CH. III.] 



CILIARY MOTION. 



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 

 mucus. 



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 attached ; in some 

 cases the knobs are prolonged into the cell pro- 

 toplasm as filaments or rootlets (fig. 43). 



The bunch of cilia is homologous with the 

 striated border of columnar cells. 



Ciliated epithelium is found in the human 

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

 alveoli of the lungs ; these are lined by pave- 

 ment 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 spermatozoon 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 tad- 

 pole, the whole surface of the body and especially 

 the gills are covered with cilia. Among the 

 invertebrates one finds many protozoa com- 

 pletely 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 mouth gives the name 

 to this particular group. The gills of many 

 animals are covered with cilia; and the cells of the kidney tubules 

 in some animals are ciliated. 



Ciliary Motion. 



Ciliary motion reminds one of amoeboid movement, but it is 

 much more rapid, and more orderly. It consists of a rhythmical 

 movement of the cilia, a bending over, followed by a lessening of 

 the curvature, repeated with great frequency. 



When living ciliated epithelium, e.g., from the gill of a mussel, 

 or from the mouth of the frog, is examined under the microscope 



Fig. 43. Ciliated 

 cell from the intes- 

 tine of a mollusc. 

 (Engelmann.) 



