The Development of <i>Rana arvalis</i> (Amphibia, Ranidae), with Attention to the Skin Texture and Timing of Metamorphosis Events

For the first time, a description and timing of the development of the main external morphological characteristics of Rana arvalis Nilsson, 1842 is presented, with particular attention to the formation of skin texture. The first signs of texture in the form of dark stripes and spots appeared in tadpole skin at stages G39 – 40. At G41 – 44, the body of the tadpole acquired a typical «frog» position with an orientation of 20 – 30° to the substrate, dorsolateral stripes transformed into folds, and dark spots into tubercles in the caudo-rostral direction. At the end of metamorphosis (G45 – 46), the texture formation was completed on the entire back, and the type of morph (striata, non-striata) was easily determined. The period between the first signs of the appearance of skin texture and its complete formation took 6 – 12 days. The most stable was the interval between the primary protrusion of the forelimbs under the skin and the eruption of the first one (~12 h). The period between the eruption of the first and second forelimbs was the most variable (from an hour to three days). The results obtained highlight the plasticity and problematic nature of the phenomenon of metamorphosis in amphibians.