If sufficient evidence can be adduced to shew that the flattened cranial arc in the Neanderthal skull does actually owe its origin to physiological factors through which environment acts, the status of that type of skull in the evolutionary sequence will be materially affected. A successful issue of the investigation will necessitate a thorough revision of all the results of Professor Schwalbe's work[54], which established the Neanderthal type as a distinct species (_Homo primigenius_) followed closely and not preceded by a type represented by the Gibraltar skull. Dr Sera commenced with a very minute examination of the Gibraltar (Forbes Quarry) skull. In particular, the characters of the face and the basal parts of the cranium were subjected to numerous and well-considered tests. As a first result of the comparison of the parts common to both crania, Dr Sera believes that he is in a position to draw correct inferences for the Neanderthal skull-cap in regard to portions absent from it but present in the Forbes Quarry skull. But in the second place, Dr Sera concludes that the characters in question reveal the fact that of the two, the Gibraltar skull is quite distinctly the lowlier form. And the very important opinion is expressed that the Gibraltar skull offers the real characters of a human being caught as it were in a lowly stage of evolution beyond which the Neanderthal skull together with all others of its class have already passed. The final extension of these arguments is also of remarkable import. The Gibraltar skull is flattened owing to its low place in evolution. But as regards the flatness of the brain-case (called the platycephalic character) of the Neanderthal calvaria and its congeners (as contrasted with the Gibraltar specimen), Dr Sera suggests dependence upon the particular environment created by glacial conditions. The effect is almost pathological, at least the boundary-line between such physiological flattening and that due to pathological processes is hard to draw. Upon this account therefore, Dr Sera's researches have been considered here in close association with the doctrines of Professor Keith.