“The pectoral muscles reach their highest development in the hummingbirds, the diurnal birds of prey, and the swallows, and we may, therefore, fairly use these groups to test Mr. Wallace’s explanation of breast plumes. In the swallows and birds of prey we find no such appendages, in spite of their further claim to them, on the ground of great vigor and activity. As to the humming-birds, we find in the genus _Aglæactis_ six species with more or less developed breast-plumes, which are also found in nine other species, scattered through different genera--in all, only fifteen species out of four hundred and twenty-six; while we find in fifty-six species the lengthened and modified tail-feathers, which, according to Mr. Wallace’s view, should be peculiar to the Gallinaceæ. “Again, there are elongated feathers from the throat or from the side of the neck in thirty-five species, while seventeen have crests from the top of the head, and seventeen, downy puffs from the tarsi.”[11] From this brief survey of the family we see that, contrary to what we should expect from Mr. Wallace’s theory, although the breast muscles are the seat of the highest activity, breast plumes are the least frequent of all the forms of ornamental plumage. “We may fairly say, then, that the humming-birds completely refute the proposition that there is any relation between the development of color and accessory plumes and ‘surfaces where muscular and nervous development is considerable.’”[12] What is true for birds is even more obvious for spiders where the special ornaments are not confined to parts of the body with high muscular development, etc. The writers make the very pertinent criticism that while Wallace objects to assuming the emotional states in females, he is less careful in regard to the males’ emotions when he speaks of the display “under the influence of jealousy or sexual excitement.... The males, in their rivalry with each other, _would see what plumes were most effective; and each would endeavor to excel his enemy_ as far as voluntary exertion would enable him.”[13] “If the males have so complex an emotion as jealousy, and further, if they are conscious of the value of the plumes, may it not be asked why the female is unable to ‘see what plumes are most effective?’ The mental state in the male is without meaning unless we suppose the female to be affected and pleased.” (Peckham, _loc. cit._, p. 144.) In regard to another interpretation of the courtship, the Peckhams point out: