350 PRACTICAL AND SCIENTIFIC ZOOLOGY. 
nomenclature of the “* Hore Entomologice” and the 
“‘ Northern Zoology,” are strictly sub-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 Latreille, 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 all 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 shall 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 resembling the parent: 
its peculiarities, 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, ina 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 all the species of a whole 
genus will be entirely black, as in the Drongo shrikes 
(Edolius), and in many of those composing the family 
