Deoxyribonucleic Acid Content of Nuclei in Tail Mesenchyme of Rana pipiens Tadpoles

Abstract

LINDAHL¹ has suggested the occurrence of reduction division of chromosomes in the micromeres of the 16-cell stage in the embryos of two species of sea urchins. This interpretation was based on the observation of haploid chromosome counts in ana-phases and early telophases, while metaphase counts showed diploid numbers. Afterwards one of us² reported haploid counts from mesenchyme cells of the tail in Rana pipiens tadpoles. These were observed in whole mounts of stained tail tips, and occurred in stages resembling prometaphases. Other evidence, however, fails to support the suggestion of somatic reduction in the mesenchyme cells of these forms. Makino and Alfert³ failed to find haploid numbers in micromere divisions of the sea urchin Strongylocentrotus purpuratus, from California; while the cytophotometric measurements of deoxyribonucleic acid in developmental stages of the sea urchin Lytechinus made by McMaster⁴ do not reveal reduction of chromatin in the micromeres or their derivatives. In Rana pipiens, the cytophotometric deoxyribonucleic acid measurements of Moore⁵ show the normal diploid chromatin condition in mesodermal elements.