The Body-Machine and Its Work 319 



warm fur-coat which mammals developed to meet the conditions of 

 an Ice Age. It is vestigial, not rudimentary, as is sometimes said. 



The pieces of gristle or cartilage on the sides of the head 

 which we call our "ears" are similar organs. They do not catch 

 waves of sound, as many suppose, and guide them into the real 

 ear inside the skull. They are too flat to do so. But if we com- 

 pare them with the useful, pointed, movable ear of a horse, we see 

 what they mean. They were once similar organs, but they have 

 fallen out of use arid are dwindling away. Underneath the skin 

 we still have seven muscles attached to the shell of cartilage, from 

 which it is obvious that the ear could once be moved in every direc- 

 tion to catch the waves of sound. Now only an individual here 

 and there can use one or two of these muscles. The pinna or "ear- 

 trumpet" is a surviving structure that tells us a little about the 

 body's remote past. 



There are very many similar muscles in the body to-day 

 which merely tell us about a strange past. Some men can twitch 

 their nostrils. Some can move their scalps. They do so by means 

 of muscles which in most of us have gone completely out of use. 

 Underneath the skin in very many parts of the body there are 

 dwindling muscles of this kind. 



In the inner corner of each eye we have a little pulpy mass 

 which recalls to us even remoter ages of the body's past. It is of 

 no use whatever in the body to-day. To understand it, one has to 

 watch a parrot or an eagle in a cage, and notice how the bird 

 flashes a white film (the "third eyelid") occasionally over its eye- 

 ball. Our superfluous bit of tissue is the shrunken remainder of 

 this. We have in our eyelids a better apparatus for sweeping the 

 dust off the eyeball, and the old membrane is disappearing. Man 

 is not, of course, descended from birds, but almost all mammals 

 have a well-developed third eyelid. 



We know from fossil remains and from examining the bodies 

 of living reptiles that in remote ages somewhere about the era 

 of the Coal Forests there were animals with a third eye, in the 



