24 



EPITHELIUM 



[CH. IIL 



and in not being stiff; they are in fact composed of protoplasm. 



During life these move to and fro, and so produce a current of 



fluid over the surface they cover. 

 Like columnar cells, they may 

 form goblet cells and discharge 

 mucin. 



In the larger ciliated cells, it 

 will be seen that the border on 

 which the cilia are set is bright, 

 and composed of little knobs, to 

 each of which a cilium is at- 

 tached ; in some cases the knobs are 

 prolonged into 



the Cell 



. 35. Ciliated epithelium of the human 



trachea. a, Layer of longitudinally arranged . c , 



elastic fibres; b, basement membrane; c, plaSHl as Ella- 



deepest cells, circular in form; d> inter- ma^fc, ^^ vr^f 



mediate elongated cells; e, outermost layer mt;Lllj b Ol 1 



of cells fully developed and bearing cilia, let 8 (fig. 36). 



According to 



some observers these rootlets are outgrowths from 

 the multiplied centrosome of the cell. 



The bunch of cilia is homologous with the 

 striated border of columnar cells. 



Ciliated epithelium is found in the human 

 body, (1) lining the air passages, but not in the 

 alveoli of the lungs ; these are lined by pavement 

 epithelium ; (2) in the Fallopian tubes and upper 

 part of the uterus ; (3) in the ducts of the testis 

 known as the vasa efferentia and coni vasculosi ; 

 here the cilia are the longest found in the body ; 

 (4) in the ventricles of the brain and central 

 canal of the spinal cord ; (5) the tail of a sperma- 

 tozoon may also be regarded as a long cilium. 



In other animals cilia are found in other 

 parts; for instance, in the frog the mouth and 

 gullet are lined by ciliated cells ; in the tadpole, 

 the whole surface of the body and especially the 

 gills are covered with cilia. Among the inverte- 

 brates one finds many protozoa completely covered 

 with cilia ; in many embryos the cilia are arranged 

 in definite bands round the body ; in the rotifers 

 or wheel animalcules, a ring of cilia round the Flo- 36 ._ ciliated cell from 

 mouth gives the name to this particular group. 

 The gills of many animals are covered with 

 cilia; and the cells of portions of the kidney tubules in some 

 animals are ciliated. 



the intestine of a mol- 

 lusc. (Engelmann.) 



