Research on the ontogeny of turtles (Emys orbicularis and Testudo graeca) leads to the reconsideration of the problem of the shell elaboration. Precise observations on the development of dermal ossifications and horny shields, which constitute the basic components of the shell, leads to the reassessment of the problem of the paleontological origin of these structural elements in the Chelonia. The morphogenetic bases of the variability of shell bony and horny parts, as well as their phylogenetic significance, are briefly described. -Author