As found by Hanna on the hymenium of any individual fruit-body of C. lagopus there are 4 sexually different types of spores, each bearing 2 sex factors belonging to Mendelian pairs, so that spores may be represented by the symbols (AB), (ab), (Ab), and (aB). Three types of basidia only are present in the hymenium of any fruit body, and they may be represented by the sex factors of their spores as follows: a 4-sex type (AB), (ab), (Ab), (aB); a 2-sex type (AB), (AB), (ab), (ab); and another 2-sex type (Ab), (Ab), (aB), (aB). Of the 3 types of basidia in the hymenium of any fruit body, 50% are of the type (AB), (ab), (Ab), (aB); 25% of the type (AB), (AB), (ab), (ab); and 25% of the type (Ab), (Ab), (aB), (aB). By cover-glass-contact and dry-needle methods spores were removed from 31basidia and sown singly in culture media, record being kept of the actual positions of the spores on their basidia. By mating the monosporous mycelia in Petri dishes and employing the clamp-connection criterion, the sexes of the spores were determined. The actual positions of the spores of diverse sex on each of the 31 basidia thus became known. For any individual fruit body the existence of 4-sex basidia as well as 2 types of 2-sex basidia, the numerical ratio in which the 3 types of basidia occur, and the actual positions of the spores of diverse sex on the individual basidia, are best explained on 2 assumptions: (1) that the 2-sex factors in the nucleus of each spore are carried by 2 separate chromosomes, and (2) that in some basidia the segregation of both pairs of sex factors takes place in the 1st division of the fusion nucleus of the basidium, while in other basidia segregation of 1 pair takes place in the 1st division and of the other in the 2nd. If in some basidia segregation of both pairs of sex factors takes place in the 2nd division of the fusion nucleus, this mode of segregation is relatively infrequent. In C. lagopus it is inferred that disjunction of homologous chromosomes may take place either at the 1st-or 2nd of the 2 divisions of the fusion nucleus. In C. rostrupianns, in which the spores on any fruit body fall into 2 opposite sexual groups, and where each basidium produces 2 spores with an (A) sex factor and 2 with an (a) sex factor, the positions of the spores as determined for 6 basidia indicate that segregation of the sex factors takes place at least sometime during the 2nd division of the fusion nucleus.