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



(4) Synthetic Comparison of the Conditions met with in 

 THE Stage op Tooth-development last described, (a) 

 with the Adolescent Condition, and (6) with the 

 Earlier "Fcetal" Stage. 



(a) With the adolescent condition. 



When we compare the condition above described with that 

 of the adolescent animal as described by Oldfield Thomas and 

 Stewart, it is evident that in the upper jaw three of the tooth- 

 representatives which we have referred to undergo eruption, 

 viz. our " \v," " X," and " y." In the lower jaw also three 

 teeth cat the gnm, but these are our " x," " y," and " z." 



(h) With the earlier foetal stage (i.e. our specimen 



"Delta"). 



When we now institute a comparison of the condition we 

 have described as occurring in our older stage with that met 

 with in the younger of our two specimens, the conclusions 

 which we are disposed to draw are not those which at first 

 suggest themselves, and which for a time we actually enter- 

 tained. 



It has been shown that in the younger specimen " Delta ^' 

 there are two well-developed enamel-organs present in each 

 jaw, but these are of widely different dimensions, the posterior 

 being much more elongated than the anterior. 



Moreover, the shape of the anterior is different from that 

 of the posterior, its papilla, as seen in coronal section, being 

 more slender and pointed. 



In the later foetal stage " Beta," on the other hand, the 

 more anterior (" x " and "x") of the two large enamel- 

 organs in each jaw are considerably more elongated than the 

 posterior ("y'^ and"y"). For this and other reasons we 



