CONNECTIVE TISSUES 37 



it out, but they may profoundly alter it before getting 

 rid of it. 



•i. Ciliated Epithelium (fig. 6 (b), p. 33). — The cells are 

 usually more or less columnar, and the free border is pro- 

 vided with a series of hair-like processes, the cilia, which 

 vary in size in dit^'erent situations. 



In the living state the cilia are in constant rhythmic 

 motion, each cilium being suddenly whipped or bent down 

 in one direction, and then again assuming the erect posi- 

 tion. 



All the cilia on a surface work harmoniously in the same 

 direction, and the movement passes from the cilia of one cell 

 to those of the next in regular order, beginning at one end 

 of the surface and passing to the other. 



As a result of this constant harmonious rhythmic move- 

 ment, any matter lying upon the surface is steadily whipped 

 along: it : and, since the cilia usually work from the inner 

 parts of the body to the outside, this matter is finally 

 expelled from the body. They line the respiratory passages, 

 and their movement plays an important part in getting rid 

 of dust which has been inhaled. 



The movements of the cilia are dependent on the changes 

 in the protoplasm, and everything which influences the rate 

 of chemical chanfje modifies the rate of ciliarv movement, 

 which may thus be taken as an index of the protoplasmic 

 activity. 



II. CONNECTIVE TISSUES. 



These are the binding and supporting tissues of the body 

 — fibrous tissue, cartilage, and bone. They are formed 

 from the mesoblast of the embryo, and most of them contain 

 blood-vessels. 



1. Mucoid Tissue. — The cells of the mesoblast of the 

 embryo, which at first lie in close apposition with one 

 another, become separated, remaining attached by elongated 

 processes. Between the cells a clear, transparent substance 



