First of all, the brains of not all eminent men are unusually large. On the contrary, a few unusually small brains have been found in the series. Furthermore, most of the brain-weights constituting the general series are obtained in anatomical institutes; and the individuals who find their way there are poorly developed, on account of malnutrition and of life under unfavorable circumstances, while the eminent men represent a much better nourished class. As poor nourishment reduces the weight and size of the whole body, it will also reduce the size and weight of the brain. It is not certain, therefore, that the observed difference is entirely due to the higher ability of the eminent men. This may also explain the larger size of the brains of the professional classes as compared to those of unskilled laborers (Ferraira). An additional number of restricting facts must be enumerated. The most important among these is the difference in brain-weight between men and women. When men and women of the same stature are compared, it is found that the brain of woman is much lighter than that of man. Nevertheless the faculty of woman while perhaps qualitatively different from that of man, cannot be deemed to be of an inferior character. This is therefore a case in which smaller brain-weight is accompanied throughout by equal faculty. We conclude from this fact that it is not impossible that the smaller brains of males of other races should do the same work as is done by the larger brain of the white race. But this comparison is not quite on equal terms, as we may assume that there is a certain structural difference between male and female, which causes the difference in size between the sexes; so that comparison between male and female is not the same as comparison between male and male. Notwithstanding these restrictions, the increase of the size of the brain in the higher animals, and the lack of development in microcephalic individuals, are fundamental facts which make it more than probable that increased size of the brain causes increased faculty, although the relation is not quite as immediate as is often assumed. The reason for a lack of close correlation between brain-weight and mental faculties is not far to seek. The functioning of the brain depends upon the nerve cells and fibres, which do not constitute, by any means, the whole mass of the brain. A brain with many cells and complex connections between the cells may contain less connective tissue than another one of simpler nervous structure. In other words, if there is a close relation between form and ability, it must be looked for rather in the morphological traits of the brain than in its size. A correlation exists between size of brain and number of cells and fibres, but the correlation is weak (Donaldson).