HE tumorous head (tu-h) abnormality and genetic mechanism were disTcussed by GARDNER (1948), GARDNER and WOOLF (1949) and NEWBY ( 1949). Penetrance, expressivity and relative viability were investigated by GARDNER and RATTY (1952). The influence of high and low temperatures on the expression was described by GARDNER and WOOLF (1950). Modifiers and alleles of tumorous head genes were found in la...