The Logic of Evohition 



structure capable of forming all the organs and 

 doing the various kinds of work required in our 

 body. Cells began to unite in groups, and some 

 of these groups took the form of a double-walled 

 sack, our zoophytic ancestor. This little animal 

 had two organs, one for digestion and the other 

 for reproduction. These are the two essential 

 functions, which insure the growth and survival 

 of the individual and the species. Power of 

 locomotion was small. But a little muscle was 

 necessary to gain food and to keep the body in 

 shape. As this was used and exercised it in- 

 creased in amount. 



Then some zoophyte changed Its mode of 

 locomotion. Instead of depending upon its mi- 

 croscopic oars (cilia) it used its muscles. It 

 was a slight change, but It revolutionized animal 

 structure. To move even a little less slowly and 

 to seek Its food over a wider area was a great 

 advantage. From this time on the animal which 

 developed muscle survived, and gradually re- 

 placed the form which developed digestion only. 

 Muscle stimulated the development of respira- 

 tory, circulatory, and excretory organs. These 

 were grouped to form the trunk of the body of 

 higher animals. The exercise stimulated the de- 



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