124 BULLETIN OF THE 
tubules (p. 138). I have found by diligent searching a few cases in 
which, as stated by the latter author, cells seemed to’ be present in the 
lumen of the tubes. I have, however, observed other cases in which a 
flattened cell lay just at the side of the tube, but separated from its 
lumen by a thin layer of secreted material. [ am therefore led by this 
and by the infrequency of the cases to believe that the cells apparently 
occupying the tube have a similar position, but that since they lie in 
radii of the tube perpendicular to the plane of the section they have the 
appearance of being in the lumen of the tube. Figure 8 will make this 
clear. At the opening of the tube is seen a cell which is apparently 
about to be enclosed between the secretion of the large odontoblast cell 
and the present wall of the canal. At a little later stage this, if seen in 
a plane at right angles to the present, would appear to lie in the lumen. 
Each of these tubes is lined by a very thin secretion from the cell 
which extends into it, —a secretion of the same character as the material 
of the scale. In later stages, after the ganoin layer has begun to be 
formed, this sheath persists even after decalcification, when the ganoin is 
entirely destroyed (Plate IV. Fig. 23). 
The scale increases both in thickness and in lateral extent by the 
deposition of new layers of material secreted by the surrounding sclero- 
blasts. Thus the edges of adjacent scales come together, and finally 
overlap one another. Owing to the slight elevation of the posterior 
margin of the scale, previously mentioned, this edge of each scale over- 
laps the anterior edges of the adjacent posterior scales; for the same 
reason, each scale is in turn overlapped on its anterior edge by the poste- 
rior edges of the scales in front of it (Plate IV. Fig. 31). 
Increase in thickness takes place upon both the outer and the inner 
surfaces, though much more rapidly upon the inner one. As the scale 
thickens inwardly, fibres which lay irregularly disposed beneath it in 
the spongy dermis are enclosed by the secretion. As the calcification 
extends deeper, the felted regularly arranged bundles of connective-tissue 
fibres of the deeper dermis are also enclosed, and help to make up the 
deeper part of the scale. These fibres extend across from one scale to 
another and so form a strong but flexible connection between adjacent 
scales. They are the “Schuppenligamente ” of Hertwig. The ratio of 
outward to inward growth is shown by the arrangement of the layers of 
the scale (Plate II. Figs. 15, 16, and Plate III. Fig. 21). The oldest 
part of the scale is that in which the dentinal tubules from the opposite 
surfaces meet and break up into minute branches (Plate HI. Fig. 21). 
In their immature state, and before the outer layer has begun to be 
