vir 



still see a horny spot, round which an ocellar marking has been formed, which 

 in this way shows the place where formerly there was a horn. Many cater- 

 pillars of this family, however, have a generally crooked, hard horn, the length 

 and shape of which differ according to different species and which kan some- 

 times be moved at will and sometimes not. Occasionally we find instead of 

 the horn only an appendix of the skin, which can also be moved. In some 

 cases the horn has remained particularly long. From the ontogeny of these cater- 

 pillars, as divided into succeeding periods by its moults, it its apparent that 

 the said organ occurs in these periods in all kinds of different stadia of atrophy 

 and that this process increases according as the caterpillar approaches the stage 

 in which it is full-grown nowadays, and in which, as has been already said, 

 the horn has already entirely disappeared in a few species. If we apply these 

 results of ontogenesis according to Haeckel's well-known biogenetical law, we 

 find that probably all these species must originally have possessed a long horn, 

 armed with long spines (poisonous?), which could be moved at will and has 

 probably been a defensive weapon; this organ however, probably because it 

 was no longer necessary to the organism, has since begun to atrophy more 

 and more and thus disappear gradually. The process in which this change 

 reveals itself, goes on little by little, as is generally the case in evolutional 

 changes, but in one species quicker than in another and, moreover, very 

 irregularly ; a process which can easily be observed in the different stages of 

 development of the caterpillars, either in the form or in the flexibility of the 

 remnant of the horn, and which also makes it easy to understand the variety 

 of this organ in the full-grown caterpillars. This only shows how far the atrophy 

 in each species has already advanced. For, though no species possesses the 

 horn anymore in its original state, the progress of this process among the 

 species differs greatly and in the end, the total disappearance of the horn has 

 only been reached by a single one, as has been already said, and even then 

 not without leaving distinct marks. This process which thus annihilates a single 

 organ, may be studied particularly well in these caterpillars. Those who want 

 more detailed information on this point, I must refer to my essay : " Ueber 

 das Horn der Sphiugideii-Ratipen " ni Vo/. XL of the " Tijdschrift voor Enlo- 

 mo/ogie" published in 1897. 



There are, however, several other suchlike processes that are not so easily 

 observable, and among those also some to which the Rhopalocera are subject, 

 which annihilate in the same way important organs of these insects, thus altering 

 the corporal form. A similar process has already formerly destroyed the 

 prothoracic wings, — it is true that this has not happened among the Lepidop- 

 tera, which did not )'et exist, but in a high degree among the Pseudoneu- 



