SCALES AND DERMAL TEETH OF SOME GANOID AND PLACOID FISH. 437 
the organic structure of the so-called ganoid scale-bones in 1840, both in recent and 
extinct fishes, showing that it militated against the theory of the development by 
successive deposition of layers being applied, at least to ganoid scales.” A reference 
is made to the ‘ Odontography,’ p. 15, where I find the following foot-note ; — ‘‘A very 
close analogy exists between the dermal bony tubercles and spines of tlie cartilagi- 
nous fishes and their teeth. The system of minute parallel tubes, with their branches 
and anastomoses in the thick scales of the extinct Lepidotus, is as complicated as in 
many teeth, and equally militates against the theory of transudation of layers being 
applied, at least to ganoid scales.” The new facts brought forward by Professor 
Owen are some observations on the opercular and other bones of the Carp and Gold- 
fish, from which he concludes that the opercular bones are not modified dermal 
scales ; the remaining illustrations had already been developed by M. Agassiz, both 
in his descriptions and by his drawings*. 
The last writer who has alluded to the subject is Mr. E. Quekett. His observa- 
tions however-l- are confined principally to the forms of the lacunee found in the scales 
of Lepidosteus osseus and Callichthys. Such was the state of this subject when I 
entered upon a further series of observations. The difficulty which I had experienced 
in identifying what I had seen of the structure and development of human bone, with 
the descriptions given by Muller, Tomes, Todd, Bowman and others, led me to take 
up the examination of these forms of osseous tissue, in the hope that they would 
throw some additional light on the question. The wide difference also which existed 
betw'een the views of Owen and Agassiz as to their mode of growth, rendered a 
further inquiry into the development of the scales necessary. I hope and believe that 
the facts about to be brought forward will at least be found sufficiently conclusive to 
settle the question ; by showing that, whilst the scales are formed, as originally stated 
by M. Agassiz, by the apposition of successive layers, these layers are not generated 
by any process of secretion, but by the calcification of an organized basis, resembling 
that of bones and teeth, as asserted by Professor Owen, 
Though M. Agassiz has already investigated the structure of the scales of Lepi- 
dosteus osseus and Polypterus niloticus\^ the importance of an accurate knowledge of 
these recent types of the Sauroid group of fish, in contributing to the illustration of 
the fossil species, led me again to subject the scales of Lepidosteus osseus to a careful 
examination : whilst the result has been confirmatory of most of the observations of 
M. Agassiz, it has also revealed one or two points which have escaped his eye, but 
which are of importance. 
Plate XL. fig. 1 represents a vertico-longitudinal section of a scale of Lepidosteus 
osseus. From a tob represents the anterior portion of the scale, which, when in situ, is 
imbedded in the skin, and covered by the posterior overlapping margin of the antece- 
dent scale, c represents the posterior margin. The whole structure is composed of 
* Poissons Fossiles, vol. i. p. 73 tab. H. ; vol. ii. tab. G. 
f Transactions of the Microscopical Society of London, vol. ii. part 2. J Vol. ii. part 2, p. 5 et seg. 
3 L 
MDCCCXLIX. 
