34 



FOOT-NOTES TO EVOLUTION. 



rudimentary eye ; /, pineal 

 eye. After Spencer. 



Within the brain of man, resting on the optic lobes, is a 



little roundish structure scarcely larger than a pea, 



known as the pineal " gland " or " conari- 



The pineal eye. ^^^„ j^ ^^^ ^^ evident purpose Of 



function, and a philosopher 



once suggested that it might 



be the seat of the soul. It 



is larger in the embryo, and 



still larger in the brains of yig. i.— Pineal body in the liz- 



SOme of the lower vertebrates. ard {Hatteria) developed as 



Recent investigations have 

 shown that it is especially de- 

 veloped in certain lizards, and that in them it ends in a 

 more or less perfect eye, which is placed between the 



others in the centre of 

 the forehead. These 

 lizards have in fact 

 three eyes, and the pi- 

 neal body is the optic 

 nerve of the third. In 

 the common horned 

 toad the pearl - like 

 scale above the pineal 

 eye can be readily rec- 

 ognised. The shrunk- 

 en rudiment found in 

 man is therefore what 

 is left of an ancestral 

 third eye, probably 

 once characteristic of 

 vertebrates, but now 

 displaced and de- 

 stroyed by the increased development and greater per- 

 fection of the outer pair. By the theory of descent the 

 presence of the pineal body in man is a simple result 



Fig. 2. — Pineal eye of the lizard 

 {Hatteria). After Spencer. 



