competent to effect fertilisation influenced the development of the secondary sexual characters, has of late been more and more generally abandoned. Many considerations tell against such a theory, more especially a comparison of the three following facts. First, if castration is not effected until after the formation of spermatozoa has already begun, the familiar results of this operation are either entirely wanting, or else appear to a small extent only, and are limited to a small number of the secondary sexual characters. Secondly, the results of castration are most marked when the operation is performed in early childhood. Thirdly, when castration is effected in the later years of childhood, but before the secretion of fertilising semen has taken place, the results are intermediate in degree, being much less marked than in the second class of cases, but more extensive than in the first. If the secretion of a fertilising semen were the principal factor in the development of the secondary sexual characters, we should expect the results of castration to be the same whether the operation were performed early in childhood or late so long as it was done before any spermatozoa had been formed. The secondary sexual characters are, therefore, independent of the formation of spermatozoa, and the appearance of these characters must depend upon other processes, occurring much earlier in life. Thus, in persons who were castrated in the eighth or ninth year of life, we note the presence of definite secondary sexual characters, which are, indeed, less strongly developed than in normal persons, but which do not appear at all when the castration has been effected at a still earlier age. The varying views of different authors regarding the influence of castration in early life upon the development of the secondary sexual characters may readily be explained with reference to the individual differences that may be observed in the functional activity of the testicles in different males before the power of reproduction has been acquired. Just as in boys the capacity for reproduction, and in girls the function of menstruation, does not appear at a fixed and definite age, so also in the case of the other processes that come into being under the influence of the activity of the reproductive glands, we have to reckon with such individual differences. For this reason, in persons who have been castrated at the same age, the subsequent course of development may vary to some degree, notwithstanding the apparent identity of the determining factor in each case. In some, the pelvis, the beard, the voice, and the mental qualities, develop in normal fashion; in others, there is interference with the development of one or all of these characters. In certain cases, the bodily structure is influenced by castration at an age when the mental development is no longer affected. This explains the fact that many oriental eunuchs, in whom castration is commonly effected