396 FISHES CHAP. XIV 
depressions, but, as a rule, when one of them is present the 
other is absent. It is probable that both these structures 
were associated with sensory organs, of which one may have 
NY 
YN NS 
\ 
\ 
ANY 
| 
\ 
| 
| 
fh 
Fia, 228.—Vertical section through the parietal eye and the pineal vesicle of Petro- 
c.t, Connective tissue ; p, pellucida ; p.o, pineal organ ; pt.o, 
mMYZ0n MATINUS. 
(From Wiedersheim, after Stud- 
parietal eye; 7, retina; iii v, third ventricle. 
niéka. ) 
been a parietal eye and the other a pineal eye. Some Teleosts 
(eg. many deep-sea Scopelidae) have a transparent, convex, 
cornea-like prominence on the upper surface of the head which 
may be related to one of these singular organs.’ 
1 Chun, Joc. cit. p. 536. 
