Dividing and non-dividing nuclei in the hyphæ of M. androsaceus and M. rotula, grown by means of agar- and cellophane-film techniques, were examined alive with phase contrast and also after various fixation and staining procedures. The division was compared with that of the nuclei found in the ultimate clamp connection, i.e. that found, associated with the developing basidium, and with the divisions of the single diploid nucleus in the mature basidium. The end products of all the hyphal divisions are the same as in organisms having a conventional mitosis but some of the steps by which this is achieved are unusual, notably the arrangement of the chromatin as a figure of eight, the twisting of one of the loops so formed above the other to create two rings and the opening of these rings in such a way that the two rods which, ultimately separate each correspond with the chromosome complement of a daughter nucleus. The first division of the diploid nucleus in the basidium is noteworthy for the linking together, in late prophase, of the four chromosomes. This division is followed by a distinct interphase in which nucleoli reappear. The second division shares the peculiarities of the division in the ultimate clamp.