THE PINEAL BODY 229 



elusion. Furthermore, in no instance is there the slightest 

 indication that the pineal body in the higher vertebrates con- 

 tains histological elements which may, in any sense, be regarded 

 as degenerated products of the visual structures in the parietal 

 eye. That the pineal body in birds and mammals may be inter- 

 preted as the result of a degenerative process affecting the 

 parietal eye seems wholly untenable in the absence of any con- 

 vincing signs of such degeneration and also because the weight 

 of evidence furnished by many facts indicates the glandular 

 nature of the organ. 



It is interesting in this connection to give the opinion of 

 Bashford Dean, 83 in which that author expresses doubt concern- 

 ing the connection between the epiphysis and the median eye of/ 

 vertebrates. 



The evidence as to the presence primitively of a median eye in fishes 

 is certainly far from satisfactory. It is possible that fishes and am- 

 phibia may in their extant forms have lost all definite traces of this 

 ancestral (visual) organ on account of some peculiar conditions 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 descendants may alone have retained 

 the living conditions which fostered its functional survival. It is of 

 interest, accordingly, 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 contained 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. Cricotus) to the ancestral reptiles.' 



The evidence that the median opening in the head-shields of ancient 

 fishes actually enclosed a pineal eye is now felt by the present writer 

 to be more than questionable. The remarkable pineal funnel of the 

 Devonian Dinichthys is evidently to be compared with the median 

 foramen of Ctenodus and Palaedophus, 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 presented by fossil fishes. 



It must, for the present, be concluded accordingly that the pineal 

 structures of true fishes do not tend to confirm the theory that the 

 epiphysis of the ancestral vertebrates was connected with a median 

 unpaired eye. More probably it was connected with the innervation 

 of the sensory canals of the head. 



The theory that the epiphysis in the true fishes is connected 

 with the innervation of the sensory canals of the head adds a 



