COLUMNAR, CILIATED, AND TRANSITIONAL EPITHELIUM 25 



during life, move spontaneously to and fro, and serve to produce a 

 current of fluid over the surface which they cover. 



The cilia are to be regarded as active prolongations of the cell- 

 protoplasm. The border upon which they are set is bright, and 

 appears formed of little juxtaposed knobs, to each of which a cilium is 

 attached. In the large ciliated cells which line the alimentary canal 

 of some molluscs (fig. 25) the knob may be observed to be prolonged 

 into the protoplasm of the cell as a fine varicose filament, termed the 

 rootlet of the 'cilium. These filaments may represent the longitudinal 

 strias often seen in the protoplasm of the columnar cell, the bunch of 

 cilia being homologous with the striated border. The protoplasm and 

 nucleus have a similar vacuolated or reticular structure in both kinds 

 of cell. Goblet cells may also occur in ciliated epithelia. 



FIG. 23. GOBLET CELL. 



FIG. 24. COLUMNAR CILI- 

 ATED EPITHELItM-CELLS. 



FIG. 25. CILIATED CELL. 

 FROM THE INTESTINE 

 OF A MOLLUSC. 



Ciliated epithelium is found throughout the whole extent of the 

 air-passages and their prolongations (but not the part of the nostrils 

 supplied by the olfactory nerves, nor in the lower part of the pharynx) ; 

 in the Fallopian tubes and the greater part of the uterus ; in some of 

 the efferent ducts of the testicle (where the cilia are much longer than 



