XXVII 



Batavia which are further advanced in this respect than form C (Plate XIX, 8c), 

 this white spot has been vigorously attacked by the darkening process, whereby 

 the lower part forms itself more and more into a peculiar white stripe, still con- 

 nected, however to the rest. In cf. that are still further advanced, form D 

 (Plate XIX, 8d), the process has gone so far, that the darkening has, as it 

 were, extend through the middle of the patch, and in so doing severed the 

 peculiar stripe from the upper part, thus forming two patches. In a still further 

 advanced stage, that of form E (Plate XIX, 8c), the darkening has covered 

 the peculiar stripe, so that only the upper patch is left, and proceeding, the stage 

 is reached in form F (Plate XIX, 8/) in which of the patch on the upperside 

 there remains only a small relic, while, on the underside, where the same 

 has been going on, but in a much less vigorous form, it has remained some- 

 what larger. 



This forms a striking example of the perfect regularity with which the 

 evolutionary process develops in individuals of this species. But there is more. 

 I possess 6 specimens of form C, 30 of from D, and 1 1 of form E, all caught 

 in Batavia indiscriminately in the dry and the rainy season, and these show very 

 clearly that the same evolutionary process, although revealing itself in each 

 individual according to the stage of evolution attained, always proceeds in the 

 same manner; that the darkening therefore always takes place in the same 

 way in the different generations. We might compare it to pupils, placed, 

 according to their knowledge, in different classes of the same school, and 

 using different books, all belonging to the same series ; a school in which no pupil 

 could pass to a higher class, but each new child, according to the account of 

 knowledge already acquired in a preparatory school, would be immediately 

 placed in the class to which it properly belonged. It is then, a regularity, 

 penetrating to the smallest details, which characterises these evolutionary processes; 

 it is absurd to try to explain it by such a phrase as "variability". We were 

 therefore correct before, in supposing that various facts which we had encountered 

 pointed to such regularity ; similarly when, on p. ix of my third introduction 

 I pointed out the course of the process of decay of the horn of the Sphingidae 

 larvae, or on p. liv of the same, the greater or smaller distinctness of the ocelli 

 on the underside of the wings of Cyllo Leda L. ; every evolutionary change 

 develops according to fixed rules. And in the example just given, development 

 takes place quite gradually without any question whatever of sudden changes. 



Working under similar conditions colour-evolution will bring about similar 

 effects, as must be the case with every evolutionary process. This is why we find 

 butterflies which resemble each other very closely in colour and shading while 

 belonging to different species, and even different genera and families. Amongst 



