UN THt: TEETH OP PETROMYZOiN AND MYXINE. G31 



On the Teeth of Petromyzon and Myxine. 



By 



Ernest AVarreii, D.Sc, 



Assistant Professor of Zoology, University College, London, 



With Plate 34. 



Those observers who regard tlie Cyclostomata as a degene- 

 rate offshoot from a gnathostonie ancestor would naturally 

 desire to look upon the horny teeth as degenerate structures, 

 and they would endeavour to find in them remains of parts 

 homologous to those of an ordinary vertebrate tooth. 



In 1889 Dr. Beard ^ published an investigation on the 

 teeth of the Marsipobranchii. The teeth of Bdellostoma, 

 Myxine, and several species of Petromyzon were examined, 

 and the results arrived at seemed conclusive as to the 

 degenerate nature of the teeth. In the young tooth of the 

 Hag-fishes a more or less complete enamel epithelium, with 

 perhaps a trace of enamel, was identified ; also semi-calcified 

 odontoblasts were described, forming a conical mass beneath 

 the enamel epithelium. More recent observers, however, 

 have thrown doubts on these interpretations. In 1894 Prof. 

 Howes ~ expressed his opinion that the " odontoblasts " 

 exhibited no calcification, and in the same year Ayers ^ stated 

 that he was unable to find a trace of enamel or dentine. 



^ " The Nature of the Teeth of the Marsipobranch Fishes," ' Zoologische 

 Jahrbiicher,' iii, IS 89. A bibliography is there given. 



- 'Nature,' Nov., 1894, Review of the Wood's HoU Lectures. 

 ' Biological Lectures at Wood's Holl, 1894. 



