128 A NURSERY FOR THE MICROSCOPE. 



a half-inch objective we may see the currents 

 produced by the cilia of the disk, whose rapid, 

 successive movement gives that impression of the 



Fig. 89. 



Disk of Melicerta, showing currents by cilia, and pelleted tube 

 (greatly magnified). 



revolutions of a cog-wheel which has procured foi 

 these creatures the name of Rotifers, or "wheel- 

 animalcules." Even more beautiful than the Melicerta 

 is the " crown animalcule " (Stephanoceros Eichornii}, 

 Fig. 90. It may be found in many ponds and rivers, 

 and easily transferred to the tank. Its five arms 



