VI 



works. Scientific certainty in respect to this has, however, not been attained. 



Very important on the contrary is, I think, a fuller explanation of my ideas 

 about the phenomena treated of in the works mentioned above under 2, 5, 4 

 and 5, though this explanation can only be shortly resumed here ; for an ampler 

 treatment of them I must refer to those books themselves. For in this respect 

 my views greatly differ from those adopted by most entomologists. -Moreover, 

 some discussion about these subjects must be considered of great consequence 

 in order to show clearly the great importance of the study of the evolutional 

 changes in the Lepidoptera and to fully understand the character of this 

 evolution, namely the basis of the whole biological science. In no other order 

 of animals can this be so easily studied ; therefore a far greater estimation is 

 due to lepidopterology than is given as a rule by zoologists. It is but few 

 who recognize the truth of what Prof. Weismann observed more than twenty- 

 five years ago, that difference of colour is nothing but a difference of form in 

 a peculiar manner; therefore they do not understand either that the difference 

 of colour also changes evolutionally or that the study of these changes for this 

 reason also includes that of the charader of the evolutional changes of the form. 



All living animals owe their present form to such changes and in the same 

 way as this has sprung from forms which existed formerly, it will pass again 

 into new ones. This evolutionary process is general, all beings are subject to 

 it; but it often seems that there is a cessation of change either in species or 

 in races, or even only in either the one or the other sex, sometimes even in 

 some individual beings, which cessation probably is only of a temporary cha- 

 racter, but may last, however, a considerable time and even continue so long 

 that the species becomes extinct altogether for some reason or other. Moreover 

 the evolutional impulse usually does not entirely alter a form ; but, as a rule 

 only affects some organs or other physiological unities and causes them to 

 vary, either by developing them differently in a special direction or by making 

 them disappear by means of weakening and lessening them. Sometimes, however, 

 a change takes place at the same time in several similar, physiological unities 

 and then, of course, the form is so much altered that it really ceases to exist. 

 The process of change here mentioned may be best observed, when for some 

 generally very uncertain reason, organs disappear in this evolutionary way. 

 The caterpillars of the Sphingidae, for instance, are characterized by a so-called 

 caudal horn, the shape of which differs, however, considerably in the different 

 species. Only in one species Deilephila Vespertilio Esp. as far as we know 

 at present, it seems that nothing has remained of that horn but a crooked 

 colour-mark which may perhaps be called a remnant of it. In Deilephila 

 Oenotherae Esp. the horn has also disappeared, but at the same place we 



