Chromosome elimination in the Japanese hagfish, Eptatretus burgeri (Agnatha, Cyclostomata).

The modal number of chromosomes in Eptatretus burgeri was 36 in 297 (81.8%) of 363 somatic cells, 52 in 13 (30.2%) of 43 spermatogonia, and 25 (46.8%) or 26 (40.3%) in 162 of 186 first spermatocytes. The relative amount of DNA in a somatic cell to that in a spermatogonium averaged 79.2%. C-band-positive chromatin was observed along almost the entire length of the associated dumbbell-shaped bivalents and part of two other bivalents in the metaphases of first spermatocytes, but was rarely observed in somatic cells. These results indicate that, in E. burgeri, chromosome elimination takes place during the early stages of cleavage, except for the ancestral germ-line cells.