CILIAET MOTIONS. 



99 



filaments, they thus become important aids to the due perform- 

 ance of the function of respiration in the invertebrate classes ; 

 and are the chief agents by which it is performed in the sub- 

 kingdom radiata. 



[ 217. The most singular fact connected with the history 

 of ciliary motions, is their independence of the nervous sys- 

 tem, or even of the life of the organism itself. In the 

 fresh-water mussel, ciliary motions are observed for many 

 days on the surface of the membranes detached from the 

 body, even when the putrefactive process has considerably 

 advanced, and the same fact has been observed on the mucous 

 membranes of decapitated tortoises ; but in birds and mam- 

 mals, they cease in a few hours after death. Wherever ciliary 

 motions have been detected, cilia are seen as their instruments. 

 Set upon a particular form of cylinder-epithelium, composed of 

 closely arranged conical cells, implanted perpendicularly upon 

 the subjacent tissues (fig. 68), each cell supporting from six 

 to eight cilia upon its free summit (b, b, b), and containing 

 internally a distinct nucleated nucleus (c, c, c) ; the cilia and 

 nucleated cells are deciduous formations, and are cast off 

 and rapidly reproduced. The functions of this form of epi- 

 thelium are still obscure, and we know nothing of the cause 

 and the mechanism of the motions of the cilia. T. W.] 



Fig. 68. 



B 



Fig. 68. Some of the cylindrate epi- 

 thelial cells are produced inferiorly into 

 a point, a*, in which case the nucleus, c, 

 occurs about the middle of the formation. 

 B, is a transverse section of the nuclei 

 and nucleoli. To obtain a view of the 

 ciliary motions in man, we have but to 

 draw the extremity of the handle of the 

 scalpel over the mucous membrane of the 

 nose, and to transfer the mucus thus ob- 

 tained, properly prepared, to the stage of 

 the microscope ; it rarely happens that 

 one or more epithelial cylinders with active 

 cilia are not discovered. The tessular 

 epithelium of the mucous membrane of 

 the mouth may be procured by lightly 

 scraping the inner surface of the cheek, 

 and should be examined at the same time, 

 by way of contrast. WAGNER.] 

 H 2 



