DISOSE AND ITS EFFECTS. 43 
to include this parietal foramen, we find it occupied 
by an organ representing an eye in miniature, con- 
nected with the pineal body by nerve-fibres. The 
relation of the parts is indicated in fig. 21, represent- 
ing a lateral view of the brain and adjoining parts 
@f the skull in the New Zealand lizard, Hatteria 
(Sphenodon). 
When the eye is examined microscopically, it pre- 
sents the structural details found in functional eyes, 
such as cornea, lens, retina, pigment, &c. (fig. 22). 
Fic. 21.—Lateral view of the brain of Sphenodon, showing 
the relation of the pineal eye, P; the cerebrum, C; and the 
medulla, M. (After Baldwin Spencer.) 
Spencer is of opinion that this suppressed eye repre- 
sents the unpaired eye of larval Tunicata. There is 
good evidence that it was highly developed in extinct 
amphibia (Ladyrinthodonta), and was probably a sense- 
organ in animals of pre-tertiary periods. 
It is not unreasonable to suppose that the gradual 
development and greater utility of the lateral eyes 
have led to the suppression of the median eye. 
Although the pineal body (regarded by Descartes as 
the seat of the soul) in man is clearly vestigial, it is 
