54 PINEAL EYE 
of the lowest vertebrates extant, —fishes and amphibia. If 
there are no suggestions of its visual nature among these 
forms, one would be inclined to believe with O. Hertwig, 
that the epiphysis was originally of a different function | 
and that its connection with a median eye may have been 
altogether of a secondary character. 
The evidence as to the presence, primitively, of a median 
eye in fishes is certainly far from satisfactory :* in all the 
forms of recent fishes, no structure has been found associ- 
ated with the epiphysis which, by the broadest interpreta- 
tion,’ could be looked upon as suggesting a visual function. 
It is possible that fishes and amphibia may, in their extant 
forms, have lost all definite traces of this ancestral organ on 
account of some peculiar condition of their aquatic living. 
On this supposition, evidence of its presence might be 
sought in the pineal structures of the earliest Palaeozoic 
fishes — whose terrestrial kindred, and probable descend- 
ants, may alone have retained the living conditions which 
fostered its functional survival. 
It is accordingly of interest to find that in a number 
of fossil fishes the pineal region retains an outward median 
opening, whose shape and position suggest that it may have 
enclosed an optic capsule. If the median eye existed in 
these forms, it may well have been passed along in the line 
of descent through the early amphibia (where substantial 
traces of a parietal foramen occur, e.g. as in Cricotus) to 
the ancestral reptiles. This view is greatly strengthened, 
as Beard has shown, by the presence in the lamprey of a 
pineal end organ (optic ?). 
The evidence, however, that the median opening in the 
head shields of ancient fishes actually enclosed a pineal 
* Hertwig (Mark), Handbook of Embryology of Vertebrates, and Cattie, v. 
Ref. p. 250. 
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