230 FREDERICK TILNEY AND LUTHER F. WARREN 



new interpretation concerning the function of the pineal organ. 

 It is not our purpose to discuss this hypothesis, but we do desire 

 to emphasize the improbability of the pineal body in higher 

 vertebrates being the vestige of any neural mechanism. This 

 opinion is based on the general absence of definitely neural 

 elements in the pineal gland other than those connected with the 

 sympathetic system. 



Terry 392 in Opsanus could find no evidence to support Dean's 

 supposition that the epiphysis of true fishes is connected with 

 the innervation of the sensory canals of the head. He was, 

 moreover, unable to discover the evidence in the teleost to sup- 

 port the theory that the pineal body is an ocular organ either 

 degenerate or rudimentary. 



The portion of the epiphyseal complex which becomes special- 

 ized as the eye-like structure of the lower vertebrates constitutes 

 the end-vesicle. This end-sac may be part of the pineal or of 

 the parapineal organ, depending upon the form in which it 

 occurs. In every instance the appearance of visual element j is 

 limited to the end-vesicle. Not only is the structure notable 

 for the eye-like character of its histological elements, but it 

 occupies a position with reference to the brain and also to the 

 skull which further serves to distinguish it. Its connection with 

 the 'roof of the interbrain is by means of an attenuated stalk, 

 which gives the entire structure the appearance of a long append- 

 age of the brain. The junction of the stalk with the roof is 

 usually not a direct one since the connection in most forms is 

 accomplished through the proximal portion. These several 

 parts, which may be recognized in the pineal and parapineal 

 organs of certain classes, should be regarded as separate mor- 

 phologic entities. The proximal portion has little in common 

 with the end-vesicle. Its position and histological characters 

 mark it as strikingly different. Its only actual relation with 

 the vesicle is one of continuity through the stalk. This con- 

 tinuity may, in some cases, be almost lost or maintained only 

 by a small filament of nerve fibers. Such, for example, is the 

 condition in amphibia, a class which, perhaps, affords the most 

 conspicuous instance of the morphologic distinction between the 



