12 THE INVISIBLE WORLD 



they are quickly shot forth from the body. When 

 no longer needed, they are as quickly withdrawn, 

 and disappear within the body. 



A few species, however, seem to have permanent 

 means of moving about in the shape of cilia, or 

 minute hairs, something at least like hairs. 

 Sometimes a single hair at one end, Fig. 14. 

 Sometimes a hair at each end, Fig. 15. Sometimes 

 a tuft of hair at one end, Fig. 16. Then a tuft of 

 hair at both ends, Fig. 17. In still other cases the 

 tuft reaches entirely around the body, Fig. 18. 



All these contrivances, like legs to the spider, 

 tail to the tadpole, fins to the fish, or wings to the 

 bird, enable the microbe to perform with ease all 

 its needed movements. 



