54 ANIMAL LIFE 



of simple fission or splitting binary fission it is often called, 

 because the division is always in two by which the body 

 of the parent becomes divided into two equal parts into 

 halves is the simplest method of multiplication. This is 

 the usual method of Amoeba (Fig. 26) and of many other of 

 the simplest animals. In this kind of reproduction it is 

 hardly exact to speak of parent and children. The chil- 

 dren, the new Amoeba, are simply the parent cut into 

 halves. The parent persists ; it does not produce off- 

 spring and die. Its whole body continues to live. The 

 new Amcebce take in and assimilate food and add new mat- 

 ter to the original matter of the parent body ; then each 

 of them divides in two. The grandparent's body is now 

 divided into four parts, one fourth of it forming one half 

 of each of the bodies of the four grandchildren. The pro- 

 cess of assimilation, growth, and subsequent division takes 

 place again, and again, and again. Each time there is given 

 to the new Amoeba an ever-lessening part of the actual 

 body substance of the original ancestor. Thus an Amoeba 

 never dies a natural death, or, as has been said, "no Amoeba 

 ever lost an ancestor by death." It may be killed outright, 

 but in that case it leaves no descendants. If it is not killed 

 before it produces new Amcebce it never dies, although it 

 ceases to exist as a single individual. The Amoeba and 

 other simple animals which multiply by direct binary 

 fission may be said to be immortal, and the " immortality 

 of the Protozoa " is a phrase which you will be sure to meet 

 if you begin to read the writings of the modern philosoph- 

 ical zoologists. 



31. Slightly complex methods of multiplication. Most of 

 the Protozoa multiply or reproduce themselves in two 

 ways by simple fission and by conjugation. Paramce- 

 cium, for example, reproduces itself for many generations 

 by fission, but a generation finally appears in which a dif- 

 ferent method of reproduction is followed. Two individu- 

 als come together and each exchanges with the other a part 



