IX 



obtain in this respect, the phenomena occuring in connection with it are evidently 

 governed by fixed rules. 



Not only that in each of these groups the process of change is evidently 

 in general of the same nature but this may also be observed in detail. Thus, 

 for instance, all the different white streaks and lines in species such as 

 D. Agleoides Felder and D. Similis Clerck bear the same character and this 

 again recurs in those of the 9 of Euploea Midamus L., a species in which 

 the c? follows the direction of Euploeas while the 9 follows principally that of 

 the species of Danais just referred to. The slight differences occurring here 

 are evidently only such deviations from a similar line of evolution which, in 

 each distinct species, arise from their special morphological peculiarities which 

 have to be taken into account in the course of the evolutionary process. I 

 have indicated this clearly in my treatise " Ueber das Horn der Sphingiden- 

 Raupcn" , which appeared in 1897 in volume XL of the Tijdschrift voor Ento- 

 mologie, where I explained how the so called horn of the caterpillar of the 

 Sphingidae, originally a long moveable organ furnished with spines, has gradually 

 become atrophied ultimately to disappear entirely. 



A process, however, which has continued from the original Sphingidae 

 through all the genera and species which have issued from them and doubdess, 

 therefore, during several thousants of years until the present day, and which, 

 as far as known, has hitherto only in one species caused this horn to dis- 

 appear while the ontogenesis of the existing kinds of caterpillars shows how 

 this process has ever continued slowly in them all and how, consequently, all 

 kinds of forms of this organ, in various stages of atrophy, have arisen, all 

 simply phenomena of the continuation of the same process, the morphological 

 operation whereof must take into account the peculiarity, occuring correlatively, 

 of each species. It is, therefore, neither accident nor chaos to which these 

 differences, arising in the course of the process of colour evolution in Danaidae, 

 must be attributed ; they are governed by rules although their operation at times 

 acquires so intricate a character that to unravel it, while not impossible, becomes 

 extremely difficult. 



The same may be observed, for instance, in the development of the white 

 in the wings of several species of Euploea. One species, very common in 

 Java, E. Leucostictos Gm., occurs also in many other islands of the Malay 

 Archipelago where it has received various names as, for instance, E. Viola 

 Butl. in Celebes. Another species of Java, E. Schlegelii Vol!., is also found 

 in Celebes where the name E. Gloriosa Butl. has been applied to it. Now 

 both these forms of Celebes differ from their allies in Java — in the case of 

 Viola especially at regards the 9 — entirely in the same manner, i. e. in 



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