320 The Outline of Science 



top of the head. We find this third or pineal eye in the heads of 

 a few reptiles to-day, but the skin has grown over it, and it is 

 degenerating. In the birds and mammals it has sunk still deeper 

 into the head, and degenerated further. In man it has become a 

 small body, about the size of a hazel-nut, rising from the middle 

 of the brain. We call it the "pineal body." It is a mysterious 

 little organ, and we will not say positively that it has no function. 

 But, whether it has or no, we clearly trace it to the third eye of 

 millions of years ago. 



The "vermiform appendix" is a well-known vestigial organ. 

 It is a little worm-like tube, about four inches long, arising as a 

 blind alley at the junction of the small and the large intestine; 

 and as a source of disease (appendicitis) and danger it is 

 notorious. Some have tried to find that it has a use in the body, 

 but the plain fact is that it has been removed from hundreds of 

 thousands of men in modern times, and no harm has ensued in 

 any single case. It is the vanishing remainder of a large, useful 

 chamber in which early vegetarian mammals let myriads of bac- 

 teria break up their coarse food. 



In short, expert investigators of the human body have found 

 107 organs, or parts of organs, that have to be understood as more 

 or less vestigial. We have the vestige of a tail in the block of 

 bone at the lower end of our backbone; and sometimes children 

 are born with distinct and movable though very short tails. 

 We have bones, muscles, and glands in many parts that are now 

 the almost or quite useless relics of a remote past. Evolution 

 beautifully explains them. The body remains a wonderful 

 mechanism because these were once useful and most cunningly 

 contrived structures. 



2 

 The Ivory Gates of the Body 



Turning now to the body-machine in its active life, we shall 

 find it most interesting to follow the progress of food until it is 



