CILIARY MOVEMENTS 



413 



Such movements are called ameboid ; and they probably are analogous 

 to ciliary movements, the cause of which, however, is obscure. 



Ciliary Movements. The epithelium covering certain of the mucous 

 membranes is provided with little hair-like processes on the borders of 

 the cells, called cilia. These are in constant motion from the beginning 

 to the end of life ; and they produce currents on the surfaces of the 



iillilll 

 &mm- 



Fig. 80. Ciliated epithelium (Engelmann). 



A, from intestinal epithelium of anodonta ; B, from gill of anodonta ; C, D, intestinal epithelium of 

 cyclas. 



membranes to which they are attached, the direction being usually 

 from within outward. In man and in the warm-blooded animals 

 generally, the ciliated or vibratile epithelium is of the variety called 

 columnar, conoidal or prismoidal. The cilia are attached to the thick 

 ends of the cells, and they form on the surface of the membrane a con- 

 tinuous sheet of moving processes. In general structure the ciliary 

 processes are homogeneous, and they gradually taper from their attach- 

 ment to the cell to an extremity of excessive tenuity. 



