IN the early months of 1951, Sir John Graham Kerr collected some three hundred Murex tribulus shells on the western shore of the Great Bitter Lake south of the village of Fayid. It will be remembered that the entire animal population has been introduced subsequent to the cutting of the Suez Canal in 1869, which opened the way for immigrant organisms from the Red Sea. Now, granted the inherent tendency of living creatures to vary when relieved of the shackles of environment, Sir John argued that, in their new environment of the Bitter Lakes, these Murex specimens had had an opportunity of responding to this tendency, and hence the remarkable variety of sculpture in the random collection. Moreover, this variation exhibited in spines and tubercles is not a matter of mere superficial markings, but rather of deep-seated causes such as the localized growth of the mantle edge or the depth in the mud occupied by the individual animal. The shells were in perfect condition, there being practically no tides in the Bitter Lakes and no violent wave action, and the bottom is soft mud.