rhyletic Parallelism in Metamorphic Species. 459 



has diverged into a variety, the other stage re- 

 maining monomorphic. The systematic division 

 of varieties is thus very often one-sided. 



Among species also incongruences are of fre- 

 quent occurrence. Sometimes the imagines are 

 much more nearly related in form than the larvae, 

 and at others the reverse happens ; whilst again the 

 case appears also to occur in which only the one 

 stage (larva) diverges to the extent of specific 

 difference, the other stage remaining monomorphic 

 (D. Euphorbia and Nicced). 



The agreement in form-relationship appears to 

 be most complete in genera. In the greater num- 

 ber of cases the larval and imaginal genera coin- 

 cide, not only in the sharpness of their limits, but 

 also as far as one can judge in the weight of 

 their distinctive characters, and therefore in the 

 amount of their divergence. Of all the systematic 

 groups, genera show the greatest congruence. 



In families there is again an increase of irregu- 

 larity. Although larval and imaginal families 

 generally agree, there are so many exceptions that 

 the groups would be smaller if they were based 

 exclusively on the larval structure than if founded 

 entirely on the imagines (Nymphalidcs^ Bomby- 

 cicUe). 



If we turn to the groups of families we find a 

 considerably increased incongruence ; complete 

 agreement is here again rather the exception, and 

 it further happens in these cases that it is always 



