[Situs inversus of the Newt (Triturus alpestris) after UV-Irradiation of Gastrulae].

Gastrulae (Harrison 9-13), and for comparison neurulae (Harrison 15-17) ofTriturus alpestris were irradiated with mixed ultraviolet light of various doses and at various body regions. Bilateral irradiation leads to a markedly higher mortality than does unilateral irradiation. Gastrulae possess a better regulation capability than neurulae. The frequency of alterations of the situs (irregularities, partial and total inversions), lethality and rate of malformations are dose dependent. Irradiation of the right side ofearly gastrulae (Harrison 9-11a) leads to a higher frequency of inversions than does irradiation of the left or animal side. The frequency of inversions oflater gastrulae (Harrison 12-13) is approximately the same after right- and left-side irradiation. The expressions of inversions are different after irradiation of gastrulae and of neurulae respectively. The problem of physiological asymmetry of the embryo, especially the change of "dominance for right" to "dominace for left" during gastrulation is discussed with regard of relations of defect and situs inversions.