SCALES AND DERMAL TEETH OF SOME GANOID AND PLACOID FISH. 443 
times, after thus giving off a group of branches, the main trunks pass on to supply 
the next lamina which lies on the inner side. 
This distribution of tubes on the extremity of each lamina, shows that the more 
strongly-marked lines of division which separate them, in contradistinction to those 
merely dividing the lamellae, are not due to “ I’usure des bords des dernieres lames 
qui ont precede un nouveau developpernent,” but to some internal physiological 
cause, which, whatever it has been, may have operated annually, as is supposed by 
M. Agassiz. 
In the central and earliest formed lamellae, these tubes terminate as at fig. 3 b, c 
and d, by subdividing into two or three small branches, but do not exhibit any exten- 
sive ramifications. The same is also the case with the tubes of the two opposite 
margins which terminate in the interior of the scale. 
We also find in this scale a development of lepidine tubes; they are not dif- 
fused throughout its whole extent, as in Lepidosteus, but appear to be chiefly con- 
fined to the margins; and even there, only exist in those portions of the lamellae 
which assume the oblique and vertical directions. These latter are copiously per 
forated by them, fig. 3 f, but the horizontal portions exhibit few, if any, traces of tlieir 
existence. 
Between each of the contiguous lamellae is distributed a layer of lacunae which 
exhibit the same features as those of the Lepidosteus already described. In the 
parallel spaces of fig. 4 we only see the edges of the lacunae and their canaliculi 
following the plane of the ascending lamellae. 
On the upper surface of the scale is found a thick deposit of ganoin, the formation 
of which, the section represented in fig. 3 enables us to comprehend. At g, like the 
subjacent part of the scale, it consists of parallel laminae, each of vvhich, under a higli 
magnifier, is seen to be again separated into still more minute lamellae. At h, we 
find that each of the laminae is merely a prolongation of a corresponding one in the 
osseous portion, only having the character of ganoin instead of bone, and separated 
from it by the thin film of kosmine already described. To some extent we found the 
same condition to exist in Lepidosteus, only the kosmine was wanting, and what 
was there seen to be a partial and unequal distribution, producing irregular superficial 
tubercles, here extends uniformly over the whole scale, showing that, in Lepidotiis at 
least, each new growth has completely surrounded all that had been previously formed, 
enclosing it as a nut does its kernel ; only the upper portion was ganoin, whilst the 
lower one was true bone. 
We also find in the large opercular bone of the same Lepidotus a still further resem- 
blance to the scales of Lepidosteus, m the existence of similar large canals communi- 
cating between its upper and lower surfaces. I have observed sections of these to 
exhibit concentric laminae surrounding the canals, showing that the membrane which 
lined them was also a secreting tissue, depositing calcareous matter, and was doubtless 
a prolongation of the periosteum already spoken of. These concentric lamellae do not 
