70 NATURAL HISTORY 



although it forms such an admirable microscopic object. 

 Found in vegetable infusions. 



101. Vibrio undula, [Spirillum undida, E.) The wavy 

 Vibrio. — This animalcule, like the last species, is in- 

 flexible, but the body is simply undulated, and not coiled 

 cylindrically : when at rest, it does not appear so waved 

 as in motion, which probably arises from its celerity, the 

 impression on the retina remaining. It generally re- 

 sides on the surface of the drop of water, and sometimes 

 fixes itself by one end, and revolves. Leeuwenhoek, 

 whose measurements are generally vague^ informs us 

 that its diameter is much less than the tail of the human 

 spermatic animalcule, and adds this remark : ^* That as 

 this minute creature, of whose animated existence there 

 can be no doubt, can inflect its extremities at pleasure, 

 we must conclude that tendons and muscles are essential 

 to its existence as in larger animals ; if to these we add 

 alimentary organs, and those of sensation, the mind is 

 lost in the astonishment which arises from the impres- 

 sion o( infinite in the indefinitely small." 



102. Vibrio serpens. The serpent Vibrio. — This spe- 

 cies is larger than the two former, and undulated like 

 the last, but the inflexions are regular and uniform ; 

 it generally moves in a direct course. A dark line may 

 be seen running along the body, which is probably its 

 alimentary canal. It is found in river-water, but is 

 scarce. 



103. Y iBRio vermiculus. The little ivorm Vibrio. — This 



