Opening the discussion on Dr. Walton's paper, Professor Wm. C. Miller (Animal Health Trust) said: “Dr. Walton has presented a paper which outlines the fundamentals of male sex behaviuor and forms an excellent skeletal strcuture into which the minutiae of behaviour can be fitted. I feel I ought to make an effort to fit some of the more precise details into their places and so contribute towards the presentation of a more complete idea of just what is involved in male sex behaviour. I am, however, inevitably faced with the limitations of available data and with the very great amount of variation in behaviour as between individuals, and even more between species of farm animals.