 

 cules are distinguished by being connected together in a 

 thread-like chain, of an inflexible nature, and their propa- 

 gating by a transverse mode of self- division. 



The three species known to us are colourless, and 



K 2 



