THE STORY OF THE BACTERIA. 5 



in the form of longer or shorter arms, and 

 then withdrawing them and sending out 

 others in another place, apparently in the 

 most aimless way ; or you may see it rolling 

 itself over and over, or, if I may so say, flow- 

 ing along so that it travels with considerable 

 speed. Perhaps some microscopic vegetable 

 may lie in its way, and it will flow over and 

 enclose this, and, after digesting portions of it, 

 expel the residue from whichever side or sur- 

 face of its body may be most convenient. If, 

 in a quiescent condition, it be touched by an 

 external object, you may see it move in direct 

 response to the irritation. If you are fortu- 

 nate in your observation, you may see a con- 

 striction appear around some part of the lump, 

 which grows gradually deeper until a portion 

 of the mass separates from the rest and crawls 

 off on its own hook as a new and independent 

 amoeba. It has no lungs and yet it breathes ; 

 no mouth, still eats ; no definite shape, yet 

 grows ; no nerves, yet is sensitive ; no sex, 

 yet may give birth to endless progeny. 



Now this amoeba is one of the lowest and 

 simplest of creatures, and is the type of a 



