CHAPTER II. 



1. THE CILIA OF BACTERIA. 



1. General Nature. The cilia, or flagellae as they are sometimes 

 called, are whip-like filaments of protoplasm projecting from the 

 sides of the cell, which, by their activity, cause the bacteria to move 

 through the liquid in which they are placed. They are not visible 



FIG. 28. Microspira, monotrich dilation. 



when observed under the microscope unless they have been stained 

 in a particular way ; their form is almost always that shown in 

 Fig. 7b, viz. wavy filaments, the number of waves depending on the 

 length of the cilium and the nature of the species. Sometimes long 

 cilia, looking like bent willow branches, are to be seen, but it is 

 probable that these are not normal struc- 

 tures. Cilia are not all inserted alike; the 

 following kinds may be distinguished : 



(1) MONOTRICH. One polar cilium 



(Fig. 28). 



(2) PERITRICH. Cilia all round the 



cell (Fig. 29). 



(3) LOPHOTRICH. Groups of polar 



cilia (Fig. 30). 



Among bacteria the number of constant 

 FIG. 29. Bacillus showing cilia characteristics is very small, but among this 



(peritrich ciliation). 



number the mode of insertion of the cilia is to 



be placed. If an organism has polar ciliation, under all circumstances 

 the ciliation remains polar. This is particularly useful for purposes of 



