THB EVOLUTION OP MAN 91 



shrunken relic of a third eyelid possessed by our fish or 

 reptile ancestor long ago. Observe the eagle or the 

 turtle closely in the zoological garden. You notice that 

 it occasionally flashes a third eyelid, or membrane, 

 across the ball from the inner corner. This feature of 

 the fish, bird, and reptile, has survived in the useless 

 fleshy particle at the inner corner of the eyes of the 

 mammals. Our fish or reptile ancestor had not only a 

 third eyelid, but a third eye, in the top of its head. In 

 nature to-day we find only a creature (Pyrosome) just 

 below the vertebrate level with such an eye actually 

 functioning. But through the reptile world we find this 

 third eye more or less depraved; the skin has closed 

 over it, but the hole or orbit remains in the top of the 

 skull. Higher still in the animal scale the skull also 

 closes over it, and then the brain. It survives in our 

 brain to-day In the "pineal body" a useless cone- 

 shaped structure in the centre of the brain. 



Metchnikoff enumerates more than a hundred struc- 

 tures in the human body that he calls "vestigial." Some 

 of them such as the thyroid and thymus glands and 

 some uterine structures seem to have taken on new 

 functions, but there are many muscles and blood-vessels 

 that have ceased to have a place or a useful place in 

 the work of the body. Patches of muscle in various 

 parts of the body like that with which we " knit our 

 brows" are traces of the large and comprehensive 

 muscle with which some remote ancestor twitched his 

 skin to keep the flies off, as the horse does. The 

 stumpy end of the back bone similar to that of the 

 anthropoid ape is the last trace of a long-tailed 

 ancestor. The human embryo has a long tail for a 

 considerable period of its development, and cases occur 

 in which children are born with real tails, which they 

 wag in anger or pleasure, and which occasionally persist 



