The all-sufficiency of the “Sexual Selection” theory to account for the development of armature, such as horns, antlers, and the huge spine-like outgrowths which form so conspicuous a feature of many of the extinct Land-dragons, or Dinosaurs, has been by no means universally accepted. Some authorities like Dr. A. Smith Woodward and Professor Osborne interpret these after another fashion. They hold that these are the “expression points” of inherent growth forces, a process of concentration marking the final stages of evolution prior to extinction. From which it may be inferred that there is a term to the life of a species as there is to the life of the individual. In many cases it is suggested the very exuberance of growth has been the exterminating factor, as in the case of the huge antlers of the Irish “elk,” whose enormous weapons hampered his endeavours to escape his enemies. This is the theory of “Orthogenesis,” or direct development. According to this, new structures, arising in the germ-plasm as “variations,” will of their own inherent vitality go on increasing in each generation unless, and until, checked by “Natural Selection.” Changes in the character of the “Hormones” might very well bring about these excesses of growth. It is well known that the exuberance of growth which produces giants among the human race is due to a derangement of the secretions or hormones of the pituitary body which largely control growth. Another factor of Sexual Selection which is commonly ignored, but which is of profound importance, is to be found in the part played by the emotions in regard to sexual relationships; the part which the “mind” has played, and plays, in the mating of animals, at any rate of the higher types. Darwin touched but lightly on this theme. Later writers have almost entirely ignored it. Almost all that is worth knowing on the subject we owe to Professor Lloyd Morgan, who was one of the first to take up this difficult line of investigation, and to Professor Groos. Their researches have shown that there can be no doubt but that the emotions have played and are playing an important part in the phenomena we are striving to analyse. Sexual selection, in short, is concerned not merely with the evolution of the physical characters of the body, but also, and no less, with the psychological attributes thereof. Many new and extremely valuable facts in this regard have been brought to light by Mr. H. Eliot Howard in the course of his remarkable studies on our native warblers. Not until the psychology of sex in the lower orders of creation has been further investigated shall we have a properly balanced account of the part played by sexual selection in the scheme of evolution.