80 Colouration in Animals and Plants. 



In local varieties, as in seasonal forms, we have again nothing 

 more than developments of a given type, as is well shown in Plates 

 IV. & V., Figs. 13-18 & 1-13. 



When, however, we come to mimetic forms, whether they mimic 

 plants, as in Plate I., or other species, as in Plates II. & III., a 

 difficulty does seem to arise. 



The leaf butterfly (Kallima inaclms), Plate I., offers no trouble 

 when we view the upper surface only with its orange bands, but its 

 under surface, so marvellously like a dead leaf that even holes and 

 microscopic fungi are suggested, does seem very like a case 

 in which structure lines are ignored. Take, for instance, the mark 

 which corresponds to the mid-ribs, running from the tail to the apex 

 of the upper wing ; it does not correspond to any structure line of 

 the insect. But if we take allied and even very different species 

 and genera of Indian and Malayan butterflies, we shall find every 

 possible intermediate form between this perfect mimicry and a total 

 lack of such characters. To cite the most recent authority, the 

 various species of the Genera Discophora, Amathusia, Zeuxidia, 

 Thaumantis, Precis, &c, figured so accurately in Distant's Rhopa- 

 locera Malayana, will give all the steps. 



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 Pieridge — and diffusing the 

 black. A similar case is seen in Figs. 4-5, Plate III., where a 

 normally white butterfly (Panoposa 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. 



