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Two features of this study have furnished direct evidence for the material continuity and individuality of the chromosomes in the epithelial cells of the larvae of Ambystoma tigrinum (1) the tracing of the complete history of a specific chromosome, the nucleolus‐containing chromosome, throughout the successive stages of mitosis and interkinesis, (2) the following of the exact parallelism in behavior (during mitosis) of the chromosomes in a given nuclear group with that in a single chromosome which has been isolated in the cytoplasm from the main chromosomal complex. Each of the two nucleoli is subterminally located in the short arm of one of two particular V‐shaped chromosomes. The latter are probably homologues. 78: In this subterminal chromosomal position the nucleolus exhibits in fixed and stained preparations an achromatic character in late prophase, metaphase, anaphase and early telophase, while it presents itself as a chromatic element in middle telophase, late telophase, interkinesis and early prophase. The nucleolus is not a simple homogeneous body, but rather a complex structure, the nature of which is revealed in the study of its evolution during the chromatic phase of its cycle in mitosis.

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