The abnormalities used in these breeding experiments are: notched shell, prong-tentacle and bifurcated tentacle in L. stagnalis appressa; coiled egg-mass, black penis, and prong-tentacle in P. gyrina. 343 F1 and F2 progeny reared in isolation and mass F3 cultures reached maturity or even old age without showing one of the expected characters. None of these characters was observed in immature progeny which died before attaining the size at which they would have been considered sexually mature. The only instance suggesting inheritance of any of the characters was that of an F1 P. gyrina which had a prong on the medial side of its right tentacle near the tip, as had its mother, but it also had a prong on the medial side of the left tentacle near the base, but none was present in the mother.