452 EVENINGS AT THE MICROSCOPE 



near the centre of the vase, a longish body of clear granu- 

 lar texture, which is called the nucleus, and which seems 

 to play an essential part in the vital economy of the 

 animal. 



The movements of a group such as that we are looking 

 at are very sprightly and pleasing. The vases turned in 

 all directions, some presenting their mouths, some their 

 sides, some their bases to the eye; inclined at various 

 angles from the perpendicular, and bending in diverse 

 degrees upon the extremity of their stalks; swaying 

 slowly and gracefully to and fro, as driven hither and 

 thither by the ciliary currents, and, above all, ever flying 

 up and down within the length of their radius, as a bird 

 when confined by a string all these circumstances 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 mo- 

 ment'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 rendered tense 

 by extension is highly sensitive to vibrations in the sur- 

 rounding medium; and as, in the circumstances in which 

 we observe the animals, such vibrations must be every 

 instant communicated to the vessel in which they are 

 confined, the stalks are no sooner tense than they con- 

 tract 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 recognize in it some of the characteristic con- 



