Roytberg E.S. (1991). Variation of head shield pattern in lizards of the genus Lacerta. (Sauria, Lacertidae): trends and constraints. - Zoologichesky Zhurnal, 1991, 70, 4: 85-96 (Russian, with English summary).
In 2920 specimens of Lacerta agilis boemica and L. strigata from Daghestan the individual variation of the head scutes pattern was studied. About 150 different deviations from the normal pattern were revealed. These deviations include: absence of individual normal shields or fissures, separating adjacent shields (A); presence of additional shields or fissures (B); alterations of shields' arrangement (C). In both species the next three properties of the Variation were shown and discussed 1) variants of group B are much more diversified and frequent than those of group A; 2) degree of the variation as well as its diversity is strictly limited; 3) deviations of groups A and B are discrete in their morphological expression. These properties are supposed to be determined by morphogenetic mechanisms, formed in the course of evolution of head scutellation in the direction of oligomerization and formation of regular and stable pattern.
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