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no real explanation, but the said theory does entirely, though it can not explain 

 the first cause of this evolution, nor the reason why it does take place. External 

 influences of unknown origin doubtlessly do exist; but the naturalist who attri- 

 butes everything he cannot explain to such influences, does not really stand 

 any higher than the ignorant man explaining all things he does not understand 

 as happening by magic, or as the work of evil spirits. That is easy enough, 

 but science is another thing. With words like " Variability " for instance 

 nothing is explained. That is a thing already known even to Hamlet. But 

 people seem slow to understand this in biological as well as in other sciences, 

 and in our whole social and political life too. 



The colour-evolution, treated of here, is of exactly the same nature as the 

 one which appears in the different 9 forms of Papilio Memnon L., which also 

 occur in the same way beside each other in the same region, but which show 

 in different regions still more small differences. Nor can this polymorphism 

 either be explained in any other way than by the theory of colour-evolution. 

 That the butterflies of the Catilla form should be avoided by other butterflies, 

 as Hagen says he had observed, and in which he surmises a phenomenon of 

 selection, is probably nothing but auto-suggestion. 



The eggs are laid on the under-side of the leaves of Cassia, as I have 

 been told, and after 4 days the larvae appear. They are often found in great 

 quantities on joiiar, called at Batavia bilalang (Cassia Florida Wahl); at 

 Buitenzorg I found them also on a species of Cassia which is called there 

 kct'cpeng manila. Dr. Martin mentions also Cassia a lata L. as foodplant. 

 They also show a strong colour-polymorphism and therein colour-evolution is 

 thus also exhibited. Some are still found that resemble the caterpillars of the 

 two other Java species of Callidryas; these have preserved the old green 

 colour, common to many larvae of Pieridae, and represent among the cater- 

 pillars of Pomona an old stage in the evolution, just as the form Catilla does 

 among the butterflies. Most of the caterpillars, however, have already left this 

 stage, while the colour of one specimen has changed already more than that 

 of others. Some of them are ochre-yellow, light brown or bronze coloured 

 on the back and the sides, while the pale streak on the sides, which also exists 

 already in the old form, has turned into yellow or into a greenish colour and is 

 sometimes doubled. The lateral row of black dots often changes into a black 

 line, which sometimes gets so broad that it almost covers the ground colour 

 of the back or even entirely, when the black of both sides is united on the 

 middle of the back ; sometimes also it grows partly or entirely steel-blue with 

 a metallic hue. The head follows the general colour, the under-side is bluish 

 grey, the fore-legs are yellow. Back and sides look like shagreen; when 



