In some insects the decoration of the body is very marked, as in our small dragon-flies, the Agrions. In one species, for example, _A. Puella_, the male is pale blue banded with black, and the female bronze black, with a blue band on the segment, bearing the sexual organ; the ovipositors are also separately decorated. The male generative organs are peculiar, in that the fertilizing fluid is conveyed from one segment to a reservoir at the other end of the abdomen. Both the segments bearing these organs are marked by special decoration. The peculiar arrangement of the sexual organs in dragon-flies is very variable, and certain segments are modified or suppressed in some forms, as was shown by J. W. Fuller.[32] In every case the decoration follows the modification. In the thorax of dragon-flies, too, the principal muscular bands are marked out in black lines. This distinct representation of the internal structure is beautifully shown in _Æschna_ and _Gomphina_, and in the thorax of _Cicada_, as shown by Dr. Haagen in the paper quoted in the last chapter. We may, then, safely pronounce that the decoration of insects is eminently structural. _Simple Variation._ Cases of simple variation have been already cited in our description of spots and stripes, and it only remains to show that in this, as in all other cases, the variation is due to a modification of original structural decoration. To take familiar examples. Newman, in his British Butterflies, figures the varieties of the very common Small Tortoiseshell (_Vanessa urticæ_). In the normal form there is a conspicuous white spot on the disc of the fore-wings, which is absent in the first variety, owing to the spreading of the red-brown ground colour. This variety is permanent on the Mediterranean shores. In variety two, the second black band, running from the costa across the cell, is continued across the wing. The third variety, Mr. Newman remarks, is "altogether abnormal, the form and colouring being entirely altered." Still, when we examine the insect closely, we find it is only a modification of the original form. The first striking difference is in the margin of the wings, which in the normal form is scalloped with scallop-markings, whereas, in the variety the margins are much simpler, and the border pattern closely corresponds with it, having lost its scalloping. In the fore-wing some of the black bands and spots are suppressed or extended, and the extensions end rigidly at nervules. The dark colouring of the hind-wings has spread over the whole wing. We thus see that the decoration, even in varieties called abnormal, still holds to structural lines, and is a development of pre-existing patterns.