These notes relate to Beale's work on intragenic recombination among the antigen-determining genes in Paramecium. Beale constructed heterozygotes involving various combinations of different 'd' antigen alleles, passed them through autogamy and screened the progeny with sera capable of immobilising the parental types. Theoretically intragenic recombinants should have appeared, but the only novel types Beale got turned out to be 'nuls' - i.e. cells unable to express any antigen controlled by the locus corresponding to the original types used.