WILLIAM T. M. FORBES 



TAXONOMY 



This is not the place for a monograph on the laws of nature, but 

 the following outline will make clearer the writer's point of view as 

 to the status of the forms discussed. 



A species is considered to be : A group of individuals separated from 

 all others by tangible characters, breeding freely among themselves, 

 but not with other individuals. Fifty years ago this would have been 

 sufficient. Now that the continuity of evolution has become obvious, 

 we must recall that at some time- any given species was coming into 

 being, was being set off from its relatives, and was acquiring its char- 

 acteristic property of not interbreeding with them. During such a 

 period-, which may conceivably have been long or short, the species 

 would be imperfectly defined; individuals would interbreed with their 

 cousins, but more and more rarely, and with imperfect fertility; and 

 the various strains would be acquiring adaptations to new environ- 

 ments or climates, which would reduce the probability of intermating. 

 And along with all this, differences of structure would be developing, 

 distinguishing them to the human eye. In fact, many groups are now in 

 this intermediate state, as witness the asters and the violets in the plant 

 kingdom, and the Apanteses and the Euxoas among the Lepidoptera. 

 Further, it is often, and in the Lepidoptera usually, unknown, to what 

 point this isolation has reached; so we must use our best judgment in 

 deciding what is a species and what a mere variety in any given case. 



In order to make clearer the relationships of animals, species are 

 grouped in a series of successively larger categories: genus, family, 

 order, class, and phylum (subkingdom} , within the animal kingdom. 

 Besides these, in groups as large and as complexly related as the insects, 

 intermediate groupings are employed: subgenus for a group of species 

 within a genus; subfamily, suborder, and subclass similarly. Super- 

 family is used to designate a group of families 3 , and tribe for a group 

 of closely related genera. The ' values of these categories are really 

 arbitrary, and there has been a continual tendency to split groups; in 

 fact, the superfamily of the present day is smaller than the genus 

 of Linnaeus (1758). As to the genus, however, we have an imperfect 

 criterion. Member of a single genus (on the average) produce hybrids, 

 but sterile or of low fertility; members of different genera do not. 

 Even here we find Nature draws no sharp lines, for, in isolated favor- 

 able cases, hybrids have been produced between widely different animals, 

 though such always seem destined to an early death, in an embryonic 

 stage. 



In the course of the splitting of groups just mentioned, it is the 

 practice to preserve the original name for one of the sections into 



* Some early authors call this a tribe. 



