THE NERVOUS SYSTEM 133 
optici. The pineal gland of Anthropoids is identical in appear- 
ance with that of Man. 
The pineal gland in Man is remarkable for its rich vascularity 
and for its cellular follicles, in which concretions (brain sand) may 
develop. 
This “gland” has all along claimed the special attention of 
morphologists; and as great difficulty has been found in under- 
Fic. 85.— LONGITUDINAL SECTION THROUGH THE PINEAL ORGAN OF A REPTILE 
(Hatteria punctata). (Slightly magnified.) (After Baldwin Spencer. ) 
cp., connective tissue capsule ; »”., “lens”; cv., cavity of the organ filled with fluid; 7’., 
retina-like portion of the vesicle ; vs., blood-vessels ; c.n., cells in the nerve stalk (s.7.). 
standing it, it has received very different explanations. It is 
only in recent years that light has been thrown upon it by 
numerous works devoted to its comparative anatomy and 
ontogeny. It has been proved that, in close connection with the 
actual stalk of the gland, there is a second vesicular outgrowth, 
which, in certain Vertebrates, shows undeniable traces of being 
a rudimentary unpaired organ of sight. [This organ is now 
known to arise during development in all classes of Vertebrates], 
