THE LIFE CYCLE 



79 



death. The new Amoebae are from their beginning like the 

 full-grown Amoeba, except as regards size. And the old 

 Amoeba does not die, because its whole body continues to 

 live, although in two parts the two new Amoebae. The life 

 cycle of the simplest animals includes birth (usually by 

 simple fission of the body of the parent), growth, and some, 

 but usually very little, development, and finally the repro- 

 duction of new individuals, not by the formation of eggs, 

 but by direct division of the body. 



48. The egg. In our study of the multiplication of ani- 

 mals (Chapter III) we learned that it is the almost univer- 



FIG. 38. Eggs of different animals showing variety in external appearance, a, egg 

 of bird ; b, eggs of toad ; c, egg of fish ; d, egg of butterfly ; e, eggs of katydid 

 on leaf ; /,egg-case of skate. 



sal rule among many-celled animals that each individual 

 begins life as a single cell, which has been produced by the 



