676 BERTHA E. MARTIN 



have almost entirely degenerated. Immediately within the ex- 

 treme outside of the cyst, the appearance is like that of the 

 deeper layers of the stratum corneum. Here the cyst is com- 

 posed of long, flat, concentrically arranged cells containing flat- 

 tened nuclei (fig. 18). Within this is a clear horny layer in which 

 no nuclei are visible and which looks exactly like the horny layer 

 on the extreme outside of the oral epithelium. This layer is 

 very resistant and splits easily, forming concentric layers. The 

 center of the cyst is less resistant and instead of splitting, it 

 usually becomes much wrinkled as if it had shrunken away from 

 the outer layers. The central portion of the cyst has a granular 

 appearance, instead of being clear and homogeneous. This 

 granular portion is evidently derived from the degenerated cen- 

 tral cells which in younger stages were swollen and vesicular. 



Discussion 



These cysts that I have described evidently belong to the 

 general class of dermoid cysts which are found in various parts 

 of the body. These cysts are supposed to arise from epithelial 

 tissues which during development have become included in the 

 mesoderm. In this new environment these inclusions produce 

 structures which are characteristic of the epithelium on the out- 

 side of the body, such as hair in man, bristles in swine, and 

 feathers in birds. The cysts occurring in the gums of D. novem- 

 cinctus conform to the descriptions of the so-called 'epithelial 

 pearls,' which are described as epithelial inclusions which re- 

 main as simple collections of cells or at least go no farther than 

 the transformation of the cells into horny substance. James 

 shows a photograph of an epithelial pearl which might well be 

 a photograph of one of the cysts in the premaxilla of the arma- 

 dillo. The following account of the formation of a horny epi- 

 thelial pearl, taken from James, is an exact description of the 

 formation of the cysts in the armadillo. ''The central cells 

 proliferate, the outer ones become flattened and elongated so 

 that together they form long coiled fibers; later the central cells 

 show marked degeneration and become swollen and indistinct." 

 Figure 18 plainly shows a differentiation between the central 



