TOOTH DEVELOPMENT — DASYPUS NOVEMCINCTUS 677 



granular i:)ortion of the cysts and an outer layer which splits into 

 concentrically arranged fibers. 



The connection between epithehal pearls and tooth formation 

 has long been recognized. Bland-Sutton believes that the fre- 

 quently occurring mesopalatine teeth de\'elop from epithelial 

 pearls which have arisen from inclusions of the oral epithelium 

 in the middle line of the hard and soft palate. This same writer 

 regards these epithelial pearls as identical with enamel organs, 

 although they sometimes form horny substance instead of enamel. 

 Bland-Sutton says that in one specimen of ovarian tumor '4t 

 was impossible to trace every stage between a typical epithelial 

 pearl and an enamel organ. In a series of sections some showed 

 the ingrowth from the surface of a loculus, in a few sections 

 pearls were visible composed of large epithelial cells, whilst 

 others exhibited laminae of horny material and in some of the 

 sections a developing tooth with its papilla, enamel organ, and 

 gubernaculum could be seen." The author here calls attention 

 to the fact that the pearls apparently arose as an independent 

 down-growth from the surface epithelium, and not from a chance 

 inclusion of the epithelium as usually described. 



In connection with the disappearing dental lamina, epithelial 

 pearls have been described by Magetal, Rose, and Leche, and 

 also by Turner and Colyer who believe that these remains of the 

 dental lamina give rise to tumors of the jaws when irritated by 

 pressure or by septic products absorbed from a decaying tooth. 

 In an early part of this paper I haxe mentioned the fact that 

 Rose and Leche described 'epithelial pearls' in the anterior 

 portion of the lower jaw of the armadillo. 



A still more intimate relation between epithelial pearls and 

 teeth has been described in the marsupials and the guinea-pig. 

 In Ornithorhynchus, Poulton has mentioned the presence of 

 epithelial nodules in connection with the developing teeth. In 

 this same form, Wilson and Hill describe two epithelial pearls 

 which overlie the cusps of the first molar in each jaw, and three 

 overlying the cusps of the second molar in each jaw. Two of 

 these nodules are described as having a connective tissue pulp, 

 inclosed by a distinct ring of dentine outside of which is a layer 

 of columnar cells representing the inner enamel epithelium, and 



