Contributions to the cytology of amphibian germ cells

I. Chromosomes in the spermatocyte divisions of five North American species of toads

Abstract

The chromosomic constitution of five American species of toads is much the saure as that described by previous authors for European and Japanese species of the same genus. The haploid set consists of 6 large and 5 small chromosomes. The fifth chromosome shows peculiarities that bear out its homology with the supposed sex chromosome of Rana temporaria. The importance of comparative studies in amphibian chromosomes with respect to the problem of the evolution of the sex chromosome mechanism is emphasized.