ORGANIC EVOLUTION 53 



intestine is joined by the small intestine. In some 

 animals this organ is large and performs an 

 important part in the process of digestion. But 

 in man it is a mere rudiment, not only of no 

 possible aid in digestion, but the source of frequent 

 disease, and even of death. 



There are in all, according to Darwin, about 

 eighty vestigial organs in the human body. But 

 these organs occur everywhere throughout the 

 animal kingdom. There is not an order of animals, 

 nor of plants either, without them. They are neces- 

 sary facts growing out of evolution. Organic struc- 

 tures are the result of adjustment to surrounding 

 conditions. The continual changes in environment 

 to which all organisms are exposed necessitate 

 corresponding changes in structure. And the 

 vestiges found in the bodies of all animals repre- 

 sent parts which in the previous existence were 

 useful and necessary to a complete adjustment of 

 the organism, but which, owing to a change of 

 emphasis in surroundings, have become useless, 

 and consequently shrunken. They are the 

 obsolete or obsolescent parts of animal structure 

 parts which have been outgrown and super- 

 seded the ' silent letters ' of morphology. They 

 sustain the same relation to the individual 

 organism as dead or dwindling species sustain to 

 a fauna. They furnish indisputable proof of the 

 kinship and unity of the animal world. 



6. It is only on the supposition that the life of 

 the earth has evolved step by step with the evolu- 

 tion of the land masses, and that the forms of life 



