PINEAL EYE 



55 



eye, is now felt by the present writer to be more than ques- 

 tionable. The remarkable pineal funnel of the Devonian 

 Dinichthys (Fig. 134) is evidently to be compared with 

 the median foramen of Ctenodus and Palcedaphus ( = Sire- 

 noids, p. 122) ; but this can no longer be looked upon as 

 having possessed an optic function, and thus practically 

 renders worthless all the evidence of a median eye pre- 

 sented by fossil fishes. It certainly appeared that in the 

 characters of the pineal foramen of Dinichthys there ex- 

 isted strong grounds for believing that a median visual 

 organ was present : its opening was in the pineal plate, 

 midway between the orbits (PN, Fig. 134). At the surface 

 it was of minute size (X, Fig. 136), but below (Fig. 137) 

 it flared out into a funnel-like form, shown in longitudinal 

 section in Fig. 137 A. The peculiar character of this 

 opening seemed to render it especially fitted for a visual 

 function ; the minute external opening forms an image 

 near the plane of the visceral opening of the funnel, with- 

 out the specialization of a lens, an image so perfect that 

 it might readily be photographed. It is evident, accord- 

 ingly, that if an optic capsule were enclosed by this fora- 

 men, it would have enabled its possessor to have looked 

 directly upward and backward ; and, without the need of 

 developing lens-like and focussing structures, it could have 

 readily received the images of all outer objects near or 

 remote. 



But the function of this pineal foramen, unfortunately 

 for speculation, could not have been optical. It occurs in 

 a fish (Titanichthys) closely related to Dinichthys, and, 

 as the writer * has recently found, is of a distinctly paired 



* He is obliged by accumulating evidence to abandon his former view that 

 the pineal foramen of Dinichthys contained a specialized optic capsule (TV. Y. 

 Rep. of Fisheries, 1891, pp. 310-314). 



