It was perhaps in connection with adaptation that Darwin obtained the most striking evidence in support of his theory, and it is clear from his writings that it was in this field he laboured with most delight. The marvellous ways in which creatures may be adapted in structure and habit for the life they lead had not escaped the attention of the older naturalists. John Ray wrote a book[1] upon the subject in which he pointed out that all things in the Universe, from the fixed stars to the structure of a bird, or the tongue of {5} a chameleon, or the means whereby some seeds are wind distributed, are "argumentative of Providence and Design" and must owe their existence to "the Direction of a Superior Cause." Nor have there been wanting other authors who have been equally struck by the wonders of adaptation. But their studies generally led to the same conclusion, an exhortation to praise the infinite Wisdom of Him Who in the days of Creation had taken thought for all these things. The advent of natural selection threw a new light upon adaptation and the appearance of design in the world. In such books as those on _The Fertilization of Orchids_ and _The Forms of Flowers_ Darwin sought to shew that many curious and elaborate structures which had long puzzled the botanist were of service to the plant, and might therefore have arisen through the agency of natural selection. Especially was this the case in orchids where Darwin was able to bring forward striking evidence in favour of regarding many a bizarre form of flower as specially adapted for securing the benefits of cross-fertilization through the visits of insects. In these and other books Darwin opened up a new and fascinating field of investigation, and thenceforward the subject of adaptation claimed the attention of many naturalists. For the most part it has been an observational rather than an experimental study. The naturalist is struck by certain peculiarities in the form or colour or habits of a species. His problem is to account for their presence, and as nearly all students of adaptation have been close {6} followers of Darwin, this generally means an interpretation in terms of natural selection. Granted this factor it remains to shew that the character in question confers some advantage upon the individuals that possess it. For unless it has a utilitarian value of some sort it clearly cannot have arisen through the operation of natural selection. However when it comes to the point direct proof of this sort is generally difficult to obtain. Consequently the work of most students of adaptation consists in a description of the character or characters studied together with such details of its life-history as may seem to bear upon the point, and a suggestion as to how the particular character studied _may_ be of value to its possessors in the struggle for existence. In this way a great body of most curious and interesting facts has been placed on record,