XIV INTRODUCTION. 



stated before, passes through white, yellow and green to red or blue, 

 then to purple and probably black. The retrogressive development of 

 green through yellow is easily illustrated by reference to our British 

 fauna. Almost all our green insects are rapidly affected by ammonia, 

 changing to yellow and in some cases to white. Halias prasinana, 

 Aplecta herlida, Agriopis aprilina, Diphthera (Moma) orion, Metrocampa 

 margaritaria, Hemitliea, strigata, Larentia pectinitaria, Lobophoravirctata, 

 Larentia olivata, Tortrix viridana, Halias chlorana and very many others 

 are well known examples of a rapid change to yellow, whilst very 

 weak acids dissolve the yellow as well, and make the insects white. 

 Probably most of the yellow specimens of these species seen in our 

 cabinets are due to the action of the ammonia or cyanide of potassium 

 used in killing them, but yellow varieties of Tortrix viridana and par- 

 tially white vars. of Halias chlorana are not at all uncommon. Halias 

 prasinana too, rapidly becomes white on exposure to the weather. All 

 these are examples of green undoubtedly derived through yellow, but 

 there is another phase in the development of green which we have to 

 consider. It has before been shown that red and brown are directly 

 derivable from yellow and orange, and therefore there is an intimate 

 connection between green on the one hand, and red and brown on the 

 other. The males of Halias prasinana exhibit this very distinctly, and 

 anyone with a fairly long series of this species can readily see the 

 facts. The female of this species is very invariable in colour, being 

 pure green and white, but with the male it is not so. Normally the 

 green is the same as in the female, but the fringes, inner margin, and 

 costal margin of the male, are generally orange and occasionally red. 

 Thus, those parts of the wing which are white in the female, exhibit 

 a development through orange to red, whilst the rest of the wing 

 passes through orange to green, the latter not being evolved from the 

 red nor that from the green, but side by side, as it were, from the 

 same orange base. 



I am also inclined to think that many other normally red species, 

 having green forms, have been evolved through the green. One of the 

 most striking instances that I can call to mind is Ellopia prosapiaria 

 (fasciarid) and its variety prasinaria. This beautiful green variety is not 

 at all uncommon in some parts of the Continent, but it is very rare in 

 Britain. Strange to say, the only specimen of this species I ever saw in 

 the woods at Cuxton, was a beautiful example of this variety, although I 

 have never seen the red type in that locality. In the var. prasinaria 

 there is generally a distinct orange costa and pale yellowish-white 

 transverse lines showing the original coloration from which the green 

 has been evolved. In the type, the green parts are red, the orange 

 costa is also red, whilst the pale transverse lines are sometimes green 

 and sometimes shaded with red. There is, therefore, a strong suspicion 

 here that the red has been formed through green, since not only does 

 red in the type replace the green of var. prasinaria, but the transverse 

 lines are also sometimes greenish and sometimes red. In Hypsipetes 

 sordidata (elutata), there would appear to be a similar order of develop- 

 ment, and not only do we obtain distinctly green and distinctly red 

 forms, but we get orange intermediates &c. That a great deal of the 

 development in this species is due to " natural selection " appears very 

 obvious, for in our South of England woods almost all the specimens 

 are green, whilst in the Island of Hoy almost all the specimens are 



