GENERA. 211 
and so few were since added, that not one of the 
modern entomologists ventured to arrange them as 
a distinct group. It happened, however, that we 
took a predilection for these butterflies when in 
Brazil, and collected them with great assiduity : 
the result is, that no less than eighteen species were 
found in that limited portion of the country which we 
explored. We are acquainted with several others, and 
new ones are still coming to light ; so that it is very 
probable, in a few years, that this single sub-genus, 
not more than one or two species of which are 
usually seen in collections, will comprise fifty. We 
mention this instance, not as encouraging the stu- 
dent to increase the present overwhelming list of 
sub-genera—as too many are now doing — but as an 
example how impossible it is, in general, to judge 
of the real’ numerical contents of a natural group, 
from the examples usually seen in cabinets, or even 
from the species that have already been described. 
(146.) The second stage of generalisation is to 
ascend from sub-genera to genera, or, in other words, 
to combine an indefinite number of those first, or 
lowest assemblages of species, just described, into a 
group of the next rank or denomination. Now, this 
group we name a genus. The question therefore is, 
whether there is any rule as to the specific number 
of sub-genera which naturally constitute a genus, or 
is this number indefinite, depending entirely on the 
greater or less variety of forms, which show a 
common tendency to unite into a circular group 
superior to themselves ? 
(147.) Here, again, the progress of the enquirer 
PZ 
