144 



J. T. WILSON AND J. P. HILL. 



(3) Description op the Phase of Tooth-Development seen 

 IN the Older Specimen '* Beta." 



In tlie specimen of our older stage (text-fig. 2) there are 

 present in each jaw two very large enamel-organs, each with 

 a number of calcified cusps with whose special arrangement 

 we are not now concerned. These enamel-organs are without 

 doubt those of the two large multicuspidate teeth which are 



Text-Fig. 2, 



found in the adolescent animal. Provisionally, and for the 

 present purpose, we designate the more anterior of these as 

 "x" and the posterior as "y" in the case of the upper teeth, 

 and as '^x" and "y" in the case of the lower (text-lig. 2^). 

 In front of "x" in the upper jaw is a very much smaller 

 conical enamel-organ with one main, prominent, well-calci- 

 fied cusp. This cusp lies above the anterior end of the large 

 tooth "x" in the lower jaw, and we distinguish it by the 

 symbol ^'w." Some distance in front of the lower tooth 

 "x" we find a calcified tooth of very small dimensions which 

 we regard as the true morj)hological opponent of "w" in the 



^ In this schematic Qgure no attempt lias been made to indicate tiie dental 

 lamina. Onlv the actual tootb-germs are shown. Magnification about 8 diam. 



