THE CHARACTEBISTICS OF LIVING THINGS 17 



frogs. We shall later study the development of some animals 

 from eggs, but for our present lesson it is sufficient to note 

 that books on embryology (the science of development) state 

 that all higher animals develop from eggs, which are small 

 masses of living matter separated from the parent animals. 

 No lifeless object has any such power of separating from it- 

 self a small body which is able to take food and grow into 

 a body like the original one. The power of reproduction 

 is, then, a striking characteristic of living animals. 



22. The frog after a time loses the power of moving, 

 breathing, etc. ; that is, it dies. We are familiar with the 

 fact that animals of a given kind or species live for a certain 

 length of time and then grow old and die. For example, 

 an elephant has been said to live 200 years, a horse 40, 

 lion 35, cat 40, toad 40, sea-anemone 50, crayfish 20, vulture 

 118, eagle 100, pike and carp 200, squirrel and mouse 6, 

 pig 20, sheep 15, fox 14, and hare 10 years. However, it 

 is certain that most individuals of these species live a much 

 shorter life ; for example, few horses live over 20 years. The 

 life of all individual animals, even though they escape 

 accidents and disease, is of limited duration. They are 

 like machines, able to run a certain period of time. Ulti- 

 mately the machinery of life stops and the animal bodies 

 rapidly decompose into substances which show no signs of 

 ever having been living. 



23. Summarizing, we have seen that a living animal has 

 the following activities : it moves ; it breathes ; it takes 

 food for assimilation; it reproduces. It has still other 

 peculiar powers which will be considered later. None of 

 these is found in lifeless objects, such as stones or dead 

 animals. All such processes moving, eating, breathing, 

 reproducing which are peculiar to living animals, are 

 known as life-activities. These are not permanent in any 

 individual animal, for after a certain length of life the in- 

 dividual animal loses its life-activities we commonly say 



