ORGANIZATION 139 



to the highest degree involves the development of an organism 

 made up of nine systems of organs: 



1. THE INTEGUMENTARY SYSTEM. 



2. THE SENSORY-NERVOUS SYSTEM. 



3. THE MUSCULAR SYSTEM. 



4. THE SKELETAL SYSTEM. 



5. THE DIGESTIVE SYSTEM. 



6. THE CIRCULATORY SYSTEM. 



7. THE RESPIRATORY SYSTEM. 



8. THE EXCRETORY SYSTEM. 



9. THE REPRODUCTIVE SYSTEM. 



332. "Higher" and "Lower" Animals. The functions per- 

 formed by these nine systems of organs are all performed by 

 the undifferentiated protoplasm of the amoeba and must like- 

 wise be provided for by every other animal. The higher forms 

 are, therefore, not distinguished by the development of new 

 functions, but by the effectiveness with which these functions 

 are performed. Under favorable conditions the functions 

 of the amoeba are equal to the demands made upon them, but 

 with a serious change in these conditions they fail and the amoeba 

 comes to naught. Against drouth, heat, cold, the lack of food 

 in the immediate vicinity and the attacks of larger animals 

 the amoeba has no defense. On the other hand, a higher animal, 

 say, e. g., a wolf, is effectually protected against dessication by 

 his skin. Ordinary climatic changes of temperature are auto- 

 matically compensated for and the body maintains an equable 

 internal temperature. When food fails he travels far in search 

 of more, and when attacked he knows how to defend himself. 

 Indeed, he is a living demonstration of his superiority, for his 

 life is maintained by the destruction of other living things 

 which are not able to defend themselves against him. He 

 demonstrates his superiority, and we habitually distinguish 

 such capable forms from the less capable by the terms higher 

 and lower. But there is still another way in which the wolf 



