The nuclei ofGelasinospora tetraspermatravel out of a mycelium of one sex and into one of opposite sex as rapidly as 10.5 mm. per hour. This occurs not only in pairings producing abundant perithecia but also in pairings that produce few or none. The nuclei migrate from cell to cell in a protoplasmic strand running through the center of the hypha. Nuclei have been observed travelling through their own mycelium. They have been seen passing from one cell, through the pore in the transverse septum, into the next cell. The shape and size of the nucleus fluctuates. Spherical nuclei may change to narrow elongate sinuous bodies, and then resume their spherical shape. Nuclei may migrate in an expanded, contracted, or elongate form.