SCALES AND DERMAL TEETH OF SOME GANOID AND PLACOID FISH. 439 
that “ ces tubes vont mourir ala limite de la substance osseuse, et jamais on ne les voit 
entrer dans la couche emaillee.” Sometimes however they do penetrate the layers of 
ganoin, as at fig. 2 d, where the tubes perforate several of its laminae, having evidently 
once passed through them to open upon the external surface of the scale, and having 
only been closed up by the subsequent addition of new laminae of ganoin. In the Lepi- 
dosteus their branching extremity always terminates in the structure below the ganoin 
and never in it. 
M. Agassiz thinks that these tubes have not served as channels for the conveyance 
of nutriment to the interior of the scale, but as depots of calcareous matter. “Je 
serais plutot dispose a croire que ces tubes ont une destination analogue aux corpus- 
cules osseux et des tubes dentaires, savoir, de servir de depots de matik’e calcaire.” 
With this conclusion I cannot agree ; the tubes appear to me to be open canals in 
the hard tissue of the scale. Besides which, most modern physiologists entertain 
a different view, both of the lacunae of bone and the dental tubes of teeth, to that 
held by the Swiss philosopher. 
The real nature and use of these tubes is a point about which I am dubious. In 
Lepidosteus osseus we only see their partial development, but in some of the fossil 
species, hereafter to be described, we shall find them assuming a new aspect. 
In addition to these, there exists an extensive development of a second set of tubes 
(fig. 2 e), which are still more minute, but which also radiate from the outer surface 
to the inner portions of the scale. They penetrate the lamellae in a much more ob- 
lique direction, crossing the larger tubes at an acute angle, verging as they do so, from 
the outer border, towards the centre of the scale. They do not ascend directly, but 
in the manner of a succession of steps, having a constant tendency to be spread out 
for a short space between the lamellae, and then obliquely penetrating those above 
them, they repeat the same process. They are very much branched. This system 
of tubes appears to have escaped the notice of M. Agassiz, and I have not seen any 
reference to their existence in Lepidosteus by subsequent writers. We shall find, as 
we proceed, that in one form or another there are very few ganoid scales in which they 
are not extensively developed, and as we shall often have to refer to them, I should 
propose to distinguish them by applying to them the term Lepidine. Though not the 
homologues of dentine, they appear to fulfill a similar function in the scales to that 
which the dentine tubes do in the teeth, though they are often limited in their distri- 
bution to particular portions of the true scale tissue, which is not the case with dentine. 
I suspect that they have much more to do with the general nutrition of the scale, than 
the more parallel and larger tubes previously described : we shall afterwards find that 
the latter only exist in a few groups of fish, and that in them the ultimate distribu- 
tion of these tubes is mainly restricted to particular regions of the scale. But the 
lepidine tubes are very different. I have seen few scales in which I could not de- 
monstrate their existence, generally crowded together in vast numbers, and giving- 
off numerous minute branches as they proceed, to each succeeding lamella, even 
3 L 2 
