404 EVENINGS AT THE MICROSCOPE. 



impart a charm to this elegant animalcule, which enables 

 us to look long at it without weariness. 



This last movement is peculiar, and worthy of a 

 moment's closer examination. The stalk, when extended 

 to the utmost, is an elastic glassy thread, nearly straight, 

 like a wire, but never so absolutely straight as not to show 

 slight undulations. The stalk, when thus drawn tight, is 

 highly sensitive to vibrations in the surrounding medium ; 

 and as in the circumstances in which we observe the 

 animals, such vibrations must be every instant communi- 

 cated to the vessel in which they are confined, the stalks 

 are no sooner fully extended than they contract with 

 alarm. This depends on a contractile cord which passes 

 throughout the entire length of the stalk, and which is 

 distinctly visible in the larger species as a narrow band. 

 We can scarcely err in considering this ribbon as a rudi- 

 mentary form of muscle, though we do not recognise 

 in it some of the characteristic conditions which we are 

 accustomed to see in it in higher animals. 



The contraction of the muscle is very sudden, energetic, 

 and complete. With a rapidity which the eye cannot fol- 

 low, the vase is brought down almost to the very base of the 

 stalk. Then it slowly rises again ; and now we see, what we 

 could not discern in the act of contraction itself, that in 

 that act the stalk was thrown into an elegant spiral of many 

 turns, which at the utmost point of contraction were packed 

 close on each other, but which in the extending act gradu- 

 ally separate, and at length straighten their curves. 



In any stage of the extension, the sudden contact of 

 the vase with any floating or fixed object apparently 

 causes alarm, and induces the vigorous contraction; but 

 vibrations, even when so violent as those produced by 

 tapping the stage of the microscope with the finger-nail, 

 have no effect unless the stalk be tense, its own power 

 of vibration being then only developed, just as a cord 

 becomes musical in proportion to its tension. 



