I see from Professor Le Gros Clark's lecture that he was much less positive in his remarks regarding the Australopithecinae than was Dr. Robert Broom when addressing the Royal Society of Edinburgh on the 16th May, 1949. Thus, although Professor Le Gros Clark stressed the Sterkfontein remains (by which I presume that he referred to Plesianthropus ), as Dr. Broom also did, he reserved his opinion as to their geological age. Dr. Broom, on the other hand, said that they were of Pliocene and “possibly Middle Pliocene” age; which contrasted with his (Dr. Broom's) own earlier opinion that all the Australopithecinae were of Pleistocene age, and Plesianthropus probably belonged to the Upper Pleistocene ( Nature , Aug. 27, 1938, pp. 377–9). Since Dr. Broom produced a replica of the skull of Plesianthropus , I showed, during the following discussion, that the outer parts of the orbits of this skull are vertical, as in the apes, and are not bent backwards as in human skulls, whether recent or early (cf. the Piltdown, Neanderthal etc. orbits); and these vertical outer sides indicate specialization for vision to the direct front, to a higher degree than in man. This is one of many features which throw the apes out of series between men and lower mammals; and it is correlated with a great reduction of olfactory powers, which is another characteristic ape specialization. I therefore remarked that the skull of Plesianthropus shows that it could not lie in the line of Man's ancestry. Dr. Broom did not dispute