444 Studies in the Theory of Descent. 



larvae of Gastropacha with which they were for- 

 merly united ; and on the other side there are the 

 naked, humped, and flat-headed larvae of the genus 

 Harpyia, Ochs., with their two long forked appen- 

 dages replacing the hindmost pair of legs, and 

 the grotesquely formed caterpillars of the genera 

 Stauropus, Germ., Hybocampa, Linn., and Noto- 

 donta, Ochs. 



The morphological congruence between larvae 

 and imagines declares itself most sharply in genera, 

 where it is the rule almost without exception. In 

 this case we can indeed be sure that a genus or 

 sub-genus founded on the imagines only will, in 

 accordance with correct principles, present a cor- 

 responding difference in the larvae. Had the latter 

 been known first we should have been led to con- 

 struct the same genera as those which are now 

 established on the structure of the imagines, and 

 these, through other circumstances, would have 

 stood in the same degree of morphological rela- 

 tionship as the genera founded on the imagines. 

 There is therefore a congruence in a double sense ; 

 in the first place the differences between the larvce 

 and imagines of any two genera are equally great, 

 and, in the next place, the common characters pos- 

 sessed by these two stages combined cause them 

 to form precisely the same groups defined with 

 equal sharpness ; the genera coincide completely. 



So also the butterflies of the sub-family Nym- 

 plialince can well be separated into genera by the 



