[Processes of scale formation in fish and Agnatha]

The formation of the scale cover in ancient fish and Agnatha was analyzed using paleontology data on some forms and by studying recent species according to the geochronological principle and morphological--genetic coupling approach. The histogenesis of true scale cover was transformed simultaneously but independently from dermal denticles, when the first process was accompanied by reinforcement of the bones and formation of head-body armor and dermal-like external elements of the skullcap. The scale cover is an independent organ system and is characterized by self-supporting conservative ancestral mechanisms of development.