But we must now return to the other questions that have been started in relation to phosphorescence in animals. There has been much speculation as to the object of this light, and to the purposes it serves in Nature. Probably no general answer can be given to this question. It is no doubt impossible to show why so many animals have been endowed with this remarkable property; but we may consider some of the effects which the possession of it has in different cases. In the first place, it will undoubtedly serve in many cases to afford light to enable the animal to see by, and in the Lampyridæ it would seem that the degree of luminosity is related to the development of the vision. In that family, according to the Rev. H.S. Gorham, the eyes are developed, as a rule, in inverse proportion to the luminosity. Where there is an ample supply of this kind of light the eyes are small, but where the light is insignificant the eyes are large by way of compensation. And moreover, where both eyes and light are small, then the antennae are large and feathery, so that the deficiency in the sense of sight is made up for by an unusual development in the organs of touch. But it is none the less certain that the presence of this light cannot always be designed to serve this purpose, for many of the animals so endowed are blind. The phosphorescent centipedes are without eyes, like all the other members of the genus (_Geophilus_) to which they belong, and probably the majority of phosphorescent marine forms are likewise destitute of organs of sight. Another suggestion is that the light derived from these marine forms, and especially from deep-sea Alcyonarians, is what enables the members of the deep-sea fauna that are possessed of eyes (which are always enormously enlarged) to see. Such is the suggestion of Dr. Carpenter, Sir Wyville Thomson, and Mr. Gwyn Jeffries; and it is possible that this actually is one of the effects of the phosphorescent property. But if so, it remains to inquire how the forms endowed with it came to be possessed of a power useful in that way to other forms, but not to themselves. According to the Darwinian doctrine of development, the powers that are developed in different organisms by the process of natural selection are such as are useful to themselves and not to others, unless incidentally.