xiv INTRODUCTION. 



Vamation. — No two organisms are exactly alike ; there is always some variation 

 from the parent form, in some cases very slight, in others considerable. (For examples 

 of variation see Plate VII., tigs. 1 to 9, varieties of Hydriomena deltoidata; Plate VIIL, 

 figs. 4-2 to 47, varieties of Epirranthis alectoraria; Plate IX., figs 6 to 14, varieties of 

 Selidosema productata; Plate X., figs. 13 to 23, varieties of Azelina gallaria; Plate X., 

 figs. 39 to 47, varieties of Declaim fioccosa.) 



Inheritance. — Many of these variations are inherited — a fact demonstrated by our 

 domestic plants and animals, where man has selected and bred from varieties suitable 

 for his purposes, and has thus produced races in which the variation is permanent. 

 Many of the races of domestic animals differ as much from one another as do some 

 distinct species of wild animals. 



Struggle for Existence. — All animals and plants produce far more offspring than 

 can possibly survive, thus giving rise to the struggle for existence. For example : The 

 average number of eggs laid by a Lepidopterous insect is certainly over 100, and in 

 many species this number is greatly exceeded. Assuming each female to lay 100 eggs, 

 the progeny from a single pair would amount, after six generations, to over six 

 million individuals. 



Natural Selection, or the Survival of the Fittest. — In the struggle for existence 

 which necessarily results from such a great increase of individuals, those variations which 

 favoured the possessors would be preserved, whilst those which did not, would be gradually 

 exterminated. This principle of the preservation of the favourable varieties in the 

 struggle for life is called Natural Selection, or the Survival of the Fittest. 



Divergence of Character. — As there are so many different places and conditions 

 in the economy of nature which can be occupied by organic beings differently constituted, 

 individuals which diverged most from the original type would be brought into less severe 

 competition, than those which diverged only in a slight degree. For instance, if we 

 represent the original form as A, occupying one place in the economy of nature ; a 

 second form as B, occupying a somewhat similar place ; a third form as C, occupying 

 a very different place to A although somewhat similar place to B, it is obvious that 

 B would enter into severe competition with both A and C, whilst A and C might not 

 trend to any great extent on one another's place in the natural economy ; hence B 

 would be exterminated before either A or C. In other words, natural selection 

 continually tends to increase the slight differences, which we call varieties, into the 

 greater differences, which we call species. 



The following phenomena, which have long been observed by students of the 

 Lepidoptera, will serve as excellent examples of the operation of natural selection : — 



Protective Besemblance. — This term is applied to those classes of form or colour 

 which enable an animal to so closely resemble its surroundings as to escape the notice 

 of its enemies. Numerous examples of protective resemblance exist in the New Zealand 

 moths and butterflies; in fact, it may safely be asserted that nearly all the colouring 

 we observe in these insects has been acquired for protective purposes. The following 

 species, amongst many others which will he described hereafter, exhibit in a very 

 marked degree the phenomenon of protective resemblance : Epirranthis alectoraria, 

 Selidosema dejectaria, and Drepaiwdes murlferata resemble dead leaves; Chloroclystis 



