10 



THE ELEMENTARY TISSUES 



Each of the ciliated epithelial cells presents on its free sur- 

 face twenty or more small, hair-like, protoplasmic append- 

 ages, called cilia. During life these small processes are in 

 constant rapid motion, waving in a direction toward the out- 



FIG. 5. Ciliated epithelium of the human trachea. 



a, layer of longitudinally arranged elastic fibers; b, basement membrane; c, 

 deeoest cells, circular in form; d, intermediate elongated cells; e, outermost 

 layer of cells fully developed and bearing cilia. X 350. (Kirkes after Kollikcr.) 



let of the cavity in which th.ey are found. In the genital or- 

 gans they are important in bringing together the male and 

 female elements of reproduction, while in the respiratory 

 tract they are concerned in aiding the 

 passage of the mucus and in the ex- 

 pulsion of foreign bodies. 



(b) Goblet cells are found on all 

 surfaces covered by columnar epithe- 

 lium, but especially in the large intes- 

 tine. They secrete mucin, the main 

 constituent of mucus, which so dis- 

 tends the cell that it ultimately bursts 

 and sets free its contents. 



(c) Pigment ed epithelium is ordi- 

 nary epithelium, the protoplasm of which has become in- 

 vaded and colored by foreign matter, such as fat, proteid, 

 etc. Such cells are constant in the deeper layers of the epi- 



FIG. 6. Goblet cells. 



(Halliburton after Klein.) 



