PRINCIPLES OF SCIENTIFIC ARRANGEMENT. 133 
Why some genera abound in species and others are 
so limited is as difficult 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, 
