30 THE STORY OF GERM LIFE. 



have a single flagellum at one end (Fig. 15 a). 

 Others have one at each end (Fig. 15 b). Others, 

 again, have, at least just before dividing, a bunch 

 at one or both ends (Fig. 15 c and d), while others, 

 again, have many flagella distributed all over the 

 body in dense profusion (Fig. 15 e). These flagella 

 keep up a lashing to and fro in the liquid, and the 

 lashing serves to propel the bacteria through the 

 liquid. 



INTERNAL STRUCTURE. 



It is hardly possible to say much about the 

 structure of the bacteria beyond the description 

 of their external forms. With all the variations 

 in detail mentioned, they are 

 extraordinarily simple, and 

 about all that can be seen is 

 their external shape. Of 

 course, they have some in- 

 ternal structure, but we 

 know very little in regard to 

 it. Some microscopists have 

 described certain appearan- 

 ces which they think indi- 

 cate internal structure. Fig. 

 16 shows some of these ap- 

 pearances. The matter is as 

 yet very obscure, however. 

 The bacteria appear to have 

 FIG. I6 ._ internal stmc- a ,. membranous covering 

 ture of bacteria. which sometimes is of a cel- 



lulose nature. Within it is 



protoplasm which shows various uncertain ap- 

 pearances. Some microscopists have thought 

 they could find a nucleus, and have regarded 

 bacteria as cells with inclosed nucleii (Figs. 10 a 



