230 Annals Entomological Society of America [Vol. VI, 



the latter only in consensus of characters and not in value. 

 They correspond to the intergeneric space that belongs with 

 the well marked genus in the old stocks, but which forms no 

 integral part of it. The writer has considered well the possi- 

 bility of interpreting the group-unit, as here constituted, to be 

 the natural genus, and thus of doing away with the necessity 

 for the name group-unit by employing the subgeneric category 

 instead of the generic for the group-unit's prime divisions. 

 This plan has proved not to be practicable. Subgeneric 

 divisions may often be recognized within the typic genus, and 

 sometimes in the atypic genera, so neither can be considered 

 subgenera. In the sum of their characters the typic and 

 atypic genera are too distinct from each other to be considered 

 as mere ill-defined groups of species under a genus embracing 

 all the forms in the group-unit. Genera are prominently 

 distinguishable groups of species, and the atypic as well as the 

 typic genera fit the definition. Furthermore, in the young 

 stocks there are inter-subtribal groups of transitionals which 

 come between the subtribes proper or typic subtribes, and 

 which may be termed transitional or atypic subtribal groups. 

 The group-unit is capable of representing in their true relation- 

 ships and thus accomodating in the taxonomic system these 

 transitional subtribal forms, which do not occur in the old 

 stocks and can not be fitted into the system of taxonomy 

 commonly applied thereto. 



Attention must be drawn to the fact that stocks become 

 fixed, and thus easily amenable to delimitation on the old 

 plan, only when their evolution is completed. The lives of 

 stocks and groups of stocks may well be likened to the lives of 

 individuals. They differ in extending over far greater periods 

 of time, which is only a relative difference. Like individuals, 

 they spring from small and embryonic beginnings, are launched 

 upon the outer world, gradually grow, unfold, develop, pass 

 through various stages of change and specialization, in time 

 reach their zenith and cease evolution, finally wane, become 

 senile and eventually extinct. Waning and senile stocks and 

 all those that have ceased evolution, that is to say fully matured 

 stocks, are easily defined because few or no transitionals are 

 present to hinder definition. But stocks that have not yet 

 reached their zenith, that is to say adolescent stocks, are filled 



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