166 H. SPENCER HAERISON. 



an enamel organ^ in which the deepest layer of cells is 

 beginning to assume the character of an enamel epithelium, 

 pai't of the cells belonging to the epithelium of the jaw at 

 this point, while the others belong to the labial side of the 

 dental lamina. There is as usual a great accumulation of 

 mesodermal cells below the epidermal cap, and also in the 

 region towards which the dental lamina is growing. This 

 enamel organ belongs to the first series, and its position is 

 obviously labial to the dental lamina; with the exception 

 of the palatine teeth of this series the dental lamina always 

 occupies this relative position. As Rose (12) says of the 

 Crocodile, "liegen die verkalkten Ziihnchen der ersteu Serie 

 nach aussen von der Zahnleiste." Leche also (14) says of 

 the embryonic teeth of Iguana tuberculata, '^ Es ist 

 besonders hervorzuheben dass die fraglichen Zahne nur im 

 Bereiche der Schmeltzleiste entstehen." In this specimen 

 o£ Hatterial found a pair of calcified teeth of the first series 

 in both upper and lower jaw ; in each case these were the 

 second in order, the anterior pair above and below being 

 represented by enamel organs. Of the latter, I found on 

 each side eight above and seven below, a number which 

 corresponds fairly well with the number of calcified teeth 

 occurring at a later stage. This is considerably more than 

 have been found in Iguana or Crocodilus. 



The presence of an enamel organ usually produces an 

 epidermal papilla, which is probably what Rose (13) found 

 in the Crocodile and described as follows: — "Die ersten 

 Zahnanlagen der Krokodile zeigen sich ganz ahnlich wie 

 die Placoid-schuppen und ersten Zahne der Selachier in 

 Form von frei liber die Kieferschleimhaut hervorstehenden 

 Papillen." He says also, "Die ersten Zahnchen entstehen 

 ganz ahnlich wie bei Selachiern durch Verkalkung von frei 

 liber die Schleimhautoberflache hervorragenden Schleim- 

 hautpapillen." Although I should scarcely describe the pro- 

 cess of formation of the first teeth in Hatteria in these 

 terms, I am inclined to think there is no fundamental point 

 of difference between this and Crocodilus. Rose in the same 



