1. Experimental conditions and methods of rearing which make it possible to obtain heteroploidy in Pleurodeles waltlii are described.

  2. A method based on silver impregnation of the tail of young larvae permits the diagnosis of haploidy, diploidy, or triploidy. This method, by outlining the cell borders, makes possible planimetric measurement in any area of the epithelial sheet of the tail skin.

  3. The general structural organization of the ectodermal layers is described for the whole of the tail skin, and the alterations and adjustments resulting from an aneuploid make-up are analysed. In aneuploid chimaeras, micro- and macrocells are formed as a result of mitotic anomalies, corresponding respectively to groups of chromosomes lost from the mitotic spindle and to highly polyploid cells. The disappearance of the most atypical cells is followed by movements and reorientations of neighbouring cells producing characteristic rosette formations.

  4. Various teratogenic effects of thermal shock to the eggs, compatible with life, are described.

  5. Strongly hypomorphic or aneuploid larvae and haploid individuals, which usually have a brief survival, may be reared by means of parabiotic grafting to a normal individual.

  6. Amongst triploid males and females, fertile individuals have been obtained.

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