In the cases of true mimicry, as in Figs. 1-3, Plates II. & III., where insects as different as sheep from cats copy one another, we find that of course structure lines are followed, though the pattern is vastly changed. The _Papilio merope_, Fig. 1, Plate II., which mimics _Danais niavius_, Fig. 3, does so by suppressing the tail appendage, changing the creamy yellow to white--a very easy change, constantly seen in our own Pieridæ--and diffusing the black. A similar case is seen in Figs. 4-5, Plate III., where a normally white butterfly (_Panopoea hirta_) mimics a normally dark one of quite a different section. Here again the change is not beyond our power of explanation. Where a Papilio like _merope_ mimics a brown species like _Danais niavius_, we have a still greater change in colour, but not in structural pattern. If we ascribe to these insects the small dose of intelligence we believe them to possess, we can readily see how the sense of need has developed such forms. Local varieties present no difficulty under such explanation. The paramount necessity for protection has given the Hebridran species the grey colour of the rocks, and the desert species their sandy hue. [Illustration: Plate VII. CATERPILLARS.] Finally, to take the case of caterpillars, Weismann has admirably worked out the life history of many forms, and shows how the complex markings have arisen by development. Broadly, a caterpillar consists of 13 segments, the head being one. The head is often marked with darker colour, and the last segment with its clasping feet is also very frequently emphasized, as in Figs. 1 & 3, Plate VII. The spiracles are generally marked by a series of spots, and often connected by a line. Here the tendency to repetition shows itself strongly, for not only the spiracles themselves, but the corresponding points in the segments without spiracles are frequently spotted, and, moreover, these spots are frequently repeated in rows above the spiracular line. Of this, _Deilephila galii_ and _D. Euphorbiæ_, Figs. 1-5, Plate VII., are good examples. The segmentation is also generally emphasized, as shown in all the examples on the plate, but in its simplicity in Fig. 10. Running down the centre of the back a more or less distinct line is often seen, as shown in the figures. This corresponds with the great dorsal alimentary canal lying just below the skin, and Weismann has shown that in young larvæ this line is transparent, and the green food can be seen through the skin. We have here, perhaps, a relic of the direct colouration noticed in the transparent coelenterata.