DOMESTICATED ANIMALS 49 



not appear at all. There is a remnant of a "third 

 eye-lid" in many animals at the inner corner of 

 the eye. Man has this remnant, in common with 

 many other animals. In birds, turtles, and other 

 animals this third lid of the eye is in full use. It 

 is the thin membrance that is pulled over the eye, 

 often when the two ordinary eye-lids are open. In 

 man and the man-like apes, the tail is vestigial, 

 consisting of only three or four vertebrae much 

 grown together. Before birth in all of these ani- 

 mals the tail is long and has muscles for wagging 

 it. The bird's tail is also a mere remnant of what 

 it once was. The oldest birds found fossil in the 

 rocks had long tails composed of twenty verte- 

 brae. 



Vestigial structures are found everywhere. 

 They are by-products of all organic evolution. 

 There are vestigial instincts in the minds of men 

 and other animals, and vestigial parts in all hu- 

 man laws, customs, and institutions. Our politi- 

 cal, industrial, religious, educational, and legal in- 

 stitutions are full of vestigial features. This is a 

 big subject. And if you will only get the key I am 

 trying to give to you, you will be able to under- 

 stand many things that are now mysteries to you. 



3. Vestigial Instincts. 



Useless instincts survive in the minds of men 

 and other animals for the same reason exactly as 

 useless organs survive in their bodies. Living be- 

 ings are, as a rule, fitted to their surroundings, 



