抄録
There has been a long term discussion on the origin of X-cells found in skin tumors of flat-fishes and gobies. There are two different views about this X-cell origin, the first is of somatic and the second is of parasitic origin. The present observations on the X-cell division clearly indicate that the X-cells divide amitotically. First the deeply stained nucleolus produced one or sometimes 3-4 slightly stained daughter nucleoli. Then the nucleus divides by constriction to make binuclear or polynuclear X-cells according to the number of newly formed daughter nucleoli. These bi-or polynuclear X-cells divide by constriction of cell membrane without any sign of mitosis. Two different dividing patterns were clearly identified on the basis of the electron density of the nucleoli of newly formed nuclei. This dividing pattern is quite different from the usual mitotic division of somatic cells indicating that the X-cell is of parasitic origin and the diseases are not real tumors but xenomas.
