204 FREDERICK TILNEY AND LUTHER F. WARREN 



The most significant feature with reference to the functional 

 activity of the pineal body appears to be the fact of its marked 

 phyletic constancy. Certainly, a structure which is marked for 

 regression or in which it is claimed that the evidences of regres- 

 sion may easily be found, would scarcely show such remarkable 

 tenacity throughout the phylum. Its occurrence in cyclostomes, 

 in all the fish, in amphibians and reptiles, in birds and mammals 

 reveals it as a structure which must have been called into being 

 in response to some definite demand, for why, otherwise, should 

 all of these classes of vertebrates so constantly present this 

 morphologic condition? 



It is, perhaps, laying overmuch stress upon the phyletic 

 constancy of the epiphyseal complex to draw from these facts 

 alone the inference that it must be a physiologically active 

 organ. Its reported absence in the Myxinoids, in Torpedo 

 ocellata, and Torpedo marmorata as well as in Crocodilia would 

 seem to call into question the full value attached to the argu- 

 ment of its otherwise general constancy. On the other hand, it 

 must not be overlooked that in the history of the observations 

 devoted to the pineal body, a relatively large number of investi- 

 gators have reported the absence of the epiphysis in one form 

 or another, only to have their error corrected by subsequent 

 research and the presence of the organ clearly demonstrated. 

 By far the greater majority of observers in the morphology of 

 this portion of the brain are to-day of the opinion that the 

 epiphyseal complex as a whole or in some of its parts exists in 

 all vertebrates. It is certainly pertinent to the reported absence 

 of the organ in the forms mentioned to recall Kidd's 203 observa- 

 tion that the conditions in Torpedo need further review before 

 final acceptance of the statement that the epiphysis is absent in 

 these forms. The same also applies to Crocodilia, and until 

 this order has been more extensively examined, much reserva- 

 tion should be made in concluding that the pineal body is absent 

 in these reptiles. Again, Kidd's 203 contention with reference to 

 the Myxinoids adds another view which would render less serious 

 the reported absence of the epiphysis in the forms mentioned. 

 According to Kidd, it is not surprising that in Myxinoids the 



