570 



GENERAL PHYSIOLOGY 



The dependence of the individual cells upon one another in 

 many tissues of the higher animals is still closer than in the 

 plants and the lowest C&lenterata. Here a pronounced despotism 

 prevails. The constitution of ciliated epithelia affords an interest- 

 ing example. As is well known, a ciliated epithelium consists of 

 many successive rows of ciliated cells arranged one after another 

 in each row, and each cell possessing a number of cilia (Fig. 

 274, /). The cilia of these cells are in rapid, rhythmic vibration, 

 but it is seen that the ciliary motion of the individual cells of one 

 row is not irregular and independent of the others ; there exists a 



FIG. 274. Ciliated epithelium. /, Three ciliated cells connected with one another, from the 

 epididymis. (After Schiefferdecker.) II, Beroe ovata, with the four rows of ciliary plates 

 upon one side. ///, Row of cilia of a Beroe seen from the side. At * a plate is fixed by 

 being bent back by means of a small scalpel, so that it cannot contract. As a result of this, 

 the ciliary waves pass from above only to this plate, while the plates below it are at a stand- 

 still. 



metachronism in the ciliary stroke 1 in such a manner that the cilia 

 of all the cells contract in regular succession, beginning with the 

 end-cell of the row. This phenomenon can be observed much 

 better in the rows of ciliary plates in the Ctenophora (Fig. 274, II) 

 than in the microscopic ciliated epithelium of the vertebrates. In 

 the former, where the ciliary plates are to be seen very distinctly 

 with the naked eye, and where the movement goes on often very 

 slowly, it is readily observed that every plate moves only when the 

 preceding one has moved, and then remains at rest until a new 

 wave comes from the first plate. If such a row with the under- 



1 Cf. p. 247. 



