In the remaining groups of Fishes, the Teleostomi and the Dipnoi, the spine of the primitive dermal denticle is either evanescent or entirely wanting, while the equivalent of the basal plate remains to form the unit of a scaly armature. Evidence of this may be found in the presence of transitory evanescent spines, provided with an enamel-cap, secreted by the basal epidermis, on the developing rhomboidal scales, as in the young _Lepidosteus_[163] (Fig. 101); while the entrance of blood-vessels into the scales through perforations on their inner surfaces, as in _Polypterus_ and _Lepidosteus_, obviously recalls the perforated base of a dermal denticle (Fig. 99). The epidermis now ceases to take any part in the formation of the scales, and hence enamel no longer enters into their structure. A more regular and definite arrangement of the scales is noticeable, and whether distinct, or articulating with one another, or overlapping like the slates on the roof of a house, they are usually disposed in a series of successive oblique transverse rows. In some of these Fishes the embryonic epidermic covering of the scales becomes lost, and their outer surfaces are naked. More frequently, as in the generality of Teleosts, and in the Dipnoi, the reverse is the case, and the scales are more or less completely invested both by the dermis and the epidermis. As regards their shape, size, and minute structure there is much variation. In some Teleostomi {186}the primitive rhomboidal shape of the dermal denticle is retained; in others a rounded or cycloid scale supplants the earlier rhombic type. Within the limits of the same group (_e.g._ Crossopterygii) there are examples of the independent evolution of a cycloid from a pre-existing rhombic squamation; and with the introduction of the cycloid type an overlapping or imbricated disposition of the scales always takes the place of the marginal articulation of the rhombic type. [Illustration: FIG. 101.—Development of a scale in _Lepidosteus osseus_ × 330. _b.p_, Basal plate, with included bone cells, at first distinct from the spine; _e_, enamel; _e.o_, enamel organ; _ep_, epidermis, with large gland cells; _p_, dermic papilla which forms the vestigial spine; _Scl_, scleroblasts. (From Klaatsch.)]