Studies in the Theory of Descent. 



the larvae of a family of Noctucs do not differ to 

 a greater extent from those of a family of butterflies 

 than do the latter from some other Rhopalocerous 

 family, or why the imagines of a Rhopalocerous and 

 a Heterocerous family present much greater form- 

 divergences than their larvae. At the same time 

 is therefore explained the unequal value that must 

 be attributed to any single family of butterflies in 

 its larvae and in its imagines. The unequal form- 

 divergences coincide exactly with the inequalities 

 in the conditions of life. 



When whole families of butterflies show the same 

 structure in their typical parts (antennae, wings, 

 &c.), and, what is of more importance, can be 

 separated as a systematic group of a higher order 

 (i. e. as a section or sub-order) from the other 

 Lepidoptera whilst their larval families do not 

 appear to be connected by any common character, 

 the cause of this incongruence lies simply in the 

 circumstance that the imagines live under some 

 peculiar conditions which are common to them all, 

 but which do not recur in other Lepidopterous 

 groups. Their larvae live in precisely the same 

 manner as those of all the other families of Lepi 

 doptera they do not differ in their mode of life 

 from those of the Heterocerous families to a greater 

 extent than they do from one another. 



We therefore see here a community of form 

 within the same compass as that in which there is 

 community in the conditions of life. In all butter- 



