[The situs viscerum in the newt (Triturus alpestris) after material defects in the ectoderm of the blastula].

In the blastula stage ofTriturus alpestris roundish pieces were removed from the animal half of the embryo, which consisted of undetermined ectoderm; some of them could perhaps contain some mesoderm on their vegetal edge. Since the median plane could not be ascertained in this stage, a chance distribution around the animal-vegetal axis has to be assumed.Most of the embryos developed to externally normal larvae. The gut situs of 193 larvae was regular in 97.9% of the cases, median in 0.5% and inverted in 1.5%. This corresponds to the inversion rate of non operated animals.Therefore mechanic defects by means of removing of material, in contrast to similar defects in the gastrula stage, provoked no gut inversions. (Confirmation of similar results of v. Kraft, 1969 following UV-irradiation). According to these observations the sensible phase for the provocation of situs inversus viscerum begins in the early gastrula stage.