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and consequently as a rule also biologists are inclined to understand by this 

 term something immutable, something which cannot be modified in its mani- 

 festations according to circumstances which is certainly not the case with these 

 so-called laws any more than with human laws. Only the leading principle 

 remains unchanged ; the method of its execution, however, is regulated according 

 to circumstances. That this process is not only possible but actually occurs in 

 this manner is admitted by the theory of colour evolution on the grounds of 

 the observations on which it is based. I will return to the subject presently. 



The ontogenetic investigations concerning the origin of the pigmental colours 

 in the wings during the pupal stage do not show this sequence. It is true 

 that one colour appears earlier than another in that stage but that the evolutional 

 sequence of the colours, as this occurs phylogenetically, should be reflected in 

 it I do not consider at alle essential. 



The method of tracing phylogenetic changes by means of ontogenetic investig- 

 ations rests entirely on the so-called fundamental law of Haeckel. The cor- 

 rectness of this law I certainly admit and it receives complete confirmation 

 from my study on the horn of the larvae of Sphingidae. But this does not 

 alter the fact that inemploying it in a scientific sense judgment should be 

 exercised since a slavish pedantic conception of it can only lead to erroneous 

 results which are of no value as scientific arguments. Vestiges or relics of all 

 the processes occuring during the phylogenetic development of an animal species 

 are not by any means traceable in the ontogenetic investigation of an existing 

 form. That Lepidoptera like all other animals have developed from older forms 

 cannot be doubted ; this is, indeed, demonstrated by a study of the wing- 

 venation and of the other evolutionary changes mentioned in the introduction 

 to my monograph of the Java Pieridae. That the same is true also as regards their 

 colours is proved irrefutably by the study of colour evolution and is evidenced, 

 moreover, by the considerable difference in colour frequently exhibited by indi- 

 viduals of a species occurring in different, and often in the same, districts at 

 different times or even contemporaneously, although they all have doubtless 

 originated from the same primordial form. Prof. Weissmann admitted this 

 years ago. In caterpillars, whose various stages of development marked off by 

 their moults greatly facilitate the ontological investigation of the later periods 

 of their development, it may actually be observed, as for instance in the larvae 

 of the Sphingidae examined by me in his connection, that the colour gradually 

 changes. The assertion, however, that in observing the first appearance of the 

 colours in the wings during the pupal stage, in which they are developed, the 

 phylogenetic sequence of the origin and changes of these colours may be traced 

 does not by any means appear to me to rest on such a firm basis. As we 



