But some butterflies have parts of the under surface as gaily decorated as the upper; and this not for protection. This may be seen to some extent in our own species, for instance in the orange-tip of the Orange-tip, and the red bar in the upper wing of the Red Admiral (_V. atalanta_). If we watch these insects, the conviction that these are true ornaments is soon forced upon us. The insect alights, perhaps alarmed, closes its wings, and becomes practically invisible. With returning confidence it will gradually open its wings and slowly vibrate them, then close them again, and lift the upper wing to disclose the colour. This it will do many times running, and the effect of the sudden appearance and disappearance of the bright hues is as beautiful as it is convincing. None can doubt the love of display exhibited in such actions. The delicacy of their organization renders butterflies peculiarly susceptible to any change, and hence they exhibit strong tendencies to variation, which make them most valuable studies. Not only do the individuals vary, but the sexes are often differently coloured. Where two broods occur in a season they are sometimes quite differently decorated, and finally a species inhabiting widely different localities may have local peculiarities. We can thus study varieties of decoration in many ways, and we shall treat of them as follows:-- 1. _Simple Variation_, in which the different individuals of a species vary in the same locality. 2. _Local Variation_, in which the species has marked peculiarities in different localities. 3. _Sexual Dimorphism_, in which the sexes vary. 4. _Seasonal Dimorphism_, in which the successive broods differ. [Illustration: Fig. 3. Diagram of Butterfly's Wing. A. Upper Wing. B. Lower Wing. _a._ Costal Margin. _b._ Hind Margin. _c._ Inner " _d._ Anal Angle. _e._ Costa. _f._ Costal nervure. _g._ Sub-costal do. _g_^{1-4}. Branches of do. _h._ Median nervure. _i._ Sub-median do. _j._ Discoidal Cell. _k._ Discoidal Veins.]