In Teleosts the usually thin and flexible scales are primarily developed from dermic papillae, but subsequently they come to lie in pockets or pouches in the dermis. As a rule no spines are developed, and so far no trace of an enamel organ has been detected during their development. The scales in their dermal pouches are disposed obliquely to the surface of the body, so that the hinder part of one scale overlaps the anterior portion of the scale next behind it (Fig. 104). Only the free hinder part of each scale has an epidermic investment (Fig. 105). In minute structure each scale consists of an outer layer of bone, which, like the bone of the endoskeleton, may either be homogeneous except for a feeble lamination, or it may contain bone-cells arranged in successive layers, parallel to the surface of the scale. In addition, there is an inner fibrous stratum in which the fibrous bundles in any one plane cross those in planes above or below them. The scales are either "cycloid," that is, they have smooth, unbroken margins (Fig. 105), or the free margin of each scale is produced into a series of tooth-like spines, and the scale is said to be "ctenoid" (Fig. 106, A). Some Teleosts, however, have scales which are neither cycloid nor ctenoid, and in certain features seem to be intermediate between ordinary Teleostean scales and dermal denticles. Thus, on certain parts of the body of _Centriscus_,[168] each scale consists {190}of a rhombic basal plate, produced into a curved, backwardly-inclined spine, the axis of which contains a pulp-cavity opening on the inner surface of the basal plate (Fig. 107). Some Malthidae (e.g. _Malthe_[169]) have similar scales, but with round basal plates and solid spines (Fig. 108, B). Similar scales (Fig. 109), sometimes rhombic in shape, with one or more spines, which may be simple or branched, are also found in the Sclerodermi (e.g. _Balistes_, _Monacanthus_, _Triacanthus_).[170] [Illustration: FIG. 105.—Cycloid scale of _Salmo fario_. _a_, Anterior portion covered by overlap of preceding scales; _b_, free portion covered only by pigmented epidermis. (From Parker and Haswell.) FIG. 106.—A, Ctenoid scale; B, "Ganoid" scale. (After Günther; from Parker and Haswell.)] [Illustration: FIG. 107.—_Centriscus scolopax_. A, Scale from the orbital region, × 50; B, scale from the base of the pectoral fin, × 100. (From Hertwig.)] Amongst some of the usually scaleless Siluroid Fishes the scales assume a very peculiar structure. In _Hypostoma_[171] (_Plecostomus_) the sides and back of the Fish are covered by large bony plates, but on the under surface and on the fins these are replaced by much smaller ones. Both kinds, however, carry numerous small movable spines implanted in sockets (Fig. 110), a fact which suggests comparison with a stage in the development of the scales of _Lepidosteus_, when the independently formed and evanescent spines have not yet fused with the basal plates.