Finally, the ornamental crests and frills, and the vivid hues which so many birds display have not arisen, as is generally supposed, as a direct result of the selection, by the females, of the most vividly coloured, or ornamented, from among a number of suitors presenting varying degrees of intensity in ornamentation. Such “frills and furbelows” are to be regarded as “expression points” of internal variations in the germ-plasm, which have been free to develop along their own lines because they have not proved in disharmony with the conditions of the birds’ environment. Their development is to be traced to the stimulating action of the “hormones” which control both pigmentation and structure, as is shown by the fact that both are modified by any interference with the glands in question. Such ornamental features then are the concomitants not the results of Sexual selection. The development of ornament, whether of colour or structure, may be taken then as an index of specialization, and as one of the many manifestations of that variation which is going on in every part of every living organism. So long as the continued increments in the development of these characters do not hamper their possessors in the struggle for existence, they are free to go on developing. Sexual selection, other things being equal, operates by according the greatest number of descendants to the most amorous, and not necessarily to those of the brightest hues. [Illustration: Plate 27. _Photos copyright, G. Herring._ SOME STRANGE ACCOMPANIMENTS OF COURTSHIP. THE WHITE-HEADED BELL-BIRD. This species is remarkable for the enormous, erectile wattles which arise from the base of the beak of the male at the courting season. THE UMBRELLA-BIRD The crest which adorns the crown of the head has many counterparts, but the long-feather clad wattle which depends from the fore-part of the breast is unique. [Face page 156.] Plate 28. SKULL OF THE AMERICAN WHITE BEAKED PELICAN. The beak of this bird develops at each breeding season an irregular horny plate which falls off at the end of this period, It is difficult to regard this as a sexual “ornament,” yet it comes under this category. _Photos copyright, H.G. Herring._ HEAD OF A PUFFIN, SHOWING THE MOULTING OF THE BEAK SHEATH. At the breeding season, in both sexes, a triangular horny plate is developed over the eye, an oblong plate below it, while the sides of the beak become deepened by means of larger triangular horny plates. All these embellishments are highly coloured, and they are shed at the end of the breeding season. A further ornament is developed at the gape, in the shape of a fleshy rosette of a bright orange colour. Face page 156.]