{xvi}ORNAMENTAL COLOURING.--This class of colouring occurs in many species, especially amongst the butterflies, and is not apparently connected in any way with protection. Darwin supposes that it has arisen through the females of each species always selecting the most beautiful males as mates, hence these alone would leave progeny, and the females themselves would afterwards become beautiful through the effects of inheritance. This principle Darwin has termed Sexual Selection, and has discussed it in great detail in his work on the 'Descent of Man.' The fact, that amongst birds and butterflies the males are nearly always the most brilliantly coloured and the most beautiful, together with an immense mass of other evidence, tends, I think, to entirely support Darwin's theory, although it should be mentioned that several eminent naturalists, including Mr. Wallace, do not admit the principle of Sexual Selection. IV.--CLASSIFICATION. From a further consideration of the foregoing principles it will be seen that all existing species are held to be descended by true generation from pre-existing species, and that, consequently, all the relationships we observe between species are explained by community of origin. The most natural system of classification is, therefore, that which best reveals the scheme of descent, or, as it is termed, the phylogeny, of the group of organisms classified. To construct a perfect system of classification on these principles a knowledge of not only all the existing species of _Lepidoptera_ would be essential, but also of all the extinct species, and it is needless to say that such knowledge is quite unattainable. Nevertheless large numbers of species are now known from many parts of the world, and a very extensive collection has recently been employed by Mr. Meyrick in framing a classification of the _Lepidoptera_, which is, to the best of my belief, the first constructed on strictly Darwinian principles. Although adopting Mr. Meyrick's system in the present work I do not agree unreservedly with all his conclusions; but I have not attempted to alter his system in accordance with my own views, as I conceive that the conclusions of a naturalist, who has only had the opportunity of studying a restricted fauna, would necessarily be liable to considerable error. The general principles on which Mr. Meyrick has founded his system are practically those laid down by Darwin in his 'Origin of Species,' and may be thus summarised:-- A. Resemblances between all organisms are explained by community of origin, the amount of difference representing the amount of modification and expressible in the classification as varieties, species, genera, families, groups, orders, &c. The amount of difference does not _necessarily_ bear any direct relation to time, many forms remaining almost stationary whilst others are undergoing development.