Memoirs: On the Histology and Regeneration of the Teleost Scale

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Abstract
The Teleost scale, as typified in the goldfish, is covered intimately by two layers of cells on the external surface. The internal surface of the young scale is invested with a cell layer which is continuous with the deeper external layer. These cells may be regarded as osteoblasts and osteocytes and are concerned with the formation of the outer bony portion of the scale. In the development of regenerate scales, osteoblasts pass from the periphery of the scale pocket to the growing edge of the scale. The latter consists at first of osteoid tissue, which later becomes calcified. The fibrillary plate is at first collagenous but apparently becomes infiltrated with ichthylepidin after being laid down. The scale is wholly mesodermal in its tissue relationships. The ridges of the scale are formed between cell rows of the deeper external cell layer. They are not the product of specific cells. Eidge formation probably depends on the presence of boneforming materials in the intercellular fluid in amounts greater than can be utilized at the growing margin. These are deposited between cells in the vicinity. The sulci of ontogenetic scales represent lines of flexibility. This condition is attained not only by the absence of the bony layer but by a special condition of the underlying fibrillary plate, which apparently does not become impregnated with ichthylepidin beneath the grooves. Regenerate scales may be monocentric, in which case a relatively large central area is devoid of ridges. Absence of ridges is interpreted as due to the utilization of all available scaleforming material at the growing margin. The size of the central area does not correspond to the size of the original scale. In the goldfish the regenerate scale is commonly polycentric, the bony portion developing from more or less numerous growth centres whose ultimate margins are indicated by grooves similar to the sulci of ontogenetic scales. The number of growth centres depends in a general way on the space available. The fibrillary plate is continuous beneath the bony islets but remains flexible beneath the grooves. Three processes contribute to the re-scaling of areas from which scales and pockets have been removed: (1) enlargement of ontogenetic scales at the margin of the wound area, (2) regeneration of scales in partially destroyed pockets at the margin of the wound area, (3) development of new scales within the wound area. New and regenerate scales always develop in the vicinity of pre-existing scales or papillae, under the influence of specific osteogenic cells which do not arise de novo from the corium.

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