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



loosely packed cells resembling the former iu character." 

 Tlieir position Avas " at the extreme edge of the stellate 

 reticnkim," and from his figures they all appear to lie inside 

 the enamel-oi'gan as defined by its outer epitlielial layer. 

 '' In some cases/' he notes, "there was the appearance of an 

 epithelial cylinder extending from the nodule towards, or 

 perhaps reaching the stratum intermedium or enamel cells 

 over the apex of the cusp." Further, there was always a 

 nodule above each of the chief cusps, while they were never 

 found elsewhere. 



We have found the same nodular structures to be present 

 in our older specimen "Beta/' which nearly corresponds with 

 the specimens which formed the subject of Poulton's investi- 

 gation, and we are therefore in a position to supplement his 

 account of these interesting structures. 



(1) Relation of the nodules to the enamel- 

 organs. — In the first place, we find that, although the 

 nodules may ajDpear to be included within the large enamel- 

 organs, they are really morphologically outside of them. 

 They have originally lain in contact with the exterior of the 

 enamel-organ and have been gradually enveloped through the 

 relatively enormous expansion of the latter. In many sections 

 the inclusion may seem to be complete, and, indeed, is so, 

 so far as such sections are concerned. But when the series 

 of neighbouring sections is carefully examined, we find that 

 an opening or depression in the surface of the environing 

 enamel-organ is discoverable, through which the engulfed 

 nodule is still in touch with the connective tissue of the tooth- 

 sac. In certain sections, indeed, the nodule appears to lie in 

 a comparatively shallow recess or bay in the surface of the 

 enamel-organ (PI. 11, figs. G and 7). In other cases it is 

 difficult to be quite certain that such a communication with 

 tlic exterior as we have described is demonstrable. But in no 

 case is it indubitably' absent, and its undoubted presence in 

 other cases is presumptive evidence that the condition in all 

 is originally identical. 



We also have observed the appearance of epithelial cylinders 



