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 

 p 2 



