Abstract
1. The problem to be solved in this investigation has been considered the elucidation of the nature of the V-shaped chromosomes of Amphibia, Triton taeniatus, Axolotl and Rana temporaria serving as material for the purpose.
2. A mixture of 50% formalin with 5% chromic acid at a ratio of 8:2 (for Triton taeniatus and Rana temporaria chromosomes), as well as a mixture of 10% formalin with 1% chromic acid at a ratio of 7:3 (for Axolotl chromosomes) have proved to be the best fixatives for exposing the structure of chromosomes of the investigated species.
3. After such a fixation the chromosomes of the species studied have clearly shown their structure consisting of two arms joined by a median or submedian constriction and proving to be strictly constant for each chromosome, owing to which it has been possible to suggest a preliminary grouping of chromosomes for each species.
4. The structure of the constrictions differs in different chromosomes. They may assume the shape either of a long, thin, achromatic fibre joining both the arms together or that of an achrometic breack, or that of a strongly marked stricture in the chromosome body.
5. Axolotl and Rana temporaria chromosomes of one and the same set do not undergo differentiation with equal readiness, displaying thus their specific peculiarities.
6. Since almost for every type of animal there exist data an biarmed chromosome structure, that haue not been as yet systematized, it seems quite probable that the chromosome constriction in animals, identical to these in plants (G. A. LEVITSKY, 1931), represent the basis of the morphological structure of chromosomes and give them a definite external organization. The discovery of constrictions in animal chromosomes is apparently a question of technique.
