ORDERS, FAMILIES, s) 
types or plans, seemingly an abstract induction of ours, are as real as the 
birds themselves. It is natural then to. divide birds into three primary 
groups: Aerial Birds (Aves Aérecw), Terrestrial Birds (Aves Terrestres) 
and Aquatic Birds (Aves Aguatice). An illustration will make this clear. 
Men build machines to transport themselves and their goods; the only 
known media of transportation are the air, the earth and the water; and 
we do not imagine any sort of vehicles more unlike than a balloon, a 
buggy, and a brig ; these, therefore, exemplify the most fundamental division 
of machines for transportation. 
§ 18. Orprrs. Taking any one of these types of structure, we find that 
it may be unfolded, or carried out, in different ways. Studying all known 
aquatic birds, for example, we see that their plan of life is fulfilled in four 
different ways; it is exhibited under four aspects, or modes of execution, 
each distinguished by some particular combination of aquatic characters 
with certain other characters that we did not take into account in framing 
our Aves Aquatice. Thus a goose, a gannet, a gull and a guillemot, all 
agree in aquatic characters, but differ from each other by each having certain 
characters that the other three lack. Characters marking such modes of ex- 
hibition are called ordinal; and the groups so organized, Orders. In our 
illustration, there are likewise four plans of aquatic machines; diving bells, 
sailing vessels, steamships and rowboats, clearly distinguished by the way 
in which motion (the prime function of all vehicles) is effected ; in this case 
it is by weight, by wind, by steam, by muscle; therefore the machinery by 
which these forces are applied, furnishes ordinal characters of aquatic 
vehicles. 
§ 19. Famintes. But all the birds of an order are not alike; some re- 
semble each other more than they do the rest; so another set of groups 
must be made. These groups are called Families; they consist in a certain 
combination of all ordinal characters with special sets of characters of the 
next lower grade or value. Let # represent the sum total of strictly ordi- 
nal characters, and suppose we find these variously combined with a certain 
number of the next lower grade of characters, as a, 6, for instance; then 
the particular combination x (abc) is one family; x (bef) another; x (cde) 
another, etc., and we shall have as many families under an order as there 
actually are such combinations. Sometimes an order may be represented 
by « (a. ..f); then there is but one family, as, for example, in the aquatic 
order Lamellirostres where the Anatide alone furnish every one of the ordi- 
nal features, and are equivalent to the order; that is to say (@...f) =, 
because no character from a to f is wanting in any member of the order. 
In our order sailing vessels, of aquatic machines, masts and sails are ordi- 
nal characters, because they are essential apparatus to catch the wind. 
But these may be of a varying number, etc., upon which we might found 
families of sailing-vessels, as the ship family, represented by « (three masts 
+ square sails) ; the schooner family x (two masts + fore-and-aft sails) ; the 
sloop family « (one mast + fore-and-aft sails), ete. Diving bells, I sup- 
KEY TO N. A. BIRDS. 2 
