There is a popular view, dating back to Aristotle and supported by many doctors and zoologists, that the castration of an animal is followed by the sudden appearance of the characters of the other sex; if the gelding of a male were to bring about the appearance of female characteristics then doubt would be thrown on the existence in every cell of a primordial sexuality independent of the genital glands. The most recent experimental results of Sellheim and Foges, however, have shown that the type of a gelded male is distinct from the female type, that gelding does not induce the feminine character. It is better to avoid too far-reaching and radical conclusions on this matter; it may be that a second latent gland of the other sex may awake into activity and sexually dominate the deteriorating organism after the removal or atrophy of the normal gland. There are many cases (too readily interpreted as instances of complete assumption of the male character) in which after the involution of the female sexual glands at the climacteric the secondary sexual characters of the male are acquired. Instances of this are the beard of the human grandam, the occasional appearance of short antlers in old does, or of a cock’s plumage in an old hen. But such changes are practically never seen except in association with senile decay or with operative interference. In the case of certain crustacean parasites of fish, however (the genera _Cymothoa_, _Anilocra_ and _Nerocila_ of the family _Cymothoidæ_), the changes I have just mentioned are part of the normal life history. These creatures are hermaphrodites of a peculiar kind; the male and female organs co-exist in them but are not functional at the same period. A sort of protandry exists; each individual exercises first the functions of a male and afterwards those of the female. During the time of their activity as males they possess ordinary male reproductive organs which are cast off when the female genital ducts and brood organs develop. That similar conditions may exist in man has been shown by those cases of “eviratio” and “effeminatio” which the sexual pathology of the old age of men has brought to light. So also we cannot deny altogether the actual occurrence of a certain degree of effeminacy when the crucial operation of extirpation of the human testes has been performed.[1] On the other hand, the fact that the relation is not universal or inevitable, that the castration of an individual does not certainly result in the appearance of the characters of the other sex, may be taken as a proof that it is necessary to assume the original presence throughout the body of cells determined by arrhenoplasm or thelyplasm. [1] So also in the opposite case; it cannot be wholly denied that ovariotomy is followed by the appearance of masculine characters.