404 EVENINGS AT THE MICROSCOPE. 



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 rudimentary condition 

 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 

 follow, 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 

 gradually 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 vibra- 

 tions, 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. 



