Phylctic I\irallclism in MMm&pku Species. 477 



adapted 10 a diurnal life gives rise in the course of 

 time to a nocturnal family, there can be no doubt 

 but that the transformation of structure would be 

 far greater on the part of the imagines than on that 

 of the larvae. The latter would not remain quite 

 unchanged not because their imagines had taken 

 to a nocturnal life which for the larva would be 

 quite immaterial, but because this change could 

 only occur very gradually in the course of a large 

 number of generations, and during this long period 

 the conditions of life would necessarily often change 

 with respect to the larvae. It has been shown 

 above that within the period of time necessary for 

 the formation of a new species impulses to change 

 occur on both sides ; how much more numerous 

 therefore must these be in the case of a group of 

 much higher rank, for the establishment of which 

 a considerably longer period is required. In the 

 case assumed, therefore, the larvae would also 

 change, but they would suffer much smaller trans- 

 formations than the imagines. Whilst in the 

 latter almost all the typical portions of the body 

 would undergo deep changes in consequence of the 

 entirely different conditions of life, the larvae would 

 perhaps only change in marking, hairs, bristles, or 

 other external characters, the typical parts ex- 

 periencing only unimportant modifications. 



In this manner it can easily be understood why 



and not because I am convinced that the existing Rhopalocera 

 are actually the oldest Lepidopterous group. 



