166 DESCRIPTION OF [Polycfastrica. 



Family.— VIBRIONIA. 



The animalcules of this family are distinctly or apparently poly- 

 gastric, but without a true alimentary canal, and, like the Monadina, 

 are incapable of changing the form of their body. They have neither 

 appendages or shell-like covering. They are associated or linked 

 together in thi-ead-like chains, fonned by their imperfect transverse 

 self-division. Considering how much we know of the organization 

 of the family Monadina, we are comparatively far behind in in- 

 formation respecting the Vibrmiia, and were it not that the cause of 

 our ignorance is manifestly attributable to the exceeding minuteness 

 of the individual animalcules, we might be justified in imagining 

 their stiaicture to be more simple than in all probability it really is. 

 The filiform and very delicate threads in which they occur, are not, as 

 we have said, scpai-ate animalcules, but chain-like clusters, whose 

 almost imperceptible links are themselves (at fii'st) single creatures. 

 The reasons to be assigned for arriving at tliis conclusion, are, that 

 the clusters or chains have never any detonninate length, or number 

 of members forming them, and that they are sometimes so short as to 

 be made up of not more than two or three individuals, and only dis- 

 tinguishable from Monas termo and M. crepusculum by their mode of 

 union, and peculiar, though not easily characterized movements. 

 Hence all their organic relationships are to be sought for in these 

 minute portions of the chain. To discover these is a task not to be 

 fully accomplished, even "with the greatest assiduity, coupled with 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 ai'ise 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 form of locomotion ; and in one genus 

 {Bacterium), 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 

 peen in the true Vibriones, a direct movement in swimming being alone 



