350 PRACTICAL AND SCIENTIFIC ZOOLOGY. 



nomenclature of the " Horse Entomologicae" and the 

 " Northern Zoology," are strictly suh-genera. They are 

 not — each taken by itself — circular, because they have 

 really but a few species ; or, what is the same thing 

 to the present question, we are only acquainted with a 

 few species ; but, taken collectively, they form a cir- 

 cular group, or, in other words, a genus, such as we 

 have here defined. These are examples of sub-genera 

 which are not in themselves circular ; but, from recent 

 researches into the large and diversified assemblage of 

 forms constituting the genus Papilio of LatreiUe, we 

 feel thoroughly persuaded that, where there is a great 

 numerical preponderance, sub-genera are not only circu- 

 lar, but that they contain their own internal types, as 

 definitely and perfectly as do genera and aU higher 

 groups. This latter question we shall probably inves- 

 tigate in its proper place. In the mean time, having 

 now enumerated all the ranks and degrees of circular 

 groups yet detected, we shaU proceed to make a few 

 concluding observations upon species and their varieties. 

 (431.) A Species, in the usual acceptation of the term, 

 is an animal which, in a state of nature, is distinguished 

 by certain peculiarities of form, size, colour, or other cir- 

 cumstances, from another animal. It propagates, " after 

 its kind," individuals perfectly resembhng the parent : 

 its pecidiarities, therefore, are permanent. When ani- 

 mals are domesticated, the changes of life, of food, and 

 frequently of country, which they undergo, are known to 

 have the effect of altering and destroying those marks 

 by which, in a state of nature, they were always distin- 

 guished. We see this in all the domestic quadrupeds and 

 birds, which, when under the dominion of man, diverge, 

 as it were, into endless variety. The discrimination of 

 species, in many instances, requires a very practised 

 eye ] but where, on the other hand, there is an obvious 

 difference in colour, size, markings, &c., the task be- 

 comes easy. Sometimes aU the species of a whole 

 genus will be entirely black, as in the Drongo shrikes 

 {Edolius), and in many of those composing the family 



