Although from the facts just stated it appears that, alike in human beings and in the lower animals, before the formation of the specific germ-cells and sperm-cells has begun in the reproductive glands of the respective sexes important processes take place in these glands, it still remains obscure what is the nature of these processes, and in what manner they influence the organism. One question complicating this problem, and one which is to-day frequently discussed, is the extent of the influence exercised by the reproductive glands on the development of the secondary sexual characters. I can here do little more than state the difficulty. Whereas it was formerly assumed that the reproductive glands exercised a direct determining influence in this direction, more recently another view has been put forward, among others by Halban.[47] According to this theory, the stimulus proceeding from the glands is protective merely, not formative, nor directly stimulating the growth of organs. In the fertilised ovum, it is supposed, the rudiment of sex already exists, likewise the rudiment of the reproductive gland, and the rudiments of the appropriate sexual characters. That is to say, the development of the secondary sexual characters is not determined by the presence of the reproductive gland; but the sex of the reproductive gland and the associated sexual characters are already determined by some common cause at the moment of fertilisation. But this theoretical controversy has no very important bearing on the problem with which we are especially concerned; and the influence of the reproductive gland upon the development of the secondary sexual characters is admitted as fully by Halban as it is by other writers, the only difference between the two views lying in the dispute whether the influence of the glands is of a formative or a protective nature. The influence exercised by the reproductive glands on the development of the secondary sexual characters can be adequately discussed, even though the precise way in which that influence is exerted remains in dispute.