CILIARY MOVEMENT. 1 1 



lu many fixed animals of low order a crown of cilije 

 encircles the mouth -opening, producing a current 

 which brings water, together with particles floating in 

 the latter, to the animal as food. Other aquatic ani- 

 mals have the whole or a part of their upper surface 

 studded with cilige, by means of which they rotate in 

 the water. Finally, there are bodies which, instead of 

 the delicate ciliate hairs, possess only a larger and 

 stronger whip-like process by the sinuous motions of 

 which these animals move themselves about in the 

 water, as a boat may be moved by the quick motion of 

 the rudder, or as a water-newt propels itself by the 

 sinuous motion of its tail. 



None of these motions are, however, equal in force 

 and effectiveness to those which are produced by muscles. 

 In higher animals, muscles occur in two forms, — either 

 as smooth muscle-fibres, or as striated muscle-fibres. The 

 former are spindle-shaped cells which have grown out 

 in a longitudinal direction, and which have rod-shaped 

 kernels (nuclei) and pointed ends, sometimes twisted 

 like a corkscrew. The latter are produced by the coa- 

 lescence and amalgamation of several cells, the contents 

 of which have undergone an important change. These, 

 and the qualities of these, will be fully discussed in 

 the following chapters. 



