. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. 548 ANATOMY OF VERTEBnATES. 364. Ganoid scales, AMblppkrus. termed ' placoid,' fig. 365, 'ganoid,' fig. 364, 'cycloid,' fig. 362, ' ctenoid,' fig. 363. In the first and second kinds bone-earth ^jredo- minates, and tlie scales arc as hard as teeth ; in the two latter kinds the earth is in less quantity, so that the scale is flexible: it is rarely want- inw. The kinds of scale graduate into each other. Most flexible scales present two structures: one next the derm is composed of gristly laminte, usually firm and elastic, f
. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. 548 ANATOMY OF VERTEBnATES. 364. Ganoid scales, AMblppkrus. termed ' placoid,' fig. 365, 'ganoid,' fig. 364, 'cycloid,' fig. 362, ' ctenoid,' fig. 363. In the first and second kinds bone-earth ^jredo- minates, and tlie scales arc as hard as teeth ; in the two latter kinds the earth is in less quantity, so that the scale is flexible: it is rarely want- inw. The kinds of scale graduate into each other. Most flexible scales present two structures: one next the derm is composed of gristly laminte, usually firm and elastic, fig. 360, c; the superficial portion, ib. d, is laminated and hardened by interla- mellar calcareous ; In the posterior or exposed part of the scale of a Carp there is a peripheral osseous layer, deve- loping the outer markings or projections of the scale, fig. 360, c?; a middle laminated layer, with 365 calcareous granules, ib. e ; and the internal layer of laminse of structureless car- tilage, ib. c. In the Tunny (Thi/imus vulgaris) the scales are com- posed of fine, partially ossi- fied, laminre, between which are elongated ' lacunas' or bone-cells: thescaleiscancel- lous atitsmiddlepart.^ In Z-e- pidosteus the scale is thicker, is composed of very thin ossi- fied layers, fig. 366,a, perfo- rated by vertical tubes about -!-thin. diameter, and having tut in ^ o numerous lacunaj in their interspaces,' the radiating canals of which communicate with a more minute series of vertical branched tubules, called ' Le- pidinc' by their describer.' These, in most ganoid fishes, have a less general through the scale thair the larger and less branched scries, which, from their analogy to dentinal tubes, I have called ' plasmatic,' conceiving them to relate to the nutrition and vitality of the scale, as doubtless also do the ' lepidine' tidnilcs in ' ' Corpuscles of MaiuU,' ccciii.: ' Ijcnticiihir liojics' of Williamson, ccxcii. ^ ccxoiii. vol. ii. p. 70. = V. p.
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