individuals not presenting that advantageous peculiarity of variation. CHAPTER XIX SCIENCE AND DANCING THERE is at the present day in this country a real and most happy revival of interest in the great art of dancing as exhibited on the stage. We owe this to the creative ability of the musical composers and directors of the Russian Imperial Ballet, as well as to the highly-trained and gifted Russian artists who have visited this country, and especially to the poetical genius of Madame Anna Pavlova. Though dancing may seem, on first thought, a subject remote from science, yet, like all other human developments, it is a matter for scientific investigation, and one upon which science can throw much light. What is the origin and essential nature of "dancing"? Do animals dance? What is its early history in mankind? What is its relation not merely historically, but from the point of view of psychology--the study of the mind--to other arts? What is its real "value" and possible achievement? To dance is to trip with measured steps, and, whilst primarily referring to human movement, the word is secondarily applied to rapid rhythmic movements even of inanimate objects. Rhythm is what distinguishes dancing from ordinary movement of progression or from simple gesture or mere antics. Dancing on the part of man or animal implies a sense of rhythm. Though not common amongst animals, it is exhibited by many birds, by spiders, and by some crustaceans! Rhythm is an essential feature of the sequence of sounds which we call "music." The singing of birds is related to their perception of and pleasure in rhythm, and it is not, therefore, surprising that they should also dance. It is, however, curious that the birds which "dance" are not the "singing birds," and that there are many birds which neither sing nor dance. The dancing of birds is usually part of the "display" of the males for the purpose of attracting the females at the breeding season. It is well known in some African cranes, as well as in rails and other similar birds, and may be witnessed at the Zoological Gardens in London. Other birds "strut" rather than dance, whilst displaying their plumage, as, for instance, the turkey and pheasant tribe and the bustards. Parrots and cockatoos will often make a rhythmical up-and-down movement of the neck in time to music, but usually the "dance" is the accompaniment of definite emotion. The male spider of some species courts the female by making dancing movements and posing itself in a very curious way, so as to display a spot of bright colour on the head to her observation. The same kind of movement and action has been observed in marine shrimp-like creatures. Some spiders are excited and made to dance by the vibrating note of a tuning-fork set going near them. I once had the chance to observe a male octopus in the aquarium at Naples, who was displaying himself to the female, changing colour rapidly from one shade to another, and rolling his