To produce large families, making little provision for them, is a wasteful and improvident way of maintaining life. This spendthrift fashion of reproduction was the early method. To limit the number of the family and to cherish and protect the young, not throwing them upon the world until they are well fitted to make a brave fight against its dangers, is the later, wiser and safer way. We have noted devices of this kind in each group of the animal kingdom, but parental care becomes more and more complete as the scale of life is ascended. Not only are the numbers in the family reduced, but the period of youth becomes longer. The protected young are permitted a longer time in which they have the opportunity of learning to live. The importance of the form of union or marriage between the parents and of the kind of home must be considered. We have found that polygamous fathers and polyandrous mothers care little for the young. The withdrawal of the interest and care of either parent is a source of weakness which can be compensated only by an added devotion on the part of the remaining parent. We have noted the withdrawal of the father from active work for the family. This came with the greater importance of the mother, which itself was not the result of any conscious act. It was a necessary step, following the change from external to internal protection, whereby the young are retained within the body of the mother. Animal parents do not teach us that mothers are always more devoted and self-sacrificing than fathers. Sometimes, indeed, the contrary would appear to be true. Even the mother’s instinct to protect and serve the young, which seems to increase as we ascend the scale towards human parentage, must, I think, be regarded as an extended egoism. Formed in her body and fed from her sustenance, the young are a part of her individuality, and her solicitude for them is but a wider caring for herself. There are many surprises in animal parenthood. The conduct of the parents may vary within very wide limits, and all kinds of devices are employed by different parents to ensure the well-being of the family. Solicitude and sacrifice for the young are common, but indifference also occurs; and there are unnatural parents of both sexes who shirk family duties. We have found, indeed, the suggestion of all the virtues of human parents as well as many of their sins, every form of devotion and intelligent parenthood as well as examples of folly and neglect. We have observed the greatest difference in particular in the conduct of the father as regards his participation in the work of building the home and in feeding and rearing the young. Thereby we have learnt that a psychic metamorphosis of the male may occur, causing him to fulfil the duties of the mother, and that accompanying this is an alteration in the character of the female which completely transforms her sexual nature.