THE AMCEBA. 17 



that is piled too high, or like a train of gunpowder that 

 is ready to be discharged. As a light touch will upset 

 the bricks and cause them to fall with great force, or as a 

 spark will ignite the gunpowder and cause a violent explo- 

 sion, so, in a small way, a slight stimulus to the amoeba 

 will cause some of these complex molecules in the proto- 

 plasm to break up into simpler ones with the liberation of 

 the forces manifested in the animal's activities. 



The simple compounds (carbonic-acid gas, water, etc.) 

 formed in this destructive process are of no use to the 

 amoeba, and must be removed. The name of the process is 

 excretion. These waste products pass out directly through 

 the body Avail into the surrounding water. It should be 

 noted that there is an important difference between this 

 true process of excretion and the mere egesting of an indi- 

 gestible bit of carmine : the latter does not become a part 

 of the animal's structure at all. Many such particles are 

 ingested in the course of feeding. It shows little choice in 

 the selection of food, ingulfing any object of convenient 

 size with which it may come in contact. 



II. Reproduction. The common method of reproduc- 

 tion in amoeba is simple division. First the nucleus divides 

 into two. Then the body elongates, and the nuclei move 

 apart toward the ends. A furrow then appears across the 

 body, between the nuclei. This furrow deepens until it 

 entirely separates the body into two pieces, each of which 

 is at once an independent, perfect amoeba. 



The converse of this process has been observed. Two 

 amoebas have been seen to fuse together into one. It is 

 believed that this process (conjugation) is necessary for 

 the continued existence of amoebas. It has been proved to 

 be necessary in the case of some other microscopic animals 

 which reproduce ordinarily by dividing. 



III. Voluntary Motion. Protoplasm is contractile, i.e., 

 capable of extending in one direction by shortening in 



NEED. ZOOL. 2 



