CILIATED EPITHELIUM. 



Ixi 



Fig. XXXT. 



of the subjacent membrane, has much engaged attention since the importance of the 

 connective-tissue-eorpuscles has 

 come to be recognised ; and a 

 strong impression or belief pre- 

 vails that such epithelium-cells 

 are structurally connected by 

 prolongations from their lower 

 ends with these corpuscles, and 

 genetically related to them. 

 As a matter of observation, 

 such anatomical connection is 

 affirmed on excellent authority 

 (Lockhart Clarke, Gerlach, and 

 others) in reference to the 

 columnar ciliated epithelium of 

 the central canal of the spinal 

 cord and the Sylvian aqueduct, 



but the evidence in other cases 

 is not so satisfactory. 



Fig. XXXI. CILIATED EPITHELIUM FROM THE 

 HUMAN WINDPIPE; MAGNIFIED 350 DIAMETERS. 



a, b, subjacent membrane ; c, lowermost or round 

 cells; d, middle layer of oval cells; e, superficial or 

 ciliated cells (from Kolliker). 



The cilia themselves differ 

 widely in size in different 

 animals, and they are not 



equal in all parts of the same animal. In the human windpipe they 

 measure ^oVoth to o-rVljth ^ an ^ nc ^ ^ length. ; but in many invertebrate 

 animals, especially such as live in salt water, they are a great deal larger. 

 In figure they have the aspect of slender, conical, or slightly flattened fila- 

 ments ; broader at the base, and usually pointed at their free extremity. 

 Their substance is transparent, soft, and flexible. It is to all appearance 

 homogeneous, and no fibres, granules, or other indications of definite 

 internal structure, have been satisfactorily demonstrated in it. 



Motion of the cilia. The manner in which the cilia move, is best seen 

 when they are not acting very briskly. Most generally they seem to execute 

 a sort of fanning or lashing movement ; and when a number of them 

 perform this motion in regular succession, as is generally the case, they give 

 rise to the appearance of a series of waves travelling along the range of 

 cilia, like the waves caused by the wind in a field of corn. When they are 

 in very rapid action the undulation is less obvious, and, as Henle remarks, 

 their motion then conveys the idea of swiftly running water. The undu- 

 lating movement may be beautifully seen on the gills of a mussel, and on 

 the arms of many polypes. The undulations, with some exceptions, seem 

 always to travel in the same direction on the same parts. The impulsion, 

 also, which the cilia communicate to the fluids or other matters in contact 

 with them, maintains a constant direction; unless in certain of the infusoria, 

 in which the motion is often variable and arbitrary in direction, and has 

 even been supposed to be voluntary. Thus in the windpipe of mammalia, 

 the mucus is conveyed upwards towards the larynx, and, if a portion of the 

 membrane be detached, matters will still be conveyed along the surface of 

 the separated fragment in the same direction relatively to that surface, as 

 before its separation. 



The persistence of the ciliary motion for some time after death, and the 

 regularity with which it goes on in parts separated from the rest of the body, 

 sufficiently prove that, with the possible exceptions alluded to, it is not 

 under the influence of the will of the animal nor dependent for its produc- 

 tion on the nervous centres, and it does not appear to be influenced in any 



