xvi INTRODUCTION. 



OENAMENTAL 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 unre- 

 servedly 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. 



B. By a consideration of the following laws the age of a division can be approxi- 

 mately arrived at; that is to say, its position in the great genealogical tree of the 

 Lepidoptera can be, to some extent, determined : 



" (1) No new organ can be produced except as a modification of some previously 

 existing structure. 



" (2) A lost organ cannot be regained. 



" (3) A rudimentary organ is rarely redeveloped."- (Meyrick.) 



