PRINCIPLES OP SCIENTIFIC ARRANGEMENT. 133 



Why some genera abound in species and others are 

 so limited is as diflBcult to determine as the differing 

 numerical abundance of individuals in species. That 

 long genera (genera numerous in species) may be the 

 result of natural selection, as Mr. Darwin surmises, and 

 the offspring of a common parentage, is contradicted, 

 not merely by peculiar although sometimes slight dis- 

 similarities of habit, combined with size and colour, but 

 also if any lines of demarcation are to be admitted, it is 

 possible, were their generic similitude to be subjected to 

 severe test, they might present characteristics normally 

 discrepant and suggestive of further division, although 

 the habit may be very like. 



The generic grouping is effected by structural pecu- 

 liarities, which are essentially of a higher class than 

 the characters of specific separation, these being deter- 

 mined by colour, pubescence, sculpture, etc. etc. ; spe- 

 cific characters combining only individuals with such 

 peculiar inferior resemblances. The generic characters 

 thus establish groups of species allied only by such more 

 general character and similarity, but conjunctively of 

 one permanent habit, although the members of the genus 

 may differ somewhat in habits, and so on of the higher 

 groups into which insects are collected, each group in 

 its ascent upwards presenting characteristics of a wider 

 range than those of the descending series. And so, 

 by degrees, we rise until we reach the characters which 

 combine the whole order. The process is necessarily 

 and imperatively synthetical, for the whole foundation is 

 based upon species, and thence emanates the supposition 

 that only species exist. 



The type of a genus is that species upon the charac- 

 ters of which the genus was originally framed and named. 



