658 
PROFESSOR WILLIAMSON ON THE STRUCTURE AND 
investing- periosteum ; only whilst in the cases of the bones we shall find that the 
growth is based upon a matrix of cartilage, we have not the slightest evidence that 
such a tissue ever entered into the composition of the scale. At the same time it is 
not easy to understand how such large cavities as exist in the interior of the latter 
structure can have been formed. 
The same lamellae, which at fig. 14 a, h and c are penetrated by Haversian canals, 
and appear to be at once osseous and ganoid, at H^are penetrated by a different set 
of tubes converting them into kosmine, and allying them with tooth-structures. Con- 
necting this fact with the analogous ones published in my preceding memoir, we can 
scarcely escape the conclusion that bone, ganoin, kosmine, dentine and the enamel of 
fishes’ teeth, are but modified forms of one common tissue; and though for the pur- 
pose of facilitating the interchange of ideas it is necessary to distinguish these modi- 
fications by various names, we must bear in mind that no clear lines of demarcation 
can be drawn between them, or definitions given, which will not in numerous instances 
fail to be strictly applicable. Inosculating examples occur which may be classed 
with several of the tissues, and yet without agreeing exactly with any one. This 
statement applies to each of the characteristic properties exhibited by individual 
examples of these structures, and of course has reference to the relative degrees 
of glossiness presented by their external surfaces, as well as the hardness, thickness, 
colour, and transparency of their respective lamellae. Hence it is perfectly possible 
to have ‘‘ganoin” without glossiness. We see something approaching to it in the 
fossil scales of Dapedius, and that such is really the case in examples recorded in the 
preceding pages, I have but little doubt. 
Fig. 15 represents a vertical section of the scale of Loricaria cataphracta,\^m^., a 
Siluroid fish from Brazil, for which also I am indebted to Sir Philip Egerton. The 
substance of the scale is of a truly osseous texture, closely resembling that seen in 
Acipenser and Lepidosteus, only wanting the curious parallel tubes seen in the latter 
of these examples. It consists of numerous lamellae, arranged like those of the Lepi- 
dosteus. Towards the posterior margin of the scale (fig. 15 a) they are wholly parallel 
to the inferior surface ; but at its anterior portion (fig. 15 b), where it has supported 
the free edge of its anterior neighbour, the laminae turn upwards, and are prolonged 
over a portion of the upper surface. In this respect its conformation is almost iden- 
tical with that of the Lepidosteus, which it also resembles in its numerous quadrate 
lacunae, with their divergent canaliculi, spread out in layers between the lamellae. 
An abundance of minute lepidine tubes penetrate the structure from below (fig. 15 c). 
In addition to these tubes, there are many large Flaversian canals (fig. 15 d)^ resem- 
bling those which in my preceding memoir I described as existing in the scale of 
Hohptychius sauroides. 
These canals run in various directions, but are especially spread out as an irregular 
network (15 e), immediately below the upper surface of the posterior half of the 
scale. The latter portion is thickly covered with large mobile recurved teeth, 
